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DESIGN AND STRUCTURAL PERFORMANCE ASSESSMENT OF A COMPOSITE INTENSIVE PASSENGER VEHICLE

Hannes Fuchs, Ph.D.

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Abstract Decoma International Inc. contracted Multimatic to develop a modular Composite Intensive

Vehicle (CIV) concept, including closures and suspension, suitable for production volumes of 50,000 units per year. The proposed CIV was required to meet all typical OEM vehicle packaging standards, and stiffness and applicable crash safety standards, while offering the potential for overall mass reduction and meeting manufacturing cost and volume requirements. The primary structural materials considered in this study were fiberglass composite and metallic materials. The study to develop the CIV Body-In-White (BIW), closures, and suspension systems concepts was conducted in 3 phases: (1) Development of the vehicle content requirements, vehicle occupant and component package, and structural performance targets based on program requirements, provided styling surface, and vehicle benchmarking. (2) Development of a package-feasible three-dimensional structural CAD concept model for the BIW, closures, and suspension system. (3) CAE-based structural stiffness optimization and crash performance assessment of the structures developed in (2). The resulting CIV vehicle concept was developed to a level suitable for prototype build, detailed manufacturing feasibility verification, and mass and cost assessment.

Background Numerous composite intensive automotive body component and BIW structural

investigations have taken place over the course of the last 30 years [1-13]. The majority of these studies have shown excellent potential to save mass, improve structural performance, and to reduce parts count. In the earlier studies, many efforts were focused on mass savings and performance potential and limited to the re-design of existing metallic structures. In more the recent efforts [8, 9, 10], significant attention has been placed on composite-specific designs and low cost / high volume manufacturing methods. Despite the many benefits of structural composites, high volume production of BIW structures has not been realized in the automotive mainstream. The only automotive production industry segment that has benefited from composite intensive BIW technology is the niche volume high performance sports car segment which includes such vehicles as the McLaren Mercedes SLR [11], Porsche Carrera GT [12], and the Ferrari Enzo [13], among others. The main drivers in this segment are ultimate performance and low tooling costs.

Decoma International Inc. envisioned a higher volume manufacturing and assembly process capable of supporting automotive production volumes of up to 50,000 units per year. In an effort to evaluate the feasibility of this approach, Decoma initiated a program to design a full composite intensive vehicle based on a modular assembly approach for the purpose of evaluating manufacturing, cost, and performance. The program ended after 14 months prior to the final optimization so that the design phase could not be 100% completed.

During the course of the program, Decoma’s responsibilities included overall program direction, manufacturing feasibility and module assembly, materials and process development, and cost modeling. Multimatic’s responsibilities included overall package and vehicle & chassis

development, structural design and composites expertise, and CAE performance assessment.

Objectives An all-new 5 passenger Composite Intensive Vehicle (CIV) design concept based on

modular assembly methods and lower cost fiberglass composite and metallic materials was proposed. The CIV was designed to demonstrate the potential for lower cost modular composite structures and to meet applicable OEM design standards. The BIW, closure, and suspension structures were to meet current day and future safety requirements while offering the potential for overall mass reduction. Furthermore, the designs were to be developed to a level suitable for prototype build, detailed manufacturing feasibility verification, and mass and cost assessment.

Phase 1: Program Content and Structural Performance Target Development Based on program requirements for the proposed CIV, the following were established:

vehicle content and targets, configuration, structural performance requirements, and mass targets. From these requirements, detailed structural requirements were developed based on benchmarking of similar vehicles, and evaluation of current and future safety standards.

Vehicle Content & Target Development

A detailed target document was established to define all of the vehicle and body structure requirements and content assumptions. The target document was developed based on program requirements, a provided surface & preliminary occupant package data, and detailed component assumptions. Structural targets were established based on current and future safety requirements and vehicle benchmarking.

Vehicle Configuration

The final vehicle package and configuration was developed based on a feasibility assessment of the surface and a preliminary occupant package. The BIW was designed with maximum possible structural section sizes to account for fiberglass composite structural properties and a flat floor to allow for the possibility of a pultruded panel and rocker sections. The powertrain was specified as a front wheel drive layout with an inline four cylinder engine with provisions for a V-6 engine and all-wheel drive. The chassis specifications included a hydraulic power-assist rack and pinion steering, a MacPherson strut front suspension with coil springs, an anti-roll bar, and an isolated subframe, an independent multi-link rear suspension with coil springs, an anti-roll bar on a non-isolated subframe. The tires were specified to be 205/65R16 run-flats on 7 inch wide aluminum wheels.

