process of creating a fatigue damage model to enable

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PROCESS OF CREATING A FATIGUE DAMAGE MODEL TO ENABLE COMPUTER AIDED ENGINEERING (CAE) FATIGUE LIFE PREDICTION TO REDUCE COSTSAndrew Blows Principal Technical Specialist Body Strength & Durability CAE 4 July 2019

Creating a fatigue damage model

• Understanding your structure & CAE Limitation

• Fatigue Modes

• Fatigue Tests Results

• Internal Force from CAE joints

• Force to Stress Equations

• Stress to Life

• CAE Fatigue Prediction

2

AGENDA



• Fatigue Modes




• Stress to Life


3

AGENDA

Understand your structure

• Exploded view showing the complexity of a BIW structure and the number of parts requiring structural joining.

DECIDE HOW MUCH TESTING IS NEEDED

All of the parts are jointed together.

CAE methods are needed to engineer the correct

number of joints in the body structure to meet all

the durability requirements


Thousand of Joints :-

• Different Materials

• Thickness of parts



WHY CREATE A FATIGUE DAMAGE MODEL ?

Force Amplitude vs. Fatigue Life

All Sheet Combinations plotted for Sheet Fatigue

Lap Shear

Coach Peel

5,000 repeats 2,000,000 repeats

Applied load

In a body structure the geometry and loading mode of each joint is not known

it is not possible to predict the fatigue life

• Design

• Costly Late design changes, New part & processes

• Pressing / Casting tool changes

• Manufacturing facility costs

• Additional facilities in an already planed and built factory.

• Assembly cycle time

• Delayed Launch

• Millions per day

• Profits

• Quality / Warranty / Loss Sales / Reputation

7

Understand the structural performance

WHY CREATE A FATIGUE DAMAGE MODEL ?


• Identify the portion structure you are interested in

• Decide thickness combination of interest

• Extract forces and moments ( Peak, Range & Mean)

• Determine which coupon loading modes are the highest priority

• Decide how much force to test to

• Over loading introduces unnecessary failure modes

• Coupons may not be able to replicate system level failure modes.


Shear & Bending

Axial

Torsion

Identify whether joining technology is symmetrical ? Direction of SPR – Significant effect

In Line Lap Shear 3:3mm

3:3mm SPR

20

0,0

00

33

8,0

00

75

0,0

00

JOT374

JOT373

JOT375

A

C

B

Rivet Head

Rivet Head

Button Interior

Variation in Fatigue Life - 7.5 times

Dependant on direction of rivet

Just

over

100,0

00

Understand your coupons

Conduct detailed literature review

Discuss proposals with test department – coupon geometry – removal on in-plane rotation

Create a Test Matrix

Manufacture coupons using “Production process parameters”

Understand damage models in CAE Fatigue software

• Identify limiting factor / specific test required to enable software to be used

• Element type (Shells /SOLID connecting using CBAR/ACM/SOLID)

• Specific tests requires e.g. Stiff & Flexible

10


Bar ACM SOLID

Understand your coupons

Create FEA Model of coupons prior to Manufacture & Testing:-

• Decide on Joint modelling method , is suitable for joining technology

• e.g. SPR low in plane rotational stiffness

• Using same mesh refinement as structure

• Model to Gripping Fixture , alignment and clamped regions

Understand influence of coupon free length of forces & moments

− Non-linear / Buckling analyses

− Significant influence on loading ratio’s (Tension - Tension, Fully Reversed)

11


3mm/3mm

DatumR5

Free Length

= =

Coupon Drawing

Lap Shear Coach Peel

Understand limitations imposed

The importance of understanding the limitation that are imposed by reducing the scope physical tests needs to be understood and countermeasures incorporated into the design to mitigate these will be discuss

• Understand the failure modes in your jointing technology.

• Understand the limitation of CAE fatigue damage models being used.

• if you have not tested peel then you need to design to minimise the axial and bending in your joints, as you fatigue damage model will not predict this failure mode.

• If you have not tested for in of plane torsion – don’t have single discrete joints (spot welds, SPR)

13

UNDERSTAND LIMITATION OF FEA & FATIGUE

Torsion

AL RSW Test Matrix

For each thickness combination following no. of specimens

Lap Shear x 15

Coach Peel x 15

Top Sheet

(mm)

Bottom Sheet

(mm)

JOT271 Lap Shear 3 3




JOT276 Coach Peel 3 3





• Fatigue Modes




• Stress to Life


15

AGENDA

Process of creating a fatigue damage model

16

UNDERSTAND YOUR JOINING TECHNOLOGY

A spot weld consists of three regions, which have different material properties :-

− weld nugget which is melted zone

− heat-affected zone (HAZ)

− base material sheets.

