Shock Pulse Amplitude Research Articles

Определение коэффициента демпфирования ударного импульса при измельчении горных пород

Introduction. The physical properties of rocks, which determine the choice of the type of mill, as well as its operating parameters, are considered. The importance of studying the damping properties of the crushed material and their influence on the energy intensity of the grinding process is noted. Research methods and materials. The differential equation of motion of the crack wall, previously obtained by the authors of the article, is applied when it is exposed to a shock wave with amplitude σ and duration τ. The classical theory of damped oscillations of the system is used to determine the damping decrement of the shock pulse amplitude. A series of experimental studies was carried out on a laboratory sample of a drum mill to determine the magnitude of the shock pulse damping coefficient. Rocks from various deposits in Russia with strictly defined strength characteristics were used as the crushed material. Research results. Dependences of the amplitude of the shock pulse on time are constructed for the grinding of granite raw materials, carbonate rocks and soft rocks (gypsum) in a drum mill. The following conclusions were drawn: 1. When grinding strong and very hard rocks in a drum mill, a strong impact occurs (with a large amplitude and duration of the shock pulse) and with its weak damping when propagating in the rock. 2. When grinding carbonate rocks, doubling the angular velocity of rotation of the grinding chamber leads to an increase in the amplitude of the shock pulse by about 1.5 times. 3. The duration of shock wave propagation in both cases is approximately equal. 4. The frequency of grinding media collisions increases significantly. This indicates a sharp increase in the energy intensity of the grinding process. 5. When grinding soft rocks in a drum mill, almost half of the input energy is spent on overcoming the damping properties of the material, and small, frequent pulses, which consume half of all energy, are not able to grind the material to the desired size. Discussion. Based on the conducted studies, graphs of dependencies between the main parameters of the drum mill were constructed. The dependences of the duration of the shock pulse on the average diameter of the particles of the crushed material are constructed. The analysis of these dependences made it possible to conclude that the duration of the shock pulse is in a parabolic dependence on the value of the average particle diameter of the crushed material. The dependences of the damping coefficient on the damping decrement of the shock pulse amplitude are constructed. The analysis of these dependences allowed us to conclude that the shock pulse damping coefficient increases almost linearly with an increase in the damping decrement of the shock pulse amplitude. The dependences of the damping coefficient of the shock pulse on the average diameter of the particles of the crushed material are constructed. The analysis of these dependences allowed us to conclude that the shock pulse damping coefficient is in a quadratic dependence on the value of the average particle diameter of the crushed material. Conclusion. In this article, based on the classical theory of damped oscillations of such system, the principle of determining the damping coefficient of the shock pulse propagating from the grinding body deep into the grinding load of the drum mill is scientifically substantiated. Resume. Experimental determination of the value of the damping factor of the shock pulse, along with the use of the energy criterion for the destruction of the rock, makes it possible to calculate the amount of energy required to destroy the rock particles to a given size. Suggestions for practical application and direction for future research: The results of the research can be used at the enterprises of the mining sector of the industry to improve the efficiency of processing mineral resources and reduce the energy intensity of the process of grinding rocks in drum mills.

Research of the properties of rocks during fragmenting and crushing in mechanical mills

Relevance and purpose. The systemic crisis in the mining industry has weakened the provision of the industry with proven reserves of the main types of minerals, which has made the search for technological solutions in order to restore the lost potential of the mineral resource base. Methodology. Theoretical studies of the movement of the grinding charge in the grinding chambers of planetary mills are based on the postulate of the equivalence of the forms of movement of the charge in mills. Grinding equipment of a new technical level is being improved in the direction of increasing the intensity of the effect of grinding bodies on the crushed material. The aim of the study is to increase the intensity of the impact of grinding bodies on the crushed mineral raw materials while minimizing the energy consumption of processing processes. The goal is achieved by integrating analytical and experimental studies with elements of engineering forecasting and modeling of the results. Results and scope. The results of studying the properties of rocks and their changes as a result of crushing and grinding in mechanical mills are presented. Information about devices for measuring the parameters of shock pulses and the practice of their application is systematized on the example of geological differences of rocks. Bench studies have confirmed the theoretically substantiated phenomenon of shock pulse amplitude suppression. The role of the processes of crushing and grinding in mills in the technological chain of waste-free utilization of the tailings of the concentration of chemically exposed ores is detailed. Сonclusions. The phenomenon of increasing the intensity of the impact of grinding bodies on the crushed mineral raw materials with the same energy consumption of processing processes can be used in the modernization of technologies for the development of mineral deposits.

Shock Acoustic Emission upon Collision of a Droplet of Variable Shape with the Water Surface

Sound emission at the stage of supersonic expansion of a contact spot upon collision of a droplet with the water surface is discussed in theoretical and experimental setting. Measurements of acoustic signals were carried out with simultaneous video recording of the falling drop. The shock pulse amplitude does not depend on the shape of the underwater drop segment; it is determined only by the impact velocity and current geometric parameters of the surface segment, of which the shape is fixed in the video frame that is last one before impact. The shape envelope is approximated by continuous function that is used to simulate the supersonic expansion of the contact spot and calculate the shock pulse amplitude. Closeness of the calculated and experimental data confirms the stability of the shape of the surface drop segment during the shock pulse emission.

