This work aims to analyse the fracture behaviour of rocks with U-shaped notches subjected to mode I loading and to different temperature conditions. To this end, an energy-based approach is used called the Strain Energy Density (SED) criterion. This study attempts to extend a previous work of the authors where the SED criterion was successfully applied to U-notched components subjected to mode I loading conditions at room temperature. In this case, the effect of temperature is considered as a new variable.

The research analyses four different types of isotropic rocks with different lithologies, namely a Floresta sandstone, a Moleano limestone, a Macael marble and a Carrara marble. An exhaustive laboratory campaign was performed to define the main mechanical properties of the selected rocks at different temperatures. In total, 144 tensile splitting (Brazilian) tests, 120 uniaxial compression tests, 410 thermal expansion measurements and more than 790 four-point bending tests have been executed under different thermal conditions. On the other hand, the range of temperatures analysed varies from room temperature up to 250 ºC, which is a common band in geothermal applications.

Temperature has proven to be a significant parameter when analysing the fracture behaviour of the four selected rocks. Its influence on the main mechanical properties of the rocks (tensile strength, fracture toughness, compressive strength, Young’s modulus, Poisson’s ratio) has been studied and similar trends have been observed for the marbles, but different or even opposite ones for the sandstone and limestone. Overall, the application of the SED criterion has led to relatively accurate fracture predictions under different temperature conditions. This methodology assumes a linear-elastic behaviour of the rocks at the studied range of temperatures. For this reason, the failure load predictions become less accurate when non-linearities are not negligible, as in the case of the Carrara marble.

这项工作旨在分析I型载荷和不同温度条件下U形槽口岩石的断裂行为。为此，使用了一种基于能量的方法，称为应变能密度（SED）标准。这项研究试图扩展作者先前的工作，在该工作中，SED标准已成功应用于室温下处于I型加载条件下的U型缺口构件。在这种情况下，温度的影响被视为一个新变量。

该研究分析了四种具有不同岩性的各向同性岩石，分别是弗洛雷斯塔砂岩，莫利诺石灰岩，马卡伊尔大理石和卡拉拉大理石。进行了详尽的实验室研究，以定义所选岩石在不同温度下的主要机械性能。在不同的热条件下，总共进行了144次拉伸断裂（巴西）测试，120次单轴压缩测试，410次热膨胀测量和790多次四点弯曲测试。另一方面，所分析的温度范围从室温到最高250ºC不等，这是地热应用中的常见温度范围。

在分析选定的四个岩石的断裂行为时，温度已被证明是一个重要的参数。研究了其对岩石主要力学性能（抗张强度，断裂韧性，抗压强度，杨氏模量，泊松比）的影响，并观察到了大理石的相似趋势，但砂岩和石灰石的趋势不同甚至相反。 。总体而言，SED标准的应用已导致在不同温度条件下相对准确的裂缝预测。该方法假设在研究温度范围内岩石的线性弹性行为。因此，当非线性不可忽略时（如卡拉拉大理石），失效载荷的预测将变得不那么准确。