ON OPTIMIZATION APPROACHES OF HYBRID STRESS ELEMENTS

A rational energy constraint to be used as the optimization condition (OPC) for hybrid finite element is presented. Based on OPC, the optima l stress pattern of the element is established in a general formulatio n. In this approach, the improvement of the element performance is car ry out by a pretreatment of the initially assumed stress field. As an alternative way for the optimization of hybrid elements, the penalty-e quilibrating approach is also suggested in the paper in which the equi librium equation is enforced to the individual elements directly. Fina lly, a discussion on the stress distribution in an element is made. So me requirements on the rational sigma-distribution are suggested. All of the points mentioned have been verified by means of some innovative hybrid elements in 2-D, 3-D and axisymmetric problems.