| Composite materials are widely used in aerospace aircraft structure due to its advantages of high specific strength,high specific stiffness and designable property et al..But composite laminate is vulnerable to damages in the process of production and application,especially damages(fiber fracture,matrix cracking and delamination)caused by low speed impact.These damages can lead to the sharp decline of the load bearing capacity and service life,thus seriously influence the safety of the structure.Therefore,study on fatigue damage propagation in low-velocity impacted composite laminate is helpful to elevate the safety of structure and cut down maintenance cost of aircraft.On this thesis,the main contents are as follow:(1)Low-velocity impaction is conducted to a carbon fiber/epoxy matrix composite laminate.Then the static compression and compression-compression fatigue tests are carried out.The fatigue damage propagations after 15 J and 25 J energies impact are measured by using ultrasonic C-scanner.The relations between the number of fatigue circles and damage area as well as compressive stiffness of the impacted laminate are obtained.(2)The intra-laminar and inter-laminar fatigue damage and final failure models of composite laminates are developed.The proposed models can not only predict evolutions of various fatigue damages in composite laminates,but also characterize the mechanisms of these damages.(3)The damage models are implemented in platform ABAQUS through user-defined material subroutines VUMAT and UMAT,and parametric modeling is developed by using Python language.In order to decrease computing cost,a brick finite element which includes multiple-plies is suggested.(4)The simulations of low-velocity impact of a composite and the consequent fatigue damage evolution are conducted by using the parameterized model.The comparisons of predicted and experimental compression-compression fatigue damage propagations for the composite laminates experienced 15 J and 25 J energy impact are conducted.The proposed models and the second developed software are validated.Based on the analysis of the test data and the results of finite element simulation,the relations between damage propagation and cycle of fatigue load are obtained for this composite laminate. |
