Issue 39

H. Xiao et alii, Frattura ed Integrità Strutturale, 39 (2017) 181-190; DOI: 10.3221/IGF-ESIS.39.18 182 becomes more precise and artistic and stone machining industry develops rapidly. However, stone material is a nonrenewable resource. Under the tendency that the society appeals to save industrial resources and protect environment, how to exploit and utilize stone materials efficiently has become a bottleneck in stone material industry [4-6]. Ogilvie SR [7] analyzed the microstructure of granite under the condition of uniaxial compression using image analysis method and found stronger aeolotropy of internal structure. By using different test specimens, it was found that, larger anisotropy inside specimens resulted in more significant directional property in the shape of micro-grains and the grain size had a remarkable influence on macroscopic strength of specimens. Under different thermal loads, real-time changes happen to temperature field and stress filed inside granite, which can result in the changes of structure and mechanical performance of granite. This study explored the rules of temperature load influencing the physical performance of granite by carrying out a thermal load difference experiment and a uniaxial compression experiment. P HYSICAL PROPERTIES UNDER THERMAL LOADING n the actual grinding processing of granite, the intensive friction between cutter and workpiece generates a large amount of heat, due to the high hardness of granite. Diamond crystals may lose cutting ability at the temperature above 800 °C due to carbonization. Hence cutter needs to be cooled using water [8, 9]. In this experiment, the cutter was cooled using water after high-temperature heating up to 800 °C. Experimental equipment and methods The workpiece used was granite G630 with a size of 100 mm × 50 mm × 20 mm. After the determination of the specification, two types of treatment named plan A and B were performed in the following. Eight specimen groups were set up for each plan. In each group, five granite rectangle blocks were used. The temperature for the groups was set as 100 °C, 200 °C, 300 °C, 400 °C, 500 °C, 600 °C, 700 °C and 800 °C. Heating stopped after 30 min at constant temperature. Granite specimens of plan A were cooled with water for 5 min and then dried with air for 24 h, while granite specimens of plan B were cooled under natural conditions. The experimental set up is shown in Fig. 1. Figure 1 : Experimental set up. Analysis of experimental results Quality changes of granite after water and air cooling are shown in Fig. 2. When the temperature was not higher than 400 °C, heating dried up the water stored on the surface or in the gap of the granite. When the temperature was higher than 400 °C, weight loss became more obvious. It was because that, micro-damage generated and micro-cracks increased in rocks under stress, which resulted in the evaporation of the water on the surface of rock cracks. Through comparing the data of the groups treated by air cooling and thermal shock, we found that, when the temperature was lower than 500 °C, the weight loss of the granite processed by air cooling was less remarkable than that of the granite processed by water cooling. It was because that, water entered into the cracks of the workpiece during water cooling and then was stored inside after cracks closed with the decreasing of temperature. When the temperature was higher than 600 °C, the weight lost in air cooling was less than the weight lost in water cooling. It was because of the excessive loss of crystal water caused by the sharp increase of micro-cracks of the granite.