Conservation of Best-Fit Paradigm at an Element Level

The projection theorem describing finite element analysis shows that the strains/stresses computed by the displacement finite element procedure are a best approximation of the true strains/stresses at a global level. For simple linear elastostatics problems this best-fit paradigm holds at an element level, too. But it has been observed that in a certain class of problems where artificial stiffening takes place due to discretization, the finite element solution deviates from the best-fit solution. In this paper we have generalized the projection theorem at the element level and shown that even for such problems the finite element model continues to perform its computation in the best-fit manner to a modified system, so that now the FEM strain in every element is a best-fit not to the original strain but to a modified strain. The analytical expressions presented here have been substantiated by actual finite element results from the relevant computer codes.

Keywords:

• Best Fit
• Elastostatics
• Finite Element Method
• Projection Theorum
• Strains/Stresses