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Modelling And Testing for Improved Safety of key composite StructurEs in alternatively powered vehicles

Collaborative Project Grant Agreement Number 314182

Start date of the project: 1 October 2012, Duration: 36 months

Deliverable D5.3

Report including all guidelines and recommendations

Status: Revision 2

Lead contractor for this deliverable: FKA

Due date of deliverable: 30.09.2015 Actual submission date: 30.09.2015

Coordinator:

Dipl.-Ing. Dipl.-Wirt. Ing. Roland Wohlecker

Forschungsgesellschaft Kraftfahrwesen mbH Aachen

Steinbachstr. 7 - 52074 Aachen - Germany

Phone +49 241 8861 191, Fax +49 241 8861 110

E-mail [email protected]

Project co-funded by the European Commission within the Seventh Framework Programme (2007-2013)

Dissemination Level

PU Public X

PP Restricted to other programme participants (including the Commission Services)

SEAM Restricted to partners of the SEAM Cluster (including the Commission Services)

RE Restricted to a group specified by the consortium (including the Commission Services)

CO Confidential, only for members of the consortium (including the Commission Services)

MATISSE Project – Grant Agreement # 314182

MATISSE received research funding from the Community’s 7th FP

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EXECUTIVE SUMMARY

To summarise, condensate and specify the results gained in the projects SafeEV and MATISSE guidelines and

recommendations for the various topics of two projects are collected within this deliverable and are brought in

a form that is applicable in future work. For this reason a template and a directory for the collection of the

guidelines are established to save all guidelines and recommendations in dedicated documents to be use for

further dissemination or possible expansion. The guidelines and recommendations comprise:

- Guidelines for adaptive pressurised components

- Guidelines for high pressure storage tanks

- Fully virtual methods for safety enhancement due to adaptive pressurised structures

- Fully virtual certification process for high-pressure storage tanks

- Simulation guidelines

- Adaptive pressurised components implemented in CNG vehicles

- Guidelines for pedestrian safety in small electric vehicles

- Guidelines on structural improvements for the occupant protection in SEV

- Guidelines future intelligent protection systems of SEV

CONTRIBUTING PARTNERS

Company/Organisation Name

Document Manager FKA Ralf Matheis

Partner 1 Autoliv Bengt Pipkorn

Partner 2 CRF Roberto Puppini, Stefano Menegazzi

Partner 3 DYNA Thomas Johansson

Partner 4 FKA Ralf Matheis, Helmi Murnisya

Partner 5 ViF Christian Kurzböck

Partner 6 TU Graz Gregor Gstrein

REVISION TABLE

Document version Date Modified sections - Details

V1 30.09.2015 All chapters

V2 30.09.2015 Final version



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Table of Contents

1 Introduction ........................................................................................................................ 4

2 Implementation Guidelines ................................................................................................ 5

2.1 Guidelines for Adaptive Pressurised Components ...................................................... 5

2.2 Guidelines for High-pressure Storage Tanks ............................................................... 6

3 Adaptive Pressurised Components Implemented in CNG Vehicles .................................. 7

4 Safety Requirements for Evaluation of Crashworthiness of Composite Materials ........... 8

4.1 Fully Virtual Methods for Safety Enhancement due to Adaptive Pressurised

Structures ................................................................................................................................. 8

4.1.1 Recommendation on Validation Tests and Corresponding Criteria ...................... 10

4.2 Fully Virtual Certification Process for High-pressure Storage Tanks ....................... 12

4.2.1 Recommendation on Validation Tests and Corresponding Criteria ...................... 17

5 Simulation Guidelines ...................................................................................................... 23

5.1 Settings in LS-DYNA ................................................................................................ 23

5.2 Results in LS-DYNA ................................................................................................. 25

6 Summary of SafeEV and MATISSE Guidelines and Recommendations........................ 27

6.1 Template and Directory ............................................................................................. 27

6.2 Summary of MATISSE Guidelines and Recommendations ...................................... 28

6.3 Summary of SafeEV Guidelines and Recommendations .......................................... 29

6.3.1 Guidelines for Pedestrian Safety in Small Electric Vehicles (SEV) ....................... 29

6.3.2 Guidelines for Structural Improvements of Occupant Protection for Future

SEVs ................................................................................................................................ 32

6.3.3 Guidelines for Future Intelligent Protection Systems for SEV Occupants ............ 34

7 Literature .......................................................................................................................... 36

8 Annex ............................................................................................................................... 38



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1 Introduction

To summarise, condensate and specify the results gained in the projects SafeEV and

MATISSE guidelines and recommendations for various topics of the two projects are

collected within this deliverable and are brought in a form that is applicable in future work.

For this reason a template and a directory for the collection of the guidelines are established to

save all guidelines and recommendations in dedicated documents to be used for further

dissemination or possible expansion.

The topics within this deliverable consider implementation guidelines for the two

demonstrator components in MATISSE, compressed natural gas (CNG) tanks and adaptive

pressurised beams. Furthermore, the possible combination of the two components in one

vehicle is considered. To evaluate the crashworthiness of these components, guidelines

concerning fully virtual methods for safety enhancement due to adaptive pressurised

structures are given as well as for a fully virtual certification process for high-pressure storage

tanks. Both guidelines include recommendations on material testing. To secure appropriate

modelling of these components guidelines for the simulation of the materials are proposed.

Concerning the results of the SafeEV project guidelines concerning small electric vehicles

(SEV) are given. This comprises the safety of pedestrians as well as of occupants. For this

reason structural improvements for the occupant protection in SEV are proposed as well as for

future intelligent protection systems of SEV.



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2 Implementation Guidelines

2.1 Guidelines for Adaptive Pressurised Components

The development process of the shape adaptive structures leads to three general key design

features which need to be understood and defined correctly to guarantee a successful

implementation:

Foreseeing fibre over-length to increase the cross section

Relation between maximum curvature at radii and matrix bending stiffness

Processability and chemical compatibility of the elastomer and thermoset matrix

material

The realisation of the change of shape with the increase in cross section as it is done at the

presented structure underlies the requirements to allow for a material over-length in defined

areas were the cross section increase takes place (see Deliverable D3.2 [MAT14a]). For the

presented structure a U-profile is chosen where the material realising the increase in cross

section is folded inwards. This material needs to be realised with flexible bending properties

to enable the change in geometry. Independent of the cross section geometry the length of the

flexible material needs to be the half circumference of a virtual circle with a diameter defined

by the structures width. This geometric relation guarantees a tangentially constant transition

from the stiff part of the structure to the flexible in case of pressurisation. Herewith, an

optimal load transfer in fibre direction between the flexible area and the stiff part of the

structure is enabled. This is the baseline to enable high inner pressure without failure at the

transition area.

A decisive design factor for the shape adaptive structure is the relation between the maximum

curvatures at the flexible areas of the cross section and the material properties defined by the

fibre angle, the material thickness and the matrix material. Investigations showed that as the

failure modes at the hinge like element of the shape adaptive crash component are

significantly influenced. Large deformation due to small curvatures together with very soft

matrix materials (elongation at break >600%) can lead to early failure of the material in the

bending area due to delamination and fibre buckling. In this case the small bending stiffness

and the large elongation properties of the matrix do not support the fibres sufficiently to

prevent them from buckling at the compression loaded area. Furthermore, the bending of the

pre-curved material leads to out-of-plane forces in the laminate. These forces lead to

delamination. The matrix material needs to be able to withstand these delamination forces to

prevent failure of the material. So far the direct correlation between maximal bending

curvature, material thickness and matrix properties are not yet fully identified. Application

oriented geometries and materials need to be tested to ensure the functionality.

