Experimental Study And Numerical Analysis On Stitched And Unstitched Composite Laminates With Impact Damages Under Compressive Load

The main works of this paper are to research the compressive deformation after impact loading of stitched and unstitched composite laminates using experimental method and numerical analysis. In the experiments, the filtering methods and phase measurement techniques for speckle fringe patterns are studied firstly, and then the carrier electronic speckle pattern interferometry (ESPI) is applied to measure the out-of-plane displacement field on stitched and unstitched composite laminates with impact damages under compressive loads. In the numerical simulations, FEM is used to investigate the effect on the compressive deformation of laminates with different impact damages. Meanwhile, stitch line that has influence on the out-of-plane displacement for laminates with impact damages under compression are taken into account.Electronic speckle pattern interferometry is a whole-field, non-contact, high accuracy measurement technique, which can be used under poor testing environment. It is well-known for micro deformation precision measurement of object surface. Due to the serious speckle grain random noise in speckle interferometry, an improved anisotropic diffusion is presented for ESPI fringe pattern denoising in this paper. Moreover, the optimal iteration times are determined based on decorrelation optimal stopping criteria. As the phase field of ESPI fringe patter reflects the deformation of object directly, the fringe-centerline method, phase shifting technology, carrier method and phase extraction method of an ESPI fringe pattern are studied. The results are helpful for improving the experimental measurement precision. It is of great useful for understanding the strength of engineering component to know the compressive deformation of laminate after impact. In this work, carrier-ESPI method is applied to measure the out-of-plane displacement of the stitched and unstitched laminates [03/903]S with impact damages or without damage.The experimental results show stitching improve the through-the-thickness constrains and the inter-laminar performance, which can effectively prevent or restrain the growth of out-of-plane displacement because of delamination damage, and can improve the damage tolerance of laminate. On one hand, the impact damage prone to produce the out-of-plane displacement of laminate. On the other hand, the impact damage leads to the dramatic decrease for in-plane rigidity of laminate. Therefore, the global deformation arises easily.Additionally, FEM is used to research the deformation behavior of laminates with different impact damages. The out-of-displacement of a point on the impact back surface corresponding to the impact axis is increase with the increasing of impact energy, maximum impact force, delamination area, length, width, et al. The effects of stitching for laminates with impact damages are also taken into account. With the increasing of delamination area, the effects of stitching which can prevent or restrain the out-of-plane displacement growth appear apparently. Meanwhile, the FEM results are compared with experimental ones. The results indicate that the both deformation feature tends generally to be consistent with each other.