干湿交替对砂岩断裂特性影响试验研究

周期性的水岩相互作用对岩石的物理力学性能有较大的影响，被认为是影响岩土工程安全稳定性的重要因素之一。以典型的均质青砂岩为试验对象，利用中心裂纹圆盘试件开展了砂岩I~II复合型断裂试验，研究了干湿交替作用对砂岩I~II复合型断裂特性的影响；通过观测干湿交替后砂岩微观结构的变化特征，探讨了干湿交替作用的劣化机理；并结合复合型断裂则对试验结果进行了有效评估。研究表明，砂岩的纯I型，纯II型以及I~II复合型断裂韧度均随着干湿交替次数的增加而逐渐减小；其劣化趋势基本一致，但劣化程度略有不同。当加载角较大或II型分量主导时，干湿交替作用对砂岩断裂韧度的劣化影响更为显著。考虑了T应力影响的广义最大周向应变准则和广义最大周向应力准则都能对试验结果进行很好的预测。在纯II型时，基于广义最大周向应变准则的理论预测值比基于广义最大周向应力准则的理论值更接近试验值。

An Experimental Study on Fracture Characteristic of Sandstone Subjected to Cyclic Wetting and Dryings

When multi-walled carbon nanotubes (MWCNTs) are added into epoxy resin (EP), the randomly distributed MWCNTs will form a complex conductive network. The MWCNTs take different shapes in the EP resin, and they are either curved or straight, separated or intersected with each other, so the MWCNT/EP nanocomposites possess the characteristics of inductance, resistance and capacitance. In this study, an equivalent RLC internal circuit of the MWCNT/EP composite material was proposed, and the response of the 0.6 wt.% MWCNT/EP composite film to electromagnetic signals was tested. It is found that the MWCNT/EP composite film can resonate under the excitation of electromagnetic waves at a specific frequency, and the resonant frequency shifts with the strain of the film. Hence, the feasibility of using MWCNT/EP composite materials to fabricate wireless strain sensors is proven. Based on the experimental and theoretical analysis of the mechanical-electric characteristics of the MWCNT/EP composite film, the idea of developing a tag-type radio frequency strain sensor is proposed in this article.