# Internal Force Calculation

However, to increase the computational speed of the process, some simplifications are applied.

## Reduced Integration Method

The force calculation is exact for the special case of the element being a parallelepiped.

## Full Integration Method

The final approach that can be used is the full generalized formulation found in Equation 1. A classical eight point integration scheme, with non-constant stress, but constant pressure is used to avoid locking problems. This is computationally expensive, having eight deviatoric stress tensors, but will produce accurate results with no hourglass.

When assumed strains are used with full integration (HA8 element), the reduced integration of pressure is no more necessary, as the assumed strain is then a free locking problem.

## ALE Improved Integration Method

This is an ALE method for computing internal forces (flag `INTEG`). A
constant stress in the element is used.

The value $\underset{\Omega}{\int}\frac{\partial {\Phi}_{I}}{\partial {x}_{j}}d\Omega$ is computed with Gauss points.