High-pressure Gas Jet Research Articles

Cuboid obstacle influence on high-pressure jet dispersion: A CFD study

In the context of the process industry safety, one of the main accidental scenarios is the release of high-pressure gaseous material. Since natural gas is highly flammable, the likelihood of ignition increases as the jet develops, with a maximum area of effect related to its lower flammability limit (LFL). This work aims at simulating and evaluating the interaction between high-pressure natural gas jets and cuboid obstacles, which were selected due to their prevalence in the process industry as storage units or buildings present in industrial parks. The maximum extent of the cloud at the LFL of natural gas is often influenced by the jet-obstacle interactions, necessitating complex numerical methods like computational fluid dynamics (CFD) for accurate estimation. Therefore, this study provides pivotal insights that challenge traditional modelling approaches, like integral ones, offering cost-effective alternatives where needed without compromising on safety.The findings indicate that using a CFD approach is not always necessary, as it largely depends on the storage pressure, diameter size, and the release height of the jet. At storage pressures of 65–130 bar with an orifice diameter of 2.54 cm, and a release height above 2.75 m, simpler methods like integral models are applicable without any substantial reliability loss. This is especially true when the cuboid obstacle is farther away from the release source. At lower release heights, especially if coupled with a larger orifice diameter, the CFD approach should be utilised as jet-cuboid interactions become highly relevant to the development of the jet.

Study on the Influence of Volute Throat Jet on Excitation Vibration Alleviation of Radial Turbine Blade

Abstract Turbine blade fracture, resulting from high-cycle fatigue (HCF), is the most commonly observed failure mode of turbochargers. In a vaneless turbine, the radial turbine blade is susceptible to HCF under excessive aerodynamic excitation due to the flow field distortion caused by the volute tongue. The present study explores a technique to mitigate blade excitation by reducing pressure disturbance in the volute tongue area. The gas with higher pressure in the inlet section of the volute is transferred to the low-static pressure area upstream of the volute tongue through a throat jet hole. The usage of high-pressure gas improved the homogeneity of the flow field near the volute tongue. The study investigates the mitigation of high-pressure gas jet on turbine blade excitation, the impact of jet hole geometry on the suppression effect of the blade vibration, and the effect of high-pressure jet on turbine performance using numerical simulation of unsteady flow fields. The results indicate that the jet flow has a substantial impact on dampening the blade vibrations. The harmonic pressure amplitude at the monitor point located within the high blade vibration amplitude region is reduced by up to 56%. Generalized pressure analysis reveals that the aerodynamic excitation of the turbine blades is significantly reduced. Experimental evidence verifies the effectiveness of the jet hole scheme in reducing blade vibration. Moreover, the jet hole has a negligible effect on turbine efficiency. However, there is a degree of increased stress in the volute tongue with a jet hole which needs to be evaluated in engineering applications.

The Spatial Development Characteristics of High-Pressure Methane Jet Impinging on Methane Lean-Burn Premixed Flame

This work investigated the effect of high-pressure (10 MPa) methane gas jet impinging on the methane lean-burn premixed flame (equivalent ratio of 0.7) based on a three-dimensional numerical simulation by CONVERGE software. The results show that laminar premixed flame is accelerated to develop into a stable turbulent flame under the action of the methane jet, the whole process of flame front development is divided into three stages: laminar (Reynolds number maintains stable, 1–1.3 ms), transition (Reynolds number shows an increasing trend, 1.4–8 ms), and turbulent (Reynolds number tends to stabilize at a high value, 1.9–3 ms). The effect of high-pressure jet on flame development along jet direction (Z axis) is greater than that on vertical direction (Y axis). During turbulence stage, the momentum and kinetic energy of Z axis are 2.7 and 6.3 times greater than that of Y axis, respectively. The high-pressure methane jet causes a change in heat distribution, resulting in local flameout. The rate of change in the local flameout area is greater than that in the flame area, causing a temperature drop in Z axis. This temperature drop increases with the increase in equivalence ratio and with the decrease in distance between cross-section position and ignition center.

