Analysis And Research On Low Velocity Impact Damage And Residual Strength Under Biaxial Load Of Composite Laminated Plates

The composite laminated plates are inevitably impacted at low velocity during manufacture and in service. The extensive sub-surface damage which caused by impacted loading weakens the mechanical properties of laminated composite structures seriously, reduces load carrying capacity of structure and even causes accident directly. Resin matrix composite materials are widely used in aeroengine case. Aeroengine case bear not only axial force and circumferential force caused by gas load and installation pre-tightening force but also redial force caused by centrifugal force of engine in working status. Therefore, it is of great importance to the research of low velocity impact damage and residual strength under biaxial load of composite structures.Research works in this paper can be summarized as follows:1. The finite element formulations are deduced to analyse gradual damage stress of laminated structures under impact load and biaxial load based on Hertz contact law, virtual displacement principle and equivalent damage principle. A whole-process method of impact gradual damage process and the residual strength of laminated composites under biaxial load after impact is proposed. Based on this method and the software of ANSYS, an anslysis software is compiled.2. A specimen design of cruciform specimen with thin slits in the spokes is proposed. The experimental results showed that the center of the specimen is damaged firstly under biaxial load.and the specimen design is feasible.3. Experimental research and numerical analysis on impact damage and biaxial residual strength of composite cruciform structures are carried out. Compared with experimental results of impact damage areas, the error of numerical analyses is less than 10%. Compared with experimental results of biaxial tensile residual strength, the error of numerical analyses is less than 9%.Numerical analyses of the fracture forms is consistent with experimental results. The results showed that the whole-process method of impact gradual damage process and the biaxial residual strength of laminated composites after impact is feasible.4. Biaxial strengthening effect of composite laminated plates is discovered by comparing the biaxial tensile residual strength with axial tensile residual strength.5. The influence of impact energy and number of layers on the biaxial residual strength is studied by the whole-process analysis method which is developed in this paper.