Rujie He

An ultra-high temperature testing instrument under oxidation environment up to 1800 °C

A new testing instrument was developed to measure the high-temperature constitutive relation and strength of materials under an oxidative environment up to 1800 °C. A high temperature electric resistance furnace was designed to provide a uniform temperature environment for the mechanical testing, and the temperature could vary from room temperature (RT) to 1800 °C. A set of semi-connected grips was designed to reduce the stress. The deformation of the specimen gauge section was measured by a high temperature extensometer. The measured results were acceptable compared with the results from the strain gauge method. Meanwhile, tensile testing of alumina was carried out at RT and 800 °C, and the specimens showed brittle fracture as expected. The obtained Youngs modulus was in agreement with the reported value. In addition, tensile experiment of ZrB2-20%SiC ceramic was conducted at 1700 °C and the high-temperature tensile stress-strain curve was first obtained. Large plastic deformation up to 0.46% and the necking phenomenon were observed before the fracture of specimen. This instrument will provide a powerful research tool to study the high temperature mechanical property of materials under oxidation and is benefit for the engineering application of materials in aerospace field.

A Study on the Compressive Performance of C/SiC Lattice Sandwich Panel at High Temperature

In this study, the mechanical properties and failure behaviors of a C/SiC lattice sandwich panel were investigated by numerical simulation approach. On the bases of Hashin’s criteria, a novel failure criterion for 2D C/SiC textile composite was proposed. An UMAT subroutine based on Abaqus code was constructed to demonstrate the fracture mechanism of the C/SiC composite, in which fiber fracture and buckling, matrix failure and the laminate delamination were considered. Out-of-plane compressive experiments of the C/SiC lattice sandwich panels at room temperature were performed to give verifications of the numerical programmer. Based on the simulation method proposed, the mechanical properties and failure features of the C/SiC lattice sandwich panels at high temperatures were studied. It was found that the junction between struts and the panels of the core firstly damaged due to fiber rupture and matrix cracking. Then fiber tensile fracture and matrix cracking occurred in struts sequentially. Finally, delami...

Surface preoxidation to improve dispersibility of zirconium diboride in aqueous medium

Abstract The dispersibility of ZrB2 particles in aqueous medium had a significant effect on colloidal forming processes of ZrB2 based ultra high temperature ceramics. To improve the dispersibility of ZrB2, surface preoxidation was developed. After preoxidation, a layer of oxides composed of ZrO2 and B2O3 formed on particle surfaces. The dispersibility of ZrB2 particles in aqueous medium was investigated using zeta potential measurements, sedimentation tests and viscosity measurements. The surface oxygen of ZrB2 particle preoxidised at 800°C was 2·66±0·12 wt-%. It was found that ZrB2 had the best dispersibility and the lowest viscosity after surface preoxidation at 800°C for 1 h.