Fracture, Compp,osites, and MAPDL Enhancements · PDF fileFracture, Compp,osites, and MAPDL...

Fracture, Composites, and p ,

MAPDL EnhancementsEnhancements

ANSYS v15.0 Update pSeminar

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Failure Modeling

Modeling of various failure modes can be accomplished in ANSYS Modeling of various failure modes can be accomplished in ANSYS. Static analysis and failure indices are a snapshot in time of a static

material state.Failure criteria describes what the material state is compared to allowables— Failure criteria describes what the material state is compared to allowables.

Composite delamination, crack growth, progressive failure, and delamination fatigue can be modeled in ANSYS.

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Delamination Failure Modeling

Two techniques exist in ANSYS to simulate the behavior of crack that will Two techniques exist in ANSYS to simulate the behavior of crack that will propagate along a known path:

— Virtual crack closure technique (VCCT).Cohesive zone model (CZM)— Cohesive zone model (CZM).

These techniques are commonly used for the modeling of delamination in composite structures since the crack is assumed to propagate at thecomposite structures, since the crack is assumed to propagate at the interface between layers

B th t h i i l l t (i t f t t) l Both techniques use special elements (interface or contact) along a pre-defined interface to model the delamination of cracks.

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Delamination Using CZM

Delamination can be analyzed using the cohesive zone method Delamination can be analyzed using the cohesive zone method. A critical fracture energy is introduced that is the energy required to break

apart the two interface surfaces.The interface s rfaces of the materials can be represented b a special set The interface surfaces of the materials can be represented by a special set of interface elements or contact elements.

A CZM material model is used to characterize the constitutive behavior of the interfacethe interface.

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Delamination Using VCCT

Virtual Crack Closure Technique (VCCT) Virtual Crack Closure Technique (VCCT)— Initially developed to calculate the energy-release rate of a cracked body.— Widely used in the interfacial crack growth simulation of laminate composites.

Crack growth is always along a predefined path which is defined by interface— Crack growth is always along a predefined path which is defined by interface elements in ANSYS.

— A crack growth simulation process involves the following steps• Create finite element model with a predefined crack pathCreate finite element model with a predefined crack path• Perform the energy-release rate calculation• Perform the crack growth calculation

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Modeling Delamination Failure

In v15 0 Delamination can now be included in Workbench under “Fracture” In v15.0 Delamination can now be included in Workbench under Fracture in the tree.

Both methods for modeling delamination are now available in WB— Both methods for modeling delamination are now available in WB• Contact Elements• Interface Elements

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Contact Debonding

To define contact debonding the user must specify the contact region that To define contact debonding the user must specify the contact region that will be allowed to “Debond” and the material properties that define the debonding.

— The contact region must be defined as Bonded contact using the Penalty— The contact region must be defined as Bonded contact using the Penalty Method.

— The only debonding method available for contact debonding is CZM.The only debonding method available for contact debonding is CZM.— CZM Properties are defined in Engineering Data

Contact element cohesive zone properties

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Interface Element Delamination

Interface elements require a matching node pattern on each side of the Interface elements require a matching node pattern on each side of the interface.

— This can be identified by defining a “Match Control” mesh item and then selecting that mesh item in the Interface Delamination definition.selecting that mesh item in the Interface Delamination definition.

— Mesh matching can also be defined by choosing “Node Matching” andMesh matching can also be defined by choosing Node Matching and specifying a source and target face

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Interface Delamination

Interface element delamination allows for either CZM or VCCT to be used Interface element delamination allows for either CZM or VCCT to be used to determine when delamination will occur.

Like contact debonding, interface element CZM delamination requires a CZM material property to define the delamination criteria

Interface element cohesive zone properties

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Interface Delamination

VCCT method does not require material properties it requires a critical VCCT method does not require material properties, it requires a critical energy release rate:

And the identification of an initial crack by adding a “Pre-meshed Crack” to the model:

A Pre-meshed crack is defined by a Named Selection of nodes and a crack coordinate system.c ac coo d ate syste

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Viscous Regularization

Interface elements (INTERnnn) now allow viscous regularization to be Interface elements (INTERnnn) now allow viscous regularization to be used for stabilizing interface delamination.

