Nonlinear Ultrasonic Evaluation Of Mechanical Properties Of Metal Bonding Interface Under Action Of Impact Fatigue

As an important connection technology, adhesive is widely used in many fields. Compared with traditional connection methods such as bolts, rivets, adhesive structure has the advantages of light weight and high strength, which meets requirement of the development of modern national economy. The integrity of adhesive structure depends largely on mechanical properties of bonding interface, so how to make an accurate evaluation on the mechanical properties of bonding interface is becoming the focus of science and engineering.When there is impact load on bonding interface, ultrasonic which goes through the bonding interface will produce nonlinear phenomenon. This phenomenon can be characterized by the ultrasonic nonlinear coefficient, namely the change of nonlinear coefficient can be used to evaluate the mechanical performance degradation of metal bonding interface.For the AZ31magnesium alloy bonding interface under the different condition of impact fatigue loading, adhesive interface is tested and analysed. The relationship between the mechanical performance degradation and ultrasonic nonlinear coefficient by using the method of nonlinear ultrasonic nondestructive testing was established. At the same time, we study the feasibility of the use of nonlinear ultrasonic on the nondestructive evaluation on the impact fatigue damage of bonding interface.The results indicate:1. To carry out nonlinear ultrasonic testing on a specific area of the adhesive specimens under the action of impact fatigue, we find that nonlinear coefficient increases with the increasing of number of impact fatigue. Nonlinear coefficient always grows slowly at the beginning of the impact fatigue in any working conditions, and in about60%of the fatigue life, nonlinear coefficient increases sharply. When the adhesive specimens destroyed completely, nonlinear coefficient reaches maximum. In addition, according to the related theory model, the mechanical performance degradation mechanism of bonding interface is analyzed under action of impact.2. To carry out nonlinear ultrasonic evaluation of experimental study on multiple regions of the adhesive specimens under the action of impact fatigue, we find that the impact fatigue life has obvious difference under the impact of the different conditions. But the relations of the normalized nonlinear coefficients as the change of impact fatigue life percentage are basically the same. Namely, nonlinear coefficient grows slowly at the beginning of the impact fatigue, and in about60%of the fatigue life, nonlinear coefficient increases obviously, until the destruction.3. Under the same impact energy, the influence of impact velocity on the impact fatigue life of bonding specimen is greater than the influence of impact quality.