Structural Performance Requirements

Basic BIW structural performance targets were based on representative benchmark vehicles in the lightweight mid-sized wagon segment. The primary BIW static stiffness performance target was a static torsional stiffness of 13,000 N-m/deg and a secondary bending stiffness target of 10,000 N/mm. BIW modal performance was considered a secondary requirement as composite vehicle structures typically exhibit higher frequencies [5, 6] than their steel counterparts due to their lighter mass.

BIW safety performance requirements encompassed current and future requirements. All of the requirements listed in Table 1 were evaluated during the course of the program. Pedestrian impact was evaluated but is beyond the scope of the current paper. Several other cases

including ECE Reg32 rear impact, US-SINCAP dynamic and Euro-NCAP side impact, and Euro-NCAP side pole impact were considered, but were not evaluated due to program cessation.

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Reference BIW and Vehicle Mass

BIW and vehicle mass were measured relative to a reference steel vehicle, which was established as part of the benchmarking process. The reference steel BIW mass was 362.8 kg (800 lbs) and the vehicle mass could range from 1,460 kg (3,219 lbs) with a four cylinder engine and a manual transmission to 1544 kg (3,404 lbs) with a six cylinder and an automatic transmission. Assuming a 20% mass reduction potential for an all-fiberglass BIW, a mass of approximately 293 kg (645 lbs) would be expected. Assuming a 50% mass reduction potential for an all-carbon fiber BIW, a mass of approximately 181 kg (400 lbs) would be expected. Allowing for secondary mass savings, it was assumed that the four cylinder manual transmission composite vehicle mass for fiberglass and carbon fiber BIW structures would be approximately 1,351 kg (2,979 lbs) and 1,188 kg (2,619 lbs), respectively.

Phase 2: Package-based Body-in-white (BIW) Structural Concept Model Development

Based on the Phase 1 target document, master sections were established and a package-based CAD model was developed to define the BIW structure concept. As illustrated in Figure 1, the Phase 2 CAD design considered clay feasibility issues, door opening and major body cut lines, all major vehicle components and systems, and the occupant package.

Category Safety Requirement

Full frontal impact NCAP: 35 mph (56 km/h) Full Frontal Barrier 0° only

Frontal offset impact Euro NCAP: 40 mph (64 km/h) ODB 0° 40% Overlap

Roof crush FMVSS 216 Roof crush (roll over) - 2.5X proposal

Rear impact FMVSS 301: 50 mph (80 km/h) Moving Deformable Barrier 70% overlap rear impact

Side impact - dynamic FMVSS 214: 33.5 mph (~54 km/h)

Side impact - static FMVSS 214

Pedestrian impact assessment EEVC Work Group 17 for MY2010 (Proposal)

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The resulting initial BIW concept is shown in Figure 2 along with the major components. Several special features were incorporated into the structure including a flat center floor section, a pultruded rocker section, and a large rear storage compartment in lieu of a spare tire tub. This model provided a baseline structure for performance-based development of BIW structure, closures, and chassis to be discussed in the following sections.

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Vehicle surface Component assumptions

Styling feasibility

Occupant package w/ maximum structural section assumptions

Flat floor panel & pultruded rocker

Aluminum front crash structure

Steel Frt & Rr bumper beams

Composite BIW structure, with bonded inner & outer panels

Engine, cradle, suspension, & drivetrain

Rear suspension, fuel system, exhaust

Radiator, battery, wiper

system, IP beam, etc

Phase 3: Performance-based Structural BIW, Closures, and Suspension Model Development

Starting with the initial package-based BIW CAD model shown in Figure 2, the structure was revised to be more “organic” in terms of parts integration and overall load paths. The vehicle architecture was iteratively updated during this phase to reflect manufacturing and assembly inputs, material assumptions and the results of extensive static stiffness and strength, and crash assessments. In parallel with the BIW development, closures and suspension structure designs were evolved as subsystems and were assessed based on structural performance requirements. The system level closures and suspension performance were evaluated as part of the vehicle level crash requirements. The development of the resulting vehicle structures are discussed in the following sections.

