Mechanical supports a number of damage results using non-linear material models, including the Mullins Effect, Progressive Damage, and Physical Failure Criteria.
Mullins Effect
The Mullins effect is a phenomenon resulting from load-induced changes to constitutive response exhibited by some hyper elastic materials, especially filled polymers. The effect is most evident during cyclic loading, where the unloading response is more compliant than the loading behavior. During the process of cyclic loading, stress-strain curve for these materials is dependent on the maximum previous load, where the load is the strain energy of the virgin hyper elastic material. As the maximum previous load increases, changes to the virgin hyper elastic constitutive model also increase, due to the Mullins effect. Below the maximum previous load, the Mullins effect changes are not evolving: however, the Mullins effect still modifies the hyper elastic constitutive response based on the maximum previous load. If the load increases beyond the maximum previous all time value, the result is an irreversible and instantaneous softening of the material, which causes a hysteresis in the stress-strain response.
The Mullins effect is modeled with the modified Ogden-Roxburgh pseudo-elastic model (TB,CDM,,,,PSE2) and is applicable to any nearly or purely incompressible hyperelastic model (TB,HYPER). For more information on the Mullins effect, see Mullins Effect Model.
Mechanical supports two results for the Mullins Effect: Mullins Damage Variable and Mullins Max. Previous Strain Energy.
The Mullins Damage Variable is a unitless scale range from 0, at which the material is completely damaged without any stiffness, to 1, at which the material is intact, without any loss of stiffness.
At a given time step, the Mullins Max. Previous Strain Energy result is the maximum value of strain energy of the virgin material in the time interval [0, t0], where t0 is the beginning of a time step. Depending on the unit system you choose, this result chooses the appropriate unit of energy. A typical unit is the Joules (J) unit.
Progressive Damage
Progressive Damage is associated with the damage phenomenon that occurs in composite materials. When a composite material is subjected to loading, the matrix and fiber controlled types of failure can occur both separately or sequentially. After a certain point, the material experiences enough damage in the form of the local failures that the material can no longer sustain the load. These local failures govern the ultimate load that the material can withstand.
Progressive Damage uses material damage initiation (TB, DMGI) and evolution criteria (TB, DMGE) to analyze the progressive damage in composites. While Physical Failure Criteria analyzes the failure criteria, Progressive Damage analyzes the progression of the damage.
Damage Initiation Criteria defines the criteria type for determining the onset of material damage under loading. Depending upon the failure mode selected here, the respective failure criteria will be computed for "Physical Failure Criteria". The available failure modes for damage are:
Maximum Strain
Maximum Stress
Puck
Hashin
LaRc03
LaRc04
The Damage Evolution Law defines the material damage evolution law (or the way a material degrades) following the initiation of damage. The stiffness reduction takes a value of 0 to 1, where 0 is no damage and 1 is completely damaged.
For more information, see Damage-Evolution Law and Fiber-Reinforced Material Damage in the Mechanical APDL documentation.
The Progressive Damage model supports the following results:
| Result | Description |
|---|---|
| Damage Status |
The Damage Status result will be an enum type with values of 0, 1, or 2, where
|
| Fiber Tensile Damage Variable |
The Fiber Tensile Damage Variable result value will be in the range of 0 to the “Tensile Fiber Stiffness Reduction” value set in the Damage Evolution Law. That is, if you set the Tensile Fiber Stiffness Reduction to 0.6, the range of Fiber Tensile damage variable result will be in the range of 0 to 0.6. A value of 0 for this result means undamaged and a value of 1 means completely damaged. The result has no units. |
| Fiber Compressive Damage Variable |
The Fiber Compressive Damage Variable result value will be in the range of 0 to the “Compressive Fiber Stiffness Reduction” value set in the Damage Evolution Law. That is, if you set the Compressive Fiber Stiffness Reduction to 0.6, the range of Fiber Tensile damage variable result will be in the range of 0 to 0.6. A value of 0 for this result means undamaged and a value of 1 means completely damaged. The result has no units. |
| Matrix Tensile Damage Variable |
The Matrix Tensile Damage Variable result value will be in the range of 0 to the “Tensile Matrix Stiffness Reduction” value set in the Damage Evolution Law, that is, if you set the Tensile Matrix Stiffness Reduction to 0.6, the range of Fiber Tensile damage variable result will be in the range of 0 to 0.6. A value of 0 for this result means undamaged and a value of 1 means completely damaged. The result has no units. |
| Matrix Compressive Damage Variable |
The Matrix Compressive Damage Variable result value will be in the range of 0 to the “Compressive Fiber Stiffness Reduction” value set in the Damage Evolution Law, that is, if you set the Compressive Fiber Stiffness Reduction to 0.6, the range of Fiber Tensile damage variable result will be in the range of 0 to 0.6. A value of 0 for this result means undamaged and a value of 1 means completely damaged. The result has no units. |
| Shear Damage Variable | The Shear Damage Variable result value will be in the range of 0 to 1. This value is computed using the results of Fiber Tensile Damage Variable, Fiber Compressive Damage Variable, Matrix Tensile Damage Variable, and Matrix Compressive Damage Variable. The result has no units. |
| Energy Dissipated Per Volume |
The Energy Dissipated Per Volume result value will be a positive real number. This result uses a unit of "Energy/Volume" in the unit system you choose. |
Physical Failure Criteria
The respective failure criteria are computed for the failure modes chosen in the damage initiation criteria. While the damage variables give you an idea where the damage is located and its likely direction of propagation, the Physical Failure Criteria helps you determine how much more load the material can handle.
These failure criteria are computed based on the parameters given using the material damage initiation (TB, DMGI) and evolution criteria (TB, DMGE). For more information, see Progressive Damage, above, as well as Damage-Evolution Law, Fiber-Reinforced Material Damage, and Physical Failure Criteria in the Mechanical APDL documentation.
The Physical Failure Criteria model supports the following results:
| Result | Description |
|---|---|
| Max Failure Criteria | The Max Failure Criteria is computed based on the maximum of Fiber Tensile Failure Criterion, Fiber Compressive Failure Criterion, Matrix Tensile Failure Criterion, and Matrix Compressive Failure Criterion. |
| Fiber Tensile Failure Criterion | The Fiber Tensile Failure Criterion result value will be a positive integer. A value of 0 indicates no failure, while 1 is a complete failure. A value above 1 indicates the material has completely failed. The higher this number, the higher the load above the prescribed limits, although specifics are dependent on the stress limits you set and the amount of loading applied. |
| Fiber Compressive Failure Criterion | The Fiber Compressive Failure Criterion result value will be a positive integer. A value of 0 indicates no failure, while 1 is a complete failure. A value above 1 indicates the material has completely failed. The higher this number, the higher the load above the prescribed limits, although specifics are dependent on the stress limits you set and the amount of loading applied. |
| Matrix Tensile Failure Criterion | The Matrix Tensile Failure Criterion result value will be a positive integer. A value of 0 indicates no failure, while 1 is a complete failure. A value above 1 indicates the material has completely failed. The higher this number, the higher the load above the prescribed limits, although specifics are dependent on the stress limits you set and the amount of loading applied. |
| Matrix Compressive Failure Criterion | The Matrix Compressive Failure Criterion result value will be a positive integer. A value of 0 indicates no failure, while 1 is a complete failure. A value above 1 indicates the material has completely failed. The higher this number, the higher the load above the prescribed limits, although specifics are dependent on the stress limits you set and the amount of loading applied. |