Influence of specimens&rsquo|thickness on flexural behavior of ultrahigh toughness cementitious composite
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摘要: 通过不同厚度超高韧性水泥基复合材料(UHTCC)试件的四点弯曲试验, 研究了厚度对其弯曲性能的影响, 并通过理论量纲分析做了进一步解释。结合ASTM C 1609标准, 提出了以单位塑性铰区体积的能量消耗Tv为参数的韧性评价方法。试验结果表明: 不同厚度试件的名义弯曲应力-弯曲应变曲线与裂缝宽度变化曲线几乎重合; 挠度随厚度增大呈反比例下降; 在极限破坏时, 中和轴高度与试件厚度比约为0.88。对于ASTM C 1609标准, 韧性指数随厚度的增大而增大, 而新提出的韧性指数Tv与试件厚度无关。对于拉应变硬化的超高韧性水泥基复合材料, 弯曲强度、韧性性能和裂缝宽度均不存在尺寸效应。建议选用与普通FRC材料韧性及弯曲性能测定相同的试件尺寸(100 mm×100 mm×400 mm)作为标准试件形式。Abstract: Four-point bending tests were performed on ultrahigh toughness cementitious composite(UHTCC)specimens for the purpose of understanding the influence of specimens’ thickness on its flexural behavior. The further explanation on this influence was made through theoretical dimension analysis. In the evaluation of toughness property, a new parameter, defined as energy dissipation per unit volume of plastic hinge region was proposed. The experimental results show that, the nominal flexural strength-flexural strain curves and crack width evolution curves of different thickness specimens are almost identical. Mid-span deflection decreases in an inversely proportional manner with the increase in specimen’s thickness. The ratio of neutral axis depth to specimens’ thickness at ultimate failure nearly keeps a constant value(about 0.88). Toughness index calculated based on ASTM C 1609 standard rises as the specimens’ thickness increases, whereas new proposed toughness index Tv is independent of specimens’ thickness. Therefore, for ultrahigh toughness cementitious composite exhibiting tensile strain-hardening characteristic, flexural strength, toughness capacity and crack width have no size effect. With these findings, standard specimen dimension, i.e., 100 mm×100 mm×400 mm specified for traditional FRC, is suggested for the flexural test of ultrahigh toughness cementitious composite.
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