STUDIES ON BEHAVIOR OF FATIGUF IN C/AI CROSS-PLIED LAMINATE

In this study C/Al cross-plied laminates with two stacking sequence used. (90/0/90)_s and (90/0/90)_s abricated by hot-press method in vacuum are used. A series of experim eats on fatigue damage and fatigue fracture are conducted using MTS NEW 810.The research works on the behavior of fatigue damage include that shakedown analysis for C/Al cross-plied laminates which relates stiffness reduction as a damage parameter is presented to prediet the stress range below which no fatigue damage accmulates in the laminate. Negt, the fatigue response of C/Al cross-plied laminates is developed at constaut maximum stress level,but with different values of 0S,which indicates the stiffness reduction at failure is reasonably similar.It is suggested that the failure criterion be determined by the maximum stress level.The results prerented for matrix fatigue damage indicate the existence of three distinct regions in the S-N plane in which one observes different responses of MMC to cyclic loadings.The three regions are:no fatigue damage region,damage accumunation region, frail,ture region.Fatigue fracture surfaces and interface characteristics can be examined using SEM, and matrix cracking,by taking photographs through a 30 to 60 power optical microscope.The results show that the fracture surfaces of C/Al cross-plied laminates are flateply cracking has three kinds of modeselocal interior delamination,matrix cracks and interaced debonding between composites wires and matrixs;the dourinated reson of fatigue failure are local ply damage and large scale fiber failures in the longitudinal plies:if the interface is made too strong,matrix fatigue cracks are more likely to propagate through fibers and lead to early la urinates fracture.More work is needed to determine the optimum fiber/matrix interface properties for the composites.