Fractal Evolution Characteristics on the Three-Dimensional Fractures in Coal Induced by CO2 Phase Transition Fracturing

To analyze the transformed effect of three-dimensional (3D) fracture in coal by CO2 phase transition fracturing (CO2-PTF), the CO2-PTF experiment under a fracturing pressure of 185 MPa was carried out. Computed Tomography (CT) scanning and fractal theory were used to analyze the 3D fracture structure parameters. The fractal evolution characteristics of the 3D fractures in coal induced by CO2-PTF were analyzed. The results indicate that the CO2 phase transition fracturing coal has the fracture generation effect and fracture expansion-transformation effect, causing the maximum fracture length, fracture number, fracture volume and fracture surface area to be increased by 71.25%, 161.94%, 3970.88% and 1330.03%. The fractal dimension (DN) for fracture number increases from 2.3523 to 2.3668, and the fractal dimension (DV) for fracture volume increases from 2.8440 to 2.9040. The early dynamic high-pressure gas jet stage of CO2-PTF coal influences the fracture generation effect and promotes the generation of 3D fractures with a length greater than 140 μm. The subsequent quasi-static high-pressure gas stage influences the fracture expansion-transformation effect, which promotes the expansion transformation of 3D fractures with a length of less than 140 μm. The 140 μm is the critical value for the fracture expansion-transformation effect and fracture generation effect. Five indicators are proposed to evaluate the 3D fracture evolution in coal caused by CO2-PTF, which can provide theoretical and methodological references for the study of fracture evolution characteristics of other unconventional natural gas reservoirs and their reservoir stimulation.

Study of Flow Field Characteristics During the Impact of a High-pressure Gas Jet on a Bulk-loaded Liquid

A visual experiment platform for high-pressure gas jet impacting the bulk-loaded liquid was designed and built in order to investigate the real law of the interaction between the high-pressure gas jet and the liquid medium during the liquid-balance launch of rocket launcher. The experiments of single-phase gas jet injection and the high-pressure gas jet at different temperatures impacting the bulk-loaded liquid were carried out, and the effects of gas temperature on the characteristics of the gas-liquid flow field have been revealed. The results show that the turbulent mixing between the high-pressure gas jet and the liquid medium leads to the appearance of pressure fluctuations in the gas chamber connected to the nozzle. The higher the gas temperature, the greater the amplitude of the pressure fluctuations. Under the impact of high-pressure gas jet, a gas cavity with an arc-shaped head is formed inside the bulk-loaded liquid. The higher the gas temperature, the faster and more unstable the development of the gas cavity and the flow field. The displacement equation of the gas cavity confirms to the first-order exponential decay function, and the error between the fitting value of the established mathematical model and the measured value is within 2%.

Visualization research of natural gas jet characteristics with ultra-high injection pressure

In this paper, based on a High-pressure direct injection (HPDI) dual-fuel valve, the schlieren imaging method combined with laser-induced fluorescence imaging method (PLIF) are used to investigate the macroscopic structure and concentration distribution characteristics of a high-pressure gas jet under different injection pressure ratio (NPR) and gas injection moment (Ti). The data processing method for macroscopic structure and concentration distribution of gas jet is optimized, and a new concentration partition method for the gas jet is proposed. The results show that comparing the gas jet penetration and volume correlation equations from Hamzehloo A and Vuorinen V, the correlation coefficients of ultra-high and small NPR conditions are quite different due to the different development processes of the shock wave structure. With the improvement of NPR, the influence on gas jet penetration is decreasing, which is the same as the conclusion of previous research. In this paper, the later stage of gas jet is divided into four regions: the Mach disk core region (A), the concentration rapidly decreasing region (B), the low concentration diffusion region (C), and the edge mixing region (D). The A and B regions are highly correlated with the shock wave structure of the under-expanded gas jet. The increase of NPR and Ti has a great promotion effect on the length and concentration distribution of regions A and B but has rarely effect on regions C and D. The transverse concentration gradient in regions A and B presents a Gaussian distribution structure. The average concentration descent gradient (G¯) in region A is about 4 times that in region B. The transverse concentrations of C and D gradually converge under the action of air turbulence. Under different Ti conditions, the length proportion of regions A and D rarely changed, while the length proportion of regions B and C presents a negative correlation. The G¯ in regions A and B are positively correlated with Ti, but the concentration increase rate keeps decreasing. The range of concentration fluctuation regions in regions C and D keeps expanding with the increase of Ti, indicating that the uniformity of gas jet concentration distribution keeps improving.

Laser surface processing of Ti6Al4V alloy precoated with hard particles

Laser gas-assisting processing of preprepared Ti6Al4V alloy is carried out and resulting surface topology, wetting state, metallurgical changes, and hardness are examined. A thin carbon film accommodating TiC and B4C particles is developed over the surface in the preparation cycle. Laser surface treatment consisting of surface ablation and melting is performed at constant laser scanning speeds and high-pressure nitrogen gas jet. Laser treatment results in surface texture topology with hierarchically distributed micro/nanopillars having 5.6 μm average surface roughness (Ra). The texture of the surface demonstrates a hydrophobic state with a contact angle of about 109° ± 3° and hysteresis of 37° ± 4°. The treated surface free energy yields ∼132 mJ/m2, which is greater than that of TiC (∼120 mJ/m2). The high spreading rate of the molten alloy wets the surface of the hard particles while minimizing nano/mesopores around the particles in the treated layer. The presence of carbon film and TiC particles forms (Ti, Al)N, (Ti, Al)CxN1-x, TiN, TiNx, Ti2N, TiCxN1-x compounds on the surface, which contributes to microhardness enhancement in the treated zone. Surface microhardness of 1670 ± 50 HV is achieved, which remains higher than that of TiN coated, plasma nitrided, and laser nitrided surfaces.

