采用四点弯曲腐蚀疲劳试验测定4340钢在人造海水中的△Kth,研究加载条件对测定△Kth的影响,并对门槛值附近裂纹扩展的形态进行观察。用降载法测得的△Kth值比升载法所测值低;门槛值附近裂纹扩展主要受机械应力控制,裂纹扩展形态以穿晶解理为主;阴极保护电位使条件门槛值△Kth稍有提高。在升载情况下,起始载荷越大,△Kth随之越高。合理选择初始临界应力强度因子范围是较精确地测得△Kth值的关键。
Four-point-bending corrosion fatigue tests were used to obtain conditional thresholdst ress intensity range (ΔK_(th)) of 4340 steel in artificial seawater under different initial loading conaition. The morphology of crack propagation near threshold area was examined by scanning electron microscope Results showed that the AKth measured by decrease loading method was lower than that by increase loading method, In stage I of da/dN～ΔK1 curves, the dominant driving force of transgranular crack near the threshold is mechaniealo A slightly increased ΔK_(th) was observed as a consequence of the cathodic protection potential, It is very important to choose an initial. stress intensity factor range(ΔK_(th))in order to determine ΔK_(th) accurately.
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