Emission during fracture

The EE and phE mechanisms for neat polymers proposed by ourselves and others all involve the consequences of breaking bonds during fracture. Zakresvskii et al. (24) have attributed EE from the deformation of polymers to free radical formation, arising from bond scission. We (1) as well as Bondareva et al. (251 hypothesized that the EE produced by the electron bombardment of polymers is due to the formation of reactive species (e.g., free radicals) which recombine and eject a nearby trapped electron, via a non-radiative process. In addition, during the most intense part of the emissions (during fracture), there are likely shorter-lived excitations (e.g., excitons) which decay in a first order fashion with submicrosecond lifetimes. The detailed mechanisms of how bond scissions create these various states during fracture and the physics of subsequent reaction-induced electron ejection need additional insight. 

J. T. Dickinson and L. C. Jensen, Crack velocity dependence of electron emission during fracture in filled elastomers, J. Polym. Sci., Polym. Phys. Ed. 20, 1925 (1982). 

Zhenyi, Ma., Langford, S. C., Dickinson, J. L, Endelhard, M. N., Baer, D. R. (1991). Fractal Character of Crack Propagation in Epoxy and Epoxy Composites as Revealed by Photon Emission during Fracture. J. Mater. Res. 6(1), 183-195. 

Fig. 5. Typical acoustic emission (AE) waves observed at different zones and during fracture of cyclic loading of PMMA. The amplitude is drawn on...

The term triboluminescence is often used to describe any light emission occurring upon impact with or grinding of a crystalline material, and is certainly more than one phenomenon (3). Light emissions caused by heating during fracture, such as thermoluminescence and blackbody radiation, are common, but neither they nor chemical reactions such as oxidation are strictly considered triboluminescence they will not be discussed in this paper. 

Triboluminescence (TL) is the phenomenon of light emission during the application of a mechanical stress or by fracture of crystals in a solid sample. The materials presenting this behavior are promising for application in real-time structural damage sensors . 

A wide variety of materials triboluminesce i.e., yield photon emission (phE) during fracture. Chandra and Zink (21) classify materials according to the emission... 

Electron emission during and after fracture of a) E-glass/epoxy and b) S-glass/epoxy strands. Note the different time scales (15). 

Ozhuku T, Tomura H, Sawai K (1997) Monitoring of particle fracture by acoustic emission during charge and discharge of Li/Mn02 cells. J Electrochem Soc 144 3496... 

To a first approximation, the emission begins and is most intense during fracture. 

The fracture of a brittle, electrically insulating material is often accompanied by the emission of electrons, photons, and/or ions. This fractoemission is probably due to microarc discharges resulting from charge separation during fracture. 

Exoemission (adhesion) The emission of electrons during fracture. Also called Fractoemission. 

However, it is possible that friction events from rubbing between fractured surfaces can be generated at low load levels also during the loading part of the cycle. This is depicted in the two correlation plots of Figure 5. In the plot at the bottom, these events are marked with a rectangle. It was decided that in addition to the previous filter, another filter based in load level should be added. Acoustic emission events were thus accepted only if they occurred at a load higher than 85% of the maximum load level of the test. 

There has been some discussion as to whether acoustic signals result from the fracture that occurs when adhesion Is lost at the paint-metal Interface during blistering and cathodic disbonding. In the present study, very sensitive Acoustic Emission measurements have been made In systems exhibiting these types of breakdown. 

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