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

据报道，与裂纹扩展行为有关的应力腐蚀破裂有两种类型：(I)不连续的和(II)连续的。在恒应力强度因子条件下，对SUS304不锈钢和2014-T652铝合金这两种材料进行了恒应力强度因子下的应力腐蚀开裂试验。在试验过程中，记录并分析了连续发射信号。结果表明，由于应力集中，缺陷处发生优先溶解，导致裂纹不连续扩展。在铝合金中，由不连续生长引起的声发射具有较大的幅度和较低的频率，与由电极产生气体引起的声发射不同。在不锈钢中，裂纹尖端发生溶解，裂纹不断扩展。在这种类型的裂纹扩展中，声发射被记录下来。声发射事件的次数随着不连续生长的增加而减少。这一声发射特征不同于不连续生长的声发射特征。通过对声发射信号的分析，推断这种类型的应力腐蚀开裂可以与其他类型的应力腐蚀开裂区分开来。

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.