— TB,CZM,,,,VREG

VREG = 1E-5, Cum Iter = 935VREG = 1E-2, Cum Iter = 412

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Without VREG problem will not converge

Delamination Methods Comparison

Interface Elements Contact Elements Interface Elements— Better convergence behavior— Can use VCCT

Bi linear or Exponential CZM

Contact Elements— Easier to set up— Arbitrary mesh (node to node

matching not required)— Bi-linear or Exponential CZM material model

— Can use viscous regularization

matching not required)— Standard contact behavior after

separation— Post processing is easierp g

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ANSYS Composite P /P tPrep/Post

ANSYS v15.0 Update SeminarSeminar


Composites in ANSYS

ANSYS Composite Prep/Post is an add on module to ANSYS Composite Prep/Post is an add-on module to existing structural solver licenses dedicated to the modeling of layered composite structuresmodeling of layered composite structures.

Enhancements in v15.0 include:— Easy Submodeling for compositesEasy Submodeling for composites— Enhanced interlaminar shear stress computation for solid

composites— Easy modeling of interface delaminations (VCCT, CZM,

Debonding) in ACP and Mechanical• To be demoed• To be demoed

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Composites in ANSYS

Enhancements in v15 0 include: Enhancements in v15.0 include:— Solid model extrusion enhancements

• Composite solid model workflows in Workbench now support theComposite solid model workflows in Workbench now support the use of SOLSH190 elements

• New extrusion methods• Adjustable warping limit to control removal of bad elements• Adjustable warping limit to control removal of bad elements• Reorganized solid model GUI

— Geometry export of ply and laminate surfaces in STEP and IGES format

— Sharing ACP composite definitions• within a Workbench Project using new shared mode of ACP• within a Workbench Project using new shared mode of ACP• across projects using new import/export functionality in ACP

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ACP - Ply Boundary Export

ACP V15 0 now allows for the export of ply boundaries as surfaces or lines ACP V15.0 now allows for the export of ply boundaries as surfaces or lines in STP or IGES format.

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Interlaminar Shear Calculation – V15

Example model of a plate in shear 16 layers Example model of a plate in shear. 16 layers

Previous ILS calculations (Values extracted from ANSYS results)

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Shell Model ILS Solid Model 1 layer per element ILS

Solid Model 4 layers per element ILS

ACP V15 has the option to recompute ILS inside of ACP

Interlaminar Shear Calculation – V15

ACP V15 has the option to recompute ILS inside of ACP . This results in very accurate ILS calculations even for solids with multiple

layers per element.Uses forces from ANSYS and stack information from ACP— Uses forces from ANSYS and stack information from ACP.

Solid Model 1 layer per element ILS

Solid Model 4 layers per element ILS

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element ILS element ILS

Interface Delamination in ACP

In v15 0 ACP has added the capability to automatically insert an interface In v15.0 ACP has added the capability to automatically insert an interface layer between any composite layers defined.

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You may also define part of that region as an “Open Area” Essentially You may also define part of that region as an Open Area . Essentially modeling an initial crack in the model.

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When the model is brought into Mechanical the interface region and initial When the model is brought into Mechanical the interface region and initial crack are automatically defined.

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ACP Demo



MAPDL E h tEnhancements



Additional Failure Modeling

ANSYS allows for progressive damage modeling ANSYS allows for progressive damage modeling— The user needs to define the failure criteria used for the compressive fiber

and matrix failure as well as for tensile fiber and matrix failure.— Maximum Stress Maximum Strain Puck Hashin LaRC03 and LaRC 04 areMaximum Stress, Maximum Strain, Puck, Hashin, LaRC03 and LaRC 04 are

available. Technique requires definition of three material models:

— Damage initiation criteria: TB DMGIDamage initiation criteria: TB,DMGI— Damage evolution law: TB,DMGE— Material strength limits: TB,FCLI

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Progressive Damage

In ANSYS the term “progressive damage” refers to spatial progression In ANSYS the term progressive damage refers to spatial progression.— Prior to v15.0 the only available damage evolution law is Material Property

Degradation Method, which is an “instant stiffness reduction”.— Thus once the stress reaches the damage limit the material stiffness isThus, once the stress reaches the damage limit, the material stiffness is

immediately reduced to a user-specified value.— In this case, damage can progress through the model into other elements in

the mesh as the load is increased, but the damage within a particular element is modeled as a step function: either undamaged or damaged.

