Loading Capacity Analysis Of Automatic Fiber Placement Laminates Considering Manufacturing Defects

The emergence and development of automatic fiber placement technology not only greatly improves the production efficiency and manufacturing level of composite materials,but also realized changing the direction of fiber when placing fibers,thus makes designers possible to design a composites laminate part with curving fiber,which greatly increasing the degree of freedom in design.This new technology is expected to further enhance the bearing capacity of laminate on the basis of straight fiber placement,so it is very important to study the bearing capacity of curved fiber laying laminates.Based on Hashin criterion and Camaho degradation model,a USDFLD subroutine for determining elements failure and mechanic performance degradation was developed.The progressive failure process of materials was analyzed and the distribution of failure in model was predicted.The difference of load-carrying capacity between straight and curved fiber placed laminates was studied.Each element in model was defined in different layer angle by using the Python script of commercial finite element software ABAQUS.Two kinds of fiber orthogonal straight fiber placed laminate and three kinds of fiber symmetrical curve fiber placed laminate was considered in study.It is found that the laminates with higher buckling loads have higher average stiffness and ultimate load,whether for straight or curve fiber placement.It is proved that the buckling resistance of the laminates can be improved by choosing a reasonable way to place fiber.A method for ascertaining if a point in plane is in the manufacturing defects area was established,and complied this method into Python function to build model with defects.According to different tow cutting schemes,the finite element models of laminates with completed gap,completed overlap and no cutting scheme are established respectively.The effects of these manufacturing defects on the bearing capacity of laminates are analyzed by comparing the three kinds of laminates with the ideal model.It is found that the bearing capacity of laminates with gap cutting scheme is lower than that of the ideal design,and the failure area of the laminates with overlapping cutting scheme is obviously different from that of the ideal design.The bearing capacity and failure area of the laminates with overlapping cutting scheme are the closest to that of the ideal design.In order to reduce the influence of different laying schemes on the delamination,a pair of straight and curve fiber placement with similar load-carrying capacity and failure area were selected according to the conclusions in the first section of Chapter IV,in the study of delamination expansion.The results show that the delamination propagation of curved fiber placed laminates is greatly inhibited compared with straight fiber placed laminates,which proves that the curved fiber placement scheme can well inhibit the delamination of laminates.