SimA Fracture Mechanics

7/24/2019 SimA Fracture Mechanics

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Fracture MechanicsCapabilities in Marc


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Presenter Information

Zhong Qin @ Storrs, Connecticut Lead Technical Representative

(12 years with MSC)

Primarily support Marc/Mentat, Nastran and Patran

Also familiar with Dytran, MSC.Fatigue, LaminateModeler,...

Education background B.S., Mechanical Engineering

M.S., Mechanical Engineering Ph.D., Computational Mechanics

Joe Satkunananthan @ Newport Beach, CA


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Seminar Agenda

Overview of fracture mechanics capabilities J-Integral Lorenzi option

Virtual Crack Closure Technique VCCT option

Delamination crack initiation based on stress criterion

Crack propagation direct and fatigue

Simulation of crack propagation Crack initiation

Crack propagation types

Crack propagation methods

Crack propagation direction

Crack propagation criteria

Demo


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Fracture Mechanics - Overview

J-Integral A path-independent contour integral

for the analysis of cracks

Equivalent to the energy releaserate for linear elastic material model

Stress intensity factors KI, KII & KIIIby mode separation


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J-Integral (cont.) Integration domain is defined

by rigid regions

Rigid region may be defined Topology search (connectivity)

Geometry search (radius) Manual

Shift vector can be definedmanually or automatically


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VCCT Virtual Crack Closure Technique

A simpler but more general way forobtaining energy release rate G

G = change in potential energy by

a change in crack length


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VCCT crack propagation Direct and fatigue crack propagation

types are supported

Crack grows when G is greater thanmaterial fracture toughness Gc

Fatigue crack growth incrementcalculated by Paris Law

Crack can grow by remeshingor splitting elements


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Crack initiators Modeling existing flaws

Splitting mesh

Cutting mesh along a curve

Remeshing with faceted surface


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Delamination Crack initiation due to service loading

Based on stress criteria

Split mesh upon failure

Insert VCCT definition

Insert cohesive interface elements Terminate loadcase when crack is initiated


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VCCT Crack Propagation

Crack propagation analysis types Low cycle fatigue

High cycle fatigue

Direct Both fatigue and direct


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Crack growth methods Remeshing

Release constraints

Split elements Cut through elements


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Crack growth direction Maximum hoop stress

Along pure mode

Along mode I User defined

Mode I and normal

User subroutine


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Fatigue crack propagation properties Fixed growth increment size

Fatigue time period

Crack growth increment

Cracks grow with constant increment at the endof fatigue time period

Useful for crack growth path


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Fatigue crack propagation properties Growth increment calculated by Paris law

In terms of energy release rate

In terms of stress intensity

Perform every fatigue cycle

Useful for low cycle fatigue


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Fatigue crack propagation properties Fixed with scaling

Specified growth increment is scaled

Fatigue law scaling

Exponential scaling

High cycle fatigue count


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Direct crack propagation properties Total energy release rate (fracture toughness)

Individual modes

Power law mixed mode Reeder mixed mode

Total using Lorenzi

Geometry based rigid regionpreferable for 3D problems


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Available results Energy release rate

Stress intensity factor

Crack growth direction Crack local system

VCCT failure index

Accumulated crack growth

Number of fatigue cyclesGlobal variable


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Summary

Marc supports J-integral and VCCT for fracture mechanics

For J-integral evaluation, rigid region can be defined byautomatic topology search or geometry search

Crack initiator may be used to generate initial crack for VCCTcrack propagation

Stress-based delamination option may work alone orgenerate initial crack for VCCT crack propagation

In fatigue crack propagation, a load sequence is repeatedand crack grows after each sequence

Paris law is used to calculate high cycle fatigue count

In direct crack propagation, crack grows if a given crackgrowth criterion is fulfilled

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DemoFatigue crack propagation in a lug


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Demo (cont.)


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Demo (cont.)


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Thank You

SimA Fracture Mechanics

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