SECTION 3 Progressive Ply Failure and Delamination...

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Composites Technology Day, January 2012

Copyright 2012 MSC.Software Corporation

Composites Technology Day, February 2012


SECTION 3

Progressive Ply Failure and

Delamination Modeling

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Composites Technology Day, January 2012


Composites Failure Modeling

• Look at types of problems you can solve today with

MSC’s composite failure technology

• Examples demonstrating how to apply this technology

and how it works

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Composite Fuselage Example

• Composite aircraft fuselage – Light weight composite components

– Constructed from layered composite

material

– Bonded and/or fastened together

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A Closer Look

Skin

Stringers Frame

Shear

clips

Simulate delamination?

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Composites Damage and Manufacturing

Defect Examples

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Composites Failure Examples

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First-Ply-Failure Analysis

• First-Ply Failure (FPF) – Linear analysis based on failure theory

– Compute failure index or strength ratio

for the ply material

– Optimization of ply angle/thickness

Critical Margin of Safety

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Going Beyond FPF

• Evaluate the load redistribution in a composite

structure as the plies fail progressively

• Simulate delamination growth from initial flaw

• Study crack propagation to design for fail-safe

structures

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VCCT CZM

Delamination Breaking Glue

PFA

Going Beyond FPF

Ply Material

Failure Delamination

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Layered Composite

definition

FAQ: What Element types are supported?

• Composite failure modeling is supported in both shell

and solid elements

Shell

element

Solid

element

Solid Shell

element

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VCCT CZM

Delamination

Breaking Glue PFA

Composites Failure Modeling - PFA

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Progressive Failure Analysis (PFA) • Also known as Progressive Ply Failure (PPF)

• Select a failure criterion

• Select a degradation option

• The composite is failed on a layer by layer basis

• Upon failure, the elastic properties are scaled down

Pin bearing on hole

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Composite Failure Criteria

Composite Failure

• Most of the criteria are semi-empirical in

nature

Composite Failure on Layer Basis

• Maximum Stress

• Maximum Strain

• Hill

• Hoffman

• Tsai-Wu

• Hashin

• Puck

• Hashin-Tape

• Hashin-Fabric

• User defined (UFAIL)

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PFA Options

Progressive Composite Failure options

• Flagged through the MATF entry (ITYPE = 2 or 3)

• Up to three failure criteria can be selected

• Only the primary failure criterion is used for PFA

• The other two are only used to calculate failure indices

• The behavior up to the failure point is linear elastic

• Upon failure…

– When failure index is larger than one, degrade material moduli

– Selective degradation – if matrix fails, do not change fiber properties

– Stiffness drops gradually or immediately

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MSC Nastran Input Data Format

ITYPE: 0 – No PFA; 2 – Gradual Selective; 3 – Immediate Selective

Criterion: 1 – Max. Stress; 2 – Max. Strain; 3 – Hill; 4 – Hoffman; 5 –

Tsai-Wu; 7 – Hashin; 8 – Puck; 10 – Hashin-Tape;11 – Hashin-

Fabric; 13 – User Subroutine

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PFA Example – Fuselage Damage

Rigid elliptical cylinder hitting composite shell

5-layered composite

Puck criterion,

gradual option

Damage of outer ply

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Copyright 2012 MSC.Software Corporation 17

PFA Example – Wing Damage

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Micromechanical Failure model

• Traditional approach computes

composites failure based on

ply-level failure properties

• The Micromechanical approach

gets down to the fiber and

matrix level and looks at the

failure mechanism at the

constituent level

• MSC has partnered with

Firehole to bring the Helius

MCT micromechanical failure

technology to our users

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19

VCCT CZM

Delamination

Breaking Glue PFA

Composites Failure Modeling - VCCT

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VCCT

• In linear fracture mechanics, a crack starts to

grow when

– Total G > Gc

– G is the energy release rate

– Gc is the fracture toughness

• The VCCT is one of the methods used to

compute the energy release rate.

