Material Improvement of A1/Cfrp Multilayered Hybrid Composite by Residual Stress Control

这种复合材料是由许多薄铝合金和单向碳纤维增强塑料层构成的。固化在120℃的温度下进行。由于铝合金和CFRP层的热膨胀系数不同，从固化温度冷却到室温后存在残余热应力。拉伸残余应力发生在铝合金板材中，因此，CFRP层中的残余应力被压缩。采用两种方法控制残余热应力。一种是将复合材料在仅施加于CFRP层的拉伸力下固化，第二种是对复合材料板施加应变，使其正常制造，直到铝层中产生一些小的塑性应变。由于第一种方法，由于未固化CFRP预浸板的弱点，残余应力的控制极限在0 MPa左右。因此，在压缩条件下，无法得到铝合金内部的残余应力。与第一种方法相比，第二种方法非常简单，可以更精确地控制残余应力。残余应力控制在较低水平的复合材料板的拉屈服应力比未控制的复合材料板的拉屈服应力增加得更多。但由于残余应力控制的作用，极限应变和层间抗剪强度均有所降低。声发射检测结果表明，在第二种方法下，铝合金层与CFRP层之间产生了匹配界面破坏。推测这是导致层间剪切强度下降的原因。残余应力控制对疲劳性能的影响尤为明显。随着铝层残余应力的减小，裂纹传播速度减小。在较低的平均应力和较窄的应力幅值条件下，铝层残余应力变为压缩的试样的裂纹传播完全停止。混合板的抗疲劳性能，即使不加以控制，也大大大于单片铝合金板的抗疲劳性能。由此可以理解，碳纤维布层对混合动力板中铝层的裂纹传播有干扰作用。少

This composite material has been built up from many thin aluminum alloy and unidirectional CFRP layers. The curing is performed at a temperature of 120ﾟC. As a result of the different thermal expansion coefficients of aluminum alloy and CFRP layer residual thermal stresses are present after cooling down from the curing temperature to room temperature. Tensile residual stress occurs in the aluminum alloy sheet, and as a consequence, the residual stress in the CFRP layer is compressed. Two methods were used to control the residual thermal stress. One is to cure the composite under tensile forec applied to the CFRP layers only and the second is to applied a strain to the composite plate, made normally, until some small plastic strain is produced in the aluminum layer. Due to the first method, because of the weakness of non-cured CFRP prepreg sheets, the controlling limit of residual stress was about 0 MPa. So the residual stress in the aluminum alloy could not be obtained in compression. … More The second method was very simple and the residual stresses could be controlled more precisely than in the first method. The tensile yield stress of the composites plate of which residual stress es were controlled in lower level increased more than that of plate not controlled. However, the ultimate strain and the inter laminar shear strength decreased due to the operation of the residual stress control. Some acoustic emission inspections showed that match interfacial failure produced between aluminum alloy and CFRP layers under the operation of the second method. It was estimated that this was the factor causing the decrease in the inter laminar shear strength. The effects of residual stress control particularly appeared on the fatigue properties. Velocity of a cluck propagation decreased with decreasing of the residual stress of aluminum layer. Under the conditions of low average stress and narrow stress amplitude, the cluck propagation of the test specimen of which residual stress of aluminum layer was changed into compression stopped completely. Fatigue resistance of hybrrid plates, even if they were not controlled, was enormously greater than that of monolithic aluminun alloy plate. By this fact we could understand that the CFRP layers disturb the cluck propagation on the aluminum layers in the hybrid plate. Less