A STRATEGY FOR THE SOLUTION OF PROBLEMS INVOLVING LARGE DEFLECTIONS, PLASTICITY AND CREEP

SUMMARY A strategy for solving problems involving simultaneously occurring large deflections, elastic-plastic material behaviour, and primary creep is described. The incremental procedure involves a double iteration loop at each load level or time. In the inner loop the material properties are held constant and the non-linear equilibrium equations are solved by the Newton-Raphson method. These equations are formulated in terms of the tangent stiffness. In the outer loop the plastic and creep strains are determined and the tangent stiffness properties are updated with use of a subincremental algorithm. The magnitude of each time subincrement is determined such that the change in effective stress is less than a preset percentage of the effective stress. The strategy is implemented in a computer pogram, BOSOR 5, for the analysis of shells of revolution. Examples are given of elastic-plastic deformations of a centrally loaded flat plate and elastic-plastic-creep deformations of a beam in bending. The major benefits of the subincremental technique are the increased reliability with which problems involving non-linear plastic and timedependent material behaviour can be solved and the greatly relaxed requirement on the number of load or time increments needed for satisfactory results.