Zhaoliang Qu

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.

An elevated-temperature depth-sensing instrumented indentation apparatus for investigating thermo-mechanical behaviour of thermal barrier coatings

In our study, an elevated-temperature depth-sensing instrumented indentation apparatus was designed and developed to investigate thermo-mechanical response of thermal barrier coatings (TBCs). A furnace was used to heat the test region up to 1600 °C and a heat protection design was proposed to protect electronic devices from high temperature environment. Load was applied by a precise loading motor and a piezoelectric actuator in high (0-440 N) and low (0-40 N) load ranges, respectively. A loading shielding scheme was designed to protect the low load sensor during the high loading process. In order to obtain reliable test data, the as-developed apparatus was calibrated at room and elevated temperatures. It is found that the developed apparatus was suitable to obtain the intended data. After that, two typical TBCs were tested from 600 to 1500 °C, and the load-depth curves were presented to show the main functions and usability of the measuring system.

Investigation of Pile-Up Behavior for Thermal Barrier Coatings Under Elevated-Temperature Indentation

The elevated-temperature indentation has been utilized to measure the elevated-temperature mechanical properties of thermal barrier coatings (TBCs), which have a major influence on their thermomechanical characteristics and failures. In this paper, the pile-up phenomenon of TBCs under elevated-temperature indentation was investigated, and a characterization method for Youngs modulus of TBCs was proposed. According to the dimensional analysis and finite-element method, a critical temperature-dependent factor was conducted as the criterion for pile-up behavior. Some experiment results agreed fairly well with the criterion. Then, the pile-up behavior of TBCs at elevated temperature was studied. It was found that the pile-up behavior depended on the temperature-dependent factor and got larger with increasing temperature. Finally, a characterization method was proposed to extract the Youngs modulus of TBCs, which was found to be more suitable for elevated-temperature indentation.