Progressive Damage of Fiber-Reinforced of Fiber-Reinforced

Compositesin in

ANSYS V15.0

© 2014 CAE Associates

Progressive Damage

Damage initiation and propagation in fiber-reinforced composites first Damage initiation and propagation in fiber-reinforced composites, first introduced in version 14.0, has been extended in version 15.0.

Technique requires definition of linear elastic orthotropic material Technique requires definition of linear elastic orthotropic material properties, and three material models:

— Damage initiation criteria: TB,DMGIDamage evolution law: TB DMGE— Damage evolution law: TB,DMGE

— Material strength limits: TB,FCLI

In MAPDL input and post processing must be performed via commands In MAPDL, input and post-processing must be performed via commands, no GUI input.

In Workbench, material input and post-processing is available, although the newest damage evolution law added in version 15.0 is not yet available.

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Progressive Damage

In ANSYS 14 0 the term “progressive damage” refers to spatial In ANSYS 14.0, the term progressive damage refers to spatial progression.

— The only available damage evolution law is Material Property Degradation Method (MPDG), which is an “instant stiffness reduction”.Method (MPDG), which is an instant stiffness reduction .

— Thus, 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 g p g gthe 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 (CDM) Method.

— In this model, damage variables increase gradually based on energy amounts di i t ddissipated.

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

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Damage Initiation

Damage initiation defines the criterion type for determining the onset of Damage initiation defines the criterion type for determining the onset of material damage (TB,DMGI).

— Can select a separate criterion for tensile and compressive failure, and for both fiber and matrix.fiber and matrix.

— Criteria include:• Maximum strain• Maximum stress• Puck• Hashin• LaRc03

L R 04• LaRc04• User can also define up to 9 user-defined criteria.

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Damage Evolution

Damage evolution defines how the material degrades following the Damage evolution defines how the material degrades following the initiation of damage (TB,DMGE).

— Setting TBOPT = 1 sets the evolution law to the Material property degradation method (MPDG), which models instant stiffness reduction.method (MPDG), which models instant stiffness reduction.

— The input to this law are the instant reduction factors for tensile and compressive stiffness, in both tension and compression.

— The values can range between 0 (no damage) and 1 (complete damage).g ( g ) ( p g )

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Damage Evolution

Damage evolution defines how the material degrades following the Damage evolution defines how the material degrades following the initiation of damage (TB,DMGE).

— Setting TBOPT = 2 sets the evolution law to the continuum damage mechanics method (CDM), which models gradually increasing damage.method (CDM), which models gradually increasing damage.

— The input to this law is the energy dissipated per unit area and the viscous damping coefficient for each damage mode (8 constants total).

— The damping coefficients are used to help overcome convergence difficulties p g p gthat can occur for softening material.

— The Hashin failure criterion must be selected in the TB,DGMI command.

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Damage Evolution

Energies dissipated per unit area G : Energies dissipated per unit area Gc:— Gc represents fracture toughness.— Standard tests are used to obtain these values.

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Damage Evolution

Viscous damping coefficients µ are specified as: Viscous damping coefficients µ are specified as:

— The lower the damping coefficient, the more severe the damage accumulation.— Damping is used to slow the accumulation of damage and overcome p g g

convergence difficulties from material softening.

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Material Strength Limits

This input is used to define the maximum stresses or strains that a This input is used to define the maximum stresses or strains that a material can sustain before damage occurs (TB,FCLI).

— The values to be input are based on the damage initiation criterion selected.

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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 1or 1.

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Damage Test Case: MPDG Method

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

Use maximum stress damage criterion in all directions— Use maximum stress damage criterion in all directions.— Assume stiffness at damage is instantly reduced by 50% for all directions.— Far-field stress = 4,000 psi.

Damage initiation stress = 10 000 psi in fiber direction (x) 8 000 psi in matrix— Damage initiation stress = 10,000 psi in fiber direction (x), 8,000 psi in matrix direction (y).

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Damage Test Case : MPDG Method

Comparison of x-displacement for undamaged and damaged models at full Comparison of x-displacement for undamaged and damaged models at full load (same contour range):

Max deflection = 0.00174 Max deflection = 0.00187

Undamaged Damaged

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Undamaged Damaged

Damage Test Case : MPDG Method

Comparison of x-stress for undamaged and damaged models at full load Comparison of x-stress for undamaged and damaged models at full load (same contour range):

Max stress = 31.1 ksi Max stress = 24.5 ksi

Undamaged Damaged

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Undamaged Damaged

Damage Test Case : MPDG Method

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

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Damage Test Case : MPDG Method

Damage status at full loading for test case: Damage status at full loading for test case:— Damage status can only be either 0 or 1 for the MPDG method.— Intermediate values are due to the averaging of integration points within a

given elementgiven element.

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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: CDM Method

Progressive damage of notched sample Progressive damage of notched sample.— Shell181 elements used to model 24-layer [90/0/45] composite specimen.— Requires Hashin damage criterion in all directions.

Thermal and mechanical loading via applied displacements are applied— Thermal and mechanical loading via applied displacements are applied.— Fracture toughness values:

• GFT = 81.5 N/mm• GFC = 106 3 N/mmGFC 106.3 N/mm• GMT = 0.2774 N/mm• GMC = 1. N/mm

— Viscosity value = 0.005y

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Damage Test Case : CDM Method

Fiber tension damage variable at end of analysis in 1st layer showing Fiber tension damage variable at end of analysis in 1st layer showing failure.

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Damage Test Case : CDM Method

Fiber compression damage variable in 1st layer Fiber compression damage variable in 1st layer.

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Damage Test Case : CDM Method

Plot of the total reaction force versus the applied displacement applied to Plot of the total reaction force versus the applied displacement applied to the specimen.

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Damage in Workbench

The damage material properties are available in Engineering Data The damage material properties are available in Engineering Data.— The DMGE CDM input is not available.

MPMP

FCLI

DMGIDMGI

DMGE (MPDG)

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DMGE (MPDG)

Damage in Workbench

In Mechanical if a damage model is included the Damage result In Mechanical, if a damage model is included, the Damage result quantities will be available.

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Damage in Workbench

Can plot the Damage Status (below) or other damage results as usual Can plot the Damage Status (below), or other damage results as usual.

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Material Damage Properties

Material damage property assessment for the MPDG approach is based Material damage property assessment for the MPDG approach is based on a step reduction in stiffness:

— Define limits where damage occurs.Define factor by which the stiffness will be reduced when the limits are— Define factor by which the stiffness will be reduced when the limits are reached.

— Select composite failure approach (max stress, max strain, etc.).

Material damage property assessment for the CDM approach is a toughness-based failure criterion:

— Define limits where damage initiates— Define limits where damage initiates.— Supply energy dissipation and viscous damping values that define how the

damage will initiate and accumulate.— Uses Hashin failure criterion.

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