Analysis Of Tensile Properties And Crack Propagation Of Composite Laminates With Pre-crack

Nowadays,countries all over the world are facing energy crisis and environmental pollution problems.Automobiles consume a lot of energy,and the application of lightweight materials can reduce energy consumption and exhaust emissions.Carbon fiber-reinforced polyamide（CF/PA）composite material is a kind of thermoplastic composite material,which will inevitably cause cracks in the complex service environment or manufacturing process.Some scholars have studied the crack defect form and propagation path of thermoset carbon fiber composite materials in which most of them are about the fatigue or bending tests of the crack.The research on the crack propagation path and tensile properties of CF/PA composite materials has not been publicly reported.Therefore,it is necessary to be studied.In this paper,CF/PA composite materials are used as the research object,and the method of experiments and simulation is used to study the crack propagation law and tensile properties of CF/PA composite laminates with different pre-cracks.First,the basic theory and material properties of composite material mechanics are explained,and then the tensile and shear test plan of the laminate are formulated,and the basic mechanical properties of the CF/PA composite material,including the parameters of E1,E2,G12,and?₁₂,are tested.Digital image correlation method is used for strain measurement.After that,the test plan for uniaxial tension of composite material laminates with different pre-cracks is developed.Two fiber directions of 0°and 45°are set,and different positions,lengths,and angles of pre-cracks are planned for each fiber direction.In additon,some of the previous test cases are selected and simulated to verify the accuracy of the finite element models,and then the verified finite element models are used to simulate the tensile properties of the laminates with pre-cracks of different angles in 0°fiber directions and different positions in 30°fiber direction.The results show that for the CF/PA composite laminates with pre-crack,the cracks of the specimens with 0°fiber direction generally show the propagation paths of"H"or"T"type of split.The crack propagation paths of the specimens with 45°fiber direction are all along the 45°fiber direction.When keeping the length and angle of the pre-crack unchanged and only the position changed,the load-bearing capacities of the specimens with 0°fiber direction are basically the same with each other,while that of the specimens with 45°fiber direction change with the changes of the positions.When keeping the position and angle of the pre-crack unchanged and only the length changed,the load-bearing capacities of the specimens with 0°and 45°fiber direction decrease with the increases of the crack lengths.When keeping the position and length of the pre-crack unchanged and only the angle changed,the load-bearing capacities of the specimens with 0°fiber direction increase firstly with the increases of the crack angles,and then slowly increase,while that of the specimens with 45°fiber direction slowly rise,then significantly increase.It is shown in the finite element simulation that,the maximal uniaxial tensile forces of the laminates with 0°and 90°fiber direction are both consistent with the experimental values.The uniaxial tensile force-displacement curves of the specimens with 0°fiber direction and containing different forms of pre-cracks are very close to the experimental curves.When keeping the length and angle of the pre-crack unchanged and only the position changed,the rule of the load-bearing capacities of the specimens with 30°fiber direction vary with the positions of pre-cracks are basically similar to that of 45°fiber direction.