Research On Load-carrying Property And Failure Behavior For Joint Structure Of C/C Composite

The near space vehicle serving in harsh environment possesses complex framework,and the materials used for that require not only sufficient mechanical property but also thermal protective performance.The woven C/C composite just meets these requirements and is one of the alternative materials of the near space vehicle.In addition,on account of different components and parts playing various roles,the C/C composite with different reinforcement architectures and the joint structures with diverse connection methods including mechanical joint,bonded joint and bonded-bolted hybrid joint can be selected in the near space vehicle.Therefore,the investigation referred to the effects of environment temperature,material woven form,connection method,as well as geometrical parameter on load-carrying property of the C/C composite joint structure exhibits significant engineering application and scientific reference value.In view of the difficulty in acquiring some material property parameters,in current research,the multiscale finite element analysis approach was first adopted to acquire the material performance for a type of two-dimension satin and two types of three-dimensional orthogonal woven C/C composite,and the corresponding calculation results were compared with the given data,validating the computational reliability and providing a foundation for the simulation analysis of mechanical property for the C/C composite joint structu res.Then,on the grounds of relevant test standard,experiments on the load-carrying performance and failure behavior of the two-dimension satin and three-dimensional orthogonal woven C/C composite joint structures subjected to double shear were performed,incorporating the acoustic emission monitoring technology to reveal material damage evolution.Meanwhile,taking the material properties obtained from the multiscale numerical calculation as input,the simulation analysis on the failure behaviors under double shear were carried out to obtain the influence of geometrical parameters on ultimate load and failure mode of the C/C composite joint structures.In order to explore the bearing failure mode,which is practical in engineering,the off-axis angle sensitivity analysis of pin-bearing strength for three-dimensional orthogonal woven C/C composite was presented via experimental and numerical methods,by which the damage evolution and deformation of the constituent materials in C/C composite around the hole edge were exposed.Subsequently,for the purpose of evaluating the mechanical property of joint structures with different connection methods at elevated temperature,the experiments and corresponding numerical modelling were presented to characterize the failure behaviors of C/C composite bonded and bonded-bolted hybrid joint structures subjected to shearing loads under 400℃,600℃ and 800℃.The failure modes and material damage forms of the specimens were acquired,and reliability of the predictions was validated by the experimental results.The variations of ultimate load for the bonded and bonded-bolted hybrid joint structures with environment temperature,overlapping length and diameter of bolt were obtained.Besides,with the intention of assessing the mechanical property of joint structures under different loading forms,the failure behaviors of C/C composite joint structures with metallic fastener under room temperature,600℃ and 800℃subjected to out-of-plane loads were investigated via experiments and numerical simulation,while the observations for failure modes of the specimens and the effects of temperature on ultimate load were presented.Meanwhile,the failure behaviors of C/C all-composite mechanical joint structures under room temperature and 1100℃ subjected to out-of-plane loads were demonstrated,exhibiting the reason for the distinction of load-displacement curves and failure modes for the specimens at each temperature and main material damage forms during the failure process.