Structural Materials

A variety of structural materials were considered during the development of the CIV. Material selection was based on each particular application along with manufacturing considerations. Thermoset and thermoplastic composites were considered beneficial due to their mass reduction potential, while metallic materials would provide structural reinforcements with robust and predictable crash performance and high elongation capability.

Various forms of thermoset composites were considered in the BIW due to their ability to meet structural requirements and provide thermal stability. Figure 3 illustrates uni-directional (UD), biaxial, triaxial, and quadraxial examples of thermoset material forms that were considered.

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Polypropylene-based Glass Mat Thermoplastic (GMT) composites were considered in areas such as the door inner panels, the liftgate inner panel, the front engine cradle & suspension cross-member, and the rear suspension cross-member. These bolt-on structures were subject to less stringent temperature requirements than other areas in the BIW but higher impact or crash requirements. Another benefit of GMT’s is the ability to tailor their stiffness and strength by combining with woven fabrics to create fabric-reinforced GMT’s (see Figure 4), or FR-GMT, which enables variable thickness parts and/or fabric-reinforced parts with randomly oriented structural ribs.

0o

UD stitchmat Quadrax mat 3WEAVETM biaxial mat Triaxial braid

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Aluminum was considered exclusively for the front crash structure due its demonstrated robustness in crash, low mass potential and the ability to analytically predict its crash performance. Another consideration was low speed crash repair. A composite front crash structure was considered outside the scope of the current effort given the extensive development that would be required [2, 3, 9, and 11]. The crush forces and energy absorption response of the current aluminum structure could be used to provide design direction for a composite solution. Steel was considered primarily for structural reinforcements for local point loads and to allow for high elongation and energy absorption in larger impact areas such as the body side.

Figure 5 provides a comparison of stress-strain responses for representative thermoset and thermoplastic fiberglass composites, 6063-T4 aluminum, and SAEJ2340 340X steel materials considered in this study. Note the wide range of material responses that can be achieved with composite materials depending on the reinforcement type and orientation. For example, the uni-directional fiberglass tensile strength is nearly twice that of steel tensile strength, and the compressive strength is approximately the same as the steel tensile strength. In contrast, the tensile strength of the quasi-isotropic quadrax mat is approximately the same as steel tensile strength, but the compressive strength is only half of the tensile strength of steel. Also, note the relatively large amounts of tensile strain that can be achieved by the biaxial composites when loaded in the ±45o direction.

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Courtesy Quadrant Plastic Composites

GMTex®

Development of the BIW Structure

The final BIW structure is illustrated in Figure 6. The main structure consists of several modules to address assembly requirements. Each module was designed as a bonded assembly, generally consisting of an inner and an outer panel with steel reinforcements as required. All panels were designed in consideration of draft angles based on manufacturing feasibility studies. The locations of the BIW metallic reinforcements can also be seen in ghosted image in Figure 6 with the primary body side reinforcements shown in red, front cross-member and rear suspension hardpoints shown in green, and the seat attachments shown in blue. All metallic reinforcements for the BIW, the front crash structure, and the closures are shown in Figure 7 including a mass breakdown. The bumper beam designs were not within the scope of this study and were therefore assumed to be steel in order to simplify the prediction of front and rear impact response. Aluminum, composite, and hybrid bumper beams are currently in production and could easily be adapted to the current structure.

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Braided composite S-rail

Aluminum crush structure

Metallic reinforcements

Composite crush structure

Tunnel close-out panel

Molded floor

Pedestrian impact beam

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Crash Energy Management

An overview of the BIW crash structures is illustrated in Figure 8.

The front crash structure includes a steel bumper beam, an aluminum crush box bolted to an aluminum lower rail with an engine cradle attachment, an aluminum upper “shotgun” rail, an aluminum shear panel, and a composite engine cradle. The lower and shotgun rails are both made of 6063-T4 aluminum extrusions, while the shear panel and cradle attachment are 6061-T6. The engine cradle is assumed to be made of GMT. The entire backup structure is designed to be a thermoset composite with a triaxially braided lower S-bend rail. A bolt-on composite pedestrian impact beam can also be seen in Figure 8.

Side impact is managed by the body side assembly which includes composite body side assembly (BSA) outer and inner panels, a two-cell composite pultrusion (see Figure 8 inset) that runs the length of the rocker, and internal steel A- and B-pillar reinforcements. Additionally, the side door structures, including the steel door beams, help manage side impact energy with additional cross-car support provided by the rear seat and underfloor structures.

