Fracture process of fiber-reinforced concrete notched beams is investigated here. Polypropylene macrosynthetic fibers are utilized for reinforcing concrete specimens, and a high-strength mix design is used to produce strong bonds between the embossed polypropylene fibers and the cementitious matrix of beams. Considering different locations for the notch, this study focuses on bridging mechanism under different conditions using both experimental and numerical approaches. First mode of fracture occurs due to opening of crack faces. This mode of failure is simulated by imposing symmetric boundary conditions on middle-notched beams. Inducing the notch with an offset from the middle, mixed-mode condition is achieved, wherein a combination of opening and sliding of crack surfaces occurs. Plain and reinforced concretes are used to cast each setup of test in order to analyze the bridging effects in different cases. Nonlinear behavior of the cementitious matrix is reproduced numerically using a continuum damage model, and instead of the common phenomenological representation of fibers (e.g., via cohesive crack method), fibers are explicitly modeled in direct numerical simulations. Once the nonlinear response of fibers is obtained, the method can provide valid responses in general loading conditions. This feature distinguishes the proposed approach from the cohesive crack method, wherein the contribution of opening mode, shearing mode, and even tearing mode in three-dimensional cases are required for simulating a general mixed-mode test. Different distributions with random locations and random orientations of fibers are generated in order to assure the objectivity of results. It is found that the prevailing dissipative mechanism within the reinforced specimens is resulted by the sliding resistance of fiber–matrix interfaces. In addition, owing to the high tensile strength of polypropylene fibers, instead of sudden cracking due to fiber rupture, ductile post-peak responses with tremendous amount of energy dissipation are obtained. Low elastic modulus of polypropylene fibers, on the other hand, leads to negligible change in pre-peak responses as the fibers are added to the mixtures.

中文翻译：

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聚丙烯增强高强度混凝土中的纤维桥接：实验和数值调查

本文研究了纤维混凝土缺口梁的断裂过程。聚丙烯粗合成纤维用于增强混凝土试样，高强度混合设计用于在压纹聚丙烯纤维和梁的水泥基体之间产生牢固的粘合。考虑到缺口的不同位置，本研究着重于使用实验和数值方法在不同条件下的桥接机制。第一种断裂模式是由于裂纹面的打开而发生的。这种失效模式是通过对中间缺口梁施加对称边界条件来模拟的。实现了从中间偏移引入凹口的混合模式条件，其中出现裂纹表面的打开和滑动的组合。为了分析不同情况下的架桥效果，每组试验均采用素混凝土和钢筋混凝土浇筑。水泥基体的非线性行为是使用连续损伤模型以数值方式再现的，而不是纤维的常见现象学表示（例如，通过内聚裂纹方法），而是在直接数值模拟中对纤维进行明确建模。一旦获得了纤维的非线性响应，该方法就可以在一般加载条件下提供有效的响应。该特征将所提出的方法与内聚裂纹方法区分开来，其中在模拟一般混合模式测试时需要在三维情况下打开模式、剪切模式甚至撕裂模式的贡献。为保证结果的客观性，产生不同分布的纤维随机位置和随机取向。研究发现，增强试样中的主要耗散机制是由纤维-基体界面的滑动阻力引起的。此外，由于聚丙烯纤维的高拉伸强度，而不是由于纤维断裂而突然开裂，而是获得了具有大量能量耗散的韧性峰后响应。另一方面，聚丙烯纤维的低弹性模量导致在将纤维添加到混合物中时峰前响应的变化可以忽略不计。此外，由于聚丙烯纤维的高拉伸强度，而不是由于纤维断裂而突然开裂，而是获得了具有大量能量耗散的韧性峰后响应。另一方面，聚丙烯纤维的低弹性模量导致在将纤维添加到混合物中时峰前响应的变化可以忽略不计。此外，由于聚丙烯纤维的高拉伸强度，而不是由于纤维断裂而突然开裂，而是获得了具有大量能量耗散的韧性峰后响应。另一方面，聚丙烯纤维的低弹性模量导致在将纤维添加到混合物中时峰前响应的变化可以忽略不计。