Study On The Strength Of Scarf Patch Repaired Composite Structures

Adhesive bonded repairs are the most common type of repair carried out with composite materials. Study of the repair effect has become an urgent problem to be settled in aeronautics of China. This paper is developed for studying the permanent repair method, the scarf patch repair of composites. A three-dimensional finite element analysis is performed in order to calculate the stress field of the repaired laminates. The calculated stresses are then coupled with failure rules, Tsai-Hill criterion for adherends and Maximal shear stress criterion for the adhesive to predict the compressive strength of repaired panels. Predicted values coincide with experimental data very well. The error is less than 10%. And it is found that carefully designed scarf patch repairs can recover more than 80% of the undamaged strength. The effect of repair parameters, such as the scarf angle, thickness of the adhesive, damaged radius, etc. on the strength of repaired structures are discussed in detail. The optimum scarf angle is about 4 to 5 degree. Moreover, some work is done about FE modeling efficiency of repaired laminates. The influence of technical errors on the repair strength is discussed. The scarf patch repaired composite stiffened panels is also analyzed. For different damage forms, the best repair methods were obtained. All of the conclusions are useful to actual repair work.