The effects of thermal treatments on the fatigue crack growth of Beishan granite: an in situ observation study
The effects of thermal treatments on the fatigue crack growth of Beishan granite: an in situ observation study
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DOI：
10.1007/s10064-020-01966-w
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发表时间：
2020-09
影响因子：
4.2
通讯作者：
Jintao Wang;J. Zuo;Yun-jiang Sun;Jinhao Wen
中科院分区：
文献类型：
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作者：
Jintao Wang;J. Zuo;Yun-jiang Sun;Jinhao Wen
在一些与温度有关的岩石工程项目中，岩石受到循环荷载的作用。深入了解温度对岩石疲劳机理的影响具有重要的工程意义。利用扫描电镜对北山花岗岩在50-600 °C热处理后的疲劳裂纹行为进行了原位观察。记录了在循环载荷下的连续开裂过程。结果表明，热处理导致热开裂，以及矿物晶界强度的削弱，这占不同的循环载荷下的裂纹行为。结果表明，随着温度的升高，裂纹的扩展方式逐渐由新裂纹的向前扩展转变为原有裂纹的继续张开。在低温条件下（50-150 °C），疲劳裂纹在缺口根部萌生，然后沿与最大拉应力近似垂直的方向沿着扩展，受温度条件影响较小。在中温（200-300 °C）条件下，疲劳裂纹以裂纹桥接的方式扩展，裂纹桥接的方式是由矿物颗粒脱粘形成的沿晶裂纹和原有裂纹之间的裂纹。在高温（400-600 °C）下，裂纹逐渐张开，几乎没有新裂纹形成;在50-250 °C下，裂纹扩展速率符合Hartman-Schijve方程。在这项研究中，所观察到的变化的H-S方程中的参数的微结构特性的依赖关系进行了讨论。随着裂纹扩展速率对ΔK敏感性的增加，Δ K的降低沿着，这是由于微结构的变化，而微结构的变化可以用线裂纹密度来定量表征。
In some temperature-related rock engineering projects, rocks are subjected to cyclic loading. A deep understanding of the influences of temperatures on rock fatigue mechanisms is of great engineering significance. In this research, in situ observations of the fatigue crack behaviors of Beishan granite after 50–600 °C thermal treatments were conducted using a scanning electron microscope equipped with a loading system. The continuous cracking processes under cyclic loading were recorded. It was found that the thermal treatments resulted in thermal cracking, as well as weakening of the mineral grain boundary strength, which accounted for different crack behaviors under cyclic loading. The observations revealed that as the temperature elevated, the cracking patterns had gradually changed from the forward propagation of new cracks to the continuous opening of the pre-existing cracks. In the low temperature cases (50–150 °C), it was found that the fatigue cracks were initiated at the notch roots, then propagated along the direction which was approximately perpendicular to the maximum tensile stress, which was less affected by the temperature conditions. In regard to the intermediate temperature cases (200–300 °C), it was observed that the fatigue cracks propagated in the manner of crack bridging between the pre-existing cracks and the intergranular cracks which had formed by mineral grain decohesion. In high-temperature cases (400–600 °C), the pre-existing cracks were observed to gradually open and few newly formed cracks were found. In addition, in the 50–250 °C cases, the crack growth rates were in good agreement with the variant Hartman–Schijve equation. In this study, the observed dependence of the parameters in the variant H-S equation on the micro-structure characteristics was discussed. The decreasing threshold of ΔKfor the crack initiation, along with the increasing sensibility of the crack growth rate to ΔK, was attributed to the changes in the micro-structure which could be quantitatively characterized by the linear crack densities.