Issue 50

L. He et alii, Frattura ed Integrità Strutturale, 50 (2019) 649-657; DOI: 10.3221/IGF-ESIS.50.55 652 in the dark area. The cracking could be attributed to the thermal stress while the local melting was caused by high temperature for the biotite enrichment. A clear fracture zone, parallel to the trend of schistosity, and a spot of solidified magma were observed in the dark area at 600 °C. In addition, micro-cracks appeared on the surface of the light colour area. Almost all of the fracture zone of the dark area was filled with solidified magma at 700 °C. Furthermore, the fracture area was pushed away by the magma, as shown in Fig. 4e. When the temperature reached 800 °C, the centre of the specimen formed a big cavity owing to the melting and flow of minerals. Many micro-cracks were observed on the surface of the light area, while macro-cracks and melting occurred mainly in the dark areas at 800 °C. Therefore, it can be concluded that the dark area dominantly determines the structural failure of Qingyuan granite. Figure 3 : TG and DSC curves for pristine granite. Figure 4 : Appearance of specimens at different temperatures after microwave radiation. Fig. 5 shows the microtopography of the analysed specimens at different temperatures after microwave radiation. As shown in Figs. 5a and 5b, with increasing temperature, the dimensions and the number of cracks increase. Also, two different types of cracks are observed in Fig. 5c. It is clear that there are small cracks on the left and right sides of minerals. Meanwhile, a larger-size crack can be seen at the junction between the two minerals. This demonstrates that the damage is more severe