Roof crush is managed primarily by the composite A-pillar structure with additional support provided by the steel B-pillar reinforcement.

The rear impact structure includes a steel bumper beam bolted to rectangular composite lower rails integrated with the storage tub. Additional crush structure is provided by the body sides as well as the storage tub itself. The backup structure consists of the composite rear torque boxes, center floor, and rockers.

Description Mass (kg) (lbs)BIW reinforcements 31.8 70.2Front crash structure 13.4 29.5Closures reinforcements 28.9 63.7

74.1 163.4Note: steel bumper beams, radiator support, and suspension reinforcements not included

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Structural Performance Assessment

Numerous design/analysis iterations were conducted to meet all of the vehicle level structural performance requirements. Initially, the BIW was optimized for minimum mass to meet static bending and torsional stiffness and local strength requirements. Modal response was also evaluated. Once a reasonable stiffness-based design was established, design/analysis iterations were conducted to evaluate and meet structural crash performance requirements (without occupants) to meet the safety requirements outlined in Table 1.

In addition, design/analysis iterations were conducted to meet the stiffness and local strength performance requirements for the closures, suspension and cross-members.

BIW Stiffness Assessment

In the BIW stiffness optimization and subsequent crash studies, minimum fiberglass UD material coupon test properties were used as the basis for all computations. The thicknesses of each ply in each BIW component were individually optimized using Optistruct 7.0-1 to determine the critical ply angles and to achieve the lowest mass structure based on a global bending and torsional requirement of 13,000 N-m/deg and 10,000 N/mm, respectively. Based on the material forms under consideration, only 0o, 90o, and ±45o ply orientations were evaluated. Optimized layups were consolidated to achieve a more manufacturable layup before further evaluations, and the static response was further analyzed using ABAQUS/Standard 6.5-1.

The general thickness map of the stiffness-optimized BIW structure (trial 1063) is shown in

Bolt-on aluminum crush structure

Composite rear crash structure

Braided composite S-rail

Rear crash structure Side crash structure

Front crash structure

Pultruded composite rail

Steel A- & B-pillar reinforcements

Steel door beams

Steel B-pillar reinforcemen

BSA inner BSA outer

2-cell pultrusion

8.5mm

8.5mm

5.0mm 6.0mm

2.0mm

Figure 9. The figure shows that the range of thicknesses was between 2.0mm and approximately 10.0mm. The thickness of the dash panel area / torque box was set to 10mm for this trial to account for frontal crash loading. The mass for the BIW model as shown is 284.9 kg, 27.1 kg of which can be attributed to the pre-set 10mm thickness. Several minimum thickness regions are evident in the figure, primarily in the floor structure and in parts of the body side outer panels. This is an indication that the structural sections are efficient and so only minimum thickness is required. Several thicker regions are also evident along the roof rail, at the top of the B-pillar, the bottom of the rockers, and the in the C-pillar / rear-suspension areas. These areas are key load paths which are section-limited due to package constraints.

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After consolidating the thickness regions for the stiffness-based model shown in Figure 9, the BIW static stiffness and modal performance figures were computed with the results shown in Table 2. The values are slightly degraded vs. the targets as a result of the consolidation process.

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Case ResultMass 288.2 kgStatic torsional stiffness 12,500 N-m/degStatic bending stiffness 9,800 N/mm1st torsional mode 31 Hz1st bending mode 37 Hz

Trial 1063

Y-section

BIW & Vehicle Crash Assessment

The stiffness- and mass-optimized BIW structure (trial 1067) was used as the basis for the development of the vehicle impact performance. LS-DYNA version 970 was used to compute the dynamic structural response for all crash load cases. Available coupon test data was used in conjunction with LS-DYNA material model type 58 [14] as the basis for predicting the progressive failure of all composite materials.

The general vehicle model content and final deformed shape for the NCAP full frontal load case are shown in Figure 10. The overall performance was deemed acceptable with a peak longitudinal acceleration of approximately 44g and a maximum toeboard intrusion of 7mm (< 94mm requirement). The primary energy absorption was achieved by the front lower rails and the backup structure remained intact with little or no damage. Key component thicknesses that were modified to achieve acceptable performance are indicated in Table 3.