These spot weld’s regions are generated by resistance welding process (pressure, heating temperature distribution, spot weld cooling). The nugget corresponds to the melted areas between the plates. This melting depth generates a thickness reduction of the welded plates, phenomena called indentation

Yi Gao, Darren Chucas, " Review of CAE Fatigue Analysis Techniques for SpotWelded

High Strength Steel Automotive Structures", SAE paper 2001-01-0835, 2001

Three regions of a spot weld

Process of creating a fatigue damage model

RSW FATIGUE MODES

Sheet Fatigue

Mode AThe crack grows almost perpendicular to the metal sheet and emerges from one side without penetrating into any part of the weld nugget

Normally occurs in spot-welded lap joints with large nugget sizes and under a predominantly shear fatigue loading. Automotive engineers generally prefer this mode of failure to other modes

Nugget Fatigue

Mode BThe crack propagates into the weld nugget but eventually emerges from one side

Mode CThe crack propagates into the weld nugget, remains parallel to the two sheets, and eventually cuts through the weld nugget

Yi Gao, Darren Chucas, " Review of CAE Fatigue Analysis Techniques for SpotWelded

High Strength Steel Automotive Structures", SAE paper 2001-01-0835, 2001



• Fatigue Modes




• Stress to Life


18

AGENDA

For use with videoForce vs. Test Life

Stress vs. Test Life

SRI1 Intercept

Slope -b

N Pred N life

Str

ess

N Test

N Test

CAE generated forces &

moments for each joint

type & thickness combination

Calc Stresses for Joint

Stress vs. CAE Life

Convert Force into Stress

Convert Stress into Life

Fatigue Damage Model Creation

As welded Lap Shear

M-6.0kN-40ms/23kA-80ms/28kA

WMG: M.Thornton & L.Han

Stiffness Change through Fatigue Test

Stiffness Drop off

Lap Shear Stiffness

2:3mm SPR JOT245_19

925,198



• Fatigue Modes




• Stress to Life


22

AGENDA


N Test





Lap Shear Joints Forces & Moments

External Force into Internal Forces

Sheet 1

Sheet 2

0,360 180

Axial Force

Shear Force Bending Moment

Torsion

Shear

Force

x

y

z

theta

Bending Moment

X

y

X

z

theta

y

z

Side view

Plan view

End view

FX1 FY1 FZ1 MX1 MY1 MZ1

T1 [Aluminium] T2 [Aluminium] Shear_2A Shear_1A Axial_A Bending_1A Bending_2A Torque_A