Regarding the manufacturing the general processability of the matrix systems needs to be

guaranteed. The main factor is the viscosity of the elastomer matrix material. Since elastomers

tend to have high viscosities up to 10.000 mPa·s and limited processing times suitable



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elastomer matrix materials have to be defined which can be processed in the vacuum infusion

process. This is strongly dependent on the pre-form and the individual cure kinetics of the

resin system. A fundamental guideline cannot be defined. For the manufacturing of the shape

adaptive structure using the Hybrid-Matrix-Process, matrix systems for the elastomer and

thermoset area have to be chosen which are chemically compatible. The simultaneous

infiltration at the co-infusion process leads to a mixing of both matrix materials in the

laminate. A co-curing process needs to be guaranteed where both matrix materials as well as

the mix cure in a determined way so that useful material properties are realised. It was found

during the development of the shape adaptive structure that matrix systems based on the same

polymer type can offer the possibility to be miscible with co-curing behaviour.

2.2 Guidelines for High-pressure Storage Tanks

From the results obtained in the VTM developed within MATISSE the main guidelines

emerged from the analysis of the vessel are:

To check the contacts caused by the surrounding shield components that should be

avoided. Here softening materials should be exploited to distribute the derived

stresses.

To check the coherence between stress results and the damage extra history variables

reported in the simulation of pressurised vessel.

To optimise the bolt preloading value by obtaining a compromise between stress on

the external vessel and the possible translation of tanks in the retaining strap mount if

it undergoes accelerations. The standard pre-tensioning is not suitable.

Use an extra *MAT_NULL surface on the most external layer of the tank to improve

the T-shell element stability in the contact phase. Most problems during stabilisation

of the retaining strap system are due to the initial contact.

This external layer should have coincident nodes with the external one and be the

reference for the contact surface generation in the model.

To guarantee a separate contact card definition for the vessel and its surrounding

systems. The insertion of the vessel in an auto-contact card is problematic in terms of

model stability. In fact, when the crash was modelled in this manner, it had been

possible to observe peaks in contact energy parts that caused the instability.

To develop an automatic script or to use an advanced composites modelling software

in order to define the material orientation on the various faces of the T-shell elements,

based on the actual composite configuration and the orientation of the vessel once

mounted, because the inclusion of the vessel model will refer the orientation of the T-

shell faced as the new orientation system, causing a mis-definition of the material

characteristics.



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3 Adaptive Pressurised Components Implemented in CNG Vehicles

The tested configuration of the adaptive pressurised components in CNG vehicles depicted in

Figure 1 leads to three general key design features which need to be understood and defined

correctly to guarantee a successful implementation:

Steel fixation to an adapted body part, not subject to large deformation in the objective

crash condition in order to avoid undesired deformations on the beam or change of

shape once inflated.

Inflatable components should be positioned at a suitable distance from the vessel

shields, permitting the complete deployment of the beam.

The beam works in a rather similar way to an airbag; therefore it must have a reaction

surface rigid to lean on and to transmit the reaction forces that arise in impact.

The introduction of the inflatable adaptive elements shall be introduced where critical

points are found or to substitute already implemented components.

Figure 1. Layout of dissipation components in MATISSE layout A configuration



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4 Safety Requirements for Evaluation of Crashworthiness of Composite

Materials

4.1 Fully Virtual Methods for Safety Enhancement due to Adaptive Pressurised

Structures

In order to use numerical models for the prediction of safety enhancements or the design of

components, these models have to fulfill certain requirements. For the case of pressurised

structures, basic requirements are discussed in the following. Furthermore, it is described to

which extent those requirements are fulfilled with the developed simulation models for the

adaptive structures.

Requirements for models:

- Good prediction of crashworthiness: The key requirement for each model is to be

capable to describe the mechanical properties of the structure. This is mainly related to

the material model(s) that links element deformation with resulting stresses. In this

regard, in particular damage and failure mechanisms have to be covered. Upon the

material model the geometrical discretisation is influencing the accuracy of the results.

This requirement is essential for the beneficial application of such tools in the

development process.

The material models developed for the adaptive structures fulfil those requirements to

a wide extent. The basis for those models form simple material tests (coupon tests)

which were used to derive the input-parameters of the models and to parameterise the

failure-models. So the simulation models of the adaptive pressurised beam can be used

in a fully virtual development. If the application of the structure (loading, geometry

etc.) changes significantly from the validated baseline, the results quality will suffer.

However, depending on the level of detail that is in focus, the developed models are

limited. Some failure modes of FRP (e.g. delamination) cannot be analysed.

- Component safety: In addition to the accurate simulation of the structures mechanical

properties, for the application in a virtual development the model has to allow for the

analysis of other aspects that are relevant for the design/application of a pressurised

structure.

First of all it is of great interest if functional safety can be evaluated. For pressurised

structures, that would be the assurance that the inner pressure is maintained within the

structure at the time of loading. A leakage can occur instantaneously or slowly, both

effects should be analysable in a model for virtual development. There exist modelling

approaches (CPM, ALE) that would allow for the simulation of such effects. One main

difficulty thereby is the definition of “holes” that open during the loading at a not pre-

defined position.



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In the current model, the uniform pressure approach (UP) is used which does not take

into account any gasdynamics. The assumption is that the pressure is the same at any

point within the structure. The simulation results show at which time elements fail (

hole leads to pressure drop within structure), but for the calculation of the inner

pressure the resulting hole is not considered. Hence, no analyses regarding inner

pressure are possible witch the current model.

For a virtual development of pressurised structures, also interactions with and possible

hazards for car occupants are in focus. Examples for such research questions are for

instance a pressure peak close to the occupant due to the bursting of the pressurised

structure and/or fragments of the failed structure that might intrude the passenger

compartment with high velocity. In that regard the currently developed model features

no capability for such analysis.

In order to develop a model that is featuring the capabilities described above, several

additional steps have to be done in the development process of such a model. In the following

the main additional steps for a model for fully virtual development are outlined.

Proposal for development process:

The figure below describes the state-of-the-art development process of a conventional

simulation model.

Figure 2. Development process

Before the actual start of the development of the model, all effects that should be represented

with the model, have to be listed. For each effect a corresponding modelling approach has to

be chosen. In addition to the material tests (coupon tests) this overview defines, which

additional tests need to be done in order to able to parameterise the model. Some of these tests

are to be done already on material level (level 1), others on the component level (level 2).

The main missing capability of the developed models for adaptive pressurised structures is,

that leakage and loss of pressure cannot be modelled in detail. So the model is very limited

regarding evaluation of occupant safety.



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In order to use that model in a fully virtual development process it has to be enhanced by an

alternative modelling approach for the pressurisation (ALE or CPM). In order to validate this

model component tests have to be carried out. The occurrence of leakage is related to material

failure and to be set by adjusting material parameters. The behaviour of the inner pressure, as

soon as the gas can escape the structure, has to be set by component tests.

By these enhancements, the models would not only be capable of predicting the deformation

under a given loading but also the behaviour of the inner pressure, which is also heavily

influencing the mechanical properties. With this step done, an application in a fully virtual

development process seems to be very beneficial.

4.1.1 Recommendation on Validation Tests and Corresponding Criteria

In order to define a suitable material model a set of material tests as given in Table 1 is

recommended. On the one hand the basic material values can be derived from the test results

and filled into the material cards. Subsequently, these tests are modelled using the proposed

simulation approach and are evaluated concerning the force displacement curve. For each

displacement value the force value of the simulation curve has to lie in a range of 90% to

110% of the target value. Additionally, the integral of the force over the displacement of the

two curves shall not deviate more than ± 10%.

