抄録
To examine the crack propagation characteristics of welded plates, we made compact tension specimens for crack propagation tests from base material and V-groove butt-welded plates. In case of the latter, specimens were made such that the direction of crack propagation follows that of the welding line. The yield and tensile strengths of the base material, SM 490A, are about 350 and 520 MPa, respectively. From the specimens, the plane strain fracture toughness, J_<1c>, crack propagation rate, da/dN , and the threshold value of the stress intensity factor, ΔK_<th>, of the base material, HAZ and HAZ annealed were measured. Crack propagation tests were carried out at 20Hz, R=, 0.1, 0.3 and 0.5. Crack length was obtained from the measurement of compliance variation. In the case of ΔK_<th> tests, tests were performed under load control at 20Hz, R=0.1, 0.3 and 0.5. Crack length was measured by using CCTV camera with magnification of 100 times. ΔK_<th> is defined at the crack propagation rate of 10^<-7> mm/cycle. In addition, micro hardness was measured and SEM photographs were taken. It was found HAZ has finer grains and larger ΔK_<th>.
