ELECTRON-SPIN-RESONANCE IN-SITU OBSERVATION OF THE BENDING STRESS PROCESS IN CORUNDUM MATERIALS AND GLASSES

A new combination of three-point bending stress and electron spin reso nance (ESR) methods was developed and successfully tested in the field of glassy and ceramic materials. Summarizing the observed phenomena, one can establish the following advantages of such an experimental com bination: (i) direct and continuous observation of the material under the action of bending stress up to mechanical destruction of the sampl e; (ii) optically transparent samples are not necessary, but a further direct combination with optical methods is, in general, possible; (ii i) the high sensitivity and selectivity of the ESR method allow the fi rst steps of stress influence on the local geometry to be followed lon g before the crack appears and fracture takes place, respectively; (iv ) local effects are observed on the atomic scale which can be related to the mechanical properties by an appropriate hamiltonian; (v) the re versibility of the effects can easily be proved by a suitable alternat ing stress/relaxation regime; (vi) variation of further parameters suc h as temperature or application of tensile stress, is possible.