Experimental investigations on the ‘shallow crack effect’, on the 10 MnMoNi 5 5 steel, and computational analysis in the upper shelf by means of the global and local approaches

摘要: Abstract Shallow cracks have been of great interest for some years now, since it has observed that standard fracture toughness parameters, determined on deep crack specimens, exhibit a geometrical dependence and most the structures containing (in particular pressure vessels) depth to width ratios a/W much lower than mechanics specimens tested in laboratory. This study performed at MPA Stuttgart collaboration with EDF, aimed first all investigating ‘shallow effect’ high ductile, strength, low strain-hardening shape welded 10 MnMoNi 5 steel over whole temperature range transition region toughness. Deep (CT25 TPB25 a/W=0.55) shallow (TPB25 a/W=0.066) were tested, providing KIC, Ji JIC results. At same time, computations performed, upper shelf with, one hand, usual elastic–plastic model (Von Mises model) other local approach Rousselier. Experiments did not any effect (no increase KIC) show slight (slight Ji, larger JIC). Computations confirmed ability ‘modified’ Rousselier describe macroscopical behaviour (F-CMOD curves) three types as well simulate their propagation (CMOD-Δa curves). The combination line contour integral method enables us develop draft an experimental determine J-integral material initial length (a/W remaining within 0.05 0.7), taking growth into account. method, based measurement energy under F-CMOD curve ηc factor indexed current ratio, provided agreement 10% time 5% between computational Consequently, also correctly predicted experimentally resistance curves, especially dependence. observation during triaxiality stress state millimeters ligament enabled understand this dependence, accelerating leading J–R curves. For tip being located close top surface, relaxation occurs surface loss ligament, delaying higher Finally, was found confirm values various specimens. Therefore, assuming can initiation, different stress–strain curves (different yield behaviours) performed: seems (Ji(shallow crack)/Ji(deep crack)) is controlled by independently stress, absence important effect.