1

Dr. Pingsha Dong

Professor, Mechanical Engineering

Professor, Naval Architecture and Marine Engineering

Director, Welded Structures Lab

University of Michigan, Ann Arbor, MI 48109

Contact: dongp@umich.edu

(https://name.engin.umich.edu/people/pingsha-dong/)

DESIGN FOR MANUFACTURE OF MULTI-MATERIAL LIGHTWEIGHT STRUCTURES:

CHALLENGES AND ENABLERS

2

Outline

Recent structural lightweighting trend

Challenges in design for manufacturing

Technological enablers• Robust dissimilar materials joining techniques

• Optimal joint design for jointability and performance

• Residual stress and distortion control

• Robust structural life evaluation method

• ONR T-Craft: integrated evaluation from design to manufacturability and performance

Concluding remarks

3

Ways to Achieve Lightweighting – Auto Industry Leads the Way

Using less materials in structures: increasing strengths of traditional materials

Using lightweight materials, e.g., aluminum alloys or composites

Using multi-material structures, i.e., using “the right material at the right place”

4

Multi-Material Structures for Lightweighting –Automotive Initiatives: Europe and USA

Porsche 970

5

Multi-Material Structures for Lightweighting -Air

Airbus A350

Boeing 787

6

Multi-Material Structures for Lightweighting – Sea

ONR T-Craft

Drivers in maritime platforms:

• Reduce fuel consumption;

• Improve speed, maneuverability, and transportability;

• Increase weapons payload

DDG Zumwalt Destroyer

7

Conventional versus Direct Joining Processes and Issues

C-Mn Martensitic

Adhesive joints

Aluminum/Steel

Transition Joints

Traditional Methods

Direct Joining

8

Unfavorable Residual

Stress State

Favorable Residual

Stresses State

Buckled! Flat!

Some Specific Construction Issues Encountered -Distortions in High Strength Thin Plate Cutting

• Two flat high strength plates

• Simultaneous slitting

• One buckled while one remaining essentially flat

9

2219/2219 RING after Welding

0.125” thick self-reacting friction-stir welding at MSFC - ARES I upper

stage common bulkhead dome body to Y-Ring connections

2219/2219 Ring Before Welding

Buckling of Friction-Stir Welded High Strength Aluminum Components

Before Welding After Welding

10

Design and Manufacture of Multi-Material Structures - Challenges

The conventional approach is no longer adequate

Math-based design for manufacturing tools are the key enabler to enlarge the workable parameter space

• Robust direct-joining processes

• Dissimilar materials weldablity/jointability

• Joint properties

• Structural performance

11

Math-Based Design for Manufacturing Research Tools – I

T-fillet with 45 degreeT-fillet with 45 degree

T-fillet with 45 degreeT-fillet with 45 degree

Prior-Operation HistoriesuMill conditionsu Forming, etc

WeldabilityAnalysisu ABAQUS & UMAT ROUTINES

Arc

+

sx

Tensile

Compressive

WeldPool

+

+

-

Crack

Fillet Weld

PCrack

P

• Residual Stresses

• Distortions

HAZHAZ WM

Yield StressSy

Performance Simulationu FEAM-WELD(Alternating Method)uVerityTM Structural Stress Method

Weld Acceptance Criteriau POLY-FEM(Hybrid Method)u FEAM-WELD

Welding Heat-Flow Simulationu WELD-FLOW2D & 3D *u THERM-WELDor commercial codes

WM

HAZHAZ

Weld/HAZ Microstructure& Property Estimationu WELD-TRAN

+

sx

Weld

* Unique solution techniques in red

Fusion welding and

related prior processes

T-fillet with 45 degreeT-fillet with 45 degree

T-fillet with 45 degreeT-fillet with 45 degree

Prior-Operation HistoriesuMill conditionsu Forming, etc

WeldabilityAnalysisu ABAQUS & UMAT ROUTINES

Arc

+

sx

Tensile

Compressive

WeldPool

+

+

-

Crack

Fillet Weld

PCrack

P

• Residual Stresses

• Distortions

HAZHAZ WM

Yield StressSy

Performance Simulationu FEAM-WELD(Alternating Method)uVerityTM Structural Stress Method

Weld Acceptance Criteriau POLY-FEM(Hybrid Method)u FEAM-WELD

Welding Heat-Flow Simulationu WELD-FLOW2D & 3D *u THERM-WELDor commercial codes

WM

HAZHAZ

Weld/HAZ Microstructure& Property Estimationu WELD-TRAN

+

sx

Weld

* Unique solution techniques in red

Fusion welding and

related prior processes

Defect assessment of

AM parts

Fusion and Associated Processes(Unique simulation techniques in red)

