碳-铝正交层板疲劳行为研究

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

本研究用真空热压法制备了两种铺层的C/AI正交层板(0/90/0)_s及(90/0/90)_s。在MTS NEW810上进行了一系列疲劳损伤及破坏试验。疲劳损伤的行为研究工作包括:以刚度下降为损伤参数对C/AI正交层板进行了降级应力分析,并由此来预计在△S_((?)h)以下,正交层板不会发生疲劳损伤累积。研究了C/Al正交层板在同一应力水平而不同应力范围作用下的疲劳响应,发现试样在疲劳损伤时其刚度下降值相近似,即疲劳破坏的门槛值依赖于所施加的应力水平。依据MMC对各种循环载荷的不同响应,基体的疲劳损伤状态在S-N平面上可分为三种不同的区域:无损伤区,损伤累积区和断裂区。利用扫描电镜及金相显微镜分别对其疲劳断口形貌、基体裂纹进行观察,对该正交层板的疲劳破坏行为进行分析及讨论。结果表明:C/Al正交层板的疲劳断口呈脆断型,其中主承力层(0°铺层)断口平齐,偏轴层(90°铺层)断口平齐最差,层间损伤形式有局部分层、界面连续开裂及复合丝之间基体开裂等三种形式;其疲劳破坏主导因素是层间局部严重损伤及主承力层中复合丝大量断裂由于其疲劳裂纹沿垂直于载荷方向迅速扩展,寻找适中的界面结合强度对改善C/Al层板的疲劳性能有很大影响。

In this study, C/Al cross-plied laminates with two stacking sequence [90/0/90]_s and [0/90/0]_s) fabricated by hot-press method in vacuum are used. A series of experiments 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 predict the stress range below which no fatigue damage acemulates in the laminate. Next, the fatigue response of C/Al cross-plied laminates is developed at constant maximum stress level, but with different values of 鈻砈, 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 presented 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 accumulation region, fraoture 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 flat; ply cracking has three kinds of modes: local interior delamination, matrix cracks and interaced debonding between composites wires and matrixs; the dominated reason of fatigue failure are local ply damage and large scale fiber failure.-, 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 laminates fracture. More work is needed to determine the optimum fiber/matrix interface properties for the composites.