In ANSYS 15.0, an additional damage evolution law has been added, called the Continuum Damage Mechanics Method.

— In this model, damage variables increase gradually based on energy amounts dissipated and viscous damping coefficients.

— Damage can therefore progress within an element as well as throughout the mesh.

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Post-Processing Damage

Result quantities are used to plot the extent of damage: Result quantities are used to plot the extent of damage:— PLESOL,PDMG,STAT

• Damage status (0 = undamaged, 1 = damaged, 2 = completely damaged)PLESOL PDMG <damage variable>:— PLESOL,PDMG,<damage variable>:

• FT = Fiber tensile damage variable• FC = Fiber compressive damage variable• MT = Matrix tensile damage variableg• MC = Matrix compressive damage variable• S = Shear damage variable• SED = Energy dissipated per unit volume• SEDV = Energy per unit volume due to viscous damping

Note that for the MPDG instant stiffness evolution, damage status is only 0 or 1 and the SED and SEDV damage variables are not definedor 1, and the SED and SEDV damage variables are not defined.

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Damage Test Case

Plate with hole under tension load Plate with hole under tension load.— 2D plane stress formulation.— Orthotropic material properties.

Define energy value = 0 02 and viscous damping = 0 4 for all directions— Define energy value = 0.02 and viscous damping = 0.4 for all directions.— Far-field stress = 4,000 psi.— Damage initiation stress = 10,000 psi in fiber direction (x), 8,000 psi in matrix

direction (y)direction (y).

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Damage Test Case : MPDG Method

Fiber tension damage variable at full loading for test case: Fiber tension damage variable at full loading for test case:— Reduction value was specified as 0.5, so any fiber tensile damage will have a

value of either 0.0 or 0.5.

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Damage Test Case : V15.0 CDM Method

Fiber tension damage variable at full loading for test case: Fiber tension damage variable at full loading for test case:— Values can range between 0 and 1 as damage is accumulated.— Maximum fiber damage is 0.83 at full loading.

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Damage Test Case : CDM Method

Stress-strain behavior in fiber (x) direction comparing no damage and Stress-strain behavior in fiber (x) direction, comparing no damage and damage and MPDG cases with the CDM case, at critical location at edge of hole:

— Note the MPDG case changes stiffness from initial to reduced in one step— Note the MPDG case changes stiffness from initial to reduced in one step. — The CDM case changes stiffness gradually due to progressive damage.

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Fracture Tools

As we have seen there are several tools are available for evaluating As we have seen there are several tools are available for evaluating fracture mechanics parameters:

— The J-Integral calculation is based on the domain integral approach and is performed during the solution phase of the analysis (CINT).performed during the solution phase of the analysis (CINT).

— Direct energy-release rate calculation, based on the virtual crack closure technique (VCCT), is performed at solution (CINT).

— Stress-intensity factors calculation with the interaction integral approach y g ppduring solution (CINT)

— Stress-intensity factors calculation with extrapolation during postprocessing(KCALC).

— In version 15.0 two additional methods were added— T-stress calculation using the interaction integral approach during solution

(CINT)(CINT).— Material force calculation is performed during the solution (CINT).

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T-Stress

T-Stress Calculation for Fracture Analysis T-Stress Calculation for Fracture Analysis— T-Stress is the stress acting parallel to the crack faces. — The calculation is the solution of a line load of magnitude f applied along the

crack front in the direction of the crack planecrack front in the direction of the crack plane

— T-stress evaluation supports the following material behavior:• Linear isotropic elasticityp y• Isotropic plasticity

— Uses the CINT command:• CINT,TYPE,TSTRESS

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Material Force

The material force also known as the configurational force is the force The material force, also known as the configurational force, is the force exerted by a surrounding body on an inclusion or defect in the body.

— Used to analyze material defects such as dislocations, voids, interfaces and cracks.

— Based on the idea that when an inclusion is incorporated into a stress-free elastic bod the entire bod ndergoes a deformationelastic body, the entire body undergoes a deformation.

— The change in total energy due to the deformation is characterized by the material force, represented by an energy-momentum tensor.

