چكيده به لاتين
Adhesive joints are currently used in different industries such as automotive, aerospace, electronics and marine. In many applications, the joints experience low energy impact loads during the service. The energy of the impact loads is too low to cause a joint failure. They even don’t change the appearance of the joints. But this kind of impact loadings can significantly reduce the strength of the adhesively bonded structures. Accordingly, it is necessary to understand the effect of impact fatigue on residual strength of the adhesive joints. To achieve this, first, the static and then the impact strength of single-lap joints (SLJs) were measured. A simple drop weight machine was also designed to apply repetitive impact to the manufactured joints. Using the designed machine, the impact fatigue strength of the joints at different levels of applied energy were analyzed. Fatigue impact tests followed by quasi static tensile tests were conducted on some joints to analyze the residual static strength of the joints subjected to different levels of impact fatigue. Fracture surface of the tested specimens were analyzed. It was observed that the impact fatigue life of SLJs increased significantly by reducing the impact energy. As obtained from the results for initial impacts the strength reduction was less than 10 % of the initial static strength. By increasing the number of impact cycles, the effect of each impact on the strength reduction increases significantly. The fracture surface showed that cracks initiate from the middle-bonded area as a result of impact stress waves then by increasing the number of impacts, a large number of cracks begin to grow from the edges of the SLJs. The impact energy has a direct influence on the cracks’ lengths, and the impact fatigue load created damage zone in the adhesive layer which reduced the effective length of adhesive bond and the joint strength.