Table 1. Validation tests on material level

Material

validation test

Measure properties Validation criterion Criterion level

for acceptance

0° tension Force-displacement/stress-strain

curve, modulus, strength

Force-displacement curve ± 10%




0° compression Force-displacement/stress-strain






In-plane ± 45° tension Force-displacement/stress-strain



3-point bending test Force-displacement curve,

fracture toughness


Double cantilever

beam

Force-displacement curve,

fracture toughness


Mixed mode bending Force-displacement curve,

fracture toughness


To fully acquire the material characteristics additional tests are recommended. They are

however not carried out for the material for the adaptive beams since a material model is

applied that requires only the data listed in Table 1. The recommended additional tests are

given in Table 2.



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Table 2. Additional tests

Material

validation test


for acceptance

End notch flexure test Force-displacement curve,

fracture toughness


Compact tension test Force-displacement curve,

fracture toughness, strength

(fibre tension)


Compact compression

test



(fibre kinking)


For all tests of Table 1 and Table 2 elevated strain rates are recommended, if enough

specimens are available, in order to investigate strain rate effects on strength and fracture

toughness.

Furthermore, validation tests on the component level are recommended. Here, three tests are

proposed. At first the component is activated without any external loading. The functional

validation of the concept is given if no leakage of the structure occurs. If leakage is defined by

the concept, this criterion is not relevant. Concerning the simulation model validity the

pressure vs. time curve is to be analyses. Here again, for each time step the pressure value of

the simulation curve has to lie in a range of 90% to 110% of the target value. The second

component validation test is the loading with a load similar to the aspired application case

without activation of the pressurisation. From the concept side no rupture is allowed, while

the simulation is evaluated using the force vs. deflection curve as well as the moment vs.

deflection curve. The simulation curve shall again not deviate from the testing more than

± 10%. The last test is the loading with an activated component. The validation criteria are

here the same as for the previous test. The component validation programme is given in Table

3.

Table 3. Validation tests on component level

Component validation

test

Concept

validation

criterion

Concept

criterion level

for acceptance

Simulation

validation

criterion

Simulation

criterion level

for acceptance

Expansion test without

external load

Integrity No leakage when

not defined

Pressure-time

curve

± 10%

External load similar to

application without

activation

Rupture No rupture Force-deflection

curve

± 10%

Moment-

deflection curve

± 10%

External load similar to

application with activation

Rupture No rupture Force-deflection

curve

± 10%

Moment-

deflection curve

± 10%



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4.2 Fully Virtual Certification Process for High-pressure Storage Tanks

One of the aims of WP5.3 was the investigation of the approach of fully virtual ‘certification’

procedures for high-pressure storage tanks.

In general, the possibility to obtain a certification on the basis of the numerical results coming

from a simulation (of the regulatory test set-up concerned) requires the compliance of the

adopted numerical models w.r.t. a series of specific verification and validation steps, to be

agreed with the Technical Service responsible for the release of the type approval certificate.

Such a procedure is needed to demonstrate that the used numerical models are capable to

reproduce, with the adequate level of correlation, the experimental results coming from

reference test set-up that are agreed with/indicated by the Technical Service: in this way, the

adequateness of the model to describe the physical phenomena involved in the selected

reference real tests can be assessed and the use of said numerical model only, for the specific

(and similar) regulatory test-set-up, can be trusted in and the certification issued on the basis

of the pure numerical results.

All the aspects related to the fully virtual certification process were examined within the past

EC project IMVITER, where Verification & Validation (V&V) templates were defined and

proposed in order to structure and support the interaction with the Technical Service during

all the steps leading to the final virtual type approval; in this past project such templates were

applied to specific regulatory pilot cases (among which the pedestrian headform and legform

impacts from EC Reg.631/2009), even if their general validity was highlighted and their use

as a basis for future applications to new pilot cases recommended.

Then within MATISSE WP5.3, a Verification & Validation report following the IMVITER

template layout was investigated and generated for the specific pilot case represented by ECE

R110 regulation.

This regulation that deals with “Uniform provisions concerning the approval” of

I. Specific components of motor vehicles using compressed natural gas (CNG) and/or

liquefied natural gas (LNG) in their propulsion system;

II. Vehicles with regard to the installation of specific components of an approved type for

the use of compressed natural gas (CNG) and/or liquefied natural gas (LNG) in

their propulsion system” [ECE13], where impact tests for the high pressure storage

tanks are required

requires indeed specific impact testing on the tanks.

More precisely, the regulation requires a drop test for the vessel, from a specified height, in

four different configurations, with different initial positions of the tank and corresponding

different impacted zone: vertical set-up (impact on both boss parts of the vessel), horizontal

set-up (impact along the cylindrical part) and oblique set-up, with an angle of 45° (impact on

the dome area); such configurations are recalled in the following Figure 3.



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Figure 3. ECE R110 drop test configurations

For completeness the detailed description given in the regulation (Annex 3A – Appendix A;

A.20. Impact damage test) is recalled in the following, too.

“One or more finished cylinders shall be drop tested at ambient temperature without internal

pressurisation or attached valves. The surface onto which the cylinders are dropped shall be a

smooth, horizontal concrete pad or flooring. One cylinder shall be dropped in a horizontal

position with the bottom 1.8 m above the surface onto which it is dropped. One cylinder shall

be dropped vertically on each end at a sufficient height above the floor or pad so that the

potential energy is 488 J, but in no case shall the height of the lower end be greater than

1.8 m. One cylinder shall be dropped at a 45° angle onto a dome from a height such that the

centre of gravity is at 1.8 m; however, if the lower end is closer to the ground than 0.6 m, the

drop angle shall be changed to maintain a minimum height of 0.6 m and a centre of gravity of

1.8 m.”

In order to evaluate in a quantitative way the effects of the damage induced on the tank by the

impacts, typically a hydrostatic pressure burst test is conducted on the tested tank and the

pressure at which the rupture of the tank occurs has to be over a specified limit (450 bar).

Again, for completeness the detailed description given in the regulation (Annex 3A –

Appendix A; A.12. Hydrostatic pressure burst test, part b) is reported in the following.

“The minimum required (calculated) burst pressure shall be at least 45 MPa, and in no case

less than the value necessary to meet the stress ratio requirements. Actual burst pressure shall

be recorded. Rupture may occur in either the cylindrical region or the dome region of the

cylinder”.

The elaboration of a Verification & Validation template for the specific ECE R110 pilot case

was conducted on the basis of the experience made within WP4: in particular, the step 4 of the

Virtual Testing Methodology (VTM) involving the so called “simplified/reduced test set-up”

was assumed/proposed as the reference test set-up that are agreed/shared with the Technical

Service in order to assess the adequateness of the tank model for the subsequent pure virtual

testing phase involving the (only) numerically simulated drop tests and burst pressure tests.



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In fact, within WP4, the simplified test rig was specified through numerical simulations first,

then physically built and used for experimental testing campaigns on real vessel, in order to

get reference data useful for the tank numerical model validation phase.

The real tanks damaged through the use of the simplified/reduced test rig were analysed in

different manner; visual inspection, burst pressure value, computerised tomography and

microscopy analysis of the damaged tank zones. As this was done in order to create references

for the validation of the numerical models developed in WP4, corresponding hypothesis for

possible correlation criteria were included in the V&V template for the ECE R110 pilot case,

even if at the end from the last two types of in depth analyses it was not possible to extract

quantitative criteria about the damage induced by the impact (only the visualisation of the

damage typology was possible).

Another important aspect of the V&V template is the specification of correlation criteria in

order to have an objective evaluation between numerical and experimental curves for the

specific monitored outputs having this form.

