The size effect of the strength for SiC/SiC composites must be considered when measuring the strength of this material using a specimen. However, the size effect and its micro-mechanisms are still unclear at present. The size effect is studied using minicomposites through experimental investigation and theoretical analysis. The strengths of specimens with different lengths are measured and it is found that the size effect of the strength for SiC/SiC composites is not remarkable. To explain this phenomenon, the distribution of fiber flaws and the stress distribution of broken fibers are analyzed. It is found that owing to the fiber/matrix interfacial shear stress, broken fibers still have the load carrying capacity and then the effected region of each fiber flaw is limited. This mechanism decreases the sensitivity of SiC/SiC composites to the size effect. A fracture model of SiC/SiC composites is developed according to this mechanism. The predicted strength, stress–strain response and fracture surface match well with the experimental results.

在使用试样测量该材料的强度时，必须考虑 SiC/SiC 复合材料强度的尺寸效应。然而，尺寸效应及其微观机制目前尚不清楚。通过实验研究和理论分析，使用微型复合材料研究了尺寸效应。对不同长度试样的强度进行了测量，发现强度对 SiC/SiC 复合材料的尺寸效应不显着。为了解释这种现象，分析了纤维缺陷的分布和断裂纤维的应力分布。发现由于纤维/基体界面剪切应力的作用，断裂的纤维仍然具有承载能力，从而限制了每个纤维缺陷的影响区域。这种机制降低了 SiC/SiC 复合材料对尺寸效应的敏感性。根据该机理建立了 SiC/SiC 复合材料的断裂模型。预测的强度、应力应变响应和断裂面与实验结果非常吻合。