预裂纹混凝土拉压疲劳荷载下裂纹扩展速率

Crack Growth Rate of Concrete with Pre-cracks in Tension-Compression Cyclic Fatigue Load

为研究C50混凝土预裂纹在拉压循环荷载下的扩展速率，进行了应力比为-1，应力幅值为0.20-1.30MPa的拉压疲劳试验.针对混凝土在拉压疲劳荷载下裂纹扩展时其长度不易确定的问题，提出潜行等效裂纹长度假说对试验结果进行分析.结果表明：混凝土裂纹第1阶段起始扩展区和第2阶段稳定扩展区比较明显，第3阶段加速扩展区不明显，在稳定扩展区后期，裂纹扩展曲线的斜率并不像金属那样快速增加，而是增幅趋缓，在稳定扩展阶段后期无征兆突然破坏，与混凝土脆性断裂的特性相一致.利用最小二乘法拟合得到裂纹扩展速率Pairs公式中的参数C，m，在考虑50%，90%，99%的存活率时，C可在0.31-0.45，0.76-0.99，1.22-1.98中取值，m取值范围对存活率大小的敏感性较低，可在3.0-4.8之间取值.

A tension compression cycle fatigue test was performed in order to study the crack growth rate of C50 concrete with pre cracks in cyclic loading.The stress ratio was -1 and the amplitude was 0.20-1.30MPa. The concrete crack length is difficult to determine when the crack is propagating in tension compression fatigue load, so the hypothesis of hidden equivalent crack length is put forward to analyze the experimental data. Compared with the 3 stage diagram of common metal crack propagation, the initial propagation at the first stage and the second stage of stable propagation are quite notable but at the third stage of accelerated expansion is not notable. At the late stage of stable propagation, the slope of fatigue crack propagation curve does not increase as fast as that for metal materials but decelerates obviously and the concrete fails suddenly without indication. It is consistent with the brittle fracture of concrete. The important parameters of Pairs formula, C and m, are fit by the least squares. When the survival rate is 50%, 90% or 99%, C value range is 0.31-0.45, 0.76-0.99, 1.22-1.98 and m value range with low survival rate sensitivity is 3.0-4.8.