Ts presentation crach

Current Techniques ENGINEERING STRESS-STRAIN

Engineering Stress [MPa]

800 700 600 500 400 300

Some areas appear to have failed at t=0ms.

200 100 0 0.00

RD0

t=100ms 0.05

0.10

0.15

0.20

Engineering Strain [-]

Conduct tensile test & determine strain or elongation at fracture

0.25

Either; 1. Add failure strain to material card & observe failure in CAE or 2. Inspect CAE results & infer areas at risk of failure

Current Techniques: Issues

10mm Mesh

8mm Mesh

6mm Mesh

Some areas appear to have failed at t=0ms.

4mm Mesh

2mm Mesh

t=0ms

Material model set to fail at EPS=0.8 Plastic Strain at Failure is mesh size dependent !

When used in crash simulation, some elements appear to have failed at t=0ms!

Major Principal Strainε1()

General Fracture Theory: Possible Fracture Prediction Methods Thinning

Maximum Principal Strain

-2.0

Measured FLC

EPS =

Plastic Strain

-1.0

0.0

2 ε 12 + ε 22 + ε 1ε 2 3

1.0

2.0

Minor Principal Strain (ε2)

ISSUES • No theories agree, FLC is used extensively for forming simulation • Current EPS method agrees only at one point

Summary of Current Technique •

Current technique is

• • • •

inaccurate mesh dependent open to interpretation

Leading to…………

• •

increased risk mass inefficient design

Improved CAE Capability of Fracture Prediction in BIW Sheet Metals • • • •

Project Justification Project History Current Technique – Statement of Issues Requirements for CAE Technique • Predict relevant modes of fracture • Accurate model of flow curve, yield locus • Accurate implementation of fracture criteria • Accurate treatment of non linear strain paths & ‘damage’ transfer from stamping to crash CAE model

•

• • •

Mesh independence of prediction

Project Examples Limitations Summary & Risks

CAE Technique: A New Approach CrachFEM •

CrachFEM is similar to a FLC approach but also includes…

•

Non-linear plastic strain accumulation

•

A more comprehensive range of fracture modes than just necking

•

Improved yield locus model (kinematic-isotropic hardening)

•

A mesh independent solution

MATFEM Example of CrachFEM Fracture Prediction (Aluminium Box)

DP600 CrachFEM Fracture Curves

Material Model: Hardening & Yield Locus Evolution 1.2

NG5754 DP600 MAT 24

0.8

0.4

0.0 -1.2

-0.8

-0.4

0.0

0.4

0.8

1.2

-0.4

-0.8

-1.2

Yield Loci for 2 materials & the Von Mises criteria as used in Dyna Mat24 FLOW CURVE 900 800

True Stress [MPa]

700 600 500

1000

400

250

500 100 10

300

1 0.1

200

0.01 0.008

100 0.0

0.2

0.4

0.6

True Plastic Strain [-]

0.8

1.0

Creation of Fracture Limit Curves

1.00 DNF

Ductile Normal Fracture

DSF FLC GENYLD

0.80

Ductile Shear Fracture 0.60 EPS

Source: W. Schatt, Einführung in die Werkstoffwissenschaften, 1991, ISBN 3-342-00521-1

0.40

Instability (necking) 0.20

-1.00

ductile fracture

Modelling Metals with MF GenYld + CrachFEM © MATFEM 2008 - Seminar

shear fracture

-0.75

-0.50

-0.25

0.00 0.00

α

0.25

0.50

0.75

1.00

Ductile Fracture Model: Strain Paths EPS =

2 ε 12 + ε 22 + ε 1ε 2 3

α = ε 2 ε1

Potential, improved criteria

Current, EPS failure criteria

Strain Paths: Single Element Test

PLANE STRAIN COMPRESSION

UNIAXIAL COMPRESSION

SHEAR (APPROX.)

UNIAXIAL TENSION

α=0

α=-2

α=-1

α=-0.5

TENSION X COMPRESSION Y

α=-1

PLANE STRAIN TENSION

α=0

BIAXIAL TENSION

α=+1

BIAXIAL COMPRESSION

α=+1

Strain Paths: FLD Domain • Gradient indicates strain path • Very difficult addition of non linear strain paths

Linear Strain Paths 1.00 DNF DSF FLC GENYLD

0.80

EPS

0.60

0.40

0.20

Shear

-1.00

Tension

-0.75

-0.50

Plane Strain

-0.25

0.00 0.00

Îą

Biaxial Tension

0.25

0.50

0.75

1.00

Non Linear Strain Paths: Damage Accumulation Material will start to fail when ‘Damage’ = 1.

0.60

Damage = 0.5 (0.25/0.5) Total Damage =1

0.40

EPS

0.50

0.30

Tension Damage = 0.5 (0.3/0.6) Total Damage =1

CRASH 1 Tension

CRASH 2 Biaxial

0.20

0.10

STAMPING Plane Strain

Damage = 0.1/0.2 = 0.5

-0.50

-0.25

0.00 0.00

0.25 α

0.50

0.75

1.00

FR5 Mesh Dependence • The CrachFEM instability risk (FR5) can be considered to be mesh independent for elements in the 2-10mm range.