In the elaboration of the document for the ECE R110, some methods used within the

IMVITER pilot cases were maintained as an exemplary indication, even if the corresponding

metrics were not checked (i.e. applied) for our specific case, due to the fact that the results

achieved with Stage 3 tank model (the one to be used for practical applications) could be

considered only very preliminary as the desired correlation level between numerical and

experimental results was not reached within the end of the project (a final iteration loop for a

conclusive validation of this model stage is in fact necessary).

In particular, the metric called OSRS (Objective Signal Rating System) that appears in the

elaborated V&V template, is the one developed within the ISO Working Group 4 on Virtual

Testing and that is described in the two following documents:

ISO/TR 16250:2013 "Road vehicles - Objective rating metrics for dynamic systems“ [ISO13]

and ISO/TS 18571:2014 " Road vehicles — Objective rating metric for non-ambiguous

signals“ [ISO14].

This metric permits to rate objectively the level of correlation between a numerical and an

experimental signal in the time domain, through the analysis of four signal aspects (corridors,

slope, magnitude and phase) leading each to a partial score that, through a proper weight,

contribute to the final ISO rating, with a corresponding grade (Excellent, Good, Fair, Poor).

The evaluation is done according to an algorithm that grants the objectivity of the analysis and

that was developed for crash applications. This metric is believed to become a reference for

the future developments of future virtual testing procedures (as already anticipated by

IMVITER), even if probably specific adaptations to the specific cases concerned need to be

considered (e.g. the minimum rating grade needed for the acceptance of the virtual models for

the virtual testing, depending on the state of the art of modelling and to be discussed case by

case within the proper places, i.e. regulatory working groups).



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The OSRS metric resulted from a proper combination of the metrics from CORA

(CORrelation and Analysis) and EEARTH (Enhanced Error Assessment of Response Time

Histories) algorithms, that are also mentioned in the V&V template (in order to highlight the

fact that different metrics could be selected for the specific case).

Taking into account the above mentioned situation about the effective level of maturity

reached by the stage 3 tank model within the end of the project, the V&V template was

completed in any case by using the available results and with the aim to provide an exemplary

documentation that can be improved in the future, when the desired level of validation of such

type of numerical model will be reached. Several comments about the contents implemented

in the sections of this document are reported, too, in order to reflect what was obtained during

the simulations performed with the available stage 3 model, according to the configuration

proposed template.

This V&V template is delivered as annex to this document (see chapter 8), in order to

maintain the format/lay-out identified and suggested by the IMVITER project unchanged.

In the following, just a brief description of the structure of this document is given, in order to

facilitate the reading of the Annex and describe some of the principles behind the template.

The first section is dedicated to the identification of the applicant (who requires the virtual

type approval for the tank), the type of vessel concerned and the input model file name that is

presented/used for the virtual evaluations, including the corresponding release date and the

information about the solver used for the simulations.

The second section provides the description of the tank model used, in order to permit the

numerical model verification: in practice the numerical model is described in all its main

parts, by giving details and remarks in a flexible way, then helping the interaction with the

Technical Service that will process the request of the virtual type approval (and that will

maintain the possibility to verify the information given about the numerical model in more

detail directly at the applicant site). Here, the correspondence between the numerical model

and the real tank is provided through the description of all its parts, including the main

information about geometry and materials. In order to maintain a certain flexibility of the

document, other than a fixed number of mandatory fields (part name, thickness, material,

material model and density), a free field for remarks is always provided, in order to add the

desired details that are relevant for the specific model to be used for the virtual testing.

As already mentioned, for the ECE R110 pilot case considered, the following sequence was

envisioned, on the basis of the experience made in WP4 with the VTM: validation of the tank

model on the basis of the simplified test-rig configuration first and then its use in the stand-

alone or isolated configuration characterising the regulatory drop and burst pressure numerical

test only. Consequently, other than the just discussed description of the isolated tank model,

the V&V template must also provide information about the reduced/simplified test-rig,



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including the adopted mounting solution (in our case, the belt system); this is indeed what can

be found in the subsequent paragraphs of the V&V template.

Then the big part of the document involving the model validation starts: first of all, the

numerical set-up to be used for the validation phase is described, for each of the test-rig

configurations selected as reference cases and for which the experimental tests were

conducted (here the configurations 2, 6 and 7 examined within WP4.2). Information about the

numerical simulations are provided (time steps, sampling frequencies, signal filtering, input

file names, computing platform used) are provided, for each reference configuration, together

with the so called calculation verification assessment, based on a series of verification criteria

(statements) which are checked according to a specified way (visual animation, energy

balance, etc.), then reflecting the classical approach followed normally by the crash analysts

during their operational activities. In this part images from the animation results and curves

for the energy balances are provided. Subsequently, the parts related to the validation of

numerical model results against the corresponding experimental test data is presented: here a

comparison in terms of tank deformations and impactor kinematics, tank acceleration curves,

load cell curves, maximum damaged tank surface and other damage aspects is provided and

assessed towards proposed correlation criteria, including also the residual burst pressure

conducted on the tank after it has been damaged on the simplified test-rig.

The correlation criteria reported in the document the proposal that arose during MATISSE

project discussion on the correlation aspects, even if they still need improvements, especially

for what concerns the identification of the corresponding acceptance limit values.

These correlation criteria proposals are shortly recalled in the following, even if they are

included in the template, too.

Maximum damaged tank surface criterion: from visual inspection on damaged real tested

(RT) tank, an externally measured area visibly damaged (Art) is recorded. From numerical

(VT) model, the same is done and an area (Avt) equal to the sum of critical/damaged/failed

element areas on the model is computed. The criterion is satisfied if:

|Avt-Art|<= reference tolerance (tbd) (1)

Number of damaged tank layers and/or decohesians: such a number should be the same or

similar for both the numerical model and the real tank (acceptable differences to be defined).

This criterion depends on the possibility to extract such type of information (or an equivalent

one) from the in depth analyses to be conducted on the real tested tanks (as already

mentioned, it was not possible to obtain this quantitative information within MATISSE, even

if computerised tomography and microscopy were used to investigate this aspect).

Residual burst pressure (BRP) of damaged tank: from burst pressure test on damaged real

tested (RT) tank, the real value is recorded (RBPrt). From numerical (VT) damaged model



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pressurisation simulation, the same indicator is monitored and then recorded (RBPvt). The

criterion is satisfied if:

|RBPvt-RBPrt| <= reference tolerance (tbd) (2)

Moreover, the location where the virtual tank model bursts has to be similar to the one seen

on the corresponding experimental test (visual comparison of the burst tanks).

After the tank model validation part, the chapter related to the pure virtual testing of ECE

R110 drop test is introduced. The approach followed here is the same used for the previous

validation part, except for the fact that there is no comparison with experimental results, as

here the numerical results are to be used directly for the virtual type approval purpose.

In the V&V template reported in the annex (chapter 8), only the oblique 45° tank drop test is

described as an example, but for a future use of this type of approach, obviously all the

required drop test should be calculated and the document filled in accordingly.

In any case, the same sequence is adopted for the final numerical simulation of the type

approval test configuration: a run performing the tank impact according to the specific drop

test set-up including the subsequent simulation of the hydraulic burst test up to the obtainment

of the tank model rupture (with associated burst pressure virtual values).

Then the final criterion used for the virtual type approval will be again the following:

Residual burst pressure (BRP) of damaged tank: from numerical (VT) damaged model

pressurisation simulation, the recorded residual burst pressure value (RBPvt) has to be above

the regulatory limit, i.e. the criterion is satisfied if:

RBPvt > 450 bar (possibly with a certain safety margin, tbd) (3)

Even if it was not possible to demonstrate a complete pure virtual testing case for the ECE

R110 within the end of the project, due to the already mentioned situation faced with the

Stage 3 model from WP4, the corresponding V&V template for this specific case was defined,

then providing the basis for future refinements in this field, when the completion of the

validation loop on the tank model will be available. Obviously, with the availability of a fully

validated model and for a future regulatory use, this V&V document should not present failed

checks/criteria along its sections, as it happened instead with the one currently reported in

Annex.

