Numerical Simulation Of Mechanically Fastened Joints Properties For Carbon Fibre Composite Laminates Subject To Low Velocity Impact Loads

With the rapid development of aerospace,automobile and other fields,the advanced composite materials have begun to flourish,the structural properties are equivalent or superior to aluminum alloy.Because of the excellent properties of the composites,they have shown great vitality once they come out.The joint of composite material structure mainly includes mechanically fastened joints and adhesively bonded joints.Mechanically fastened joints is one of the most important forms of the composite structure.The mechanically fastened joints quality is easy to control,low intensity dispersion,can transmit more load,for convenient handling,safe and reliable.However,due to the opening of the hole,the fibre would be cut off during production processes,it will bring stress concentration,weaken the bearing capacity of composite material structure.Meanwhile due to the impact resistance of the composite materials is very weak,so under low velocity impact loads,It is necessary to research the effects of mechanical properties of composite structures all the above critical factors by numerical simulation.First of all,introduces the constitutive model of composite material including two dimensional Hashin failure criterion and composite layer damage model.On this basis,the static tensile model of single-lap bolted joint of carbon fiber composite laminates and the low velocity impact loads finite element model of carbon fiber composite laminates are established by using ABAQUS,the mechanical response of the single-lap bolted joint of carbon fiber composite laminates to the static tension load and the mechanical response of the carbon fiber composite laminates under the low velocity impact loads respectively,the simulation results match well with experimental data,which verifys the accuracy of the modeling method and material parameters.Then,the finite element model of single-lap double bolted joints and single-lap four bolted joints of carbon fibre copmosite are established by using ABAQUS,analyse the effects of geometrrical parameters,unidirectional laminate angle,unidirectional plies ratio on joint properties of double bolted joints and a study was carried out to investigate the joint properties effects of joining region and arrange styles of pins about four bolted joints under the low velocity impact loads.The resultsshow that the geometrrical parameters,the unidirectional laminate angle and the unidirectional plies ratio have significant influence on the joint properties of the single-lap double bolted joints of carbon fiber composite laminates,and the arrangement of the rhombus is more helpful to improve the connection performance of the single-lap four bolted joints of carbon fiber composite laminates.Finally,analyse the circumferential radial stress under different bolts-holes fit,research the influence of mechanical joint properties of connection hole interference and bolt pretightening force and two set of composite-to-titanium single-lap bolted joints under the low velocity impact loads.The results show that the size of interference and pretightening force will affect the connection performance of the composite structure,but the influence of pretension is greater than the interference.and the two set of composite-to-titanium single-lap bolted joints have significant effect of the circumferential radial stress and meanwhile have effect of the single-lap double bolted joints of connection properties of carbon fiber composite laminates,but it has no effect of the failure mode.