Abstract: With the widespread application of carbon fiber, glass fiber and natural fiber‑reinforced composites in aerospace, civil engineering and high‑end equipment manufacturing, fracture and failure issues induced by surface defects have received increasing attention. These composites typically exhibit quasi‑brittle fracture characteristics, with crack propagation behavior influenced by material heterogeneity, anisotropy and size effects. In engineering practice, the fracture performance of large‑scale components is often evaluated based on small‑scale specimen tests; however, conventional fracture mechanics methods cannot effectively eliminate the influence of size effects on fracture parameter identification, thereby limiting the applicability of experimental results to engineering structures. Therefore, developing a theoretical model capable of stably predicting intrinsic fracture parameters from small‑scale specimens holds significant engineering relevance.The boundary effect model provides an effective theoretical framework to address the size effect problem in quasi‑brittle material fracture. The model posits that the essence of size effects originates from the interaction between the fracture process zone at the crack tip and the specimen boundary conditions, and it quantitatively characterizes this effect by introducing the equivalent crack \(a_\text{e}\). Building on this concept, the boundary effect model further incorporates the characteristic composite unit \(C_\text{ch}\), introducing material microstructural features into the fracture analysis. This approach allows a unified description of crack propagation behavior and actual failure modes while reducing computational complexity. Within this framework, the fracture behavior of composites can be classified into three regimes: strength‑controlled, toughness‑controlled and transitional ones. This classification facilitates the elucidation of the intrinsic relationship between crack propagation mechanisms and the governing fracture parameters.Based on the boundary effect model framework, this review systematically summarizes its application progress in the fracture analysis of quasi‑brittle composites, including carbon fiber, glass fiber, bamboo fiber and ceramic‑reinforced materials. The focus is placed on its application to predicting crack propagation behavior, ultimate load capacity and damage modes. Relevant studies indicate that the model can stably identify intrinsic tensile strength \(f_\text{t}\) and fracture toughness \(K_\text{IC}\) using small‑scale three‑point bending test data, effectively mitigating the influence of size effects on fracture parameter determination and significantly improving prediction accuracy. By introducing the characteristic composite unit \(C_\text{ch}\), the boundary effect model demonstrates good applicability and engineering potential for quantitatively describing fracture behavior in multiphase composites, providing important theoretical support for the safe design, damage assessment and reliability evaluation of composite structures.

Key words: boundary effect model, composite materials, fracture toughness, tensile strength, size effect

摘要： 随着碳纤维、玻璃纤维等复合材料在大型轻量化结构中的广泛应用,其表面缺陷引发的尺寸效应断裂问题日益突出,使得小尺寸试样的数据难以直接外推至大构件的性能预测。 而边界效应模型可通过引入等效裂纹 ae 和特征复合单元 Cch ,将裂纹尖端断裂过程区与试样边界的相互作用纳入分析框架,从而解决该问题。 首先阐述了边界效应模型的理论基础与断裂准则,随后系统总结了其在碳纤维、玻璃纤维、竹基纤维及陶瓷等复合材料中对裂纹扩展、极限承载力及损伤模式预测的研究进展。 结果表明,该模型能基于小尺寸试样试验稳定获取材料的本征抗拉强度 ft 和断裂韧性 KIC ,有效克服尺寸效应并提升预测精度,可为复合材料构件的安全设计与可靠性评估提供重要理论依据。

关键词: 边界效应模型, 复合材料, 断裂韧性, 抗拉强度, 尺寸效应