In this study, we prepare the specimens of three-dimensional random fibrous (3D RF) material along its through-the-thickness (TTT) and in-plane (IP) directions. The experimental tests of tensile and compressive properties as well as fracture toughness of 3D RF material are performed at elevated temperatures. Then, the porosity (83%, 87% and 89%) and temperature dependence of the tensile and compressive strength, elastic modulus, fracture toughness and fracture surface energy of the 3D RF materials for both the TTT and IP directions are analyzed. From the results of the tensile strength and elastic modulus versus material porosities at various temperatures, we find that tensile strength and elastic modulus for the TTT direction are more sensitive to the porosity, but not for the IP direction. Fracture toughness increases firstly and then decreases at a certain critical temperature. Such critical temperature is found to be the lowest for the porosity of 83%. On the other hand, at below 1073 K, the temperature-dependent fracture surface energies with three porosities for the TTT direction show similar variation trends.

中文翻译：

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高温下孔隙度对3D随机纤维材料力学性能的影响

在这项研究中，我们准备沿其厚度方向（TTT）和面内（IP）方向制作三维随机纤维（3D RF）材料的标本。3D RF材料的拉伸和压缩特性以及断裂韧性的实验测试是在高温下进行的。然后，分析了3D RF材料在TTT和IP方向上的孔隙率（83％，87％和89％）和温度依赖性，以及拉伸和压缩强度，弹性模量，断裂韧性和断裂表面能。从在不同温度下抗张强度和弹性模量与材料孔隙率的结果，我们发现，TTT方向的抗张强度和弹性模量对孔隙率更敏感，而对IP方向则不敏感。在一定的临界温度下，断裂韧性首先增加，然后降低。发现该临界温度对于83％的孔隙率是最低的。另一方面，在1073 K以下，在TTT方向上具有三个孔隙度的随温度变化的断裂表面能显示出相似的变化趋势。