29 May 2020 Stress Strain Curves in FEA
The deformation of a material is best described by its stress-strain curve (https://www.fea-solutions.co.uk/stress-strain-curves/). This curve covers elastic and plastic behaviour (https://www.fea-solutions.co.uk/elasticity-and-plasticity/).
In an FEA model, the stress-strain curve is represented in a simplified way, depending on what kind of material behaviour has to be simulated.
In most cases, a linear-elastic material will be assumed, with the actual stress-strain curve represented by just an infinitely long straight line.
When plasticity is included, different stress-strain curve representations can be used, depending on the analysis being run. These are elastic-perfectly plastic (EPP), bi-linear, tri-linear or multi-linear curves.
The elastic-perfectly plastic curve is the most conservative as it assumes the stress does not increase beyond Yield.
For a bi-linear curve, the stress can increase beyond Yield, but failure is assumed not to occur, with the straight line between yield and ultimate increasing infinitely. The slope of the line is called the tangent modulus.
The tri-linear curve is like the bi-linear curve up to the ultimate strength of the material, but then continues horizontally, hence stresses will not increase beyond the ultimate strength of the material.
Finally, the multi-linear curve is the most accurate representation of the actual curve but is rarely required.
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