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

据报道，在裂纹扩展行为方面，应力腐蚀裂纹有两种类型：裂纹裂纹(i)不连续和（ii）连续。摘要在恒应力强度因子条件下，采用环型试样在3.5% NaCl溶液中进行了SUS304不锈钢和2014-T652铝合金的应力腐蚀试验。在试验过程中，对声发射信号进行了记录和分析。在铝合金中，由于应力集中，缺陷处发生优先溶解，导致裂纹不连续扩展。不连续生长引起的声发射具有较大的振幅和较低的频率，可以与电极处气体产生引起的声发射区分开来。在不锈钢中，裂纹尖端发生溶解，裂纹不断扩大。在这种类型的裂纹扩展中，记录了声发射。声发射事件数随振幅的增大而减小。这种声发射特性不同于不连续生长的声发射特性。通过对声发射信号的分析，可以将这种类型的应力腐蚀裂纹与其他类型的应力腐蚀裂纹区分开来。

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.