Exploration on Thermal Shock Mechanical Properties of Ceramic Materials

Abstract

Fatigue failure is very common phenomenon in engineering field, and fatigue problem is more and more prominent with the development of modern social production to high speed, high temperature, high strength load. In process of college undergraduate course graduation design and innovative experiments, this paper studies elastic modulus and bending strength change rule curve of the mullite ceramic specimens under different factors such as temperature difference, thermal shock times and different cooling medium. The paper studies the effects of different heat shock factors influence on the mechanical properties of mullite ceramics, and determines the thermal shock damage degree of ceramics materials, and then cultivate students the research ideas and research methods of fatigue failure. Introduction With the development of modern science and technology, materials are puts forward high demands on the departments such as space technology, industrial, energy, transportation and so on. Materials are required having high temperature resistance, erosion resistance, good thermal shock, heat preservation, oxidation resistance, excellent comprehensive performance. High temperature structure ceramic material has a series of excellent performance such as high temperature resistance, scouring resistance, corrosion resistance, high hardness, high wear resistance, high strength and oxidation resistance, so ceramic material is the focus and hotspot in the research of the scientific research workers[1-5]. In the current engineering mechanics course, the fatigue, especially the thermal fatigue, almost is not involved due to the limitation of school hours, The students almost have not fatigue failure concept, and have not scientific ideas and methods to solve the problem of fatigue. This paper studies elastic modulus and bending strength change rule curve of the mullite ceramic specimens under different factors in process of college undergraduate course graduation design and innovative experiments, and determines the thermal shock damage degree of ceramics materials, and then cultivate students the research ideas and research methods of fatigue failure[6-10]. Experiment Method The Experimental Scheme. The specimen made by high temperature solid method, the size of the test piece for 10×20×100mm. Experiment includes thermal shock test and mechanical properties test. Design of experiments was shown in Table 1. International Conference on Materials, Environmental and Biological Engineering (MEBE 2015) © 2015. The authors Published by Atlantis Press 52 Table 1 Thermal shock experiment Test method Elastic modulus Bending break strength A thermal shock test Temperature difference cycles Temperature difference cycles 0,200°C、 400°C...1200°C Air cooling one time 0,100°C、 200°C...900°C Air cooling and water cooling each one time Thermal fatigue test Temperature difference cycles Temperature difference cycles 400°C Air cooled 60 times 500°C Air cooled 40 times 600°C Air cooled 60 times 800°C Air cooled 40 times 800°C Air cooled 45 times Determination of Elastic modulus. Elastic modulus is measured by ultrasonic method under the condition of air cooling. Wave velocity measurement is shown in Fig.1. Fig. 1 Ultrasonic wave velocity measurement schematic diagram Formula of wave velocity is that ultrasonic wave velocity is equal to (walk path of the ultrasound in material) divide by (probe emission and receiving of ultrasonic time interval). The elastic modulus of materials is calculated according to the formula (1)[11] : ( ) 2 2 1 3 1 T L T E c c c ρ   = −   −     (1) Where L c is the velocity of longitudinal waves (m/s), T c is the velocity of shear waves (m/s), ρ is density. Determination of Flexural Strength. Bending strength is determined by three point bending method, which is according to the provisions of GB3001-82. Measuring instrument is the electronic universal testing machine, and the loading rate is 0.5mm/min. The three point bending method is shown in Fig.2. The flexural strength is calculated according to the formula (2): 3 2 PL BW σ = (2) where P is the load of fracture (N) , L is the distance of the two supports (mm), W is the width of specimen (mm) and B is the height of the specimen (mm). Result and Discussion. Elastic properties results and analysis. Fig.3 was the elastic modulus variation curve with thermal shock temperature in air cooling condition. With increasing of the thermal shock temperature difference, the value of the elastic modulus decreased greatly. Fig.4 was elastic modulus changing curve with the cycles of thermal shock. It can be seen that with the increase of thermal shock cycles, the trend of elastic modulus was decreasing in a ladder shaped.