Porosity Effects on Mechanical Properties of 3D Random Fibrous Materials at Elevated Temperatures

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.