Damage Analysis Methods Of Advanced Composite Material And Applications

Advanced composite materials have been widely used in the field of aerospace due to their excellent mechanical properties.Damage and fatigue life analysis have always been the key and difficult points of the research on composite materials.Accoding to the damage and fatigue analysis methods,a combination of experiments and numerical studies was ciarred out.The main contends and conclusions are listed as follows:(1)For intralaminar damage of composite materials,a three-dimensional constitutive model including stress analysis,damage initiation criteria and damage evolution criteria was established based on the continuum damage mechanics method.A nonlinear shear model that contains only one parameter was used to characterize the nonlinear shear behaviors.The maximum strain failure criteria and physically based Puck criteria were employed to indicate the initiation of fiber damage and matrix damage,respectively.This paper also combined the Golden Section Search algorithm with a curve interpolation technique called Inverse Parabolic Interpolation to improve the efficiency and precision of the fracture angle search methods.The bilinear damage evolution laws based on the viewpoint of energy was built.The open-hole tensile tests and the bearing tests of pinned joints were combine to validate the accuracy of the proposed model.(2)Based on the developed intralaminar continuum damage mechanics model.The maximum stress criteria and Puck criteria were extended to the fatigue criteria.Then a progressive fatigue damage model was established with a combination of the material properties gradual degradation model,the normalized fatigue life model and the fatigue damage cumulative model.The proposed fatigue damage model was used to predict the fatigue life of composite lamiantes and pinned joints,and then the model was validated by fatigue tests.The experiments and numerical results were analysed to study the the fatigue evolution and failure mechanism of spciemens under fatigue loadings.(3)The constitutive models of interlaminar static and fatigue delamination were built.As for static delaimination model,the bilinear cohesive constitutive mode was adopted.The quadratic stress criterion was used to predict the initiation of delamination damage,and the B-K law was employed to characterize the damage evolution.Classic numerical cases(DCB,ENF and MMB)were selected for validating the built static model.The results showed that the static model can predict the initiation and evolution of mixed delamination damage.The static tensile tests on single-lapped adhesively-bonded joints were conducted to study the deformation,damage evolution and failure mechanism comparing with numerical results.Based on the static constitutive model of cohesive element,the fatigue delamination model was proposed by combing the fatigue crack propagation model of fracture mechanics and the damage mechanics.DCB and 4ENF numerical cases were chosen to verify the interlaminar fatigue delamiantion model.The fatigue tests on single-lapped adhesively-bonded joints were carried out,and a numerical model was established.The experimental results were in good agreement with the numerical results,which showed that the model established in this paper could effectively predict the interlaminar fatigue damage propagation behavior.(4)The detailed experimental and numerical studies were conducted on low-velocity impact and CAI issues.The impact response,impact damage and residual compression strength were systematically studied.Infrared thermography was used to study the the distribution laws of thermal filed under low-velocity impact and CAI loadings.DIC,load-displacement curves and strain-load curves were combined to give a deep insight of the failure mechanism of thin and thick compsote lamiantes under compressive loading.The finite element model,which accounts for both intralaminar(matrix and fiber damage)and interlaminar(delamination)damage,was built to achieve the full analysis of impact damage and CAI without major simplifications and idealizations of damage.The numerical results matched well with the experimental results,which prove the accucy of the damage model.(5)The fatigue tests and numerical simulations were conducted on composite lamiantes with initial impact damage.The damage evolution was monitored online by infrared thermpgraphy,and the delamination damage evolution characteristics and failure mechanism were studied by ultrasonic c-scan.During fatigue process,the stiffness of the laminates was measured,and the evolution process of fatigue damage of the laminated plate with impact damage was characterized from the viewpoint of stiffness degradation.A three dimensional finite element model was built,and the damage sate after impact was selected as the initial state.Then use the intralaminar fatigue damage model and interlaminar fatigue delamination damage model proposed in this paper to study the damage evolution and failure mechanism of laminated laminates with initial impact damage comparing with experimental results.