Fracto-emission

Fracto-emission (FE) is the emission of particles (electrons, positive ions, and neutral species) and photons, when a material is stressed to failure. In this paper, we examine various FE signals accompanying the deformation and fracture of fiber-reinforced and alumina-filled epoxy, and relate them to the locus and mode of fracture. The intensities are orders of magnitude greater than those observed from the fracture of neat fibers and resins. This difference is attributed to the intense charge separation that accompanies the separation of dissimilar materials (interfacial failure) when a composite fractures. 

When stressed, a material releases various types of emission prior to, during, and subsequent to ultimate failure. This emission includes electrons, positive ions, neutral molecules, and photons - including long wavelength electromagnetic radiation (radio waves), which we have collectively termed fracto-emission (FE). 

Fracto-emission (FE) is the emission of particles and photons accompanying deformation and fracture. These emissions typically include electrons (EE), positive ions (PIE), neutral atoms and molecules, including both ground state neutrals (NE) and excited neutrals (NE ), visible photons (phE)—also called triboluminescence in this context, and long wavelength electromagnetic radiation (RE radio emission). 

Recent work by Dickinson on fracto-emission(36) indicates that ions, neutral particles, electrons and photons could be detected during the polymer fracture processes. The identification of these species during polymer wear may be of future research interests. 

J. T. Dickinson, "Fracto-Emission Accompanying Adhesive Failure," in Ref. 14. 

For a wide range of materials the emission of electrons (EE), positive ions (PIE), neutral species (NE), and photons (phE) has been observed accompanying fracture. We refer collectively to these emissions as fracto-emission. In this paper we review our work on fracto-emission where the fracture event involves interfacial or adhesive failure. The interfaces to be discussed include the following brittle materials/epoxy, glass/elastomers, and brittle materials/pressure sensitive adhesives. 

Fig. 2. Schematic Design of Experimental Arrangement of Fracto-emission Investigation.

Our initial work in fracto-emission examined a number of details of the EE and PIE accompanying fracture in oxide coatings which served as surface preparations for the adhesive bonding of aluminum. This work can be found... 

I have tried to show a wide variety of FE results on a number of systems involving adhesive failure at interfaces and indicate some of the parameters that are influencing this emission. The need for careful studies of the physics and chemistry of these phenomena is obvious. The usefulness of FE as a tool for NDT or for investigation of failure mechanisms requires a broad based attack combining fracture mechanics materials science, and fundamental fracto-emission studies on materials of mutual interest. Since the field is relatively unexplored, I will conclude by speculating on some potential areas of usefulness of FE, many of which depend critically on further understanding of FE itself. 

L. H. Lee (Xerox Corporation) Dr. Dickinson should be congratulated for developing this new technique of fracto-emission to explore the fracture phenomena at the molecular level. By this technique, not only have many energetic species been identified during the fracture process but the energy distribution of each species has also been accurately measured. 

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