Learning Forum

[HarsihilZLHZ]

If we want the Geometry/Part to behave within elastic limit, Why we consider Plasticity ?nAs soon as the equi Stress is greater than the yield Stress, then we can modify our Model to functional within Elastic limit.nIn one of ANSYS Course of Plasticity, they are comparing plastic strain from the experimental data to simulation, that I got it.nBut as we know that the Model has cross the yield Strength, then we can easily Modify Geometry/Part to behave within Elastic Limit. Hence my Question is , Why we need to Consider Strain hardening in the Simulation?.n

[peteroznewman]

nYou don't need to add plasticity to the material model if the goal of the analysis is to evaluate the stress during the operational life of the structure and the requirement is to stay below yield. Just use a material model with linear elastic material properties.nThere are useful results plots to use in this evaluation. Insert the Stress Tool and choose max equivalent stress to get a Safety Factor plot or a Safety Margin plot.nOne reason to add plasticity is when there is a requirement that the structure does not collapse if a load that is four times the design load is applied. You may find that the maximum stress in the model at 4x Load with a linear elastic material has gone above the Ultimate Tensile Strength (UTS). In that case, you can't claim that the structure will pass the 4x Load test. nAdd plasticity to the material and solve the 4x Load model. In a Bilinear Hardening model with Tangent Modulus set to 0, that is known as an Elastic Perfectly Plastic (EPP) material and stress will never be above yield, so comparing to the UTS is pointless. The Safety Factor (or Safety Margin) to compute is to divide the Elongation at Break by the Total Strain (subtract 1 for the Margin). Elongation at break is a material property.nYou will likely find a small volume of the mesh goes plastic, but the surrounding material will remain elastic and support the 4x Load. However, if the whole section goes plastic, that predicts that the structure will collapse and not support the 4x Load. These models are generally run using Displacement BC and a Probe on that of the Reaction Force shows when the model passes the 4x Load point. In the case when the structure fails the 4x Load case, the reaction force will never reach that value, it will go up, flatten then go down before reaching the 4x Load value.n