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[FAQ]

Nonlinear results cannot be linearly extrapolated because they are *nonlinear*. To linearly extrapolate a result, such as stress or strain, would mean that the quantity deviates from the constitutive model. For example, SEQV and EPPL,EQV, if linearly extrapolated when plasticity is active, would mean SEQV and EPTO,EQV would no longer lie on the stress-strain curve. A similar situation would exist for hyperelasticity or with other nonlinear constitutive models being active. Hence, linear extrapolation of nonlinear results is meaningless, and the best we can do is copy from integration points to node. (Of course, the reason why we have calculations of stresses, strains, etc. at the integration points is that although we solve DOF solution at nodes, element quantities are over the volume, so the integration points provide the best locations of evaluation of those quantities rather than at the nodes.) Note that ERESX does not apply to BEAM188/189 nor to the through-thickness results for SHELL elements (ERESX affects in-plane results only for SHELLs).