Failure Behavior Investigation Of The Composite Structures With Discrete Resource Damage

As one of advanced composite materials,carbon fiber reinforced plastic has high specific strength,high specific stiffness,mechanical properties designed,good anti-fatigue properties and other advancement.It is widely used in the aerospace,aviation,navigation,mechanical engineering and civil structures.The composite parts,which were carried less load in the past,have been used in load-carrying constructions more and more.The natural flaw and damage caused in manufacture and usage of carbon reinforced composite structures,such as void,crack,debond,delamination,cutout,and so on,could not be avoid.The discontinuous damages,which casually were caused by accidents,change the mechanical responses of composite structures.Discrete source damage shown as breakthrough cutout can be easily found in the visual check.The load-carrying ability of the composite structures significantly decreases because of discrete source damage.It is very important to find out the mechanical responses of composite structures with discrete source damage.The composite structures with discrete source damage were studied in this paper.Analysis,experiment and numerical calculation have been conducted to investigate the failure behaviors of the composite structures with discrete source damage.1.Based on the analysis of composite structure characteristic,the characterization of discrete source damage in the composite structures is accurately defined.The distinguished feature of failure responses in composite laminate is analysis in detail.The failure behaviors of composite structure with discrete source damage are influenced by parameters such as material properties,geometry styles,loading conditions,damage size and so on.2.Based on progressive damage analysis,the equivalent stiffness method is proposed to be used in the failure analysis of composite structure.The relationship of nominal strain with damage patern needs to be got from the strength calculation process of composite laminate.The equivalent stiffness changing with nominal strain was calculated from the process.Finite element models(FEM)in the equivalent numerical method in were set up to simulate the damage process and to predict the residul intensity of composite structure with discrete source damage.Compared to the traditional progressive damage in layer,the equivalent numerical method got the rational progressive damage process.3.Failure behaviors of composite laminate with in-plane damage under tensile loading have been studied.The symmetrical laminate model with damage was set up to analysis stress under tensile load.The relationship of critical stress with layer parameters is deduced from the equation.Two groups of tensile experiments were designed to study the effect of damage layer thickness and stiffness.The FEM was set up to calculate interlaminar stress distribution.All the results show that critical stress increases with the decreasing of damage layers tensile modulus,continuous layers thickness and interface shear modulus.4.Thermo-mechanical coupling behaviors in notched Carbon/Polyimide composite laminate have been studied.Both un-notched laminates and open-hole laminates were test under tension load at three temperatures.The failure mode,tensile modulus and strength at different temperatures have been determined from the experiments.The results confirmed that the temperature effect on the stiffness mainly by the transverse modulus and shear modulus.The longitudinal modulus is biggest at 200?.The strength of unnotched laminate and the residual intensity of notched laminate all decrease gradually with the increasing of working temperature.A three-dimensional FEM was carried out to study the thermo-mechanical coupling behavior in notched laminate.The in-plane stress and interlaminar stress around the open-hole changing with temperature and tensile loading have been discussed in detail.The temperature has more effect on the transverse stress.Failure analysis was carried out to predict the residual strength of notched laminates at different temperatures.Compared to the experimental data,the numerical results have an excellent agreement.5.Failure behaviors of composite laminate with discrete source damage under tensile loading have been studied.The stress distribution,strain concentration factor and residual tensile intensity of composite laminates with discrete source damage have been got from the mechanics analysis.The specimens were designed to study the mechanical behaviors of composite laminates with discrete source damage.The deformation process,the broken results and the residual intensity of the laminates determined from the experiment.The parameter of damage length and angle effection for the residual intensity was study in the test.Two FEMs were set up with the method of progressive damage in layer and the equivalent numerical method separately.Comparation of failure process and tensile residul intensity in these two methods,the validity of the equivalent numerical method has been further testified.6.Failure behaviors of composite laminate with discrete source damage under compression loading have been studied.The stability and buckling behaviors of the composite laminates with discrete source damage under compression load have been studied.The specimens were designed to study the composite laminates with discrete source damage.The deformation process,the broken results and the residual intensity of the laminates determined from the experiment.The parameter of damage length and angle effection for the residual intensity was considered in the test.The equivalent numerical method in FEM was used to simulate the damage process and to predict the compression residul intensity of composite laminate with discrete source damage.7.Failure behaviors of stiffened composite panel with discrete source damage have been studied.Based on the mechanical properties of stiffened composite panels with discrete source damage,the empirical formula was set up to prediction the residual strength of stiffened composite panels.The tensile and compression experiments were carried out.The structure size,discrete source damage size and through-thickness stitching effection were considered in three groups of experiments.We have got the deformation process and the breakage results,and determined the residual intensity of the stiffened composite laminates with discrete source damage.The equivalent numerical method was used to simulate the failure behaviors and to calculate the residual intensity of the stiffened panels with discrete source damage.