G. A. Volkov

On the dependence of the threshold energy of small erodent particles on their geometry in erosion fracture

The structural-temporal approach and the incubation time criterion are used to study the threshold energy necessary to initiate erosion fracture of a material surface. The behavior of the energy threshold values depending on the indentor geometry (ball, cylinder, and body of revolution) is analyzed. The graphs of threshold energy versus impact pulse duration and radius are drawn. The difference in the behavior of energy for small particles in these cases is established.

On the effect of the geometrical shape of a particle on threshold energy in erosion damage

The structural-temporal approach is used for analyzing the energy required for fracture. The behaviors of the threshold fracture energy in the impact of spherical and cylindrical particles against an elastic half-space are compared. It is shown that the threshold energy minimum can be attained using spherical particles. The plots of the dependence of the threshold energy on the impact duration and on the particle radius are constructed for the cases under investigation.

The Incubation Time Criterion and the Acoustic Strength of Sea Water

The approach based on the incubation time concept is used to analyze experimental data on acoustic cavitation in degassed water and in sea water. Earlier, a similar approach proved to be effective in analyzing the cavitation due to pulse loading and in studying the dynamic strength of solids. The proposed criterion takes into account the existence of the static cavitation threshold for low-frequency loading and makes it possible to explain the growth of the cavitation threshold for high-frequency loading, as well as the appreciable spread in experimental data.

On some principal features of data processing of spall fracture tests

A method for processing the results of dynamic spall fracture tests, based on the exact solution of the wave equation, and its commonly used simplified version based on the assumed unique relation between the free surface velocity drop and the ultimate medium fracture stress, are analyzed. Using the considered exact solutions of the wave technique, tensile stress pulses during spalling are determined. The obtained stress levels at the fracture point are compared with the spall strength calculated by the velocity drop technique. The cases of agreement and disagreement of the results obtained using both techniques are shown. By the example of differently shaped loading pulses, possible scenarios of sample fracture are presented, in particular, the probability of the fracture delay effect is shown, which can be lost in the simplified processing method.

Simulation of the Behavior of the Cutting Force during Ultrasonic Rotary Machining of Materials Using Structure-Time Fracture Mechanics

An analytical model is developed for the behavior of the cutting force during ultrasonic rotary polishing, and it is based on the concepts of dynamic fracture mechanics and the solution to the problem of impact surface fracture. The dependence of the threshold fracture energy obtained in the problem of erosion using a structure-time approach is used to construct the cutting force model. The dependences of the cutting force on the material feed rate and the rate of tool rotation are obtained, and the developed model is shown to be efficient to explain the effects observed in experiments.

On the Possibility of Using the Method of Sign-Perturbed Sums for the Processing of Dynamic Test Data

At the present time, the methods for the measurement and prediction of the dynamic strength of materials are complicated and unstandardized. An experimental data processing method based on the incubation time criterion is considered. Only a finite number of measurements containing random errors and limited statistical information are usually available in practice, since dynamic tests are laborious, and every individual test requires a lot of time. This strongly restricts the number of applicable data processing methods unless we are satisfied with approximate and heuristic solutions. The method of sign-perturbed sums (SPS) is used for the estimation of finite-sample confidence regions with a specified confidence probability under the assumption of noise symmetries. It is shown that several experimental points are sufficient to determine the strength parameter with an accuracy acceptable for engineering calculations. The applicability of the proposed method is demonstrated in the processing of a number of experiments on the dynamic fracture of rocks.

Failure-delay effect in destruction of steel samples under spalling conditions

Dynamic spalling tests have been run on two batches of 30KhN4M steel samples. Experimental data have been processed with the classical technique based on solution of the elastic wave equation. Three samples have been revealed that demonstrated the failure-delay effect under testing. The incubation-time criterion has been used to show the conditions of emergence of failure delay with the example of triangular loading pulses. A rate strength curve has been constructed for the other samples. It has been shown that the limiting strengths under dynamic loads considerably differ for samples from different batches despite the same chemical composition and static strength.

Acoustic strength of water and effect of ultrasound on the liquid-vapor phase diagram

The structure-time approach is used to develop an analytical model that makes it possible to predict the dependences of the acoustic cavitation threshold of water on temperature and background pressure. The calculated dependences are compared with the results of experiments carried out in the leading laboratories. It is demonstrated that the proposed approach allows the estimation of the effect of the acoustic field on the phase state of the substance under study. The calculated liquid-vapor phase curves for water in the presence of acoustic fields are presented.

Liquid-vapor phase equilibrium conditions in an ultrasonic field

An analytical model is proposed that allows predicting the effect of an acoustic field on the phase equilibrium conditions of liquid continua. Under the conditions of an arbitrary ultrasonic wave, an equilibrium interaction value analogous to the effect on the phase state of a substance is determined with use of the incubation time criterion. As an example, improved phase diagrams are built for the state of water affected by ultrasonic waves with frequencies in the range 10–100 kHz.

Cavitation Resistance of Cryogenic Liquids: Incubation Time Criterion

Experimental data on acoustic cavitation in cryogenic liquids are analyzed using a criterion based on the incubation time concept. An analogous approach was successfully used earlier for analyzing the cavitation resistance of degassed and sea water at constant temperature. The proposed criterion takes into account the change in the static cavitation threshold and incubation time upon an increase in temperature.