This paper investigates the high cycle tensile fatigue behavior of steel rebar reinforced − UHPFRC elements, at a fatigue load ratio, i.e., R-ratio of 0.3, representative for structural applications. Prior to testing, magnetoscopy is conducted on each specimen to determine the local fiber orientation and volume inside UHPFRC. During testing, global specimen deformation is recorded by displacement transducers; specimen surface is monitored by digital image correlation; and strain along rebars inside the specimen is measured by fiber-optic sensors. Based on the test results, an S-N diagram with a high regression coefficient is obtained. Hereby, the normalized fatigue force S is defined as the ratio between the maximum fatigue force and the estimated specimen ultimate tensile resistance. The fatigue endurance limit is identified as being about S = 0.40. It is found that fatigue deformation of the specimen mainly occurs in the zones with low fiber orientation coefficient μ0,y of UHPFRC (μ0,y decreases when average angle between fiber axis and principle tensile direction changes from 0° to 90°), where the strain along steel rebars also have their higher value and increase rates during fatigue testing. The lowest UHPFRC fiber orientation determines the locus of crack localization and of fatigue fracture of steel rebars, thus final fracture of the elements.

中文翻译：

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钢筋增强的高周拉伸疲劳行为 - 高 R 比下的 UHPFRC


本文研究了钢筋加固 − UHPFRC 元件在疲劳载荷比（即 R 比为 0.3）下的高周拉伸疲劳行为，具有结构应用的代表性。在测试之前，对每个样本进行磁镜检查，以确定 UHPFRC 内部的局部纤维取向和体积。在测试过程中，位移传感器记录整体试样变形;通过数字图像相关性监测标本表面;通过光纤传感器测量试样内部沿钢筋的应变。根据测试结果，得到了具有高回归系数的 S-N 图。因此，归一化疲劳力 S 定义为最大疲劳力与估计的试样极限拉伸阻力之间的比率。疲劳耐久极限被确定为大约 S = 0.40。研究发现，试件的疲劳变形主要发生在UHPFRC纤维取向系数μ0，y低的区域（当纤维轴线与主拉伸方向的平均夹角从0°变为90°时，μ0，y减小），其中沿钢筋的应变在疲劳试验中也有其较高的值和增加率。最低的 UHPFRC 纤维取向决定了钢筋的裂纹定位和疲劳断裂的轨迹，从而决定了元件的最终断裂。