13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- of the broken material can be electrified, whereas the contact electrification means the two materials surfaces can be electrified after they contacted with each other. Therefore we infer that the electrification mechanisms are different. Recent studies on the contact electrification indicate that the charges transferred are electron, iron and material sites [15-18]. Though some researchers think that the electrification of fracture results from the electrons escaping during the break of the material, the fracture of material is always accompanied with the chemical bonds breaking in microscope [19]. Therefore the asymmetrical break of the chemical bonds may be one of main reasons leading to the electrification of fracture. In this paper we set up a instrument to measure the charges carried by a part of glass slab broken by a glass sphere. The calculated surface charge density indicates that the amount of charges carried by the broken part of the glass slab is proportion to the broken area, and we infer the mechanism of electrification of fracture by scanning the broken surface. 2 Experiment setup and measurement We set up an instrument to measure the charges carried by the broken part of the glass slab shown as Fig.1. Main part of the instrument was put into a closed glass container with a wire netting fixed on its inside wall to shield the electric field. We also can observe the experimental procedure through the glass wall. One end of a glass slab was fixed on a moveable slideway which can be controlled outside the glass container. When the glass slab moves above the Faraday’s cup, it will stop. A metal sphere falls and impacts with the glass slab which will be broken into two parts, and one part will fall into Faraday’s cup. Faraday’ cup induces the charge carried by the part of glass slab, which was named charge of fracture or broken charge, and the electric signal is displayed by electrometer (Type: Keighley 6517A; Precision: 100pC; Rang: 0~20nC). Fig.1 A sketch of instrument of electrification of fraction, in which 1 is slideway, 2 is specimen, 3 is metal sphere, 4 is Faraday cup, 5 is wire netting and 6 is electrometer
RkJQdWJsaXNoZXIy MjM0NDE=