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VCCT (Virtual Crack Closure Technique)

• FEM approximation: Use consistent nodal force at

tip and crack opening at first crack segment

• Energy release rate:

G = Fu/2a

• Growth method

• Release glued contact

• Grow along element edge

• Remeshing

Marc Only

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VCCT

• Supported in both Marc and MSC Nastran

• Supported crack types are shown below

line crack – 2D or shell face crack – shell to shell face crack – 3D solid

line crack – shell edge to solid or shell face crack – shell to solid

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Modes of Crack Extension

• All three modes of crack extension are supported

Mode I:

Opening

Mode II:

Sliding

Mode III:

Tearing

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VCCT Example – Release glued contact

• Skin-Stringer Delamination – Wagner/Balzani, Computers & Structures 2008

– Stringer glued to skin

initial crack front

fixed stringer push skin downward

stringer

skin Initial

delamination

VCCT key ingredients:

- Initial crack

- Define crack front nodes

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Animation shows region

released from glued


Animation shows glued

region

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• Benchmark Problems

SLB

DCB

DCB

DCB

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F

F

• 4-Ply Composite

modeled with 2

layers of solid

elements

• Defect between

3rd and 4th ply

• Glue parts

together, except

at defect

Embedded circular defect

Buckling Delamination

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VCCT Example – Grow Along Element Edge

clamped Initial crack

Growth direction: maximum hoop stress criterion

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Quad mesh

Tria mesh

Remesh

VCCT Example – Grow Along Element Edge

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VCCT Example – Crack Bifurcation

glued

shell thickness with offsets

elastic orthotropic material

composite with four layers: [-45/90/0/45]

8 layers

4 layers

• New technology

– Crack tip automatically generated as the crack reaches

the stiffener

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• Growth through composite skin with stiffeners

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Courtesy of Dr. Kim Parnell

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VCCT CZM

Delamination

Breaking Glue PFA

Composites Failure Modeling - CZM

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Cohesive Zone Modeling (CZM)

• Cohesive Zone Modeling (CZM) is a technique

used to simulate delamination growth.

• The implementation of CZM is based on:

• Library of special interface elements

• Material model to characterize the interface behavior

Interface Element

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• The constitutive behavior of these elements is

expressed in terms of tractions versus relative

displacements between the top and bottom

edge/surface of the elements

• Top and bottom faces may coincide

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V is the effective opening displacement

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• Material models

• Bilinear

• Exponential

• Linear-exponential

• Material behavior

• Initially reversible

• Irreversible if v > vc

bottom face

1

2

3

4

5

6

7

8 top face

s

n

t

top and bottom face may coincide (zero thickness)

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CZM – Example

• Lap-Shear Joint:

• Reference: M.N. Cavalli, M.D. Thouless and Q.D. Yang, Cohesive-Zone

Modeling of the Deformation and Fracture of Weld-Bonded Joints;

Welding Journal Vol. 83, no. 4, 2004

Plates

Adhesive Region

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CZM – Example

• Finite element model:

– Mesh plates and adhesive layer independently using

higher order elements

– Utilize the contact option to glue the adhesive layer

to the plates

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CZM – Example

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VCCT

CZM

Delamination

Breaking Glue

PFA

Composites Failure Modeling –

Breaking Glue Contact

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Breaking Glued Contact

• Release glued contact when the

following stress criterion is met

• Use contact normal and

tangential stresses

• After break, do regular contact

with friction and separation

User specified

User specified

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Example - Breaking glued contact

• Coating

debonding

• Load with

rigid body

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Example - Breaking glued contact

• Coating

debonding

• Load with

rigid body

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PFA

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VCCT

CZM

Delamination

Breaking Glue

Composites Failure Modeling –

Delamination (Marc only)

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Delamination

• Split up mesh between materials or within a material when the following stress criterion is met

• Use stresses normal and tangential to interface

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Delamination Examples

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Delamination with CZM

• Option to insert interface element where mesh

is split

– Fully automatic

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Delamination Example: Plate impact

• Composite plate, 8 layers, [0/45/-45/90]s

• Stacked solid shell elements – One element per layer

– No double nodes

• Clamped edges, prescribed downward motion of circular region in the center

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• View quarter

model

• Outline plot

• Delamination

between layers

(mesh

splitting)

• Contact

occurs

between layers

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• Automatic

insertion of

interface

elements

• Self contact

not needed

• Show only

interface

elements

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Summary

• Progressive Failure Analysis (PFA)

• Virtual Crack Closure Technique (VCCT)

– Fracture mechanics

• Cohesive Zone Model (CZM)

– Interface elements

• Breaking glued contact

– Stress Criterion

• Delamination

– Stress Criterion

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End of Section 3

SECTION 3 Progressive Ply Failure and Delamination...

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