1

Introduction to Safe Technology

Pawel Sobczak

Safe Technology Limited

2

Safe Technology

• Privately-owned - we can commit to long term developments,

we remain flexible enough to react to market demands and we

drive our own R&D programs

• Focused entirely on the development of fatigue analysis

software, associated consultancy, training & support

Our Corporate Strategy:

…to develop the most accurate fatigue analysis software, in a

format that is easy to use for specialist and non-specialist

engineers…

3

fe-safe™

• a leading suite of software for fatigue design and

analysis

• Sold worldwide to companies that design everything

from mobile phones to heavy engineering structures,

heart valves to engines to power plants

44

fe-safe™

• Over 300 customers are using fe-safe, worldwide

55

Agents

Safe Technology USA Cincinnati

LEAP- Australia

Belcan- Illinois

Safe Technology UK

CAE soft- Spain

Servo2000- Italy

A-Ztech- Turkey

Taesung- South Korea

ANSYS China- China

APIC- Taiwan

SMART-tech- Brazil

Worley- Singapore

CETIM- France

6

Introduction to fe-safe

Pawel Sobczak

Safe Technology Limited

7

INTERFACES

Input/output

ABAQUS .fil

ABAQUS .odb

NASTRAN f06

NASTRAN op2

ANSYS .rst

I-DEAS .unv

Pro/M s01..., d01

General .csv

Output

Hypermesh .hmres

PATRAN

FEMVIEW

CADFIX

FEMAP

Redesign

Design

FEAABAQUS, ANSYS

I-DEAS,

NASTRAN, Pro/E

Stress

resultsfe-safe

fefe-safe durability analysis from FEA

Loading

Lifecontours

8

Mean stress

Stress

amplitude

Haigh Diagram

Stress

amplitude

N cycles

S-N curve

ampP (sf-sm)/E 2.00E+05 ampE ampP amp amp/Sao

0.000328 0.001855 1.25113 0.006059 0.313619 0.0019 0.000947 0.002848 1.194403

0.000328 0.001793 1.209275 0.005813 0.313619 0.001823 0.000947 0.00277 1.162002

0.000328 0.001731 1.16742 0.005567 0.313619 0.001746 0.000947 0.002693 1.129602

0.000328 0.001669 1.125565 0.00532 0.313619 0.001669 0.000947 0.002616 1.097201

0.000328 0.001607 1.08371 0.005074 0.313619 0.001591 0.000947 0.002539 1.064801

0.000328 0.001545 1.041855 0.004828 0.313619 0.001514 0.000947 0.002461 1.0324

0.000328 0.001483 1 0.004581 0.313619 0.001437 0.000947 0.002384 1

0.000328 0.001421 0.958145 0.004335 0.313619 0.00136 0.000947 0.002307 0.9676

0.000328 0.001359 0.91629 0.004089 0.313619 0.001282 0.000947 0.00223 0.935199

0.000328 0.001297 0.874435 0.003842 0.313619 0.001205 0.000947 0.002152 0.902799

0.000328 0.001235 0.83258 0.003596 0.313619 0.001128 0.000947 0.002075 0.870398

0.000328 0.001173 0.790725 0.00335 0.313619 0.001051 0.000947 0.001998 0.837998

0.000328 0.001111 0.74887 0.003103 0.313619 0.000973 0.000947 0.001921 0.805597

0.000328 0.001048 0.707015 0.002857 0.313619 0.000896 0.000947 0.001843 0.773197

0.000328 0.000986 0.665161 0.002611 0.313619 0.000819 0.000947 0.001766 0.740796

Location of max stress.

Calculate stress amplitude

and mean stress

Durability by design?

9

Dana Automotive Systems Group Case Study

Part of an automotive driveshaft assembly joint.

Cracks did not start from the maximum stress location.

This was corroborated by lab tests on actual specimens

fe-safe life contours Stress contours

Max principal stress

Shortest life

10

This can be true where stresses

from different types of loading or

at different frequencies are

superimposed.

Stents experience both heart-

beat and articulation stresses

Why do we need fatigue analysis from FEA ?

