Numerical Simulation Of Delamination In Composite Laminates Subjected To Fatigue Loading

Composite laminates have been widely used in various engineering fields due to their excellent mechanical properties,such as high specific strength,high specific stiffness,designability and corrosion resistance.In composite laminate structures,delamination is a common failure mode in structural engineering due to the relatively weak interlayer interface strength.In addition,composite structural delamination tests often require a lot of time and resources,so the development of reliable and efficient finite element models is important to evaluate the mechanical behavior of composite structural delamination.Since the delamination extension of composite laminates involves multiple complex damage mechanisms,the accurate simulation of their mechanical response under fatigue loading remains a great challenge.The purpose and focus of this thesis is to establish a cohesive zone model based on continuum damage mechanics to simulate the delamination of composite laminates under quasi-static and fatigue loads,respectively.First,the cohesive zone model under quasi-static load is analyzed.Based on the bilinear traction-separation law and combined with the damage criterion and geometric relation,the constitutive of the mixed-mode cohesive zone model is derived.Subsequently,the existing fatigue cohesive zone models are compared and analyzed based on the different fatigue damage rate calculation strategies.Next,the method of numerical application of cohesive zone model in the simulation of delamination damage of composite laminates is analyzed.The VUMAT subroutine was compiled based on Fortran language and Abaqus software platform for secondary development to define the constitutive of cohesion units.Then,based on the bilinear cohesive zone model,the VUMAT subroutine was used to simulate the quasi-static delamination of composite laminates under mode I,mdoe II and mixed-mode loading conditions.The effects of the initial stiffness as well as the mesh density on the simulation results are discussed by comparing and analyzing the simulation results with different initial stiffness and cohesive cell sizes.The validity of the proposed subroutine model is verified by comparing the simulation results with experimental data under different mixed-mode ratios.Finally,an improved fatigue damage evolution algorithm is proposed based on the Paris law.The algorithm does not require additional parameter fitting and cohesive zone length estimation,and does not require crack tip tracking algorithm.Based on this algorithm,the fatigue delamination of composite laminates under mode I and mdoe II loading conditions is simulated by using the VUMAT subroutine,and the mesh sensitivity and simulation errors are analyzed.The results show that the fatigue damage rate curves of the algorithm under both loading forms are in good agreement with the Paris law,which verifies the validity of the proposed fatigue damage evolution algorithm model.