Material force evaluation supports the following material behavior: Material force evaluation supports the following material behavior:— Linear isotropic elasticity— Nonlinear isotropic elasticity

Isotropic hardening plasticity

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— Isotropic hardening plasticity— Kinematic hardening plasticity

Modeling Wear

ANSYS has introduce the capability to model wear using contact ANSYS has introduce the capability to model wear using contact elements.

A new material property TB,WEAR is assigned to the contact elements.The onl b ilt in ear model a ailable is Archard Wear The only built-in wear model available is Archard Wear.

— The Archard wear model relates the rate of wear, to contact pressure, sliding velocity, and material hardness.

• Since the wear is a function of velocity a quasi-static or transient structural analysis• Since the wear is a function of velocity a quasi-static or transient structural analysis is required (i.e time is important).

— The wear is in the direction opposite to the contact normal. — Inputs: Wear coefficient, Material Hardness, Pressure Exponent, Velocity p , , p , y

Exponent— In an elastic-plastic analysis the hardness can be automatically derived from

the current yield stress. H=yield stress/3

The user can also define their own wear model: USERWEAR.

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Modeling Wear

In a wear analysis the contact nodes are moved to represent the wear In a wear analysis the contact nodes are moved to represent the wear increment each step, to simulate the actual removal of material.

As the contact nodes are moved, the contact penetration (and therefore the pressure) decreasesthe pressure) decreases.

Mesh before wear Mesh at end of wear analysis

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Modeling Wear

Animation of stress during wear analysis Animation of stress during wear analysis

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Other APDL Contact Enhancements

Bolt thread modeling Bolt thread modeling— Discussed in Workbench Mechanical

User programmable subroutines for defining contact properties and User programmable subroutines for defining contact properties and contact interaction.

— USERCNPROPUSERCNINTER— USERCNINTER

CNTR command allows you to redirect contact pair output information to a t filseparate file.

— Avoids having to search through output file — Jobname.cnm

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Other APDL Contact Enhancements

Tabular Real Constants Using X Y Z Primary Variables Tabular Real Constants Using X,Y,Z Primary Variables— In the previous release, these variables represented the current location of

contact detection, causing the associated real constants to be updated as the model deformed.

— Now, primary variables X, Y, and Z represent the location of contact detection at the beginning of the solution (the undeformed configuration).

Normal Contact Stiffness— In prior releases, the internal contact stiffness in the normal direction did not

vary with the user-defined penetration tolerance (contact element real constant FTOLN).

— In this release, the internal stiffness is inversely proportional to the user-defined penetration tolerance; that is, the tighter the tolerance, the higher the normal contact stiffnessnormal contact stiffness.

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Other APDL Enhancements

The new Lkey = FIXED option on the FDELE command applies the The new Lkey = FIXED option on the FDELE command applies the current relative displacement value to the specified degree of freedom in addition to deleting the force.

— Usually used for pretension elements— Usually used for pretension elements.

Strain Energy Density Output Strain Energy Density Output— The strain energy density can now be output via the following

commands: ESOL, ETABLE,PLESOL, PRNSOL, PRESOL, PRNSOL.

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Rezoning

There is a new “mesh splitting” rezoning option the user can choose a There is a new mesh splitting rezoning option the user can choose a region to rezone by splitting the existing mesh.

— Works with 2D Quads and Tri elements.

— Also works with 3D but only on LINEAR tetrahedrons (SOLID285)

— Results in large increase in number of elements.• 4X for 2D elements• 8X for 3D elements

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8X for 3D elements

Rezoning

There are a couple of options for transitioning to the non-split regions There are a couple of options for transitioning to the non-split regions

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Automatic Rezoning

ANSYS has introduced the capability for automatic mesh rezoning via ANSYS has introduced the capability for automatic mesh rezoning via Mesh Nonlinear Adaptivity

— Unlike regular rezoning, nonlinear adaptivity is completely automatic, requiring no user input during solution.no user input during solution.

— Mesh adaptivity through refinement can improve solution accuracy in general. — It can help to capture local deformations in more detail, useful in applications

such as:• rubber sealing for small cavities• local necking• local buckling.

— The program offers contact-based, energy-based, and position-based criteria to determine whether the mesh needs to be modified and, if so, what parts of the mesh should be modified.

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Automatic Rezoning

The NLADAPTIVE command allows you to control the regions that will be The NLADAPTIVE command allows you to control the regions that will be refined, the criteria for refining and the frequency of refinement.

