Extrapolation of stress/strain curve after the curve's last data points: for plasticity or nonlinearĮlastic material definition the last couple of data points are extrapolated linearly to calculate pairs of data points outside the defined stress/strain curve.For viscoelastic material model, the definition of stress versus strain is replaced by relaxation.Measure that is dependent upon the final length of the model, is used for large strain Logarithmic strain, which is a nonlinear strain Is no longer "small" (approximately larger than 5%). Engineering strain is a small strain measure which is invalid once the strain in your model.The engineering strain (or nominal strain) is where Δl is the final bar deformation. The engineering stress (or nominal stress), where A is the initial undeformed cross-sectional area. The true strain is, where l is the final length and L is the initial undeformed length of the bar. The true stress is, where a is the final deformed cross-sectional area. Alternative names for these quantities are Cauchy stress, logarithmic strain, and natural strain.
![engineering stress vs true stress graph engineering stress vs true stress graph](http://pubs.sciepub.com/ajcea/2/1/6/image/fig10.png)
The traditional engineering definitions for stress and strain are no longer accurate and new measures, namely true stress and true strain, are introduced. If the deformation of a bar in tension becomes significant, its cross-sectional area will change. The strain output depends on the material model and the choice of small or large strain formulation.įor non-linear elastic models: von Mises Plasticity, Tresca Plasticity,ĭrucker Prager, Super Elastic, and Viscoelastic the small strain option produces engineering strains the large strain option produces logarithmic strains. After the analysis completes, the stress output is the Cauchy stress, which is the true stress in the deformed geometry.