We investigate the simultaneous emission of electrons and photons during the deformation and fracture of two types of high-purity single-crystal MgO. These crystals exhibit significant differences in optical opacity due to differences in void and precipitate concentrations. Measurements of the emission of visible photons during deformation and prior to failure of the crystals are presented, along with the time dependencies of the photon and electron emission during and after fracture. Correlations with fracture strength and fractographic features are also discussed.

Fracto-emission is the emission of particles (e.g., electrons, ions, ground state and excited neutrals, and photons) during and following fracture. We have found that during fracture in vacuum of adhesive bonds and crystalline materials involving large amounts of charge separation on the surface the emission of charged particles, excited neutrals, light, and radio waves occurs with unique and revealing time dependencies. In this paper we report simultaneous fractoemission measurements on several systems. We interpret the results in terms of a conceptual model involving the following steps: (1) charge separation due to fracture, (2) desorption of gases from the material into the crack tip, (3) a gas discharge in the crack, (4) energetic bombardment of the freshly created crack walls, and (5) thermally stimulated electron emission, accompanied by electron stimulated desorption of ions and excited neutrals. In addition to evidence from fracture experiments, we present results from studies of electron bombardment of a polymer surface.

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During and following fracture of a number of materials, the emission of photons, electrons, ± ions, and neutral species are observed; these emissions are collectively known as fracto-emission. In this work, we present measurements of the neutral particle emission following fracture of two single crystal fcc alkali halides: NaCl and LiF. We observe no measurable emission attributable to release during the fracture event itself. However, after relatively long time intervals of ∼0.5–250 ms, we observe rapid bursts of alkali atoms, as well as molecular species which include NaCl and (LiF)n where n = 1,2,3. Bursts of alkali containing species also occur during loading prior to fracture and for unloaded specimens during heat treatment. We argue that these bursts are due to energetic emergence (“popout”) of dislocations at free surfaces.