Threshold Characteristics of Stress Corrosion Cracking under Dynamic Combined Multiaxial Loading Conditions

对4135高强度钢在3.5%的氯化钠溶液中进行了光滑试件的循环应力腐蚀试验。加载方式有弯曲(R=-1)、扭转(R=-1)、同时拉伸(R=0)和扭转(R=0)。&lt；tau&gt；_&lt；max&gt；与&lt；sigma&gt；_&lt；max&gt；的比率从零(拉伸)到无穷大(扭转)。当扭矩大于或等于780 Mpa时，试件发生垂直于纵向的穿晶断裂。当500 Mpa等于或小于&gt；&lt；tau&gt；_&lt；_&lt；max&gt；&lt；780 Mpa时，腐蚀坑底部由剪应力引起的纵向裂纹被认为是溶解引起的，然后在腐蚀坑尖端开始以最大前应力为主的沿晶循环应力腐蚀裂纹。在500 Mpa扭转和弯曲、拉扭复合载荷作用下，腐蚀坑底部发生以最大主应力或最大拉应力范围为主的循环应力腐蚀开裂。控制腐蚀坑底部裂纹萌生的力学条件由应力强度因子范围-lt；Delta&gt；_&lt；IFSCC&gt；决定，假设腐蚀坑为尖端裂纹。同样，当凹坑的K值超过Klt；IIIFSCC&>；时，由溶解引起的纵向裂纹开始出现。

Cyclic stress corrosion cracking (SCC) tests of smooth specimens were conducted on 4135 high-strength steels in 3.5% NaCl solution. Loading types were bendin (R = -1), torsion (R = -1), and combined in-phase tensio( (R = 0) and torsion (R = 0). The ratio of <tau>_<max> to <sigma>_<max> ranged from zero (tension) to infinity (torsion). In torsion at <tau>_<max> <greater than or equal> 780 MPa, specimens were fractured by transgranular cracking normal to the longitudinal direction. At 500 MPa <equal or less than> <tau>_<max> < 780MPa, a longitudinal creack by shear stresses, which is considered to be caused by dissolution, was initiated at the bottom of corrosion pit, and then intergranular cyclic SCC crack dominated by maximum proincipal stress was started at the tip of it. In torsion at <tau>_<max> < 500 MPa and in bending and combined tension and torsion loading, however, cyclic SCC crack dominated by maximum principal stress or maximum tensile stress range was initiated at the bottom of corrosion pits. Mechanical condition dominating crack initiation at the bottom of corrosion pit was determined by stress intensity factor range <DELTA>_<IFSCC>, which was obtained by assuming the corrosion pit as a sharp crack. Similarly, a longitudinal crack by dissolution was initiated when a K_<III> value of a pit exceeded the K_<IIIFSCC>.