Papers by Author: Gui Qiong Jiao

Abstract: 2D C/SiC ceramic matrix composite (CMC) displays significant damage characteristic coupled with inelastic strain under tension and shear loads, which should be considered in the constitutive model. In this study, a continuum damage mechanics (CDM) model was proposed for this material, in which the process degradation of the material property was described by introducing a set of scalar damage variables, and the damage-coupling effect was also considered. Meanwhile, isotropic hardening theory was applied to form the evolution rule of inelastic strains. The model was then implemented into the UMAT in ABAQUS software and validated by comparison between the simulation and experiment results.

Abstract: Base on the micro-structure of self-healing 2.5D-C/SiC composite, a new mechanical model was established, By changing the tensile strength of matrix and volume fraction of boron carbide, the tensile behavior of self-healing 2.5D-C/SiC composite in weft direction was studied. The result shows that the increase of volume fraction of boron carbide has little influence on the tensile behavior in weft direction, and the influence is primarily due to the change of the tensile strength of matrix.

Abstract: Based on the analysis of the woven structure, the compressive fracture process and strength of a 2.5D-C/SiC ceramic matrix composite were investigated by the classical laminate theory. The porous composite was regarded as a spatial layered structure, and the two classes of the warps and wefts in the 2.5D-C/SiC composite were treated as the corresponding layers. The strengths of the C/SiC bundle and C/SiC lamina were determined, and the compression strength for the composite was calculated by progressive fracture method of the layers and elastic degradation. The failure mechanisms and the angles of the compressive fracture surfaces coincided with the experimental result well. It was demonstrated that the strength predictive method of the classical laminate theory can be applied to the analysis of 2.5D-C/SiC composite.

Abstract: The aim of this article was to propose a macroscopic damage model, which describes the nonlinear behavior observed on woven C/SiC ceramic matrix composites. The model was built within a thermodynamic framework with internal variables. The anisotropic damage evolution processes of the material were described by nonlinear damage isotropic and kinematic hardening functions in this model. The anisotropic damage and damage coupling were considered with a damage yield function including anisotropic coefficients. Using the principle of energy equivalence, the damage variables were defined by the unloading modulus and initial modulus. The damage variable and the irrecoverable strain induced by micro-crack propagation were deduced by thermodynamics. The constants of constitutive model were identified and the damage evolution processes under tensile and shear loading. Uniaxial tension and shear tests had been used to valid the constitutive model to C/SiC composites.

Abstract: An anisotropic damage constitutive model is developed to describe the damage behavior of C/SiC composites. Different kinematic and isotropic hardening functions were employed in damage yield function to describe accurately the damage nonlinear hardening. The damage variable is defined by the principle of energy equivalence. The degradation of stiffness and the unrecoverable deformation induced by micro-crack propagation were considered in this model. The constants of constitutive model are identified and the damage evolution processes under tensile and shear loading. Uniaxial tension and shear tests have been used to valid the constitutive model to C/SiC composites.

Abstract: The various damage mechanisms in 3D-C/SiC composites are identified using acoustic emission (AE) signal parameters, and the Felicity effect is studied on different unloading stress. As a result, the damage mechanisms in 3D-C/SiC composites can be identified successfully by the amplitude, average frequency and relative energy, and there are several damage modes together during uniaxial tensile process. The Kaiser effect is almost absent and the Felicity ratio fluctuates at 0.95 on lower stress stage and drops when the relative stress is above 65%.

Abstract: The tensile damage evolution of 2D plain woven C/SiC composites strengthened with 1K and 3K carbon fiber bundles and microstructure’s influence on material’s damage evolution were investigated using the Acoustic Emission technology (AE) and failure observation. Experimental results reveal that damage evolution of these two kinds of composites is a gradual procedure and this procedure consists of three phases. There is no damage during the first phase. During the second phase, the damage, mainly consisting of matrix microcrack cracking, interface debonding of fiber and joining of microcrack, random takes place in the whole area of specimen. During the third damage phase, the damage, mainly consisting of macrocrack cracking, fibers breaking and fibers pulling out, mainly takes place in the local failure area of specimen. Because the microstructures of composites with 1K and 3K carbon fiber bundles are different, their damage mechanisms are different. Composite strengthened with 1K carbon fiber bundles get in second phase at 90% failure stress, and their main energy dissipation occurred during the second damage phase. While Composite strengthened with 3K carbon fiber bundles get in second phase at 80% failure stress, and their main energy dissipation occurred during the third damage phase.

Abstract: Mechanical tests have been conducted to understand compressive behavior of a plain weave C/SiC composite, especially to investigate the failure mechanism. The stress-strain curves of this composite show linear feature in compression. The specimens fail along a flat plane 13°~15° to the weave plane, running across four typical regions in the bulk: weft bundle, warp/weft interface, warp bundle, and inter-ply. According to the observed fracture route, four basic failure modes are schematically presented. Cracks form and develop in these areas along fiber/matrix interphase or within matrix, depending on the strength competition between interphase and matrix. The fracture mechanism reveals dependence of compress strength on matrix abundance between and within bundles. Based on the failure modes new method for compress strength prediction can be further investigated.

Abstract: Stitched laminates is a low-cost structure panels with carbon fiber face sheets, and through-the-thickness Kevlar stitching. Through-the thickness stitching is proposed to increase the interlaminar strength and damage tolerance of composite laminates. Tensile and shear experiment of stitched laminates at room temperature and in hygrothermal environment was carried out according to corresponding national standards. Experiment results indicate that the tensile and shear modulus and strength were much reduced by the stitching, especially in hygrothermal environment. Micrographs of fracture appearance showed that the exist of resin-rich area is the source of crack both in normal room temperature environment and hygrothermal environment. It is concluded that hygrothermal environment and initial crack in resin-rich area were prime reason for performance lost of stitched laminates.

Abstract: Tensile tests of two-dimensionally braided C/SiC composites and three-dimensionally braided C/SiC composites had been carried out at room temperature. Some specimens had been unloaded during experiments. Acoustic Emission signals also had been collected during experiments. The following conclusions were arrived. The stress-strain curves of these two materials were of nonlinear characters, and there were no obvious linear segments on those curves. Failure characters of these two materials were different: There appeared ply pull-out for 2D braided C/SiC specimens and there appeared zigzag shape for 3D braided C/SiC specimens. Stress-strain curves of loading-unloading tests and Acoustic Emission signals of those two materials showed damage evaluation during tests. There were different AE counts and AE energy characters between two materials.