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The general vehicle model content and final deformed shape for the Euro NCAP frontal ODB (Offset Deformable Barrier) impact are shown in Figure 11. The overall performance was deemed acceptable with a peak longitudinal acceleration of approximately 56g and a maximum toeboard intrusion of 60mm (<150mm requirement) at the end of the analysis. The primary energy absorption was achieved by the front rails and the backup structure remained intact with an acceptable amount of damage. Key component thicknesses that were modified to achieve acceptable performance are indicated in Table 3.

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The general vehicle model content and final deformed shape for the FMVSS 216 roof crush are shown in Figure 12. The loading corresponds to the 2.5Xweight target proposal rather than current 1.5Xweight requirements. The overall performance was deemed acceptable with the 33kN load requirement achieved at approximately 89mm of deflection. The internal B-pillar reinforcement provided additional post-composite failure strength as anticipated.

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The general vehicle model content and final deformed shape for the FMVSS 301 rear impact load case are shown in Figure 13. Note that surrogate aluminum rear rails were used to determine the crush force and energy absorption requirements for the design-intent composite rails and to assess the strength of the backup structure. The overall performance was deemed acceptable with a peak longitudinal intrusion of approximately 516mm. Key component thicknesses that were modified to achieve acceptable performance are indicated in Table 3.

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The general vehicle model content and final deformed shape for the FMVSS 214 dynamic side impact load case are shown in Figure 14. The overall performance was deemed acceptable with the predicted 284mm peak B-pillar intrusion. The internal B-pillar reinforcement provided additional post-composite failure strength as anticipated. Key component thicknesses that were modified to achieve acceptable performance are indicated in Table 3.

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The general vehicle model content and final deformed shape for the front and rear door FMVSS 214 quasi-static side intrusion are shown in Figure 15. The average load requirements for each door were predicted to be met.

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Overall, the predicted BIW impact performance was deemed to be reasonable given current capabilities to predict the progressive failure of composite materials and structures. As with all complex crash structures, and composite ones in particular, actual impact performance should be validated via extensive physical testing to ensure that composite material performance and failure modes are well understood.

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Component Key load case MaterialFinal thickness

[mm]Aluminum crushbox NCAP full frontal, Euro NCAP ODB Alum 6063-T4 4.5Aluminum lower rail NCAP full frontal, Euro NCAP ODB Alum 6063-T4 4.0Aluminum shotgun NCAP full frontal, Euro NCAP ODB Alum 6063-T4 2.0Shocktower NCAP full frontal, Euro NCAP ODB Fiberglass laminate 6.0Braided S-bend rail Euro NCAP ODB Fiberglass triax braid 11.0Torque box NCAP full frontal, Euro NCAP ODB Fiberglass laminate 6.0Dash panel / floorboard Euro NCAP ODB Fiberglass laminate 8.0Upper floor panel NCAP full frontal, Euro NCAP ODB Fiberglass laminate 5.0Lower floor panel NCAP full frontal, Euro NCAP ODB Fiberglass laminate 4.0Frt subrame, upper NCAP full frontal, Euro NCAP ODB Fabric-reinforced GMT 5.0Frt subrame, lower NCAP full frontal, Euro NCAP ODB Fabric-reinforced GMT 5.0Rear crush rail FMVSS 301 rear impact Alum 6063-T4 surrogate 6.0/8.0Rear torquebox/rail FMVSS 301 rear impact Fiberglass laminate 10.0Hinge pillar outer FMVSS 214 dynamic side impact Fiberglass laminate 3.4B-pillar reinforcement FMVSS 214 dynamic side impact SAEJ2340 340X steel 1.0

BIW Mass

The BIW mass increased throughout the development phase as additional load cases were introduced. A graph of the BIW mass vs. the stage of development is shown in Figure 16. The figure indicates that a mass savings of approximately 30% was achieved vs. the baseline steel BIW based on stiffness performance only. However, with the additional considerations of BIW hardpoints and severe crash load cases a significant amount of mass was incurred. At the time of program cessation, the predicted mass reduction of the fiberglass-based BIW was reduced to approximately 5% vs. the baseline steel BIW. While seemingly disappointing, it should be kept in mind that the final mass numbers do not represent a fully optimized structure, but rather a starting point for further development.

