Abstract
Two types of laminated composite plates reinforcing pure copper with carbon steel were prepared. One was the steel-copper-steel (SCS) hot-rolled clad plates, and the other the copper-steel-copper (CSC) diffusion-bonded plates. As a result of fatigue testing using these specimens, the fatigue crack showed a zigzag crack front with a large roughness on the fracture surface of the inner copper sandwiched between both carbon steels in the SCS type plate with large thickness, while it showed a relatively smooth crack front on the fracture surface of the steel part. An influence of such a fracture surface roughness on the fatigue crack propagation was discussed in terms of fracture mechanics parameter. The fatigue crack propagation rate, da/dN, for all the laminated composite plates and the carbon steel base plates gathered in a small band expressed by the power law of ΔK_<est>/E, using the stress intensity factor range Δ K_<est> evaluated from the measured crack opening displacement and Young's modulus E. If examined in detail, however, the da/dN was lower in the thicker SCS type plate than in the CSC and the base plates, due to the large roughness on the fracture surface of the inner copper part.