Study on the ignitability of a high-pressure direct-injected methane jet using a scavenged pre-chamber under a wide range of conditions

Natural gas is a promising alternative fuel for internal combustion engines, it allows for a reduction of engine-out emissions without impairing high engine efficiencies. Although this approach is already utilized from small to large engine classes, it is almost exclusively based on the combustion of a premixed homogeneous charge. For ignition, small engines use standard spark plugs or pre-chambers, while large and lean-operated engines use pre-chambers and pilot injections. Direct high-pressure gas injection is a more recent, alternative way to operate gas engines which offers benefits compared to premixed operation such as high combustion pressures, leaner operation, easier quantity regulation, and higher compression ratios, among others. However, in contrast to diesel injection, the compression temperatures are too low for the auto-ignition of the gas jets. Therefore, an additional ignition system is required, usually a pilot injection system is used. In this study, the usability and performance of a scavenged pre-chamber used for the ignition a high-pressure gas jet has been investigated in an optically accessible test-rig that is able to operate at engine-like conditions. Results show that the turbulent hot jet generated by the pre-chamber was able to ignite the high-pressure gas jet under a wide range of operating conditions. Moreover, it also appears to be a promising ignition strategy for very early direct injection during the compression stroke as well as for port injection. The good performance is attributed to the intense mixing of the main gas jet with the hot jet exiting the pre-chamber.

Experimental Study on Entrainment Characteristics of High-Pressure Methane Free Jet.

Entrainment occurs during the high-pressure gas jet process, which is crucial for a natural gas direct injection engine. This study presents an experimental investigation on the high-pressure methane jet from one single-hole injector and proposes a method to obtain the entrainment mass flow rate based on kinetic energy conservation. The entrainment is related to three variables, i.e., spring plate moving distance Δx, gas jet mass at the nozzle outlet mn, and gas jet velocity u1. A spring-set test rig is built to measure the spring plate moving distance Δx, and the schlieren method is adopted to test the gas jet velocity u1 based on a constant-volume bomb (CVB) optical test rig; finally, the weight method is used to obtain the methane gas jet mass at the nozzle outlet mn. This combined measuring method is verified to be valid in the near field to the nozzle. The results show that the methane jet mass flow rate gradually increases along the jet direction and has a two-zone entrainment process. Zone I: near field (Lr < 10), the methane jet mass flow rate linearly increases up to the maximum; in the nozzle exit field (Lr < 1), it is conserved, and no entrainment occurs. Zone II: far field (Lr ≥ 10), the jet mass flow rate maintains the maximum, and the entrainment becomes saturated with a saturation value larger than the initial value at the nozzle outlet. The entrainment rate experiences three stages, linearly increasing in stage I and early stage II but not in late stage II and stage III. The methane injection pressure causes great effects on the mass flow rate and entrainment. As the injection pressure increases, the methane jet mass flow rate increases linearly, but the entrainment rate decreases.

Study on the ignitability of a high-pressure direct-injected methane jet using a diesel pilot, a glow-plug, and a pre-chamber

Natural gas is a promising alternative fuel for internal combustion engines, it allows for a reduction of engine-out emissions without impairing high engine efficiencies. Although this approach is already utilized from small to large engine classes, it is almost exclusively based on the combustion of a premixed, homogeneous charge. For ignition, small engines use standard spark-plugs or pre-chambers, while large and lean-operated engines use pre-chambers and pilot injections. Direct high-pressure gas injection is a more recent, alternative way to operate gas engines which offers benefits compared to premixed operation such as high compression ratio, high combustion pressures, lean operation, quantity regulation, among others. However, in contrast to diesel direct injection, the compression temperatures are too low for the auto-ignition of the gas jets. Therefore, an additional ignition system is required, usually a pilot injection system is used. In this study, the usability and performance of three ignition strategies for direct injected high-pressure gas jets have been investigated in an optically accessible test-rig that is able to operate at engine-like conditions. The first type of ignition system is a pilot injection with a liquid fuel, the second is a glow-plug located near the main gas jet, and the third system is a pre-chamber with a nozzle hole aimed at the main gas jet. Results show that all three strategies are feasible options under the studied conditions. Ignition by a pilot fuel injection is a safe and reliable way to ignite the main fuel. The glow-plug is less reliable and leads to high cycle-to-cycle variation. The best option in the present study is the pre-chamber, it is very reliable, delivers the highest peak cylinder pressure and exhibits the lowest cyclic variability. The good performance is attributed to the intense mixing of the main gas jet with the hot jet exiting the pre-chamber.

