13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- Before the experiment, we firstly mad a linear nick on the glass slab to ensure that the glass slab can be easily broken and also just broken into only two parts, by which we can easily calculate the broken area. If the linear nick is made in the middle of the glass slab, the glass slab can be symmetrically broken but otherwise asymmetrically broken, and in this paper the linear nick was made in one third of glass slabs. Then all glass slabs and glass spheres were cleaned by water and alcohol to eliminate the impurity of glass’s surface and the net surface charges. The glass slabs used in our experiment were 3mm and 4mm in thickness, and 15mm and 20mm in breadth, and 150mm and 200mm in length. Given a size of the glass slab, we measured 30 results at least, that means we measured charges of 30 specimens. 3 Results and discussions For all data we collected, we firstly eliminate the abnormal data by using Grubbs method and then classified the data by positive and negative signs. Fig. 2(a) and Fig. 2(b) show the amount of charge carried by parts of broken glass slabs, 4mm×20mm×200mm in size. The charges carried by the symmetrically broken parts shown in Fig. 2(a) and the ones carried by the asymmetrically broken parts shown in Fig. 2(b). It can be found that two parts of the glass slab broken by a metal sphere can be electrified, and the one part carried positive charge, whereas the other carried identically negative charge. The probability of presence of positive charge of negative charge is equal. For the asymmetrical case, mean amount of positive charges carried by the part is nC 0.032059 and mean amount of negative charges carried by the other part is nC 0.03062 . By comparison Fig. 2(a) with Fig. 2(b), both the polarity and amount of charges carried by the broken glass slab are not related to the broken position, which is accordant with the results observed by Kornfeld [1]. We also measured the charges carried by broken parts of glass slabs with different length, and the results showed that the charge of fracture is not related to length of specimen. Therefore we only introduce the measurement results of symmetrical broken glass slabs with 200mm in length. 0 5 10 15 20 25 30 35 0.0 0.1 Charge (nC) Number positive charge average of positive charge negitive charge average of negative charge (a) 0 5 10 15 20 25 30 -0.06 -0.03 0.00 0.03 0.06 0.09 Charge (nC) Number positive charge average of positive charge negetive charge average of negative charge (b) Fig.2 Charges carried by the broken part of glass slab, 4×20×200mm in size, (a) symmetric break and (b) asymmetric break
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