盐岩间隔疲劳的声发射特性试验研究

Experimental study on character of acoustic emission caused by interval fatigue of salt rock

为研究时间间隔作用下盐岩疲劳试验的声发射特征,进一步揭示时间间隔对盐岩残余应变及疲劳寿命的影响,利用多功能盐岩试验机和声发射设备对时间间隔作用下的疲劳损伤及声发射特征进行试验研究,将声发射参数与损伤演化、晶体位错相联系,阐述时间间隔对疲劳力学行为的影响机理。结合损伤演化理论建立基于声发射振铃数的累积损伤变量与时间间隔之间的定性关系。研究结果表明:时间间隔的插入会加速疲劳过程中塑性变形的积累,时间间隔越长,塑性变形积累越快,疲劳寿命随之显著降低;时间间隔后循环内声发射振铃数比时间间隔前的多,经过一定时间的无应力静置,后续循环内的声发射变得更为活跃,且时间间隔越长,此现象越明显;在时间间隔内,残余应力参与并主导了细观尺度上盐岩内部结构的调整,由Bauschinger效应导致的反向软化使盐岩结构更为松散,加速塑性变形的积累。时间间隔对疲劳损伤有加速效应。

An experimental research on salt rock＇s fatigue damage and character of its acoustic emission（AE） to reveal the influence of time interval for residual strain and fatigue life further was done using the multifunctional test machine and AE facility. The mechanism of fatigue activities influenced by interval was expounded by combination of AE parameter, damage evolution and crystal dislocation. Qualitative relationship between accumulated damage variable and time interval was established by AE counts based on damage theory and fatigue disturbance theory. The results show that time interval accelerates accumulation of plastic deformation during fatigue progress. The longer interval, the faster plastic deformation accumulates, and consequently, fatigue life has a larger decrease. AE count produced in circle after interval is more than that produced in circle before interval. Acoustic emission in circle after interval becomes more active after standing of interval, and the longer the interval, the more obvious the phenomenon is. Residual stress leads to adjustment of internal structure of salt rock in the mesoscopic scale. The reverse softening caused by Bauschinger effect makes structure of salt rock more unconsolidated and accelerates accumulation of plastic deformation. Interval has accelerating effect on fatigue damage.