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Composites Technology Day, January 2012
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Composites Technology Day, February 2012
Copyright 2012 MSC.Software Corporation
SECTION 3
Progressive Ply Failure and
Delamination Modeling
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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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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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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
VCCT Example – Release glued contact
Animation shows glued
region
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VCCT Example – Release glued contact
• Benchmark Problems
SLB
DCB
DCB
DCB
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VCCT Example – Release glued contact
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 – Release glued contact
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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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VCCT Example – Crack Bifurcation
• Growth through composite skin with stiffeners
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VCCT Example – Crack Bifurcation
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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Cohesive Zone Modeling (CZM)
• 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
36
V is the effective opening displacement
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Cohesive Zone Modeling (CZM)
• 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
45
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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Delamination Example: Plate impact
• View quarter
model
• Outline plot
• Delamination
between layers
(mesh
splitting)
• Contact
occurs
between layers
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Delamination Example: Plate impact
• 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
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