4.2.1 Recommendation on Validation Tests and Corresponding Criteria

To set up a Type IV high-pressure storage tank model using the modelling approach

developed in MATISSE and presented in D4.5 [MAT15a] a number of material values are

necessary to develop the correspondent material cards. For the winding layers these values are

in detail:



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- Elastic moduli in fibre and transversal direction for tension and compression

- Elastic moduli in the three shear planes

- Strength in fibre and transversal direction for tension and compression

- Strength for in-plane shear

- Fracture toughness in fibre and transversal direction for tension and compression

- Fracture toughness in shear

- Fracture toughness values to define bilinear damage evolution

And for the delamination model:

- Force displacement curves of mode I and mode II delamination (DCB and ENF)

It has been discussed in D2.3 [MAT14d] that the production of specimens (coupon or ring)

for direct identification of these values using the winding process is not possible without

deviation of the material properties. For flat coupons changes in the production process would

have to be made that were considered (by Xperion experts) to influence the material

properties strongly. Especially the applicable fibre tension is of relevance since it influences

the fibre volume fraction. The production of ring-shaped laminates with a constant fibre

direction is also not possible. In radial direction a 90° orientation is not achievable to 100%

since the roving has to be transferred also longitudinally. In longitudinal direction a lower

angle than circa 10° is not windable, furthermore the positive and negative direction have to

be wound simultaneously, so that no unidirectional structure can be achieved. Another factor

that hinders the production of appropriate specimens is that in order to have the same material

conditions (e.g. in terms of fibre volume fraction) the ring diameter should be comparable to

the components diameter. For CNG tanks this leads in the most cases to ring specimens that

are too large to clamp in a conventional test apparatus.

To apply the reverse FEM approach that is proposed in D2.3 and to create the full set of

parameter values using calculations, assumptions and literature, the following information is

indispensible:

- Fibre volume share (e.g. by pyrolysis)

- Mechanical matrix properties (typically from producer’s data sheet)

- Mechanical fibre properties (typically from producer’s data sheet)

- Winding information (orientation and thickness of layers)

As presented in D4.4 [MAT15b] a macroscopic approach is pursued for the validation of the

material models. Therefore, three point bending (3PB) tests on tubular specimens with

different winding structures are proposed to be tested. At least three different laminate set-ups

that have relevance to the winding structure of the tank to be modelled should be tested. At



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least five specimens for each winding structure are recommended. The validation approach on

the macroscopic material level is given in Table 4.

Table 4. Validation tests on material level if significant coupon specimens are available

Material

validation test


for acceptance

3PB test on different

winding structures

Force-displacement curve Force-displacement curve ± 10%

50 50

550

50

1 m

m/s

Figure 4. 3PB test

If future research will identify a possibility to measure the material parameters with

significant coupon specimens the test programme and validation approach given in Table 5 is

recommended. This approach allows identifying the full necessary set of parameters. If

research leads to significant ring-shaped specimens, the test programme and validation

approach of Table 6 is recommended. Here, still literature values have to be applied

concerning delamination and fracture toughness. For both test programmes five specimens for

each test set-up are recommended.



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Table 5. Validation tests on material level if significant coupon specimens are available

Material

validation test


for acceptance
















3PB test Force-displacement curve,

fracture toughness


Double cantilever

beam


fracture toughness


Mixed mode bending Force-displacement curve,

fracture toughness


End notch flexure test Force-displacement curve,

fracture toughness




(fibre tension)


Compact compression

test



(fibre kinking)


Table 6. Validation tests on material level if significant ring specimens are available

Material

validation test


for acceptance
















3PB test Force-displacement curve,

fracture toughness




(fibre tension)


Compact compression

test



(fibre kinking)




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On the component level the test procedure of the VTM (see D4.1 [MAT14f]) can be applied

for validation purposes as presented in D4.5 (see Figure 5) and/or a test according to ECE

R110 as it is presented in D4.4 (see Figure 6). Additionally the pressurisation of the model

until burst and the comparison to the quality batch check in production should be considered.

For the validation the criteria according to Table 7 are recommended.

Figure 5. Test bench set-up for configuration 2

Figure 6. ECE R110 drop test



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Table 7. Validation tests on component level

Component validation

test

Measure properties Validation

criterion

Criterion level for

acceptance

Impact test on MATISSE

test-rig set-up or ECE

R110 drop test

- Impact force (only

MATISSE test)

- Damaged area

- Impact force

- Damaged area

- ± 10%

- Comparable area borders

Pressurisation until burst - Burst pressure - Burst pressure - In the range of the results

achieved in the batch

check



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5 Simulation Guidelines

As has been discussed in other MATISSE deliverables ([MAT14b], [MAT14c], [MAT14d]

and [MAT14e]), the strive towards more complex simulation models capable of capturing

phenomena of advanced materials such as composites implies that the FE software also need

to become more comprehensive in terms of functionality. As research and development

progress in all kind of fields, more features and material models are continuously added to the

software making it more complete.

Within MATISSE, the FE software LS-DYNA is used, which is global leader when it comes

to simulation of crash in the automotive industry. In LS-DYNA today, there are a number of

different material models capable of representing the physics of composite materials.

However, in order to be able to accurately perform simulations, the users need to be aware of

which settings to be used in the simulation model. There are some settings, which can be

considered as general but most of them are strongly dependent on application, geometry of the

structure being analysed, choice of element formulation (shell, solids) etc.

Also, there is always the trade-off between CPU resources available and through put time.

The more detailed and complex models, the more time required to run the simulations. The

models need to be as simple as possible but as complex as necessary, both in terms of number

of elements being used as well as material models.

5.1 Settings in LS-DYNA

There are a number of settings in the keyword input file, which are recommended (but not

mandatory) to be used to achieve more stable, accurate or time efficient results. Most of the

settings presented in this chapter concerns shells, where a plane stress assumption is made.

Unit system:

Every LS-DYNA user has to be aware of the use of a consistent unit system in order to get

reasonable results. This seems obvious, but is nevertheless a very common mistake. Example

of consistent units for length time mass and force are m, s, kg and N, mm, s, t, N or mm, ms,

kg, kN.

Invariant node numbering:

The material coordinate system is automatically updated following the rotation of the element

coordinate system, which is important in order to avoid wrong results working with

anisotropic materials. This is controlled by the *CONTROL_ACCURACY keyword. There

will be an additional CPU cost for turning this flag on, but it is highly recommended.

Material directions:

As composite materials generally have very different behavior in the different directions (x, y

and z), is it very important that the user makes sure that the material directions are properly



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defined. This may be difficult if the structure has a complex geometry/shape why the

graphical pre-processor is an invaluable tool. Note that one element may have multiple

material directions through the thickness at each integration point.

Different pre-processors have different ways working with this. In the pre-processor LS-

PREPOST which is design for LS-DYNA and recommended by LS-DYNA distributer, there

is a composite option in the element editing menu.

If CMPFLG is set to 1 in the *DATABASE_EXTENT_BINARY keyword, LS-DYNA will

output stresses and strains in the local material coordinate system. If zero, the stresses and

strains will be global in the d3plot result files. Also, MAXINT must be set to the number of

integration point used in the shells (either defined by a *SECTION_SHELL card or a

*PART_COMPOSITE card).

