Static fracture toughness characteristics are traditionally determined in tests of standard notched specimens using a P-V curve, where P is the load and V is the notchopening displacement. This curve has a characteristic point Q. At the load P Q corresponding to this point, the crack starts to propagate. For this load, the fracture toughness characteristics are then calculated. In brittle (elastic) fracture, the P-V curve at the onset of crack propagation has an extremum (or a local extremum), from whose ordinate P Q is determined with sufficient accuracy. In ductile and elastic-ductile fracture, P-V curves are monotonically increasing, and P Q is calculated using the 5% secant offset method without taking into account the characteristics of the material, so that the P Q is determined inaccurately. To improve the accuracy of P Q determination, we propose a thermographic method for determining the fracture toughness of metals. This method involves plotting the load P against the temperature change ∆Т over a relatively short period of time at the notch tip. This plot is then transformed to a P-ΔS curve, where ΔS is the specific entropy increment at the notch tip, which is calculated through ∆Т. This thermodynamic diagram has a characteristic step at the beginning of crack propagation, and from the ordinate of this step, P Q can be determined much more accurately. Furthermore, in the thermographic method, the preparation of test specimens can be simplified by replacing the process of growing a fatigue crack at the tip of a notch by making a sharp cut, which provides significant time savings. Statistical processing and comparison of test results of steel 20 specimens using the conventional and thermographic methods have shown the advantages of the thermographic method in accuracy and complexity.
Computational and experimental studies of the amplitude-time and spectroscopic characteristics of an IR parametric laser based on mercury thiogallate with frequency tuning in the range from 5 to 9 mi-crons, an output energy of 10 MJ and a spectral emission width of ≤ 0,7 cm-1 have been carried out. A multifunctional IR parametric laser complex for remote detection and identification of atmospheric gases, including explosive and chemically aggressive substances in the range of electromagnetic wave-lengths from 1,41–9,07 microns, by differential absorption and dispersing has been developed, created and tested. The paper presents the results of computational and experimental studies on remote determination of spectroscopic characteristics of the most famous explosives TNT, RDX, PETN. It shows the possibility of highly sensitive determination of the concentration (~1 ppm) of explosives using a multifunctional optical system based on an IR parametric laser.
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