Impact Damage Mechanism Of Composite Laminates And Shear-after-impact Behaviors Of Different Hybrid Structures

In this paper, impact performance of the composite laminates with different hybrid structure are investigated experimentally and numerically for the sake of exploring the impact damage mechanism of composite laminates and how hybrid influence on the impact property. Further studies on shear properties of composite laminates are carried on to analysis its’ impact characteristic and failure modes by testing the shear properties of composites laminates after impact and observing the crack propagation in specimen under stereomicroscope Nikon SMZ 745 T.Firstly, low-velocity impact experiments on unidirectional stacked in a sequence of [0/90/0/90]2s and [+45/-45/0/90]2s and woven carbon/epoxy laminates are conducted. By making a comparison between different composite laminates on the basis of circular specimen, the mechanism of impact damage can be analysised from the perspective of composite laminates’ impact energy transmission. And studies on the mechanism of impact damage by finite element software ABAQUS are also needed to do in this sector.Then have low-velocity impact on five kinds of composite laminates with different structures, which conclude carbon fiber woven fabric composite laminate, carbon fiber and glass fiber cross-ply woven fabric composite laminate( intraply hybrid composite), carbon fiber woven fabric and glass fiber woven fabric alternately lay-up composite laminates(inter-laminated hybrid composite), carbon fiber woven fabric and carbon fiber unidirectional alternately lay-up composite laminates(inter-laminated hybrid composite), carbon fiber and glass fiber cross-ply woven fabric and carbon fiber unidirectional alternately lay-up composite laminates(intraply/inter-laminated hybrid composite). By numerically testing the shear properties, we study the residual mechanical properties after impact. Meanwhile set a control group made of samples which haven’t been impact to explore the impact properties between different composite laminates. Experimental results have shown that:1. T he transmission of impact energy changes greatly in association with fabrics’ layer structure along the thickness direction in composite laminates. Meanwhile it has relation to the fiber orientation in each layer of fabrics and the fibrous interlocking texture. Impact energy spreads faster in fibers arranged straightly and easier in fibers arranged along axial direction, which leads to a less damage and a larger range damage in the central area of the unidirectional fabric composite laminates, compared to woven fabric composite laminates. The bending of fiber can slow the speed of the transmission of impact energy along the axial direction. Fibers in each layer of woven fabrics exist a weaving point and impact energy is focused on the central area, which results in woven fabric composite laminates’ focusing on the central area impacted and a lager degree of damage when compared with unidirectional fabric composite laminates, namely more fiber breakage. If there are more fiber orientations in composite laminates, there would be more orientations of impact energy along axial direction and the impact energy would transmit more evenly in each layer, which finally could decrease the degree of the composite’s damage caused by impacting.2. In the case of a same hybrid ratio of carbon fiber and glass fiber, the inter-laminated hybrid composite laminates have better impact properties and show a smaller displacement of the impact damage area and impact sag displacement when compared with intraply hybrid composite laminates.3. Under the effect of shear, the crack of woven fabric composite laminates represent the fibers’ breakage in most cases. However the damages of hybrid composite laminates composed of unidirectional/woven fabrics are mainly delamination.