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.