I am curious as to how finite element analysis software(like Hypermesh) go about superposition of loadcases(applied on the same model). I constrain my vehicle body for 1.loadcase (say bending) with the standard SPC's and constrain my 2.loadcase(say torsion) with Inertia relief constraints. Given that inertia relief constraints require the FEA software to do a completely different set of calculations as compared to the standard SPCs, how is it possible to even superimpose the 2 loadcases? FYI: Inertia relief analysis is regarded as an effective technique for the modeling of unconstrained structural systems, for example- aircraft in flight, car on a test track etc. Inertia or mass of the structure is used in Hypermesh to resist the applied loadings. The ‘Inertia relief method’ applies an acceleration to the mass of the model in a way to balance the force applied. In essence, ‘inertia relief’ creates a fictitious force on each grid point associated with a mass.