Laminated shell theory:

By setting the parameter LAMSHT (*CONTROL_SHELL), the laminated shell theory is

activated. If this is not set, the stiffness of the shell can be exaggerated if there are differences

in the elastic constants from ply to ply (integration point). This option is valid for both shells

and thick shells.

Thickness update due to membrane straining:

The parameter ISTUPD (*CONTROL_SHELL) controls the thickness update of the shell

caused by membrane straining of the element. This is very important when simulating

material forming of ductile materials, e.g. metals. For composites however with a more brittle

behavior, it is often beneficial to keep the default value (=0).

Damping/stability

Adding some damping (*DAMPING_PART_STIFFNESS) may be beneficial in order to

decrease noise in the simulation when elements start to fail and setting the

*CONTROL_BULK_VISCOSITY = -2 may increase stability in compressive modes. To

further reduce the risk of having badly shaped shells, NFAIL1 (under-integrated) and NFAIL4

(fully integrated) can be set on the *CONTROL_SHELL to remove highly distorted shells.

Part, element and section definition

There are different ways of defining parts made of composite material. One convenient way is

the set material thicknesses and orientation of the element cards using the keyword

*ELEMENT_SHELL_COMPOSITE for shells and *ELEMENT_TSHELL_COMPOSITE

for thick shells respectively. The structure of such an input is displayed in Figure 7 below.



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Figure 7. Example of part, section and material definition

Delamination

As already discussed in WP2 deliverables ([MAT14b], [MAT14c], [MAT14d] and

[MAT14e]), there are two well-established ways of modelling delamination between different

plies in the composite structure. Either by using cohesive elements between the shells or by

contact tiebreak definition. The same results can be achieved regardless of approach, but from

a modelling point of view, using a tiebreak contact requires less effort since no elements need

to be meshed. It is recommended to carry out a contact check (e.g. in LS-PREPOST) before

running the simulation to verify that all nodes are properly attached to a surface segment.

Using cohesive, the user needs to verify node connectivity and make sure that the proper

element formulation for cohesives is used.

From a post processing point of view, it may be easier to visualize delamination due the fact

that the cohesive elements are eroded after failure. When using tie-break, delamination can be

tracked using *DATABASE_BINARY_INTFOR.

5.2 Results in LS-DYNA

After the solving has successfully finished, there are a number of standard checks which need

to be carried out. First of all the numerical stability needs to be verified. Examples of this are

checking for the normal termination message in the d3hsp result file, checking the time step

used in the simulation and verifying energy balance (glstat). The visualisation of the results

(d3plot) in LS-PREPOST (or other post-processor) allows a visual inspection of the deformed

shape.

The numerical accuracy is verified by looking at e.g. hourglass energy, added mass (if mass

scaling is used) or checking how many time steps the simulation required. For large models,

running the job in double precision may be required. If the time step used is larger compared



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to the stable time step for the contact, the user must verify that the contacts are working

properly.

After the numerical stability and accuracy is verified, it is good practice to verify the

simulation results by analysing, acceleration, velocities, forces, moments or other results

relevant for the simulation.

History variables:

Many of the material models in LS-DYNA which are used for modelling composites have so

called history variables which stores additional information during the simulation, e.g.

damage in different directions, flags for failure etc. A list of history variables can be found

here: http://www.dynasupport.com/howtos/material/history-variables

The user needs to set how many history variables LS-DYNA shall kept track of during the

simulation by defining parameters NEIPS (shells) and/or NEIPH (solids) in the

*DATABASE_EXTENT_BINARY keyword.

http://www.dynasupport.com/howtos/material/history-variables



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6 Summary of SafeEV and MATISSE Guidelines and Recommendations

6.1 Template and Directory

In order to document the guidelines and recommendations that were developed within the two

projects SafeEV and MATISSE (both funded by the European Community's Seventh

Framework Programme and part of the SEAM project cluster) a common template for

Microsoft Word was proposed. The template’s layout can be seen in Figure 8.

Figure 8. Common template for documentation of guidelines and recommendations for SafeEV and

MATISSE

The header of the template shows the logos of the two projects, of the SEAM cluster and of

the Framework Programme. Below that the “Guidelines and Recommendations” is headlined

and the page number is given. Next the information concerning the specific guidelines and

recommendations can be given: the project title, the date, the topic and the contributing

partners. The main part of the template is a text box where the author can fill in all necessary

information. Besides continuous text this can also consist of tables and figures. Therefore,



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examples for their notation and layout are given. For the data management the guidelines and

recommendations are to be named as follows: PROJECTNAME_TOPIC_yyyymmdd.docx.

Figure 9 shows the common directory that was established for the summary of the guidelines

and recommendations.

Figure 9. Directory for the summary of the guidelines and recommendations

Within this deliverable the guidelines and recommendations are presented using the

MATISSE deliverable template.

6.2 Summary of MATISSE Guidelines and Recommendations

The guidelines and recommendations concerning MATISSE have been presented in the

previous chapters of this deliverable. Namely, these are:

- Guidelines for adaptive pressurised components (see chapter 2.1)

- Guidelines for high pressure storage tanks (see chapter 2.2)

- Adaptive pressurised components implemented in CNG vehicles (see chapter 3)

- Fully virtual methods for safety enhancement due to adaptive pressurised structures

(see chapter 4.1)

o Recommendations on validation tests and corresponding criteria (see chapter

4.1.1)

- Fully virtual certification process for high-pressure storage tanks (see chapter 4.2)

- Simulation guidelines (see chapter 5)



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6.3 Summary of SafeEV Guidelines and Recommendations

In the following the guidelines and recommendations of the project SafeEV cooperating with

MATISSE within the SEAM project cluster are documented. SafeEV has received funding

from the European Community's Seventh Framework Programme (FP7/2007-2013) under

grant agreement n° 314265.

6.3.1 Guidelines for Pedestrian Safety in Small Electric Vehicles (SEV)

During the development of the advanced safety solutions described in chapter 4 of [SAF15a]

different approaches were followed. Lessons learned and different guidelines could be

extracted from the development process and are summarised in the following.

Guidelines for the development of in-crash sensor signals:

For the assessment/evaluation of the pedestrian safety sensor system (in-crash sensors)

following points must be considered:

• The structural layout of the front structure on which the in-crash sensors have to be

mounted should be stiff enough not to cause too high vibrations (determination of use and

misuse crash signals should be possible).

• Depending on the vehicle size and the structural design a 2-, 3- or 4-sensor-system can

be chosen.

• To enable a crash signal calibration a set of crash load case with different impactors

(e.g. leg, ball), velocities (e.g. 25 km/h to 55 km/h) and impact positions (y- and z-direction)

must be generated.

Guidelines for the development of pedestrian friendly bumpers:

In the definition of the new bumper concept for REVM1 (reference electric vehicle model),

the following general guidelines for a good leg protection were followed/applied:

• Grant an adequate/sufficient crash depth, in order to contain the accelerations

sustained by the leg (tibia accelerations).

• Provide an appropriate deformation stiffness/strength level within the available crash

depth.

• Generate an appropriate force distribution on the legform impactor, by obtaining a

balanced support during the impact through the introduction of a supporting frame in the

lower part of the bumper (dam area), in order to limit the knee injuries (bending angle /

ligaments elongation).

• Control such force distribution along the vertical direction of the bumper, by properly

differentiating the stiffness between the upper (fascia) and the lower (dam) part of the

bumper, so that the lower area is stiffer than the upper one.



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In the definition of the new bumper concept for REVM2, the following general guidelines for

a good leg protection were followed/applied:

• Analyse the front structure of the car identifying the major stiff components that can

create a problem to the lower leg impact.

