Study On Mechanical Properties Of Automated Fiber Placement Laminates With Defects

Composite materials are widely used in the aerospace industry.The development of Automatic Fiber Placement(AFP)technology makes the manufacture of composite materials more efficient.In the process of manufacturing composite materials,gaps,overlaps,half gap/overlaps and twisted tow defects are formed,which lead to the mechanical properties of the final product uncertain.In order to reduce the dependence of composite structural failure analysis on experiments and improve the finite element modeling and analysis method of AFP composites with defects,the effects of defects on the mechanical properties of the AFP composite laminates were studied by numerical simulation and experimental verification.In this paper,the finite element model of composite laminates with gap and overlap defects under tensile,compression and shear loading conditions is established.In the numerical simulation,based on the Hashin criterion and the Ye criterion,the six failure modes of the elements in the model are judged by the user subroutine USDFLD,and the load carrying capacity analysis as well as the progressive failure analysis of the laminated plates are carried out,and the comparison of the finite element results is included.The effect of defects on the ultimate load carrying capacity of composite laminates was determined by comparing the ultimate load carrying capacity of the model containing gap defects and the model containing overlap defects with the perfect composite model in the finite element results.Comparing the stress distribution in the laminates,the characteristics of the stress distribution in the laminates with different defects are analyzed.The failure modes and distributions of the failure elements in the laminate ply are compared and analyzed,and the influence of different defect types on the element failure in the laminate ply is studied.The main failure mode of the laminate is judged by the change of the number of failures element in the laminate with the change of the analysis time step,and the main control factor of the failure of the laminate is judged by the change of the element failure rate in the laminate with the time step.By comparing the finite element results with the experimental results,the rationality and effectiveness of the finite element results are verified.In the experiment,AFP composite laminates with gap,overlap,half gap/overlap and twisted tow defects were studied.The effects of tensile,compression and shear conditions on the mechanical properties of the laminate were analyzed.The ultimate load carrying capacity,main failure mode and location of failure occurred in the AFP composite laminates with defects were analyzed by experimental results.Numerical simulations and experimental studies have shown that the effect of defects on the mechanical load bearing capacity of composite laminates is less than 12%.The effect of defects on the failure mode of the elements in the layup in the composite model will change the distribution of element failure and the number of failures of the element,but the presence of defects will not affect the main failure mode of the laminate.