## 1. Damage model VS Damage criterion

They are both part of predicting how a material will break or fail, but they serve different purposes:

Damage Model: This describes the overall process of how damage accumulates in a material over time. It’s like a recipe with steps describing how the material weakens from a perfect state to a complete break. There are different models for different materials and failure mechanisms, like metals failing from tiny holes growing over time or concrete cracking under pressure.

Damage Criterion (damage criteria): This is a specific condition within the damage model that needs to be met for damage to start. It’s like a trigger point in the recipe. For example, a damage criterion for a metal might be a certain amount of bending or stretching, and once that happens, the material starts to develop those tiny holes.

Here’s an analogy: Imagine a material like a piece of taffy. The damage model would be the whole process of the taffy getting pulled and stretched until it breaks. The damage criterion would be the specific point at which the taffy gets stretched thin enough to tear.

Damage criteria are specific conditions within a damage model that trigger the initiation of damage.

Think of them as thresholds within the damage roadmap. Once a criterion is met, the damage model starts to take effect.

## 2. What damage criteria are supported by the Abaqus/CAE?

Abaqus CAE provides a range of damage criteria and models that can be used to simulate the behavior of materials under different loading conditions. Here are all the damage criteria supported by Abaqus CAE:

*Maximum Principal Stress (MPS) criterion:*This criterion predicts failure when the maximum principal stress in the material exceeds a certain limit. The MPS criterion is commonly used for brittle materials and is based on the idea that failure occurs when the tensile stress exceeds the material’s strength.*Maximum Principal Strain (MPS) criterion:*This criterion predicts failure when the maximum principal strain in the material exceeds a certain limit. The MPS criterion is commonly used for ductile materials and is based on the idea that failure occurs when the material reaches a certain level of deformation.*Modified Mohr-Coulomb (MMC) criterion:*This criterion predicts failure when the maximum shear stress in the material exceeds a certain limit. The MMC criterion is commonly used for soils and rocks and is based on the idea that failure occurs when the shear stress exceeds a certain level.*Drucker-Prager (DP) criterion:*This criterion predicts failure when the deviatoric stress in the material exceeds a certain limit. The DP criterion is commonly used for metals and other ductile materials and is based on the idea that failure occurs when the material reaches a certain level of plastic deformation.*Continuum Damage Mechanics (CDM) model:*This model describes the behavior of materials as they undergo damage due to the growth and coalescence of microcracks. The CDM approach is based on the idea that damage accumulates as the material undergoes loading and can be used to predict the onset and evolution of damage in a material.*Johnson-Cook (JC) model:*This model is a damage model that combines a failure criterion with a plasticity model to simulate the behavior of materials subjected to high strain rates and temperatures. The JC model takes into account the material’s strain rate sensitivity, thermal softening, and strain hardening properties and can be useful for simulating the behavior of materials in extreme loading conditions.*Puck criterion:*This criterion predicts failure when the maximum hydrostatic stress in the material exceeds a certain limit. The Puck criterion is commonly used for brittle materials and is based on the idea that failure occurs when the material reaches a certain level of compression.*Tsai-Wu criterion:*This criterion is a failure criterion for composite materials that takes into account both stress and strain components. The criterion predicts failure when the combined stress and strain components exceed a certain limit, taking into account the material’s properties and orientation.*Hashin criterion:*This criterion is another failure criterion for composite materials that takes into account the properties and orientation of the fibers and matrix. The criterion predicts failure when the stresses and strains in the material exceed certain limits, taking into account the fiber and matrix properties.*Johnson-Cook Damage model:*This model is a damage model that combines the Johnson-Cook plasticity model with a damage criterion. The model predicts damage accumulation and failure in materials subjected to high strain rates and temperatures, taking into account the material’s properties and the loading conditions.

If you want to know more about the Abaqus damage criteria, you can visit the Abaqus documentation. Also, if you want to familiar with the Damage and fracture concepts and know the difference between them, read this article: Damage and Fracture Mechanics Analysis in Abaqus