• If the front structure is already designed, a foamed material can be integrated that can

reduce the deceleration of the lower leg. The foamed component can also help to reduce the

knee shear.

• If there is a possibility to change the front structure and in particular the transversal

beam, one solution could be to introduce a transversal beam with a lower stiffness. One

possible solution might be a stiffness adaptable carbon fibre reinforced polymer (CFRP)

material, which advantage is that it can work in the soft and stiff version in function of the

topology of the impact.

Guidelines for the development of pedestrian friendly windscreens:

During the development of the windscreen for REVM1, the following general guidelines for a

good head protection were followed/applied:

• Due to the outer shape of small electric vehicles, which in general have a small vehicle

length, the complete windscreen lies within the head impact area.

• In general the laminated safety glass of the windscreen in unbroken condition has a

high stiffness, which usually results in a small deformation and an increased injury risk for an

impact in the windscreen centre. An early stiffness reduction by glass fracture in the first 1 ms

to 2 ms after first impact shows a high potential to reduce the injury risk.

• The glass fracture depends on defects in the material and the glass surface. Thus, an

early fracture cannot be assured for all impacts. Due to this stochastic fracture behaviour, the

developed assessment method presented in chapter 4.1.1.2 of [SAF15a] shall be used for the

design of pedestrian friendly windscreens.

• Assuming that during a head impact in the windscreen centre an early fracture

initiation time results in low injury risk, a small windscreen mounting angle, a small

windscreen height, a small windscreen width, a small transverse curvature at the middle of the

windscreen, a small transverse curvature at the windscreen side and a high longitudinal

curvature at the bottom result in a low injury risk.

• The positioning of the float glass within the laminated safety glass influences the

injury risk as well. A TFFT-design (laminated windscreen with tin-fire-fire-tin-position of

glass sides) and an FTFT-design (laminated windscreen with fire-tin-tin-fire-position of glass

sides) could lead an injury risk reduction.

• Advanced fracture criteria might not be available in early software versions. Thus, the

software to be used shall be clearly communicated.



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Guidelines for the development of pedestrian friendly windscreen frames:

During the development of the lower windscreen cross beam for REVM1 and the external

airbag for windscreen frame area for REVM1, the following general guidelines for a good

head protection were followed/applied:

• Due to the outer shape of small electric vehicles, which in general have a small vehicle

length, the complete windscreen frame area lies within the head impact area.

• In general the components in the windscreen frame area have an increased stiffness,

which usually results in a small deformation and an increased injury risk. Reducing the

stiffness of the impacted components, e.g. by means of a stiffness adaptable CFRP or an

external airbag, shows a high potential to reduce the injury risk.

Guidelines for the development of pedestrian friendly outboard wheels:

During the development of outboard wheels for REVM2, the following general guidelines for

a good leg protection were followed/applied:

• In case of outboard wheel design without chassis covers, additional foams are only

able to reduce the injury risk for impacts with a small vehicle velocity. In order to reduce the

injury risks during high velocity impacts, further active safety systems, e.g. automated-

braking systems, are recommended.

Guidelines for the development of safety measures for the ground impact:

The following general guidelines are proposed related to safety measures for ground impact:

• Hybrid approach of modelling the road surface reduces the overall computation time

small mesh size (~ 5 mm) is required to model road lengths around 11.8 m are required.

Therefore, modelling road surface with small element size can be restricted to a limited area

(approx. 1 m by 1 m) and the rest of road surface can be meshed with bigger mesh size based

on impact location of head.

• Full pedestrian kinematic simulation is not a viable approach for the assessment of

ground surface respectively development tool for the optimisation of road surfaces because of

random pedestrian kinematics (influencing parameters: braking/no braking/car velocity/

multiple vehicle impacts). Nevertheless, full body pedestrian simulation delivers global

kinematic parameters and indicates the range of (head) impact velocity (for specific car design

or collision scenario).

• Based on this, an impactor or head model should be used in order to assess the head

injury risk during secondary impact and the potential of e.g. ground surface modification.

This impactor or head model should be sensitive to relevant head injury mechanisms:

neurological injuries, subdural hematoma and skull fracture.



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6.3.2 Guidelines for Structural Improvements of Occupant Protection for Future

SEVs

Within the working groups of the SafeEV work package 4 subtask 4.2.1 different structural

improvements were implemented focusing on the different REVM architectures and crash

load cases discussed within the project. General conclusions on the improvement potential of

the different structural solutions are drawn directly in the respective document chapters 2.1 to

2.4 of [SAF15b].

This guidelines chapter has the aim to summarize the lessons learnt within the working group

activities. The statements listed here can be considered as starting point for future SEV design

activities with focus on occupant protection for SEV architectures that are comparable to the

REVMs.

Front crash optimisations of SEVs with focus on occupant protection:

Lessons learnt concerning front crash optimisation of SEVs with respect to the 35 km/h to

35 km/h oblique movable progressive deformable barrier (MPDB) and the 50 km/h full width

deformable barrier (FWDB) load cases:

• The high energy absorption potential of extrusion profiles qualifies the use of this

manufacturing technique for crash energy management – energy absorption and load

spreading – within front vehicles of low length. Therefore, the consideration of the related

techniques is recommended for SEV structural design. The realisation of extrusion profiles in

multi-chamber cross-section design offers the opportunity to further increase the stiffness or

energy absorption capacities of profiles while conserving the design space. The positive effect

of this component behaviour on front crash occupant protection has to be verified for any

given SEV design especially in case of the oblique MPDB test configuration.

• The application of Al-space frame design to the front vehicle allows to realise weight

reductions comparable to values discussed in literature for M class vehicles, when focusing on

the defined SEV front crash load cases for SEV structures comparable to the REVM1

structural design.

• Without sufficiently dimensioned upper load path structures, passenger compartment

intrusions in the upper zone of the passenger compartment front cannot be significantly

reduced in case of the oblique MPDB crash test. In addition to longitudinal load path

structures supporting the upper vehicle architecture, the application of reinforcements to the

passenger compartment front in transversal direction is recommended. Structural

reinforcement measures of the passenger compartment result in increasing deceleration

parameters – mean and peak accelerations – that require the adaptation of restraint system

features. The influence of structural modifications on the deceleration properties has to be

considered at an early stage of the structural optimisation process, to allow for a suitable

adaptation of the restraint system triggering features relying on the structural deceleration

signals.



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• The bending deformation of conventional longmembers within the SEV’s front vehicle

in case of oblique impacting by the MPDB crash opponent might reduce the energy

absorption capacity of the front crash deformation zone. This potential issue is strongly linked

to the possible additional deformation load paths triggering when front vehicle package

components get in contact with the bending longmembers resulting in increased passenger

compartment front intrusions. Structural countermeasures to support the longmembers or

increase their bending stiffness have to be considered in this case. No significant issue related

to this question is to be expected in case of a low front vehicle packaging level.

• The adaptation of front components like front crossmembers or crashboxes to the

requirements related to improved vulnerable road user (VRU) protection can be achieved

without declining the front crash occupant protection properties. To achieve a trade-off

between the possibly contradictory design targets VRU and occupant protection in case of

front crash the application of advanced materials, e.g. offering the opportunity to trigger its

stiffness properties, have to be considered. To combine these targets with defined weight

reduction targets remains a significant challenge within the SEV structural design process.

Lessons learnt concerning front crash optimisation of SEVs aiming at improved structural

interaction and occupant protection within in-line vehicle-to-vehicle front crashes at high

mass ratio:

• Structural improvements of the horizontal load spreading capacity focusing on the

front crossmember- like width enlargement or bending stiffness increase- result in an

improved loading of the energy absorption structures of the front vehicle. Nevertheless no

major improvements to the occupant safety of the lighter crash partner can be expected by

measures exclusively focusing on crossmember components.