11

fe-safe™

Redesign

DesignFEA

ABAQUS, ANSYSI-DEAS,

NASTRAN, Pro/E

Stress

results

Loading

Fatiguefe-safe

Life

contours

Stresses at more

than 1 million

points

12

fe-safe™

Redesign

DesignFEA

ANSYS, ABAQUSI-DEAS,

NASTRAN, Pro/E

Stressresults

Loading

Fatiguefe-safe

Lifecontours

Lives at more

than 1 million

points

13

Duty cycle

Stress

Material

data

Fatigue

analysisLife

All stresses and

temperatures

Define failure criteria

– based on risk

Duty cycles

Not just the

‘most severe’

Life

contours

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07 1.00E+08

Endurance 2Nf

2

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07 1.00E+08

Endurance 2Nf

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07 1.00E+08

Endurance 2Nf

2

0

100

200

300

400

500

600

0 0.005 0.01 0.015 0.02 0.025 0.03

Strain

Str

ess (

MP

a)

Strain-based,

high temp.

Biaxial, strain-based,

critical plane, critical

distance

14

Redesign

DesignFEA

ABAQUS, ANSYSI-DEAS,

NASTRAN, Pro/E

Stress

results

Loading

Fatiguefe-safe

Life

contours

fe-safe durability analysis from FEA

INTERFACES

Input/output

ANSYS .rst

ABAQUS .fil

ABAQUS .odb

NASTRAN f06

NASTRAN op2

I-DEAS .unv

Pro/M s01..., d01

General .csv

Output

Hypermesh .hmres

PATRAN

FEMVIEW

CADFIX

FEMAP

15

fe-safe not only identifies crack locations, but also

predicts life to crack initiation

fe-safe is more than just fatigue analysis from FEA…

16

RESULTS

• fatigue lives and crack sites

• how much the stresses must be changed to

achieve the design life

• probability of failure at design life

• probability of survival at specified lives

- to predict warranty claims 99.7

99.8

99.9

100

1 10 100 1000 10000 100000 1000000

Miles

Su

rviv

al (%

)

User profile 1

User profile 2

• which loads need to be included during lab testing

17

RESULTS

• fatigue lives and crack sites

• how much the stresses must be changed to

achieve the design life

• probability of failure at design life

• probability of survival at specified lives -

to predict warranty claims 99.7

99.8

99.9

100

1 10 100 1000 10000 100000 1000000

Miles

Su

rviv

al (%

)

User profile 1

User profile 2

• which loads need to be included during lab testing

18

fe-safe has two methods

FRF - fatigue reserve factor

From a standard or user-defined mean stress

curve.

Applies only to infinite life design.

FOS – factor of strength for specified life or lives

An iterative process -

Scales the elastic FEA stresses

Recalculates the plasticity for the whole stress history

Recalculates the life

Repeats until it finds the scale factor to give the required life

Applies for finite and infinite life

Stress amplitude

Mean stress

19

RESULTS

• fatigue lives and crack sites

• how much the stresses must be changed to

achieve the design life

• probability of failure at design life

• probability of survival at specified lives -

to predict warranty claims 99.7

99.8

99.9

100

1 10 100 1000 10000 100000 1000000

Miles

Su

rviv

al (%

)

User profile 1

User profile 2

• which loads need to be included during lab testing

20

fe-safe combines material and load variability

Probability of survival

Uses Weibull distribution of

fatigue strength and Gaussian

variability in load values

Endurance

2

Loading

21

RESULTS

• fatigue lives and crack sites

• probability of failure at design life

• probability of survival at specified lives -

to predict warranty claims 99.7

99.8

99.9

100

1 10 100 1000 10000 100000 1000000

Miles

Su

rviv

al (%

)

User profile 1

User profile 2

• which loads need to be included during lab testing

• how much the stresses must be changed to

achieve the design life

22

Damage per block

0

5

10

15

20

25

30

35

40

45

1 2 3 4 5 6 7 8

Block

Da

ma

ge

(%

)

Damage for N repeats of each loading block

fe-safe – where does the damage come from?

23

• Dang Van diagram

RESULTS

• max stress at each node

• max stress / yield stress

• max stress / tensile strength

• Haigh diagram, Smith diagram

• Time histories of stress tensor, principal stress/strain ...