12

Math-Based Design for Manufacturing Research Tools – II

y

x

MPaCompressive

y

x

MPaCompressive

Induction Heating(Electro-Magnetic-Thermal)

Friction Stir Welding

Inertia Bonding

Finite Difference Model Finite Element Model

Electrical- Thermal- Mechanical SimulationElectrical- Thermal Simulation

• WELD-FLOW2D

• WELD-FLOW3D

ABAQUS

Fracture/Fatigue/Crash

• VerityTMSSM• HPE

• SWE

Residual Stress/Distortion

• THERM-WELD

• UMAT Weld Models

Weld Quality

• HPE Method

Weld Quality

• HPE Method

Microstructure/

Property

• WELD-TRAN

ABA-DRIVER

ANSYSThermomechanical

Analysis

ANS-DRIVER

ANSYS ABAQUSThermomechanical

Analysis

Nugget

x

sy

sx

y+

+

HAZ

I, F

Electrical-Thermal

Analysis

Nugget

* Unique solution techniques in red

Applications:

• Resistance Welding

• Friction Welding

• Inertia Bonding

• Friction Stir Welding

• Diffusion Bonding and Brazing

Solid-State Processes(Unique simulation techniques in red)

Applications:• Resistance welding

• Friction/inertia bonding

• Friction stir joining

• Diffusion bonding

• Dissimilar metals joining

• Metal/polymer joining

• Hybrid 3D printing,

• …

Aluminum

Polymer

Hybrid Multi-Scale Model Finite Element Model

13

A Novel Method for Joining Aluminum to Steel without Detrimental Intermetallics

Multi-Scale Modeling

Experimental Validation

Liu, F. C., Dong, P., Zhang, J., Lu, W., Taub, A., & Sun, K. (2020). Alloy

amorphization through nanoscale shear localization at Al-Fe interface.

Materials Today Physics, 15, 100252.

APT Image

14

A High Speed Direct Welding Method for Joining Polymer to Metal

A

A

A-A cross section

Mechanical test results:

Al/Nylon sample joined at 5 meters per minutes

The Technology

The Mechanism

XPS confirmation

Aluminum

Nylon

Liu, F. C., Dong, P., Lu, W., & Sun, K. (2018). On formation of Al-O-C

bonds at aluminum/polyamide joint interface. Applied Surface Science.

15

Singularity Positions in Welded and Adhesive Joints

F. Lawrence, 04

Notch Radius=?

16

Effects of Stress Singularity on FEA-Calculated Stresses: Mesh-Sensitivity

Stress/strain

singularityStress/strain

singularity

Conventional FEA: mesh-size sensitive

17

e.g., IIW

Through-thickness stress

1.0

2.0

3.0

4.0

0.0

No

rmal

ized

Str

ess

Element Size (l/t)

F/A

Peak stress at Weld Toe

from FE Model

1.0

2.0

3.0

4.0

0.0

No

rmal

ized

Str

ess

Element Size (l/t)

F/A

Peak stress at Weld Toe

from FE Model

st

F

st

F

1. What stress to use? 2. Which S-N curve to use?

Two Key Issues in Any FE Based Fatigue Analysis Methods

18

t

t

a

b

F

Element Size at

Weld Toe:

.8t/t.8t/t

.16t/.1t.16t/.1t

(a)

(b)

(c)

t

tt

8t

25t

Structural Stress

0

0.4

0.8

1.2

1.6

.16t/0.1t .4t/.5t .4t/t .8t/.5t .8t/t 2t/t

Element Size: a/b

Nor

mal

ized

Stre

ss

(d)

Element Size (a/b)

Str

uctu

ral S

tress S

CF

W/ Grip W/o Grip

1.0

Note:

• Effects of Boundary Conditions

• Implications: Lower life W/Grip than W/o Grip

1.17

Parabolic Elements with Reduced Integration

Structural Stress Calculation Example: a Lap Fillet Joint – 2D

19

Structural Strain Based Master S-N Curve for Evaluation of Multi-Materials Structures

Master E-N curve

Mild steel

High strength steel

Stainless steel

Titanium alloys

Aluminum alloys

Magnesium alloys

1/*(2 )/(2 ) mms m

s

t I rE

20

Fatigue Test Data Analysis – Friction Stir Welded Dissimilar Aluminum Components

21

Dissimilar Material Joints –Transferability for CAE durability design

100

1000

10000

1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07

No

min

al S

tres

s R

ange

(N

)

N Cycles

Traditional Method

Coach Peel 1mm-1mm Coach Peel 1mm-2mm

Coach Peel 2mm-2mm Lap Shear 1mm-1mm

y = 204.92x-0.091

R² = 0.7302

10

100

1000

1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07

Stre

ss (

MP

a)

