STUDY ON STRESS CORROSION CRACKING MECHANISM AND CRACK GROWTH VELOCITY BY MEANS OF FREQUENCY ANALYSIS OF ACOUSTIC EMISSION.

据报道，关于裂纹扩展行为，应力腐蚀开裂有两种类型：裂纹GEOWS（I）不连续和（II）连续。对两种类型的材料（SUS 304不锈钢和2014-T652铝合金）进行应力腐蚀开裂试验，在恒应力强度因子条件下，在3.5%的恒电化学电位下使用环形试样在试验过程中记录并分析了声发射信号，发现由于应力集中，在缺陷处发生优先溶解，这导致裂纹不连续扩展，在铝合金中，不连续生长引起的声发射幅度较大，频率较低，不能与电极处产生气体引起的声发射区别开来，在不锈钢中，裂纹尖端发生溶解，裂纹继续扩展，在这种裂纹扩展中，记录了声发射，声发射次数随幅值的增加而减少，这种声发射模式与不连续增长的声发射模式不同，推测这种应力腐蚀通过分析声发射信号可以区分裂纹和其它类型的裂纹。

IT HAS BEEN REPORTED THAT THERE ARE TWO TYPES OF STRESS CORROSION CRACKING CONCERNING CRACK GROWTH BEHAVIOUR : CRACK GEOWS (I) DISCONTINUOUSLY AND (II) CONTINUOUSLY.STRESS CORROSION CRACING TESTS WERE CARRIED OUT ON MATERIALS OF BOTH TYPES,A SUS304 STAINLESS STEEL AND A 2014-T652 ALUMINIUM ALLOY,UNDER CONSTANT STRESS INTENSITY FACTOR CONDITIONS USING RING TYPE SPECIMENS AT CONSTANT ELECTROCHEMICAL POTENTIALS IN A 3.5% NaCl SOLUTION.aCOUSTIC EMISSION SIGNALS WERE RECORDED AND ANALYSED DURING THE TESTS.IT HAS BEEN FOUND THAT PREFERENTIAL DISSOLUTION OCCURS AT DEFECTS DUE TO STRESS CONCENTRATION AND THIS LEADS TO A DISCONTINUOUS CRACK GROWTH,IN THE ALUMINIUM ALLOY.THE ACOUSTIC EMISSION CAUSED BY THE DISCONTINUOUS GROWTH HAS RELATIVELY LARGE AMPLITUDE AND LOW FREQUENCY,AND CNA BE DISTINGUISHED FROM THE ACOUSTIC EMISSION CAUSED BY THE GENERATION OF GASES AT THE ELECTRODES.IN THE STAINLESS STEEL,DISSOLUTION OCCURS AT THE CRACK TIP AND CRACK GROWS CONTINUOUSLY.IN THIS TYPE OF CRACK GROWTH,ACOUSTIC EMISSION WAS RECORDED.THE NUMBER OF ACOUSTIC EMISSION EVENTS DECREASED WITH AN INCREASE IN THE AMPLITUDE.THIS ACOUSTIC EMISSION CHARACTERISTIC IS DIFFERENT FROM THAT OF THE DISCONTINUOUS GROWTH.IT HAS BEEN DEDUCED THAT THIS TYPE OF STRESS CORROSION CRACKING CAN BE DISTINGUISHED FROM THE OTHER TYPE BY ANALYSING ACOUSTIC EMISSION SIGNALS.