三维四向C/C复合材料高温氧化环境强度预测

在细观尺度下,基于逐渐损伤理论,建立了一种三维四向C/C复合材料高温强度预测模型。模型考虑了纤维束挤压后的截面形状、单胞的周期性以及纤维束和基体的脱黏等因素,引入考虑温度的三维Hashin失效准则进行单元的失效判定,预测了三维四向C/C复合材料室温和有防氧化保护700 ℃的拉伸强度。为了将模型发展到高温氧化环境,建立了考虑氧化速率的纤维束高温氧化环境力学性能退化模型,结合纤维束和单向板力学性能等价性原理,实现了无防氧化保护下三维四向C/C复合材料700 ℃拉伸强度的预测。研究了切边加工对三维四向复合材料强度的影响,建立了考虑切边宽度的切边三维四向复合材料强度预测模型,预测了有、无防氧化保护切边宽度为18 mm的三维四向C/C复合材料拉伸强度。结果表明:对非切边试验件在室温、有防氧化涂层700 ℃和无防氧化涂层700 ℃的预测误差分别为5.51%、7.20%和7.13%,拉伸过程的应力-应变曲线与试验结果吻合度较好;对切边试验件在室温和有防氧化涂层700 ℃的预测误差分别为0.88%和4.53%。多种类的算例表明预测模型合理、可靠。 

Strength prediction of 3-D four directional C/C composites by high temperature and oxidation environment

Based on progressive damage method, a kind of high temperature strength prediction model of 3-D four directional C/C composites was established on microscopic scale. The section shape of fiber bundle after extrusion, periodicity of unit cell, and fiber bundles debonding were taken into account in the model. The 3-D Hashin failure criterion considering temperature was introduced to determine the elements failure. And then the tensile strength prediction of 3-D four directional C/C composites at room temperature and 700 ℃ under oxidation protection was achieved. In order to introduce the model in high temperature oxidation environment, the mechanical property degradation model of fiber bundles was established in consideration of oxidation rate. The mechanical properties equivalence of fiber bundles and unidirectional plates was proposed. The tensile strength of 3-D four directional C/C composites without oxidation protection was predicted. Trimming process influence on the strength of 3-D four directional composites was investigated, and the strength prediction model of trimming 3-D four directional composites considering trimming width was established. The tensile strength of trimming 3-D four directional C/C composites with and without oxidation protection 18 mm width was predicted. Results show that the prediction errors are 5.51%, 7.20% and 7.13% for non-trimming specimens at room temperature, 700 ℃ with anti-oxidation coating and 700 ℃ without anti-oxidation coating. The stress-strain curve of tensile process for prediction is quite in accord with experiment. The prediction errors are 0.88% and 4.53% for trimming specimens at room temperature, 700 ℃ with anti-oxidation coating. Several kinds of examples show that the prediction model is reasonable and reliable.