• To improve the occupant safety level for the light crash partner in vehicle-to-vehicle

crashes at high mass ratio, additional reinforcement measures increasing the front vehicle’s

energy absorption potential and the stiffness of the passenger compartment are crucial in

addition to possible measures improving the horizontal load spreading capacities of the front

vehicle. As the overall deformation length of the front vehicle is significantly limited in case

of SEVs, structural design measures resulting in high energy absorption potential at the given

limited design space are to be considered. These measures nevertheless have to balance the

contradictory design targets of high passenger compartment stiffness and soft crash

deceleration pulses that are especially challenging for very light vehicles.

• Possible incompatibility issues related to vertical load spreading deficits are addressed

by considering the vertical load spreading requirements defined for the 50 km/h FWDB crash

test used for SEV front crash assessment. In any case, a strong structural linking of the

different vertical load path levels within the front vehicle is beneficial.

• Steering wheel intrusion is a fundamental safety hazard for SEV occupants in vehicle-

to-vehicle front crash. Structural reinforcement measures aiming at a reduction of the



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movement of the steering wheel are identified as contradictory to defined weight saving

targets for SEVs. Retractable steering wheel concepts offer the potential to increase the

survival space for the SEV driver while respecting lightweighting strategies. Nevertheless,

such advanced safety solutions are to be considered together with updates to the restraint

system behaviour to avoid unexpected negative interactions between the systems not only

reducing the improvement potential of the discussed modifications but even increasing the

injury risk for the occupant.

Side crash optimisations of SEVs with focus on occupant protection:

Lessons learnt concerning side crash optimisation of SEVs aiming at an improvement of the

occupant safety and the structural compatibility of the SEV side with impacting bigger crash

opponent front structures:

• Within the investigated side crash test configurations conventional side crash

improvement approaches relying on reinforced anti-intrusion beams are not identified as

showing sufficient potential to reach the defined occupant protection targets for the analysed

SEV type. Therefore, it is recommended to discuss the improvement potential of active door

beam structures.

• The aim of active door beam components should focus on shifting the starting point of

structural interaction between the door and the impacting barrier to an earlier time during the

crash process. Meanwhile, it is crucial to design the active system in a way resulting in

reduced intrusion of the door into the occupant compartment and postponed first contact

between the occupant and the side structure.

• To reduce the design space requirement of active door beams the use of space-saving

folded structures that only inflate and bend in the event of crash, is proposed for

consideration. In order to design such inflatable systems in agreement with the previously

defined targets of passenger compartment intrusion reduction the unfolding should be directed

towards the car exterior.

• Any design feature meant to modify the deformation behaviour of the side structure in

case of side impact has to work in a way to avoid the occurrence of sharp edges oriented

towards the passenger compartment.

• The design process for adaptive side protection structures has to be harmonised with

measures updating the restraint system behaviour to the altered crash deformation to assure an

optimal occupant protection level.

6.3.3 Guidelines for Future Intelligent Protection Systems for SEV Occupants

Within the subtask 4.2.2 of the SafeEV project, different intelligent occupant protection

systems were included in FE models of SEVs and evaluated regarding their potential to

protect the car driver. These guidelines summarise the findings within subtask 4.2.2 and are

subdivided into general guidelines and guidelines by system.



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General guidelines

• The increased stiffness in the vehicle structure of SEVs to avoid intrusions into the

cabin will result in more aggressive crash pulses. Reduction of velocity, as in an advanced

emergency breaking (AEB) system, and the use of pre-pretensioners; and moving the seat

laterally before a side crash, are two systems that have been evaluated in this subtask. Both

systems show the benefit of integrated systems to prepare the car and restraint systems once

an imminent crash is detected.

• Virtual tools will be required in the design of SEVs. In this subtask, the simulation

with the human body model (HBM) delivered quite valuable indications beside the standard

evaluation parameters for injury risk. So, also further optimisation of the system within a

regular development process could be based on this virtual tool chain. The inclusion of pre-

crash scenarios required also the use of active HBMs.

• Optimisation will be required for a variety of load conditions and combinations of

safety systems including the more severe regulatory and consumer testing conditions. The

interaction of the different restraint systems and the variation in this interaction under

different load cases need to be considered in the design process.

• It is foreseen that adaptive systems that consider differences in size, gender, age, etc.

will be particularly beneficial for SEVs. There is a potential that HBMs of various sizes,

gender, ages, etc. could be applied in the development of adaptive systems. The present

project did not investigate all these possibilities but the simulations that have been carried out

already indicate a great potential for further adaptation and optimisation.

Guidelines by system (lateral/frontal)

• A retractable steering wheel will create increased space for occupant ride-down. In

order to make optimal use of this additional space it will be important to incorporate adaptive

restraint systems. These systems should be connected to advanced sensor systems and take

individualised decisions on restraint timing and force.

• Give support to the head and neck. The systems to move the seats and occupant prior

to impact, such as the lateral movable seat, need to be complemented if possible in practice,

with a support for the head and neck to reduce the relative displacement between the head and

the rest of the body.

• Vehicles with autonomous brake systems need to be equipped with seat belt pre-

pretensioners. The maximum forward excursions are delayed and/or decreased while using a

pre-pretensioner compared to a non-pre-pretensioner belt, which helps to reduce the risk of

injury.

• Define the time for onset of crash while developing in tests methods that include

autonomous braking before the crash. The difference in time of crash onset can lead different

vehicle velocity and also different occupant velocities due to response of the safety system.



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7 Literature

[ECE13] N.N.

ECE R110

High pressure cylinders for the onboard storage of natural gas as a fuel for

automotive vehicles

International Organization for Standardization, Geneva, Switzerland, 2013

[ISO13] N.N.

ISO/TR 16250:2013

Road vehicles - Objective rating metrics for dynamic systems

Economic Commission for Europe, Geneva, Switzerland, 2013

[ISO14] N.N.

ISO/TS 18571:2014

Road vehicles - Objective rating metric for non-ambiguous signals

Economic Commission for Europe, Geneva, Switzerland, 2014

[MAT14a] N.N.

MATISSE Project

Deliverable 3.2

Design of Simplified Structure(s) and Adaptive Inflator

European Commission, Brussels, Belgium, 2014

[MAT14b] N.N.

MATISSE Project

Deliverable 2.1

Material cards for crash simulation of adaptive composite structures


[MAT14c] N.N.

MATISSE Project

Deliverable 2.2

Report on modelling for fabric reinforced structures


[MAT14d] N.N.

MATISSE Project

Deliverable 2.3

Material cards for impacts and static loads of composite pressure vessels




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[MAT14e] N.N.

MATISSE Project

Deliverable 2.4

Report on thick UD-composite structure modelling


[MAT14f] N.N.

MATISSE Project

Deliverable 4.1

General virtual testing procedure for Type-IV CNG storage tanks


[MAT15a] N.N.

MATISSE Project

Deliverable 4.5

Detailed mathematical models of Type-IV tanks which are fully representative of

dynamic load cases


[MAT15b] N.N.

MATISSE Project

Deliverable 4.4

High-pressure storage tanks experimental testing results


[SAF15a] N.N.

SafeEV Project

Deliverable 4.1

Generic safety solutions and design candidates evaluated with the advanced

methodology for pedestrian safety


[SAF15b] N.N.

SafeEV Project

Deliverable 4.2

Generic safety solutions and design candidates for occupant protection including

compatibility improvements




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8 Annex

Figure 10. IMVITER V&V template for MATISSE CNG tank (1)



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