Effect of grinding nozzles pressure on particle and fluid flow patterns in a spiral jet mill

Spiral jet mills utilise high-pressure gas jets, which induce particle breakage by collisions. Appropriately angled jets force particles to circulate in dense phase near the wall due to the centrifugal field. Moving radially inwards towards the mill centre, the two-phase dense flow is transformed into a lean phase and fine particles are entrained out by the fluid drag. Here we analyse the effect of grinding nozzles pressure on the particle dynamics and fluid flow by numerical simulation. The average velocity gradient in the radial direction is very steep for low mass loadings, indicative of rapid shearing, but it decreases significantly as the particle mass loading is increased. The dissipated collisional energy, accountable for size reduction, is strongly influenced by the jet penetration through the circulating bed, which in turn depends on the mass loading and operating pressure of grinding gas nozzles. As a result of jet penetration, the grinding gas nozzles pressure becomes less effective at high pressures. The analysis developed here elucidates the coupled effect of mass loading and grinding nozzles pressure on the dissipated collisional energy, which accounts for particle breakage.

PIV measurements of entrainment process of directly injected media in internal combustion engines

PIV measurements have been successfully applied to various flow fields relating internal combustion engines such as in-cylinder air motion, air flow in an intake port, and even a discharging passage of an ignition plug. Measurements of induced air motion around diesel sprays can be said to be a significant example of the PIV applications because the air motion is reflected in an unsteady complicated flow structure. Instead of the apparent entrainment exaggerated by spray droplet dispersing, substantial air entrainment through momentum exchange between liquid and gas was finally obtained by combining PIV and spray profile observation.&#x0D; PIV measurements of this kind were extensionally applied to other direct fluid injection by the authors. The second object was a high-pressure gas jet directly injected under gas pressure as high as 30 MPa. It was found the gas jet has strong air entrainment through momentum exchange in a single gaseous phase between fuel gas and ambient air. The third directly injected medium in internal combustion engines should be torch flame ejected from nozzle holes of a pre-combustion chamber (PCC) to a main combustion chamber (MCC) of a so-called DF (dual-fuel) engine.&#x0D; In this study, mixture entrainment process of torch flames is discussed on the PIV results for the first time. However, chamber configurations of a real DF engine are hard to simulate since itrequires several auxiliary PCC devices such as an ignition plug, a sub gas injector, and so on. All of them should be actuated synchronously with an engine crank angle. In the case of a constant volume vessel (CVV), the synchronization is not necessary, but the mixture control in the PCC becomes problematic because of the lack of compression and expansion strokes that assures PCCgas exchange. For overcoming the situation, rupture of a membrane was introduced in this study. The membrane turns the upper part of the PCC into an air pressure reservoir and low-pressure air jets eject from the nozzle holes after a solenoid-driven needle pierces the membrane for rupturing. The differential pressure between the upper chamber and the lower one was chosen as a main parameter of the experiment.&#x0D; Since the measurements and analysis of the entrainment of the low-pressure air jets are yet to finalize, the outlook of the CVV, the PIV specifications, and prime results of the air entrainment are attached herewith. After all, the PIV measurements revealed essential difference among air entrainment processes of the above three directly injected media in internal combustion engines.

Quantitative 1-D LIBS measurements of fuel concentration in natural gas jets at high ambient pressure

Fuel concentration information is critical to the development of high-efficiency combustion system of direct-injection natural gas engines. In this study, a one-dimensional (1-D) measurement approach based on laser induced breakdown spectroscopy (LIBS) is developed to quantitatively measure 1-D fuel concentration distributions in gas jets at high ambient pressures. Except for the spectral dimension, another dimension of the intensified charge coupled device (ICCD) is employed for the spatial resolution of measurements. The effects of laser energy and ambient pressure on plasma dynamics are investigated to explore the feasibility of 1-D LIBS in concentration measurements at high ambient pressure. Since the peak intensity ratio (PIR) of H656/N746 shows significant spatial variations in the plasma volume, a 1-D calibration strategy is developed by establishing respective calibration curves at different spatial positions to quantify the fuel concentration distributions. The measurement uncertainties are evaluated, including both the systematic and random errors. The temporal variations of the 1-D fuel concentration distributions in methane jets are presented, and the shot-to-shot fluctuations are analyzed in detail. The results show that the coefficient of variation of equivalence ratio is lowest at the end of injection (EOI), suggesting that ignition at the EOI could enable a relatively stable flame kernel formation. Along the radial direction of the jet, a high ignitable mixture percentage appears at approximately 3.0 mm from the jet axis at the EOI, suggesting an optimal ignition position. The results reveal that the 1-D LIBS could be a powerful tool for calibration of numerical models and optimal designs of combustion engines taking advantage of high-pressure gas jets.

