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为了研究大型试件的裂缝扩展过程,本文采用光弹性贴片法对平面尺寸分别为3.6×3.0m,3.0×2.5m,2.4×2.0m,1.8×1.5m,1.2×1.0m,0.6×0.5m的大型紧凑拉伸试件,预制裂缝的起裂。确定扩展直至失稳破坏的全过程进行了系统的研究,并用录像机拍摄了光弹性贴片所显示的裂缝扩展的全过程,得到了混凝土裂缝在不同荷载阶段从起裂、稳定扩展直到失稳破坏整个全过程的完整而直观的观察结果。结果发现,在试件高度达到1m以上的实验范围内,失稳破坏前裂缝稳定扩展长度几乎是一个稳定的常数值,这个值约为200mm,它与试件尺寸初始缝长α_o无关。同时发现,宏观裂缝的起裂与初始缝长α_o有关,初始缝长α_o愈大,裂缝起裂愈早,α_o愈小,裂缝起裂愈晚。该现象对于了解像高混凝土坝那样大型结构裂缝扩展有着重要的意义。
In order to study the crack propagation process of large specimens, the photoelasticity of the specimens was used to measure the plane dimensions of 3.6 × 3.0m, 3.0 × 2.5m, 2.4 × 2.0m, 1.8 × 1.5m, 1.2 × 1.0m, 0.6 × 0.5 m large compact tensile specimens, prefabricated crack initiation. The whole process of determining the extension until the failure is studied systematically. The whole process of crack growth by the photoelastic film was photographed by VCR, and the crack propagation was obtained at different load stages from initiation of fracture to stability failure The entire process of complete and intuitive observation. The results show that the stable crack propagation length before instability failure is almost a constant value within the experimental range of 1m above the specimen height. This value is about 200mm, which is independent of the initial seam length α_o. At the same time, it is found that the initiation of macroscopic fracture is related to the initial fracture length α_o. The larger the initial fracture length α_o, the earlier fracture initiation, the smaller α_o, and the later fracture initiation. This phenomenon is of great significance for understanding the crack propagation in large structures like high concrete dams.