Research On Crack Growth And Progressive Damage Mechanism Of Aerospace Composite Constitution With Holes

In the process of manufacturing,transportation,installation,use and maintenance of composite materials,a lot of damage will inevitably occur inside the structure,which seriously threatens the safety of the structure.As the working environment of composite laminates becomes more and more complex,and the variety of damage forms brings great challenges to the traditional numerical analysis methods.Therefore,it is of great significance to establish a numerical method for damage analysis of composite materials.A progressive damage model considering the influence of temperature is established.The model not only considers the influence of temperature on the constitutive equation,but also considers the influence of temperature on the basic properties of composite materials.The mixed failure criterion is used as the failure criterion,and the appropriate stiffness degradation model is selected as the stiffness reduction scheme after material failure.Considering the highly nonlinear problem of the model,ABAQUS/Explicit solver is selected to solve.The influence of temperature,failure criterion and stiffness degradation model are added to the finite element analysis by programming the VUMAT subroutine.Firstly,the influence of different temperature on the bearing strength of the laminated plate structure under compression load and the riveted lap structure under tensile load is studied.Furthermore,the influence of different temperature and bolt preload on the failure load,stiffness and failure displacement of bolted composite lap structure is studied.The results show that with the increment of temperature,the failure load,stiffness and failure displacement of the model decrease continuously;at the initial stage of the increment of preload,the failure load,stiffness and failure displacement of the model increase,and when the preload exceeds the critical value,they will decrease.A bridging model considering the damage of bridging fiber is established.In order to consider the bridging effect of the fiber,the combined element of the coupling degree of freedom between the rod element and the plane element is established,which avoids the contact problem between the fiber and the plane model.It is assumed that the constitutive relationship of the bridging fiber is bilinear to simulate the damage of the bridging fiber.Firstly,the conventional XFEM model with unilateral crack and central crack is studied,and the stress intensity factor at the crack tip is compared with the exact solution to verify the correctness of the model and program.Then the effects of bridging effect and the damage of bridging fiber on the stress field and displacement field of the model are studied.The influence of the distance between the bridging fibers on the stress intensity factor at the crack tip and the opening displacement of bridging fiber is further studied.The results show that the model can effectively simulate the damage of bridging fiber which has a great influence on stress intensity factor,stress distribution,displacement distribution and bridging fiber opening displacement at the crack tip.The predicted failure mode and displacement load curve of the progressive damage model considering the temperature effect are in good agreement with the test results,which is of great significance to the damage research of composite components in complex environment.The stress intensity factor at the crack tip predicted by the bridging model considering the damage of bridging fiber is in good agreement with the exact solution,which is of great significance to the study of delamination and matrix crack of composite structure.