Dynamic behavior of delayed fracture of low alloy steel thin plate by quantitative analysis of lamb wave acoustic emission

摘要

Dynamic behavior of micro-cracks in delayed fracture of low alloy steel thin plate was studied by quantitative analysis of Lamb wave acoustic emission (AE). Three dimensional source locations were identified using the first arrival times of So-mode at the sheet velocity and the ratio of maximum amplitude of the Ao-mode to that of first arrival So-mode. Fracture dynamics of Mode I crack were studied by the waveform simulation of So-packet. Delayed fracture in a 1 mm thick plate was found to occur at high hydrostatic stress field in front of a notch and at mid thickness of the plate, and to progress inside the plate for 11 mm and finally to emerge at the free surface. Opening velocity of Mode I micro-fracture along prior austenitic grains reached the maximum velocity of 250 m/s.