Internal Forces

The internal force vector is given by:(1)
f int = ∫ Ω e B t σ d Ω e
In elasticity it becomes:(2)
f int = ∫ Ω e B t C B v d Ω e
It can be written as:(3)
f int = f int 0 + f int h g r

with the constant part f int 0 being computed with one-point quadrature and the non constant part or hourglass part f int h g r being computed by perturbation stabilization (Ishell = 1, 2 ,3 ...) or by physical stabilization (Ishell = 22).