循环温度疲劳作用下粘接界面损伤的非线性超声评价

材料损伤以及性能退化与超声波的非线性效应密切相关.为研究循环温度疲劳作用下粘接界面的损伤情况,本文采用超声波透射法,研究了6061型铝合金/改性丙烯酸酯胶粘接界面的声学非线性系数随高温、低温循环次数的变化情况.结果表明,在高温循环疲劳作用的初始阶段,试件的非线性系数变化不明显,但随着高温循环次数的不断增加,非线性系数随循环次数的变化十分明显;对于低温循环疲劳作用的初始阶段,试件的非线性系数迅速增大,随着循环次数的增加,其值增速减缓.在低温循环疲劳寿命的后期,试件的非线性系数随循环次数的增加而继续增大.进一步的讨论结果表明,胶层三阶弹性常数的变化是造成高温循环疲劳时非线性系数变化的主要原因,而对于低温循环疲劳,粘接界面拉伸刚度的变化是引起非线性系数变化的主要原因.

Nonlinear ultrasonic evaluation of damage to bonding interface under cyclic temperature fatigue

Adhesively bonded structures possess various industrial applications, such as safety-critical structures in the aerospace and automotive industries. With the increasing using of adhesive joints, corresponding methods of evaluating and testing the structural integrity and quality of bonded joints have been widely investigated and developed for the structural health monitoring. Studies show that the damage and degradation of material are closely related to the nonlinearity of ultrasonic waves propagating within the material. In this paper, for the evaluating of the damage to bonding interface under cyclic temperature fatigue, acoustic nonlinear parameters (ANPs) of specimens made of aluminum alloy 6061 and modified acrylate adhesive are measured experimentally by using the nonlinear ultrasonic technique; and thus the variations of the ANPs with the fatigue time under high and low cyclic temperature are obtained for the bonded specimens. The study shows that the ANP, which serves as an indicator of material properties, remains nearly unchanged in the initial stage of high temperature cyclic fatigue test, and the ANP obviously increases with temperature cyclic time increasing. For low temperature cyclic fatigue test, the ANP increases rapidly with the increase of temperature cyclic time in the initial stage, and its value growth slows down in the later stage. Further discussion shows that the increase of third order elastic constant is the main reason for the change of ANP for high temperature cyclic fatigue, and that the change of the tensile stiffness of the bonding interface is the main source for the change of the ANP for low temperature cyclic fatigue. It is shown that the ANP based on the theoretical model increases consistently with the experimentally measured values. The present research is expected to provide a promising way of characterizing and monitoring the damage to bonding interface under cyclic temperature fatigue.