| The Carbon Fiber Reinforced Polymer（CFRP）materials exhibit excellent service performance in mechanical properties,as one of the advanced composite material,including specific strength,specific stiffness and specific modulus,etc.Considering the carbon fiber composite materials wide application potential in the field of automotive,aerospace,construction and bionic engineering,as well as the application in these areas will subject to external load,different working conditions such as quasi static load and dynamic load.Hence,research into the multidirectional layers of CFRP laminated board structure mechanical properties provides important support for the design of the new carbon fiber composite materials.In this paper,the test experiments of mechanical properties and related failure theory research of CFRP materials in China and abroad are summarized and analyzed.In order to fully understand the mechanical properties of CFRP laminates,it is necessary to study the relationship between strain rate and failure deformation under conventional continuous loading rate,and to uniformly explain the complexity of failure behavior of CFRP laminates under different strain rates.Meanwhile,considering the complex damage modeling should consider the interaction of different interlayer cracks,and the failure analysis of crack propagation in CFRP laminates with different angles is limited.In addition,considering the unpredictable failure mechanism caused by multi-layer and multi-directional braided modes,the failure mechanism can be revealed by studying the interlayer deformation behavior of multi-layer and multi-directional carbon fiber composites.Therefore,this paper developed the following three aspects of research,the specific research content are as follows:（1）The mechanical properties and microscopic failure of carbon fiber composite laminates about the effect of wide strain rate range on was studied.A small horizontal in-situ mechanical property testing instrument and Olympus optical microscope were integrated,and an error correction algorithm was proposed for the tensile strain measured by the instrument to meet the test requirements from quasi-static to low-speed loading range.Meanwhile,CFRP specimens with different structures were prepared by manual layup process.The effects of strain rate and failure deformation on[0°/0°]and[0°/90°]CFRP laminates under quasi-static and low-speed continuous loading rates were investigated.It was found that the fracture strength and fracture elongation exhibited a"low-high-low"trend in the strain rates range of 2.6×10-6s-1～2.6×10-3s-1.A universal failure model of multilayer/multi-orientation carbon fiber composite laminates under different strain rates was established.（2）The single-layer crack propagation mechanism of CFRP laminates is studied,and the micro-crack propagation modelsⅠandⅡfor CFRP laminates with different angles are proposed.Under the condition of quasi static(2.6×10-6s-1)and low speed loading(2.6×10-3s-1),he relationship between the fracture strength,fracture elongation,Young’s modulus and equivalent fracture energy of seven kinds of unbalanced symmetric composite laminates under in-plane tensile load and the stacking orientation angle was studied.The theoretical model of the off-axis carbon fiber composite element of the laminates is established.The fracture micromorphology of fracture samples was characterized by scanning electron microscopy（SEM）,revealing and the differences of fracture failure of laminates with different orientations.Further,the microcrack propagation modelsⅠandⅡof the CFRP laminates with different angles were proposed,revealing the fracture damage failure mechanism induced by the matrix microcracks.（3）Through in-situ tensile test and finite element simulation analysis,revealing that the tensile failure mechanism of carbon fiber reinforced polymer laminates is related to the number of layers and the direction of layer.Considering that the failure mechanism caused by the multi-layer/multi-orientation braiding mode is unpredictable,the tests were carried out on the defect-free specimens and the prefabricated V-shaped defect specimens at a constant strain rate of 2.6×10-5s-1.With the increase of layers,the tensile strength,equivalent fracture energy and strain hardening coefficient gradually decreased,and on the contrary,the elongation after fracture slowly gradually increased.Based on the stiffness theory of CFRP laminates,the finite element simulation analysis was carried out to study CFRP laminates,and the scanning electron microscopy was used to characterize the interface failure behavior of laminates.The order of contribution to the failure of interface was 90°/braided layer,0°/90°layer and0°/braided layer in sequence. |
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