N Cycles

Equivalent Structural Stress Range

Lap Shear 1mm-1mm Lap Shear 1mm-2mm

Lap Shear 2mm-2mm Coach Peel 1mm-1mm

Coach Peel 1mm-2mm Coach Peel 2mm-2mm

Power ( )

22

Joint Strength Transferability by Means of Mesh-Insensitive Method for Use in CAE Model

0

20

40

60

80

100

120

140

160

180

200

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Trac

tio

n B

ased

Jo

int

Stre

ngt

h (

MP

a)

Specimen ID

1.55Al+2.35Fe 1.55Al+0.7F

6.5Al+1.4Fe 6.5Al+6.35Fe

0

20

40

60

80

100

120

140

160

180

200

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

No

min

al S

hea

r Jo

int

Stre

ngt

h (

MP

a)

Specimen ID

1.55Al+2.35Fe 1.55Al+0.7F

6.5Al+1.4Fe 6.5Al+6.35Fe

Coefficient of Variation: 0.457 Coefficient of Variation: 0.152

Nominal Stress Based

AL 6000

Steel

Structural Stress Based

23

Example: Interface-Based Bonding

𝐸1 ≫ 𝐸2

1 2

2 1

Bad

Good

24

Example: Adhesive Joints

𝜎: 𝑙 = 0.5"

𝜏: 𝑙 = 0.5"

𝜏: 𝑙 = 0.25"

• Reduce overlap “length 𝑙”• Increase overlap “width” in the

direction perpendicular to dominant

loading direction

• Reduce adhesive shear modulus

25

Math-Based Mitigation Technique: Before and After

Before

After

26

Math-Based Mitigation Technique: Before and After

Plastic zone

conditioning

Support collapsed

during testing

Before

After

27

ONR T Craft: Manufacturabiltiy and Structural Performance Evaluation

ONR T-Craft

28

Titanium (CP) TIG Weld Fatigue Test Results and Comparison with Japanese Data

100

1000

10000 100000 1000000 10000000

Eq

uiv

alen

t T

ract

ion

Str

ess,

MP

a

Cycle to Failure (N)

Mean

+2*STD

-2*STD

Japan

UNO-TIG

Slope -4.95

STD 0.176

50

500

10000 100000 1000000 10000000

No

min

al S

tres

s R

ang

e, M

Pa

Cycle to Failure (N)

Mean

+2*std

-2*STD

Japan

UNO

Slope -1.84

STD 0.44

Conventional method

New method

29

Before ONR Titanium T-Craft Program – Mesh-Insensitivity up to about 10t

7.5tx7.5t

Models – Different Mesh Refinements

3.75tx3.75t

0

0.5

1

1.5

2

2.5

3

3.5

4

7.5tx7.5t (1ele) 3.75tx3.75t (2ele) 1.875tx1.875t (4ele) 1.0tx1.0t (8 ele) Sol (ref)

1.875tx1.875t1.0tx1.0t

SCF

30

As a Result of ONR Titanium T-Craft Program

1

2

3

4

5

6

7

SC

F

VNM - Old

VNM - New

3D Solid Model

Element size=50t

Element size=25t

Element =12.5t

Element size=100t)

Coarse Models

31

Aluminum and Titanium T-Craft Mid-Ship Section FE Models

Model Details:

Shell elements:72470

Element size: ~300mm

Model Details:

Shell element s: 85178

Element size: ~250mm

Titanium Aluminum

32

Load Cases (Ref. MiNO Report)

1. Cross Structure Bending: Prying 21,600 ft-LT/100ft; Squeezing

4320ft-LT /40ft

2. Longitudinal Bending: +- 25,600 ft-LT (Hogging and Sagging)

3. Torsion (Pitch-Conn. Moment) – 31,600 ft-LT

33

Comparison of Estimated Fatigue Lives between Al and Ti Mid-Ship Sections - II

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

1.0E+07

1 2 5 11

Cyc

le t

o F

ailu

re

Weld ID

Al Weldline

Ti_MIG Weld lines

Ti_TIG Weldline

34

Concluding Remarks

Multi-material structures become necessary for achieving effective structural lightweighting

Advanced CAE design methods can be powerless without considering dissimilar joining processes and joint properties

Math-based design-for-manufacturing tools are the enabler for:• Developing novel dissimilar materials joining processes

• Generalizing joint properties

• Developing effective accuracy control procedures for modular assembly

• Achieving model-based structural lifing

• Effective multidisciplinary approaches through integrated modeling tools

Many challenges ahead and plenty of technology innovation opportunities