Effect of Boundary Condition on Impact Response and Damage Meso-mechanism for Scarf Bonded Repair of Load-bearing Composite Structures

摘要

Composite scarf repair is applied in airplane load-bearing structures. But the repairs would have different boundary supports in real situation,such as simply support,clamped support and flexible support. With different boundary supports, the bonded scarf repair of composite structures could have diverse damage mechanisms and responses. This work intends to study the impact performance of different boundaries. For this purpose,experimental tests were carried out on the specimens with two sides support and four sides support. The impact load and deflection was monitored during the tests. After impact being finished,the meso-mechanism was studied by means of micro-cracks of the side section for two sides support condition and cross section for the four sides support condition. It was possible to conclude that the four sides boundary possess higher impact resistance maximum loads,lower displacements and lower extent load dropping. In terms of damage modes,as the impact energy relative low 12 J and 16 J,the central position of scarf bonding zone for two sides support appears adhesive cohesive failure and adhesive-composite interface failure. When the energy increases to 20 J,the dominated damage of two sides support moves down to the feathered tip. For four sides support,the critical energy level is 25 J,under which the scarf adhesive begins to be damaged.