— Criteria can be:Contact based: Defines number of elements that should be in contact with— Contact based: Defines number of elements that should be in contact with target. Used to allow a contact region to follow the geometry of targets more accurately.

— Energy based: Compare the strain energy of an element to the average strain gy p gy genergy of all elements in component to be refined.

— Position based: Define a bounding box, elements that enter this box during the solution will be refined.

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Automatic Rezoning

Rubber seal compression Rubber seal compression. — No mesh adaptivity

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Automatic Rezoning

Using automatic adaptive rezoning Using automatic adaptive rezoning

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Linear Dynamics

Mode-Superposition Harmonic Analysis for Cyclic Structures Mode-Superposition Harmonic Analysis for Cyclic Structures— Harmonic analyses of cyclic structures can now be performed using the mode-

superposition method, including support for prestressed structures using linear perturbation. p

• Use CYCOPT,MSUP,ON— Loading occurs via engine order excitation: CYCFREQ,EO

• Apply the require load then specify the order of the excitation• Typically, the engine order is simply a count of the number of stators, combustion

nozzles, etc., that cause the disturbance.— Mapping of complex pressures from a CFD analysis is supported.

O l th b t l ti i t d th MODE d RST fil th— Only the base sector solution is stored on the MODE and RST files, so they are significantly smaller than the non-mode-superposition modal files.

Use the CYCFILES command to Post Process the harmonic results— Use the CYCFILES command to Post Process the harmonic results

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Linear Dynamics

Large Deflection Prestressed Cyclic Symmetry Mode Superpostion Large Deflection Prestressed Cyclic Symmetry Mode SuperpostionExample:

— Impeller: 1/13 sector modeled6000 RPM applied in static analysis— 6000 RPM applied in static analysis

— 1000 Psi pressure applied on base and duplicate sector— Engine order of 3 specified (CYCFREQ,EO,3)

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Linear Dynamics

Large Deflection Prestressed Cyclic Symmetry Mode Superpostion Large Deflection Prestressed Cyclic Symmetry Mode SuperpostionExample:

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Linear Dynamics

There is a “new” subspace modal eigensolver There is a new subspace modal eigensolver— MODOPT,SUBSP

This solver performs well when the goal is to obtain a moderate number of— This solver performs well when the goal is to obtain a moderate number of eigenvalues on large modes run in distributed parallel.

ANSYSR15Modal Analysis Run

8 0

9.0

ANSYS R15 Modal Analysis Run Comparison, Model Size = 9.5M DOF

6.0

7.0

8.0

ed Tim

e [hr]

3 0

4.0

5.0Elaps

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3.0PCG 8 Cores PCG 12 Cores Subspace 8 Cores Subspace 12 Cores

Solver Enhancements

Sparse Solver Enhancements Sparse Solver Enhancements— The sparse solver has been improved to perform better detection and handling

of singular (or nearly singular) matrices.

— Typically, such matrices indicate modeling issues such as rigid body motion or the introduction of hourglass.

— The new logic may result in some poorly constructed models no longer solving, when they may have solved in prior releases.

— In a nonlinear analysis using the Newton-Raphson method, the error detection for a singular matrix is performed at the first iteration of the first load step.

— See Singular Matrices in the Basic Analysis Guide for a list of conditions that may trigger this message and suggestions on how to isolate the portion of the model that may not be properly constrained.

It i ibl t b th d t ti l i f i l t i

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— It is possible to bypass the error detection logic for singular matrices (PIVCHECK,OFF).

Solver Enhancements

Distributed Solver Enhancements Distributed Solver Enhancements— The domain decomposition algorithm has been improved. Better performance

and scaling (particularly at higher core counts) may be noticed, especially for problems with a large number of contact pair definitions.p g p

— Support is now available for thermal transient analyses which use the quasi matrix reform method (THOPT,QUASI).

— The algorithm for handling multipoint constraint equations and coupling equations (including related usages by contact and MPC184 elements) has b i d i ll id if l d f f d dbeen improved to automatically identify slave degrees-of-freedom and remove redundancy in global solution matrices.

For performance reasons the program no longer allows Distributed ANSYS to— For performance reasons, the program no longer allows Distributed ANSYS to be launched with more processors (per simulation) than the number of physical CPU cores that exist in the system.

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