24

Loading Methods in

fe-safe

25

1. Single load history

2. Multiple load histories

Loading Methods in fe-safe

Signal

Summary of Tests - DEF STAN 00-35

0.00001

0.0001

0.001

0.01

0.1

1 10 100 1000 10000

Hz

g2 /H

zPSD

Rainflow

cycles

26

Loading Methods in fe-safe

3. Sequences of FEA Solutions

4. Modal superimposition –

steady state and transient

dynamic+

+

28

Complex loading sequences

Complex loading sequences can be defined as load ‘blocks’ for

simulating ‘proving ground’ testing

An unlimited number of blocks can be defined

Additional loading considerations and capabilities

Residual Stresses

Superimposition of high and low frequency loads

Intermittent contact conditions

fe-safe/Rotate

33

Property Mapping

34

Property Mapping

• Casting changes the material properties at

every node on the model, therefore fe-safe™

will change the fatigue strength at every node

on the model.

35

Generate an fe-safe™ fatigue life contour

plot

Node 1:: Material 1

Node 2 :: Material 2

Mapping model eqn

ID for each property

Property Mapping

Create a casting simulation and solidification model Create a contour plot of material properties

(which vary node by node)

Generate a property mapping file

36

Property Mapping

• Very powerful technique

• The fatigue strength at each node on the model can be

varied in response to an external input, for example:

- variations in tensile strength throughout a casting

- variations in yield strength throughout a forging

37

Fatigue of Cast Iron

38

Comparison of Iron Characteristics

Characteristics Stress-strain Response Damage Accumulation

SG (Nodular) Iron Graphite in tiny spheres.

Relatively expensive to

produce. Low thermal

conductivity, but quite strong.

Loops tend to be

symmetrical.

Damage accumulation may

be slightly non-linear.

Compacted Graphite

Iron

Graphite has rounded flakes. Loops usually slightly non-

symmetrical.

Damage accumulation may

be non-linear.

Grey Iron Long sharp flakes. Relatively

cheap to produce. High

thermal conductivity, but weak

(effectively notched).Loops are non-symmetrical.

Damage accumulation is non-

linear.

39

Graphite

Crack Closure

Bulk

Total Response

s

Grey cast iron – stress/strain response

Loops change as

damage increases

(free graphite is stiff in

compression but weak in

tension)

Damage accumulates

non-linearly

40

• Asymmetric stress-strain response

• Non-linear accumulation of damage

(Additional material properties are required)

Cast Iron Module considers…

41

Fatigue strength of welded joints

42

Fatigue strength of welded joints

Comparison of fatigue strength of welded joint with the

fatigue strength of notched and smooth specimens

Smooth specimen

Notched specimen

Welded specimen

43

Fatigue strength of welded joints

Conventional analysis of welds using BS5400/7608

New mesh and load insensitive approach to analysing welds using

VerityTM in fe-safe

- based on the Equivalent Structural Stress calculated from nodal forces

56

High Temperature Fatigue

63

Material Data Fatigue Analysis FE data

Creep Fatigue Temperature-dependent

fatigue properties PLUS

additional creep and creep-

fatigue interaction data

Thermomechanical fatigue

damage, creep damage and

creep-fatigue interaction

Elastic FE solution

Thermomechanical

Fatigue (both stress and

temperature fluctuate)

Temperature-dependent

fatigue properties PLUS

additional time-dependent

thermomechanical properties

(i.e. strain-rate dependent)

Conventional principal strain

fatigue method with time-

dependent thermomechnical

fatigue mechanisms

incorporated

A sequence of stress and

temperature solutions from an

elastic FE analysis (i.e. time

history of temperature and

stress)

Conventional high

temperature fatigue

Temperature dependent

fatigue properties

Room temperature

fatigue

Room temperature fatigue

properties

Conventional fatigue methods

using temperature-dependent

material properties

Elastic or elastic-plastic FE

solution

Conventional low

temperature fatigue

Temperature-dependent

fatigue properties

Inc

rea

sin

g T

em

pe

ratu

re

fe-safe

fe-safe

fe-safe

fe-safe/TMF

fe-safe/TURBOlife

High Temperature Fatigue Methods

64

Multiaxial Fatigue from Strain Gauges

65

66

67

When analysing an FE model using fe-safe, the user also has the

option to export a simulated strain gauge output.

For a specified node on the FE model, the orientation of the strain

gauge rosette can be defined.

The simulated strain gauge reading generated by fe-safe can be

compared with real test strain gauge readings.