1.0 1.0 -0.500 0.000 0.006 0.031 -0.250 -0.003

1.0 1.1 -0.500 0.002 0.007 0.031 -0.252 -0.003

1.0 1.2 -0.500 0.004 0.007 0.032 -0.253 -0.003

1.0 1.3 -0.500 0.005 0.007 0.032 -0.253 -0.003

1.0 1.4 -0.500 0.007 0.007 0.032 -0.252 -0.003

1.0 1.5 -0.500 0.008 0.007 0.032 -0.251 -0.003

1.0 1.6 -0.500 0.010 0.007 0.032 -0.248 -0.003

1.0 1.7 -0.500 0.011 0.007 0.031 -0.244 -0.003

1.0 1.8 -0.500 0.012 0.007 0.031 -0.239 -0.003

1.0 1.9 -0.500 0.013 0.007 0.030 -0.234 -0.003

1.0 2.0 -0.500 0.014 0.007 0.030 -0.228 -0.003

1.0 2.1 -0.500 0.015 0.006 0.029 -0.221 -0.003

1.0 2.2 -0.500 0.015 0.006 0.028 -0.214 -0.002

1.0 2.3 -0.500 0.016 0.006 0.027 -0.207 -0.002

1.0 2.4 -0.500 0.016 0.006 0.026 -0.199 -0.002

1.0 2.5 -0.500 0.016 0.006 0.025 -0.191 -0.002

1.0 2.6 -0.500 0.016 0.005 0.024 -0.184 -0.002

1.0 2.7 -0.500 0.016 0.005 0.023 -0.176 -0.002

1.0 2.8 -0.500 0.016 0.005 0.023 -0.169 -0.002

1.0 2.9 -0.500 0.016 0.005 0.022 -0.162 -0.002

1.0 3.0 -0.500 0.016 0.005 0.021 -0.155 -0.002

1.1 1.0 -0.500 -0.002 0.007 0.033 -0.273 -0.003

1.1 1.1 -0.500 0.000 0.007 0.034 -0.275 -0.003

1.1 1.2 -0.500 0.002 0.007 0.034 -0.277 -0.003

1.1 1.3 -0.500 0.003 0.007 0.035 -0.278 -0.003

1.1 1.4 -0.500 0.005 0.008 0.035 -0.278 -0.003

1.1 1.5 -0.500 0.006 0.008 0.035 -0.278 -0.003

1.1 1.6 -0.500 0.008 0.008 0.035 -0.277 -0.003

1.1 1.7 -0.500 0.009 0.008 0.035 -0.274 -0.003

1.1 1.8 -0.500 0.010 0.008 0.035 -0.271 -0.003

1.1 1.9 -0.500 0.011 0.008 0.034 -0.267 -0.003

1.1 2.0 -0.500 0.012 0.007 0.034 -0.262 -0.003

Lap Shear response data (Alu – Alu)

Designlife

response

Optistruct

equivalent

Recommendation: Reduce FY, FZ, MX and MZ to zero to avoid unrepresentative compensating of small force and moment values in the solver.

NN NmmN NmmNmm



• Fatigue Modes




• Stress to Life


26

AGENDA


N Test







Force to Stress Equations- Sheet Fatigue Calculate Stress in joint from Forces and Moment for Sheet 1, Sheet 2

Source nCode :-

http://www.mscsoftware.com/support/library/conf/wuc96/07b_heye.pdf

Stress = f ( F, M t, d ) * Scale Factor * (d) ^ Diameter Exponent

* ( t ) ^ Thickness Exponent

Tension

Compression

Shear

Axial

Bending

http://www.mscsoftware.com/support/library/conf/wuc96/07b_heye.pdf

0,3

60

18

0X

y

the

ta

Lap Shear Stress Distribution for 2:2 mm Joint with 3kN total Force

9 Material constants for Al Spot Weld

Factor Diameter Exponent ThicknessExponent Empirical factor

SfFxy SfMxy SfFz DeFxy DeMxy DeFz TeFxy TeMxy TeFz Fz M

1 +1 1.00 0.50 0.50 0.00 -0.25 -0.25 1.00 1.744 1.872

Using a Positive Bending Moment Factor SfMxy

Region in Compression

as expected on sheet 1

at interface

Region in Tension

as expected on sheet 1

at interface

Shear Force

in Compression

at 180 deg

Axial Stress

Bending Stress

Shear Stress

Combined Stress

Optimisation issues

The solver results can be dependant on the initial starting conditions

Limits used for upper and lower bound .

These need to be established using engineering principals.

Local minimum

Global minimum



• Fatigue Modes




• Stress to Life


31

AGENDA


N Test

N Test








Fatigue Damage Model Published

Rupp parameters for AL RSWForce Convert to Stress using Rupp EquationsTwo Separate Families (Lap Shear & Coach Peel) merge into one stressComparison between CAE Predicted Life and Measures test life

N t

es

ted

N P

red



• Fatigue Modes




• Stress to Life


34

AGENDA



SRI1 Intercept

Slope -b

N Pred N life

Str

ess

N Test

N Test





Stress vs. CAE Life


Convert Stress into Life


Force Amplitude vs. Fatigue Life

All Sheet Combinations plotted for Sheet Fatigue

Coupon Fatigue Test

Lap Shear

Coach Peel

5,000 repeats 2,000,000 repeats

Applied load

In a body structure the geometry and loading mode of each joint is not known

it is not possible to predict the fatigue life

AL RSW Damage Model Force Convert to Stress using Rupp Equations plotted against Test LifeTwo Separate Bands for Lap Shear and Coach Peel merge into one stress for Test Data

N t

es

ted

N P

red

.

N t

es

ted

One Standard Distribution of CAE life

Single Fatigue Damage Curve for all joint geometries and loading

Test Variation

C

A

E

CAE ModelsBody in White

Body In White Discrete Joints



• Fatigue Modes




• Stress to Life


39

AGENDA

Process of creating a fatigue damage model to enable Computer Aided Engineering (CAE) fatigue life prediction to reduce costs

Thank you very much for Listening

Do you have any Questions ?

Acknowledgements:

This project was co-funded by the Technology Strategy Board's Collaborative Research and Development programme.

The Technology Strategy Board is an executive body established by the Government to drive innovation. It promotes and

invests in research, development and the exploitation of science, technology and new ideas for the benefit of business -

increasing sustainable economic growth in the UK and improving quality of life.

For more information about the TSB visit www.innovateuk.org

Jaguar Land RoverW/1/26 Abbey Road, WhitleyCoventry CV3 4LF, UK

jaguarlandrover.com

THANK YOU Andrew Blows Principal Technical Specialist

M +44(0)7774 557 820

[email protected]

41

process of creating a fatigue damage model to enable

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