3mm element deletion range 10mm Mesh

8mm Mesh

6mm Mesh

4mm Mesh

2mm Mesh

Error ~ 8%

Improved CAE Capability of Fracture Prediction in BIW Sheet Metals • • • •

Project Justification Project History Current Technique – Statement of Issues Requirements for CAE Technique • Predict relevant modes of fracture • Accurate model of flow curve, yield locus • Accurate implementation of fracture criteria • Accurate treatment of non linear strain paths & ‘damage’ transfer from stamping to crash CAE model

•

• • •

Mesh independence of prediction

Project Examples Limitations Summary & Risks

Example: L359 DP600 X-Member Drop Test X-Member with cutaway arches 60kg Impactor Drop height up to 5m

CAE Prediction 2.3m Drop

No failure predicted (c.f. EPS) -Fracture is predicted at the ∅15mm U slot -Note: CAE model includes damage from stamping simulation

Fracture Risk

Test 2.3m Drop

Fracture occurs at the apex of the U slot

Summary of 2.3m Drop • •

Tested part fractured CAE predicted the failure

But………..

•

2.3m drop had more than enough energy to create fracture

So………...

•

Can we predict the energy required to take part to limit without failure?

CAE Prediction 1.95m + 0.5m Drop 1.95m Drop

Subsequent 0.5m Drop

Fracture Risk

Fracture risk at the ∅15mm U slot is 0.88 – no fracture predicted

Fracture is predicted at the ∅15mm U slot – fracture predicted

Drop Test – 1.95m +0.5m Drop

In the 1.95m drop, no fractures occur.

In the subsequent 0.5m drop, fracture occurs from the apex of the ∅15mm U slot

Summary of Component Test •

New CAE technology for predicting fracture in thin sheet metals has been validated through component testing.

•

CAE accurately predicted the energy to fracture, at the correct location

•

CrachFEM is easy to use, providing a simple fracture risk without the need for extensive knowledge of methods.

•

CrachFEM technology shows significant improvement over current state of the art.

Limitations of Current FE Analysis • Discontinuities created by welds or rivets affect fracture performance.

SPR

RSW

5mm Finite Element

5mm Finite Element

• Difference in cut edge can’t be captured in shell elements • Capture of notches etc. is limited by mesh size e.g. SPR model requires 0.1mm solids.

5mm Finite Element

Cut Edges Thickness

=> Further work required to characterise increased risk from these features.

Phase II Project – Effect of SPR & Welds • • • •

Al:Al SPR & RSW, Steel:Steel RSW, Al:Steel SPR (Mixed Metal) Coupons manufactured by WMG & STC Coupons joined by WMG Testing at STC

JLR

NG5754 2mm SPR Direction = Patch to Sample

NG5754 2mm SPR Direction = Sample to Patch

NG5754 2mm RSW

TOTAL

Sample 1

3

3

3

9

Sample 2

3

3

3

9

Sample 3

3

3

3

9

Sample 4

3

3

3

9

No Patch

3

0

0

3

TOTAL

15

12

12

39

CORUS Spotwelded Steel Patch SPR Aluminium Patch No Patch TOTAL

Boron Steel Coupon (0.95mm) 12 12 3 27

DP800 Coupon DP600 Coupon (1.5mm) (1.5mm) 12 12 3 27

TOTAL

12 12 3 27

36 36 9 81

TOTAL

120

Phase II Coupon Tests – Effect of SPR/Weld Proximity to Edge Investigations into the effects of RSW & SPR on aluminium, steel & mixed metal coupons.

Sample 2, 3 almost identical

SPR Centre is 18mm from hole edge SPR Centre is 13mm from hole edge SPR centre is 8mm from hole edge (standard minimum).

SPR Centre is 5mm from hole edge 10mm Dia. Hole Gauge is 2mm 160mm

Discretisation adequate to detect differences in test

Example 1: L538 Side Impact EPS

Max EPS 24%

Max FR 0.74

Plots @ 60ms IIHS(SC5)- 5dr Baseline (Run A504b)

BENTELER BORON CrachFEM MAT (A507a)

L538 Door Beam Example

Very high risk using EPS => large change in gauge to fix the issue

Very small area of risk using CrachFEM => small change in gauge to fix the issue

L538 SC4 Door Beam

Original Design

Improved Design

Plastic Strain @ 45ms

Plastic Strain @ 80ms

CrachFEM @ 50ms

CrachFEM @ 80ms

Plastic Strain @ 45ms

Plastic Strain @ 80ms

CrachFEM @ 50ms

CrachFEM @ 80ms

Example 2: L538 Side Impact Max FR 1.59

EPS

CrachFEM

Elements deletion starts @ 57.5ms

Max EPS 29%

Max FR 1.59

Europole(SC4)-5dr Baseline (Run A504e)

L538 5DR B Post: UPDWG SC5

Test?

Max. EPS = 0.25

Max. FR = 0.86

Failure Criteria = >0.06

Failure Criteria = >1

L538 3DR B Post: UPDWG SC7

Test?

Max. EPS = 0.19

Max. FR = 0.56

Failure Criteria = >0.06

Failure Criteria = >1

Extra •

New CAE technology for predicting fracture in thin sheet metals has been validated through component testing.

•

CrachFEM is easy to use, providing a simple fracture risk without the need for extensive knowledge of methods.

•

CrachFEM technology shows significant improvement over current state of the art.

•

‘Damage’ accumulated in stamping & crash needs to be included in the simulation.

•

Technology can be implemented on program for cold formed panels.

Strain Paths Practical 0.50 Example 0.45

Equivilent Plastic Strain

0.40 2. CRASH Damage to fracture = 0.3 (1-0.7) along uniaxial tension strain path.

0.35 0.30

X Fracture

0.25

e ur l i Fa

Cr

ria e it 6111T4 2mm

EPS Limit from Tensile Test

0.20 0.15 0.10

1. STAMPING Damage = 0.7 along plane strain tension path (Îą=0)

0.05 0.00 -1.0 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Ratio of Principal Strains