Study On The Bearing Properties Of Braided Carbon/Epoxy Composite Laminates

The scope of application of composite materials has been expanded gradually,and it has been extended from non-bearing components to large-scale complex bearing components,It is necessary to carry on the connection assembly in these large-scale composite components.And in the structure of the connection,the mechanical connection is still widely used,so its strength is essential for the safety of structural parts.In the mechanical connection area,the composite material is mainly affected by the extrusion of bolts,rivets and other fasteners.Therefore,it is important to study the mechanical properties of composite materials for the safety design of composite laminated plates.In this paper,the extrusion behavior of carbon / epoxy braided composites is studied from the perspective of experiment and numerical simulation.The main results are as follows:(1)Under the same conditions,the extrusion strength of single bolt double lap composite joint is obviously higher than the single / double bolt single lap composite joint;The double bolt single lap composite joint has a higher failure load than the bolt single lap composite joint.And with the load increase makes the net tensile stress of the laminates increase significantly,which leads to the failure of the laminates.(2)The temperature and humidity environment has a great influence on the extrusion performance of single bolt double lap composite joint.Compared with the room temperature dry environment(RTD),the Initial extrusion strength of the laminates decreased by 23.4% and the ultimate extrusion strength decreased by 21.6% under the hot and humid environment;In the low temperature dry environment,the extrusion strength increased by 16.68%,and the structural parts have a higher safety margin.(3)The main damage forms of the laminates in the 0 ply are fiber compression and a small amount of fiber tensile damage,matrix tension and compression damage,fiber matrix shear damage;The main damage forms of the 45 degree layer are fiber compression,matrix compression and fiber matrix shear failure;90 degree layer is mainly the matrix damage;The carrying capacity of the ± 45 degrees layer are higher than 0 degrees,90 degrees layer;In the laminates,the damage propagation direction of the 45 degrees,0 degrees and 90 degrees layers is also different,The 45°overlay mainly along the direction of ±45°.0°and 90°are mainly along the ±45°and 0°.(4)The extrusion strength in the form of single blot double lap composite joint decreases with the increase of the D/t,but the extrusion failure load increases with the increase of the D/t.At the same time,the numerical simulation method is used to simulate the compressive strength and D/t value curve?failure load and D/t value curve.Finally founded that the single blot double lap composite joint has the highest connection efficiency when D/t=1.8.(5)The compressive strength of single blot double lap composite joint was increased nonlinearly with the increase of ± 45 °layer.The results of ABAQUS simulation are basically consistent with the experimental results;With the increase of the content of ±45°layers,the compressive strength and shear strength of the laminated plate can be enhanced,so as to improve the extrusion strength;With the increase of the content of ±45°layers can enhance the anti-extrusion resistance,shear capacity,Thereby increasing its extrusion strength.And the proportion of ± 45 ° laying should not be less than 50%,0 ° laying ratio in the range of 25% ~ 30% is appropriate.