13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- We also measured the charge of fracture of specimens in other thickness and breadth to know the effect of sizes of slabs on the amount of broken charge. Fig. 3(a) showed charges carried by broken slabs, 3mm×20mm×200mm in size. By comparing Fig. 2(a) and Fig.3(a), we found that they have a same charging law but the amount of charges shown in Fig. 2(a) is significantly lower than the one shown in Fig. 3(a), which shows that the thickness of glass slabs have an effect on the amount of broken charges. With increase of the thickness of the glass slab, the amount of charges also increases. Fig. 3(b) and Fig. 3(c) showed the charges carried by the broken parts of the glass slabs, 4mm×15mm×200mm and 3mm×15mm×200mm in sizes, respectively. We found that the breadth also has an effect on the charge of fracture, which increases with the increase of the breadth of glass slab. As mentioned above, the charge of fracture increases with the both the breadth and thickness. As well as we known, with the increase of both the breadth and thickness broken area increases, that means the increase of the broken area will lead to the increase of the charge of fracture. Therefore we calculated the mean values and standard variances of the surface charge density shown in Fig.4. From Fig.4, it can be found that the breadth has a significant effect on the charge of fracture. Especially, for the amounts of charges carried by the broken part of glass slabs, 4mm×15mm×200 and 3mm×20mm×200mm in sizes, the areas of these two cases are equal, but the surface charge densities are different and the amount of charges carried by the former is higher than the latter. The surface charge density can reach up to 0.5C/m2. 0 5 10 15 -0.02 0.00 0.02 0.04 positive charge average of positive charge negetive charge average of negative charge Number (a) 0 5 10 -0.04 -0.02 0.00 0.02 0.04 0.06 positive charge average of postive charge negetive charge average of negative charge Charge(nC) Number (b) 0 5 10 15 -0.04 -0.02 0.00 0.02 0.04 positive charge average of positive charge negetive charge average of negative charge Charge (nC) Number (c) Fig. 3 Charges carried by the broken glass slab, (a) 3mm×20mm×200mm, (b) 4mm ×15mm ×200mm and (c) 3mm×15 mm×200mm in sizes Although the charge of fracture increases with the thickness increasing when the broken areas of the specimen are given, it is still difficult to infer that the charge of fracture increases with the thickness. Because we make the linear nick on the specimen, it also has the effect on the real broken thickness. For given the deepness of nick, it has a significant effect on the broken thickness of glass slab with thinner thickness. But it is difficult to carry out the experiments to measure the charge of fracture with thickness more than 4mm, so if the surface charge density is related to the thickness is still open. It is interesting that how to explain the electrification of fracture, which may be related to the glass network structure. We scanned the broken surface of glass by using SEM (Type: JSM-5600LV. Precision for SEM: 3.5nm. Precision for DES: 131.7eV) shown in Fig. 5(a). From the Fig. 5(a), it can be found that the broken surface is smooth but a few black spots (I), and white spots (II), which indicates it is a brittle fracture. Because the grayscale of the image is related to the atomic number to some extent, we analyzed the energy dispersive spectrum of black spots, I of Fig. 5a and white spots, II of Fig. 5(a), shown as in Figs. 5(b)-5(c), respectively. The chemical formula of glass used C ha rg e ︵ nC ︶
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