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CFRP层组成的。固化温度为120ﾟC，由于铝合金和碳纤维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。铝合金板材中存在拉伸残余应力，导致CFRP层中的残余应力被压缩。采用两种方法控制残余热应力。一种是在只施加于CFRP层的拉伸下固化复合材料，另一种是在复合材料板上施加应变，直到铝层产生一些小的塑性应变。由于第一种方法，由于未固化的CFRP预浸片的弱点，残余应力的控制下限约为0 Mpa。因此，在压缩过程中不能获得铝合金的残余应力。…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材的拉伸屈服应力比未控制的板材提高得更多。然而，由于残余应力控制的操作，极限应变和层间剪切强度降低。声发射检测表明，在第二种方法的作用下，铝合金与CFRP层之间产生了匹配界面失效。据估计，这是导致层间剪切强度下降的因素。残余应力控制对疲劳性能的影响尤为明显。裂纹扩展速度随着铝层残余应力的降低而减小。在低平均应力和窄应力幅值条件下，铝层残余应力转变为压缩后试件的裂纹扩展完全停止。即使不加控制，混杂板材的疲劳抗力也比整体铝合金板材大得多。通过这一事实，我们可以理解CFRP层对杂交板中铝层上的咯咯声传播的干扰。较少

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