Exporting a simulated strain gauge reading from fe-safe

68

Using fe-safe to design and validate test

command signals

69

Fatigue testing can be accelerated, for example by scaling input loads

or using cycle emission

However, all fatigue tests introduce errors to some extent

We should be aware of the potential errors in each type of test

fe-safe can be used to design the component, then to design and

validate the test

Using fe-safe to design and validate test command signals

70

Results

FE-SAFE 2400, test life 2160B: FE-SAFE 2700, test life 2420

C: FE-SAFE 2600, test life 2160

Results

FE-SAFE 4300, test life 6800

Results

Original signal

-800

-600

-400

-200

0

200

400

10 20 30 40 50 60Tim e:Secs

stra

in:u

E

Signal

Results

FE-SAFE 2400, test life 2160B: FE-SAFE 2700, test life 2420

C: FE-SAFE 2600, test life 2160

Results

FE-SAFE 4300, test life 6800

ResultsTest signal

-800

-600

-400

-200

0

200

400

0 0.05 0. 1 0. 15 0.2 0.25Tim e

stra

in:u

E

Compare lives and hot-spots in fe-safe

Producing a test command signal

Using fe-safe to design and validate test command signals

71

Overview of Developments in fe-safe™

John Draper, CEO

Ian Mercer, Software Director

Safe Technology Limited

72

Increased speed

User interface enhancements

Property mapping

Improved usability

Integration and interfaces

Platform support

Analysis refinements

Overview of Developments in fe-safe™

73

Increased speed

Multi-processor support

New distributed processing model

74

New distributed processing model

Master Node

- Supervises distribution

of process and data

- Queues analysis jobs

- Supervises licensing

Analysis

Node*

Interactive

workstation

- Analysis process configured

and initiated from the fe-safe

user interface

Command line

workstation

- Analysis process initiated

from the command line,

macros or batch file

Embedded

workstation

- Analysis process initiated

from within a third-party

application

Analysis

Node*

Analysis

Node*

Analysis

Node*

Analysis

Node*

Licence server

* Analysis nodes

may be single or

multi-processor

75

User interface enhancements

User interface separated from analysis engine

Separate command line version of fe-safe

New libraries

Comprehensive cross-platform support

Faster development of new capabilities

More robust code

5.4-04 R

5.4-04 R

76

Property mapping

Importing a property map

Definition of property map templates

Automatic mapping of properties in fe-safe based on, for example:

Depth

Thickness

Contact

5.3 R

77

Usability

Focus on fatigue window

Project-based directory structure

Selective loading of models

Surface only

By element or node group

Enhancements to automated scripting

Improved dataset management

Association of stress, strain, temperature and force datasets

Simplified load definition

78

Integration and interfaces

ANSYS

Integration into ANSYS Workbench 2

ABAQUS

Importing structural stresses directly from ODB file for use with Verity

Hyperworks

H3D import/export

New FEA interfaces:

Cosmos

LSDyna

Adina

Ansa

79

Platform support

fe-safe on IBM Power / AIX

80

Analysis Refinement

Surface detection

Hot spot detection

Correction methods

Stressed area correction

Stress gradient correction

Speed-up of analysis on the surface

5.4-04 R

5.3 R

81

Allows analysis of the surface nodes – for faster analysis

Allows stress gradient correction from surface nodes

Will allow faster fatigue solvers for surface nodes

Inner and outer surfaces indentified

5.4-4 R

5.4-4 R

5.4-4 R

fe-safe analysis capabilities

Identification of model surfaces

Identifies all surfaces in a model or assembly

82

85

fe-safe analysis capabilities

Forms groups of hotspots from the fe-safe results file

Identification of hotspots

Re-analysis can focus on these hotspots

Stress gradient correction will be applied

automatically to the hotspots

Goal is to pre-identify hotspots as the focus for

initial analysis

86

1.2

fe-safe analysis capabilities

90

fe-safe analyses the surface

fe-safe identifies the hotspots

fe-safe applies corrections – stress gradient, sub-surface

residual stress…

fe-safe analysis capabilities

An analysis process could be…

91

Applied to cast iron and cast aluminium alloys

More complex strain-life and mean stress relationships

More algorithms to be added to TurboLife

R&D in thermo-mechanical fatigue

Goal is to produce a single TMF and TurboLife module

fe-safe analysis capabilities

Improvements to the analysis of cast metals

Developments in high temperature fatigue