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Several mass reduction opportunities were identified but could not be evaluated during the course of this study:

• Continued structural development and optimization (e.g. refinement of geometry)

• Localized substitution of carbon fiber or hybrid composite material to reduce gage in thick section areas (e.g. braided rails, front and rear backup structure, upper and lower floor panels, C-pillar area, etc.)

• Reduction of composite thickness based on better-than-predicted physical impact performance of composite structures (e.g. braided rails, front and rear backup structure, etc.)

• Reduction of steel reinforcement thickness based on higher strength material grades (e.g. reduce typical 2mm thickness of typical SAEJ2340 340X reinforcements)

Closures Design

An overview of the closures design is provided in Figure 17. The hood and fenders were designed with pedestrian impact safety in mind. The horizontal hood and roof panels were both designed as Class A SMC (Sheet Molding Compound) thermoset composites. The vertical side door and liftgate outer panels were designed as TPO (ThermoPlastic Olefinic elastomer) panels with fabric-reinforced GMT inner panels. Reinforcements in all closures were designed to be steel.

Further design details can be seen in Figure 18 for the front side door and in Figure 19 for the hood and liftgate. Note that the rear side door construction is similar to the front side door construction. All panel designs featured high levels of component integration including local reinforcements, attachments, impact structures, etc.

258

288

330 330 330

343348

311

200

250

300

350

400

stiffness only

+prelim stiffn

ess model front crash plyups*

+prelim steel re

inforcements

+plyups to meet full fr

ontal 35mph NCAP

+plyups to meet FMVSS 216 roof crush (2.5X)

+plyups to meet 40mph front O

DB Euro NCAP

+plyups to meet 50 mph FMVSS 301 rear

+plyups to meet 33.5 mph FMVSS 214 side impact

Mas

s, k

g

-45%

-40%

-35%

-30%

-25%

-20%

-15%

-10%

-5%

0%

5%

10%

% r

educ

tion

Baseline Steel BIW MassBIW MassMass reduction vs. target

includes surrogate aluminum rails

Program cessation precluded further development

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Side Doors: GMT/FR-GMT thermoplastic inner panel, TPO outer panel, steel window track, reinforcements, and intrusion beam

Hood: SMC outer panel, RTM fabric composite inner panel (perimeter bond)

Liftgate: GMT/FR-GMT thermoplastic inner panel, TPO outer panel, bonded glass, steel reinforcements

Pedestrian-friendly surface

TPO outer panel

GMT FR-GMT

panel

Steel intrusion

beam

FR-GMT panel

Steel window frame and reinforcements

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Closures Performance Assessment

Nominal performance targets for closures were set based on experience with OEM closure systems. The structural loading requirements are summarized in Table 4. ABAQUS/Standard was used to evaluate the structural performance of all of the closures. Some typical analysis results are illustrated in Figure 20.

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Closure RequirementWindow frame front lateral rigidityWindow frame rear lateral rigidityTorsional rigidityVertical sag stiffnessStatic and dynamic FMVSS 214Torsional rigidityBeaming stiffness (reference only)Torsional rigidityBeaming stiffness (reference only)

Front and rear side doors

Hood

Liftgate

SMC outer panel

Fiberglass fabric RTM inner panel

Steel reinforcements

Steel reinforcements TPO outer panel

Bonded glass

Ribbed GMT / FR-GMT panel

Steel hinges

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Based on the structural requirements set forth in Table 4, a summary of the estimated closures structural mass is provided in Table 5.

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Closure Est'd Mass [kg]Front door (ea) 13.2Rear door (ea) 12.0Hood 10.0Liftgate 24.3

Suspension Design

An overview of the front and rear suspension design is provided in Figure 21. The front suspension features a 2-piece bonded fabric-reinforced GMT composite engine cradle and steel subcomponents. The rear suspension features a 2-piece bonded GMT composite cradle, combination composite lateral leaf spring / upper control arm and LightcastTM composite lateral links, and steel front lower control arms and trailing arms.

