Tribobreakdown in glasses induced by subthreshold high-intensity radiation

Abstract

In the experiments we used the procedure for determining the emission of electromagnetic waves presented in [6], in which the signals are measured to within 0.i mV. The experiments were performed with careful shielding of the samples from external signals. The high-intensity radiation (% = 1.06 units, T ~ 10 -3 and 3"i0 -s sec) with different intensity acted on the sample placed in a metallic jacket. Electromagnetic signals (noise) from the light interaction were not recorded, which was monitored by tests: without and with a sample, but no fracturing (the sample was additionally shielded). A sample with a mechanical break was also placed in the same jacket the entire mechanical action system was carefully shielded. The samples consisted of K-8 silicate glass with dimensions of i  1  5 cm, organic glass (polymethyl methacrylate -- PMMA) with dimensions 1 x 1 x 3 cm, and colorless quartz with dimensions of 1.5 x 1.5 x 2 cm. The radiation was focused inside the samples by a lens with a focal length F = 5 cm. The radiation intensity (I) wasequal to0.1, 0.3,0,5, 0.7,0.9, 1.5,2 Ith(with one-time action of threshold radiation with I = Ip single mechanical fractures with minimum dimensions of ~50-i00 ~m appear). At least 20 experiments were performed for each type of sample and value of E. Figures la and 2a show the measurements of the electromagnetic signals (EMS), which appear with "purely mechanical" fracture of the PPM and K-8 glass samples. The maximum magnitude of the EMS in the experiments is equal to 30-40 mV. In the presence of fracturing (motion of the crack) new free surfaces, on which charge is located and the field of the charge is sufficient to breakdown the gas filling the space between the surfaces being formed, are constantly forming [7, 8]. Thus, it can be conjectured that the EMS recorded is produced by tribobreakdown accompanying the mechanical fracturing of the samples. Figures la and 2a contain an entire series of separate spikes-signals, which can be attributed to the appearance of a series of cracks: new cracks appear in front of the main cracks [9]. Judging from the duration of the EMS, the time for the motion of the cracks is equal to ~i0 -2 sec in PMMA and ~2"i0 -3 sec in K-8 glass, which is an entirely reasonable value. In fracturing the K-8 glass samples, we made a cut on their surfaces, which probably encourages the forward motion of the crack.