PLE can perform both material linear and material non-linear calculations. With linear calculations, the relation between strain and stress always remains linear. In case of non-linear (or elasto-plastic) calculations the relation between stress and strain is more complex, but basically the stress is limited to an upper value, even if the strain is increasing further. Plastic deformation occurs, which the program will calculate as long as material yielding is limited to localised areas. Otherwise, the program will warn about imminent collapse of the pipeline.