Study On Fatigue Crack Growth Characteristic Of Adhesive Bonding

With the continuous development of the automobile industry, the automobile industry has put forward more and more requirements on the lightweight. Lightweight put forward higher requirements for metal materials, structure and the connection mode of the car. Because of its excellent fatigue properties compared with the traditional welding, riveting, and bolt connection, the adhesive bonding is getting gradually widely used in the vehicle. Adhesive bonding connection can be Homogeneous, and its stress concentration is small, which has long service life.Adhesive bonding can realize the connection of dissimilar and similar materials, such as metal and metal, metal and nonmetal. In order to study the fatigue properties of adhesive connection, this paper has carried out the following work:(1) Propose a new method to measure fatigue crack growth of the adhesive bonded specimens. The method uses the direct current potential method. Compared with the traditional microscopic observation method, it can be used to observe the crack inside the sample. The method is used to measure the crack growth by using the relation between the potential variation and the crack growth information.(2) Set up the adhesive fatigue crack growth test platform. The whole test system includes a universal fatigue test machine, special fixture, the DC voltage source, shunt resistor, NI data acquisition equipment and wire and other test accessories. Taking the insulation of the experimental environment into account, a section of an insulated piece connecting the fixture with the fatigue machine has been installed. After fully preparing the experimental equipment, we have carried out the fatigue crack growth test of adhesive bonding.(3) Obtain the curve of the voltage of the sample and the force displacement curve during the loading process. For the force displacement curve, we analyze the characteristics of the fatigue hysteresis loop. Aiming at the voltage curve, the change curve of the crack length can be obtained by using the formula of the crack voltage transformation and observe the characteristics of the change of the crack length.(4) Establish the crack growth model based on the curve of crack length. For further data processing, The Paris formula is applied to assess the crack value,generally used to characterize crack propagation medium speed region. The mathematical formula of Paris’ s theorem is da/d N=C(ΔK)m. Stress intensity factor(K)is a physical quantity that reflects the stress distribution at the crack tip. We use J-integral algorithm to solve the stress intensity factor. Finally we draw the double logarithmic curve of the crack growth rate and obtain the expression for the Paris-law.