Can I simulate tensile test using transient structural analysis in ansys? If I can do so how can I add failure criteria in transient structural analysis in ansys?

Yes, you can simulate a tensile test using Transient Structural Analysis in ANSYS, but there are some important nuances to consider. Typically, tensile tests are better suited for Static Structural analysis when the deformation is not time-dependent (i.e., when you're interested in the material's response under constant loading). However, if you are interested in the behavior of materials under time-dependent loading, large deformation, or dynamic loading, then Transient Structural Analysis could be appropriate.

Steps to Perform Tensile Test Simulation Using Transient Structural Analysis:

1. Model Geometry and Material Properties:
- Define your specimen geometry (e.g., a dogbone specimen for a tensile test).
- Apply material properties, including Young's Modulus, Poisson’s Ratio, and, most importantly, the material's plasticity behavior (for large deformation).

2. Apply Boundary Conditions:
- Apply the appropriate boundary conditions. Typically, a fixed boundary condition would be applied to one end (anchor point), and a displacement or force boundary condition would be applied at the other end, representing the tensile load.

3. Define Transient Loading:
- If your loading is dynamic (varying with time), apply the loading as a time-dependent force or displacement. For example, a step load or a ramping displacement could be applied over time to simulate the tensile test loading.

4. Setup Nonlinearities:
- For large deformations, enable large deflection in the solution settings.
- If the material undergoes plastic deformation, enable plasticity models such as von Mises or Johnson-Cook for the material model to capture inelastic behavior under tensile loading.

5. Transient Analysis Settings:
- In the Transient Structural setup, make sure to select Large Deformation in the solver settings under Nonlinear behavior.
- Choose an appropriate time step for the simulation, ensuring that the time increments are small enough to capture any important dynamic effects.

Adding Failure Criteria to Transient Structural Analysis:

To stop the simulation when failure occurs (e.g., material rupture or excessive plastic strain), you need to define failure criteria. ANSYS provides various ways to include failure mechanisms:

1. Plasticity Failure (Ductile Failure):
You can define a failure criterion using Plastic Strain or Equivalent Stress (Von Mises) criteria:

- Go to Solution > Insert > Solution Information.
- Define failure criteria based on plastic strain (e.g., when the strain reaches a critical value) or equivalent stress (e.g., when it exceeds the yield stress).
- You can define failure limits by using the "Failure Criterion" option under material properties. Common options include:
- Ductile damage (based on plastic strain): Once the plastic strain reaches a critical value, the material is considered to have failed.
- Shear failure: Some materials fail when the shear stress exceeds a certain limit, which can be modeled using the Johnson-Cook damage model.

2. Fracture or Rupture (Brittle Failure):
If the material undergoes brittle failure (such as a sudden fracture), you can use fracture mechanics techniques. In ANSYS, this can be done by:

- Defining crack propagation or fracture mechanics models, such as Cohesive Zone Models (CZM), to simulate material separation once a critical stress or strain limit is reached.
- Implement a fracture toughness parameter, which defines when crack propagation starts.

3. ANSYS Failure Criteria for Transient Structural:
To stop the simulation based on failure, you can use Failure Definition:

- In Solution Settings, use the option to specify failure by plastic strain or damage initiation (based on equivalent stress, strain, or a custom criterion).
- Set the failure threshold in the material properties (e.g., for plastic strain, set a value such as `0.1` or the material’s ductile fracture strain).
- Add monitoring of certain variables, such as maximum stress, plastic strain, or displacement, to detect the point of failure during the simulation.

ANSYS can stop the analysis at the failure point, and the results can show when the specimen reaches its failure point (for instance, the point where plastic strain exceeds a certain threshold).

Steps to Set Failure Criteria in ANSYS (General Process):

1. Define Material Damage Model:
- Go to Engineering Data and select the material. Enable a damage model (like Johnson-Cook or ductile damage).
- Define critical values for damage initiation (stress/strain values) and damage evolution (how damage increases over time).

2. Post-processing Failure Results:
- After the simulation, in the Results tab, examine the plastic strain or damage values.
- Use contour plots or time history plots to visualize when the material reaches the failure threshold.

3. Monitor Failure (Optional):
- You can monitor key variables during the simulation using solution monitors (e.g., for plastic strain or equivalent stress).
- Set the solver to stop if these monitored values exceed a predefined failure threshold.

Common Issues in Transient Structural Analysis with Large Deformations:
If you're experiencing issues with results not showing up when large deformations are involved, it is likely due to:
- Insufficient time steps: Make sure the time step is small enough to accurately capture large deformations.
- Numerical instability: Large deformations can cause convergence problems. Try adjusting the solver settings, enabling automatic time stepping, or using a nonlinear solver.
- Material models: Ensure that the material model supports large deformation and inelastic behavior (e.g., nonlinear plasticity, viscoplasticity).

Conclusion:
Yes, you can simulate tensile tests using Transient Structural Analysis in ANSYS, especially for time-dependent or dynamic loads. To add failure criteria, you can define failure based on plastic strain or stress and stop the simulation once those thresholds are met. Additionally, ensure you configure the analysis to handle large deformations and set appropriate time steps to avoid convergence issues.