Further design details can be seen in Figure 22 for the front and rear suspension systems. Note that all bushing and hardpoint attachments feature either bond-on or integral steel reinforcements

Liftgate: Strain energy for torsion

Hood: Tsai-Wu failure for bending

Front side door: Strain energy for torsion

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Front suspension (strut type): • 2-pc bonded GMT/FR-GMT composite

cradle w/ integral steel hardpoints • Multimatic’s patented steel front lower L-

arm, coil spring, and anti-roll bar

Rear suspension: • 2-pc bonded GMT composite cradle w/ integral hardpoints • Composite leaf spring / rear upper control arm • Steel front lower control arm and anti-roll bar • Composite rear lower control arm (aluminum ends over

pultruded fiberglass tube)

Engine mounts

S-rack mounts ARB

mounts

Body mount inserts (X4)

Composite upper and lower clamshell

components

Steel inserts and bond-on hardpoints

Note: Anti-roll bars not shown

Composite upper and lower clamshell and

reinforcements

Body mounts

Steel trailing

arm

Composite leaf spring / RUCA

Steel FLCA

Composite RLCA

Bump stop

Suspension Performance Assessment

Based on experience with OEM suspension subsystem load requirements, several worst-case strength front and rear suspension load cases were selected. The structural loading requirements are summarized in Table 6. ABAQUS/Standard was used to evaluate the structural performance of all of the suspension components. In order to pass each load case, material failure and/or yielding was not permitted. In addition to the static subsystem load cases, component performance was monitored during vehicle impact analyses (LS-DYNA) to ensure acceptable failure modes. Some typical analysis results are illustrated in Figure 23.

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No. Front Suspension Load Units X Y Z X Y Z1 One-Wheel Vertical Pothole (G) 2 0 5 0 0 12 Two-Wheel Pothole (G) 3.25 0.75 4 3.25 -0.75 43 One-Wheel Side Curb Impact (G) 4 4 3 0 0 0

No. Rear Suspension Load Units X Y Z X Y Z1 One-Wheel Vertical Pothole (G) 2 0 5 0 0 12 One-Wheel Side Curb Impact (G) 4 4 3 0 0 03 Two-Wheel Rearward Curb Impact (G) -0.5 0 3 -0.5 0 3

LH RH

LH RH

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Summary A hybrid composite passenger vehicle BIW, closures, and suspension was designed and

developed based on OEM packaging and structural standards. Material types, composite layups, thickness, and mass were assessed based on static and crash performance requirements. The BIW made extensive use of low cost thermoset fiberglass composites, with aluminum and steel being used for crash structures and structural reinforcements. Lightweight

One-Wheel Side Curb Impact Two-Wheeled Pothole Impact

closures made use of both thermoset (hood) and thermoplastic composites (liftgate, side doors) with steel reinforcements. Lightweight suspension modules made use of thermoplastic subframes, steel control arms, and composite links. Due to program cessation, the design was not completely optimized and a 5% mass reduction was predicted for the BIW; however, several mass reduction opportunities were identified. The design of the BIW, closures, and suspension was developed to a level suitable for prototype build, detailed manufacturing feasibility verification, and mass and cost assessment (see Figure 24).

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Acknowledgements The author is grateful for the permission granted by Decoma International, Inc. to publish

the results and status of the Composite Intensive Vehicle study. The author further would like to acknowledge all of the efforts of the Decoma / Multimatic team provided during the course of the program.

• Decoma International Inc.: Jack Henderson (Product/Program Engineer), Greg Brower (Program Manager), Brad Armstrong (Manufacturing), Mandar Garware (Materials)

• Multimatic Engineering Services Group:

o Design: Eleu Um (Design Mgr), Larry Zhou, Quinton McBlain, Jeff Laidman, Christian Jansen, Felix Kim; Package: Bill Stuef

o Predictive methods: Alex Duquette (Analysis Mgr), Eric Gillund, Young Lee, Mark Kuhn, Jim Prsa, Nuno Simoes, Frank Tomassini, Rafal Smerd

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Components in Graphite Fiber-Reinforced Composites,” SAE Paper 790031,The Society of Automotive Engineers, Warrendale, PA.

2. P. H. Thornton and R. A. Jeryan, “Composite Structures for Automotive Energy Management,” Proceedings of the Third Annual Conference on Advanced Composites, Detroit, MI, pp.75-81, Sept 15-17, 1987. “Crash Energy Management in Composite Automotive Structures”, Int. J. Impact Engng., 7 (2), pp. 167-180, 1988.

3. R. L. Frutiger, S. Baskar, K. H. Lo, R. Farris, “Design Synthesis and Assessment of Energy Management in a Composite Front End Vehicle Structure,” Proceedings of the 5th Annual ASM/ESD

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