2018 ncode user group meeting of... · 2018. 4. 26. · • acm • penta method • abaqusodb •...

© 2018 HBM

HBM Prenscia: Public

2018 nCode User Group Meeting

February 28 ‐ March 1, 2018 – Novi, MI USA

© 2018 HBM


New Capabilities for Predicting the Durability of Welded Structures

Jeff MentleyApplications Engineer

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• The fatigue properties of a welded joint are quite different from those of the parent plate due to

• Weld geometry usually has• Large stress concentrations factors

• Existing crack initiation sites

• High tensile residual stresses• Non‐uniform material distribution

• Deposited weld metal

• Heat‐affected zone in parent metal

• Fatigue properties of welds are much lower than those of the parent metal• Parent metal strength not reflected in the weld fatigue strength• Weld fatigue behavior is primarily crack growth

Observations on the Fatigue Behavior of Welds

Life (cycles)

S

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4Weld Fatigue Calculation Approaches

Local Notch StressCrack

Growth

Structural Stress

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• Typical fatigue process requires detailed material and geometry data• Using structural stresses, weld is treated as a component• Component fatigue curves represent the weld, not the weld material

The Fatigue Analysis Process using Structural Stresses

MaterialProperties

LoadHistory

Geometry(FEA)

DamageAnalysis

FatigueLife

CombineWöhler circa 1850

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• Load life curves from physical fatigue tests• Finite element models of test specimens• Structural stresses calculated from FE models• With appropriate corrections load life curves collapse

to single structural stress life scatter band• The resulting structural stress curve represents the

typical behavior of the welds in the specimens tested

How a Structural Stress Approach is Applied

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7Structural Stresses used in DesignLife

• Spot welds• Stresses calculated from forces and

moments transferred through the connector

• Shell Seam welds• Structural stresses from nodal forces and

moments along weld toe

• Solid Seam welds• Through thickness integration (TTI) of actual

FE stresses to obtain linearized stresses

T

linearizedpeak

Fz

Mxt

d

Fx

Fy My

)cosθσ(M)sinθσ(M)σ(F)sinθσ(F)cosθσ(FΔS(θ) yxxyx

© 2018 HBM


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• Nastran OP2, Optistruct OP2 & H3D• Point to Point (P2P)

• CWELD

• ACM

• PENTA method

• Abaqus ODB• Point to Point (P2P)

• ACM

• LS‐DYNA MAT SPOT WELD• Beam

• Hex

• ANSYS Workbench Spot weld

• Support for Vibration Fatigue• Curves for Steel, Aluminum, and Self Piercing Rivets

Spot Welds

Beam Element, CWELD

*Rupp, A., Störzel, K. and Grubisic, V. (1995) “Computer Aided Dimensioning of Spot-Welded Automotive Structures”. SAE Technical Paper 950711

New in 2018

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• Simple shell representation of weld• Predefined failure locations

• Toes, root, throat

• Automatic bending ratio and thickness corrections

• Generic seam weld curves• Nastran OP2, Optistruct OP2 & H3D

• Nodal Force and Moment

• Cubic Stresses

• Abaqus ODB, Ansys• Nodal Force and Moment

• Support for Vibration Fatigue

Shell Seam Weld

New in 2018

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• Applicable to broader range of applications and modeling

• Some things just can not be accurately modeled in shells

• Linearized stress at weld is not dependent on FE mesh density or element type

• 1st & 2nd order TET, PYR, WED & HEX

• Weld definition based on geometry, not FE model• User controlled failure locations• Uses same solution procedure and fatigue curves as

shell seamweld• Weld configuration file generators

• Hypermesh

• Ansys Workbench

• Abaqus CAE

• Support for Vibration Fatigue

Solid Seam Weld

New in 2018

© 2018 HBM


11Stresses Calculated Directly by the Finite Element Model

Smax = 133 Smax = 142

Smax = 170 Smax = 252

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• However useful, the structural stress approach is not perfect for all welds• Weld fatigue is crack growth, and to analyze it more accurately we need to use crack

growth• Structural stress approaches either ignore the detailed weld geometry or group

welds into relatively simple geometry classes • Since the structural stress approach represents the fatigue behavior of a typical

weld, it doesn’t reflect improvements in weld geometry or welding procedure

Limitations of Structural Stress Approach

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• Complex weld geometries where the standard methods don’t give the correct answers and are too conservative

Thick Welds – “Design the weld”

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• Increasing use of different materials and manufacturing techniques means that more complex welded joint are being used in main stream automotive applications

Automotive Lightweighting

2018 ncode user group meeting of... · 2018. 4. 26. · • acm • penta method • abaqusodb •...

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