DEVELOPMENT OF DYNAMIC FRACTURE TOUGHNESS TESTING APPARATUS

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In this year, using the dynamic fracture toughness testing system developed so far, the dynamic toughness values of a nuclear pressure vessel steel A508 class 3 were evaluated in a broad temperature range from lower self to upper shelf, and compared with the static values obtained from the three point bending test in literature. It was shown that the dynamic toughness data seemed about 30 to 50% smaller than the static ones, and that the transition temperature shifted by 40 to 50 deg to the higher temperature range. In the upper shelf temperature range, the dynamic toughness data were also a little reduced compared with the static data. The toughness data obtained from the surface force loading test were well coincident with those from the body force ones although the number of surface force loading data was very small. It is expected from the result that the influences of the Joule heating at the vicinity of the crack tip on the fracture toughness data are almost negligible in practic … More e.Also, it seems that the high-strain-rate dependent plasticity as well as inertia forces must be taken into account simultaneously in order to describe accurately the dynamic ductile fracture phenomena. Then we depeloped the finite element analysis program based on an implicit visco-plastic formulation as well as a dynamic and nonlinear fracture mechanics, which was utilized to re-evaluate the dynamic toughness data. The results showed that the dynamic toughness data in upper shelf temperature range increased by about 5% in consideration of strain-rate effects for the fracture parameter calculation. However, the modified dynamic data were still smaller than the static data.The dynamic strain measurement system based on the computer picture processing technique was applied to experimentally evaluate fracture mechanics parameter such as the J-integral. In this method, basing on the deformation theory of plasticity, one calculates the stress distribution for the strain distribution measered by the picture processing technique. Then the J integral can calculated according to the usual path integration scheme. The obtained values of the J-integral had the good path independence and the coincidence with the J integral value from the COD method. The present method can be applied to calculate the J-integral of any shaped two-dimensional cracked specimen since it utilizes the strain-stress data very close a crack tip. Less