NUMERICAL-ANALYSIS OF IPIRG CRACKED PIPE EXPERIMENTS SUBJECTED TO DYNAMIC AND CYCLIC LOADING

This report contains results of a finite element study aiming to ident ify the influence of loading history and geometry for cracked pipes su bjected to complex loading. The experiments have been performed within the International Piping Integrity Research Group (IPIRG) Program. Th e majority of the numerically analyzed experiments were conducted on s traight pipes with an outside diameter of 168 mm and containing a larg e circumferential through-wall crack. The considered pipes were loaded in four-point bending under displacement control and at a temperature of 288-degrees-C. The types of loading were combinations of either qu asi-static or dynamic and also monotonic or cyclic loading with differ ent loading ratios R. Some analyses were also performed on surface-cra cked pipes subjected to slow, monotonic loading. In the finite element study, 20-node solid elements were used for the through-wall cracked pipes and a combination of shell and non-linear line spring elements f or the surface-cracked pipes. Stable crack growth was simulated by gra dual node relaxation and crack closure is accounted for by using simpl e contact elements. The J-integral for a remote contour is calculated and used as a characterizing fracture parameter although the cyclic lo ading violates the theoretical basis for this procedure. The near-tip J can not be used for growing cracks because of the weak energy singul arity. The results of the numerical study confirm the trends from the experiments in that a high loading rate has a negative influence on th e fracture properties of the studied carbon steel and that large cycli c loading, especially at R = - 1, lowers the apparent JR-curve for bot h carbon and stainless steels. To some extent geometry effects appear to be present when comparing the results from pipes containing surface cracks and through-wall cracks with results from CT specimens. These effects are more pronounced for large amounts of stable crack growth t han at initiation.