Evolution of shock compression pulses in polymethylmethacrylate and aluminum

The numerical study of the dynamics of shock compression pulses in polymethylmethacrylate (PMMA) and aluminum is performed in both viscoelastic and hydrodynamic approximations. The Maxwell relaxation model with two parameters, the relaxation time and the static yield strength, is used for both materials for a description of their viscoelastic properties. Constant values of the parameters suffice for a description of shock-wave profiles in the case of PMMA, while changes of these parameters in the course of deformation are needed to be taken into account in the case of aluminum. A method of accounting of such changes is proposed based on the kinetic equations for mobile and immobilized dislocations. The proposed approach lets us take into account the main features of the elastic precursor in aluminum, as well as its change with distance and target temperature. The approach by its complexity and accuracy lies between the simple relaxation models and the complete dislocation-based ones. Using the proposed models, we investigate the influence of stress deviators on the change of compression-pulse amplitude with the propagation distance inside the material. The shock pulse in the viscoelastic approximation has greater amplitude in comparison with the hydrodynamic one for low distances due to higher stiffness and conversely at larger distances due to the greater velocity of propagation of the unloading wave that overtakes the shock wave front. The maximum difference between two approximations in the value of the shock pulse amplitude is about 35% for PMMA and about 90% for aluminum.

SHOCK PULSE AMPLITUDE AND WIDTH EFFECTS ON THE SHOCK RESPONSE OF AN OPERATIONAL DISK DRIVE

The interest in the effects of shock on HDDs has come into currency due to the reduction of the flying height of the head/disk interface and the increasingly hostile environments encountered in the usage of many consumer electronics and portable devices. This paper discusses the shock pulse amplitude and width effects on the shock response of an operational disk drive. The drive is subjected to half sine acceleration shock pulse with varying amplitude and width. A finite element model of the hard disk drive is developed in the commercially available finite element package, ANSYS/LSDYNA. The air bearing between the disk and the slider is modeled by nonlinear springs. The contact between the disk and the slider is also considered. It is found that the shock response of the drive is sensitive to both the shock pulse amplitude and width.

Wave processes when driving metal pipes into the ground using shock-pulse generators

1. For the example of sinusoidal pulses applied to the end of a pipe, we have shown that a pulse with the greatest amplitude at fixed shock energy will drive the pipe furthest into the ground. 2. Other conditions being equal, the greatest distance to which the pipe is driven in the ground is directly proportional to the amplitude of the initial pulse applied to the end of the pipe. 3. The residual strain (stress) in the pipe due to the presence of external friction increases with the length of the shock pulse. 4. The damping of the shock-pulse amplitude is linear, regardless of the elastic properties of the ground, as long as individual sections of the pipe slip relative to the ground. The damping coefficient is directly proportional to the frictional coefficient of the pipe in the ground and does not depend on the shock-pulse configuration. 5. Analysis shows that the distance to which the pipe is driven in the ground may be increased by a factor of more than 1.5, at constant shock energy, by eliminating the intermediate mass from the model of the shock-pulse generator; in practice, the intermediate mass corresponds to the housing of the shock machine rigidly connected to the anvil.

High strain rate deformation of Mo and Mo-33re by shock loading: Part I. Substructure development

The details of substructure development in Mo and Mo-33Re deformed at ultrahigh strain rates by shock loading have been studied quantitatively with optical, electron optical, and X-ray diffraction techniques. The finite rates of dislocation generation, apparently limited to rates of the order of 10 21 m−2 s−1, cause shock-induced dislocation densities to decrease at short shock pulse durations for a constant shock pulse amplitude. Similarly, the volume fraction of deformation twins in Mo-33Re also decreases at short pulse durations. Twin thicknesses were found to be 32 nm and 200 nm for Mo-33Re and Mo, respectively, with these thicknesses independent of pulse duration. Measurements of the dislocation loop densities support the concept of loop formation by a dislocation mechanism, rather than through the agglomeration of shock-induced excess point defects.

Strengthening effects of deformation twins and dislocations introduced by short duration shock pulses in cu-8.7ge

Shock hardening of Cu-8.7Ge has been shown to depend strongly on both shock pulse amplitude and shock pulse duration. Because of the time dependent nature of plastic deformation processes, the strengthening effects associated with changes in pulse duration at a constant pulse amplitude pass through a maximum at ∼0.07 μs, followed by an increase to the same high level for durations above lμs. The maximum at short pulse durations arises from twin boundary strengthening, which is related to the development of extremely fine twins with a large amount of twin boundary area per unit volume of twinned material. For longer durations, the twins increase in thickness with less twin boundary area, thus decreasing the strengthening contribution. At the same time, the strengthening from dislocation substructures increases monotonically over the entire range of pulse durations. Estimates of the dislocation generation rate indicate that it is at least 1021 - 1022/m2/s for the conditions studied. Also, it has been found that twins form in Cu-8.7 Ge in less than 0.0lμs. Finally, it has been established that very short duration shock pulses provide an important new technique to study the time dependence of plastic deformation processes.

Propagation characteristics of acoustic shock pulse in Fe‐Cr‐Al alloy

High‐damping materials have become to be interesting for noise control and vibration damping. Fe‐Cr‐Al alloy is called Silent alloy and shows high mechanical strength in addition to its high damping capacity. The acoustic shock pulse was used in order to obtain the fundamental data of the acoustic characteristics for longitudinal wave of this alloy. The amplitude dependence of attenuation and propagation velocity of acoustic shock pulse was measured at room temperature. The attenuation constant increases as the amplitude of shock pulse increases, and shows a maximum value at about 6.5 × 10−5. The propagation velocity of shock pulse slightly decreases with increasing the amplitude of shock pulse. To obtain the clear amplitude dependence of attenuation constant and propagation velocity, it is necessary to measure them in the higher amplitude range.