Study Of Experimental And Numerical Analysis Method Of FMLs Subjected To Low-velocity Impact

Fibre metal laminates(FMLs) is a type of hybrid material which consists of alternating layers of thin metallic sheets bonded together with fibre reinforced layers. With excellent properties of both composite and metal material, FMLs has become one of popular materials in aircraft structure application in recent years. At present, a great deal of research on the impact response of FMLs has been done and great achievements have been made abroad. With the development of the aviation industry in our country, the need to study the structure property and fracture mechanism of FMLs under impact loading becomes urgent. Therefore, the low velocity impact tests of domestic FMLs and numerical analysis method were deeply studied in this paper. The main contents are as follows:According to the related standards and the papers published at home and abroad, series impact test samples and related testing fixtures were designed. A range of low velocity impact tests with different energies were performed on domestic FMLs, aluminum alloy plate, glass fiber composite and carbon fiber composite panels by Instron 9250 drop weight impact test machine. The surface visual damage and impact response of four different samples under different impact energies were compared and analyzed. The effects of two boundary conditions with clamped and simply supported and the rolling direction of aluminium layers on the impact resistance of FMLs were studied respectively, and response mechanism of FMLs was analyzed under low velocity impact loading as well. The results show that response and damage of FMLs has its own special feature and rule after impact; boundary conditions have a certain effect on the impact response of FMLs, while the impact resistance of FMLs with different rolling direction of aluminium layers doesn’t change greatly. Mainly thanks to 0/90 degrees of alternate glass fiber layers in FMLs, the penetration energy of FMLs is 22% higher than the aluminum alloy plate which has the same thickness.Based on the continuum damage mechanic theory, the 3D composite damage model was deduced and established, and then VUMAT program was made. ABAQUS software is used to build a numerical analysis model to simulate response of FMLs under impacting, and the model result was then verified by comparing with the test ones. The impact damage and response of FMLs under typical test condition was mainly analyzed by numerical calculation, and the impact response characteristics at different stages were carried out. The damage type and response of each layer of FMLs during impact process were studied. And the effect of size and shape of samples, thickness of aluminum layer and the number of metal/composite layers on the impact resistance of FMLs were explored. Consequently, every sudden drop in the impact response force-time curve exactly corresponds to an emergent failure in the FMLs. The more the delamination on both sides of aluminium layer, the less is the delamination between adjacent 90 degrees fibre layers. Conclusions of this research can provide basic information and analysis method to design FMLs stucture.