Nonlinear wakefields and electron injection in cluster plasma

Laser and beam driven wakefields promise orders of magnitude increases in electric field gradients for particle accelerators for future applications. Key areas to explore include the emittance properties of the generated beams and overcoming the dephasing limit in the plasma. In this paper, the first in-depth study of the self-injection mechanism into wakefield structures from non-homogeneous cluster plasmas is provided using high-resolution two dimensional particle-in-cell simulations. The clusters which are typical structures caused by ejection of gases from a high-pressure gas jet have a diameter much smaller than the laser wavelength. Conclusive evidence is provided for the underlying mechanism that leads to particle trapping, comparing uniform and cluster plasma cases. The accelerated electron beam properties are found to be tunable by changing the cluster parameters. The mechanism explains enhanced beam charge paired with large transverse momentum and energy which has implications for the betatron x-ray flux. Finally, the impact of clusters on the high-power laser propagation behavior is discussed.

Experimental investigation on the microscopic characteristics of underexpanded transient hydrogen jets

The microscopic characteristics of hydrogen jet affect the concentration distribution and gas-air mixing of high-pressure gas jets for a hydrogen engine. In this study, the schlieren method was used to record the hydrogen jet for an outward-opening injector. The results showed that the jet asymmetricity was large in the initial stage of the jet development, then decreased rapidly as the jet developed, and finally entered a stable range of 13%–38% when the valve fully opened. The increase of the ambient pressure was beneficial to reduce the fluctuation range of the asymmetricity. The steady S of an outward-opening injector (S = 0.7 ± 0.03) is larger than that of a single-hole injector (S = 0.25 ± 0.05). The increase in injection pressure and the decrease in ambient pressure caused S to decrease to 1 faster. The steady Γ of an outward-opening injector was experimentally determined, and the value (Γ = 0.98 ± 0.1) was smaller than that of a single-hole injector. According to the transient Γ, the injection process can be divided into the developing phase and the self-similar phase. Γ increased rapidly with time and then stabilized after the injector valve reached its maximum lift position. The gas concentration distribution was uneven along the axial direction. The mole fraction decreased with the increase in axial penetration, and entered a stable range of 0.27–0.37 when axial penetration was greater than 20 mm. The average equivalent ratio was large at the beginning of injection under different pressure ratios, and then decreased and finally stabilized in the range of 1.4–5.

Acoustic Characteristics of Self-Sustained Oscillations Occurring due to the Interaction of a Supersonic Underexpanded Jet with a Cylindrical Cavity

In high-pressure gas–jet Hartmann generators, the source of acoustic energy is kinetic energy of a gas jet by the supercritical ratio between the operation and ambient pressure. Under certain conditions, onflow of a supersonic jet to a resonator is accompanied by powerful self-sustained oscillations with irradiation of acoustic waves into the environment and resonator cavity. A model of a self-oscillating process arising from the interaction of a nonisobaric jet with semi-closed cylindrical cavities is considered, which allows one to identify typical elements of the gas-dynamic structure of the forming flow. The physical pattern of the flow in the gas–jet generator has been discussed and the study of the dependence of the self-sustained oscillation characteristics on the key gas-dynamic and geometric parameters has been performed.

Modeling and analysis of the visualized gas-assisted laser cutting flow from both conical and supersonic nozzles

A coaxial high-pressure gas jet is normally used to assist and enhance laser cutting quality and capability. However, the gas nozzles are mostly of conical type causing the deterioration of the dynamic characteristics of the exit jet. In this research, the effect of both nozzle type and nozzle dimensions on the uniformity and behavior of the exit jet has been investigated. A total of three different supersonic nozzles have been designed in accordance to gas dynamics theory and manufactured using wire electrical discharge machining (WEDM). The exit jet patterns from these supersonic nozzles and a reference conical nozzle have been numerically modeled and compared with the experimental observations made through Schlieren visualization. The experimental results are found to match and hence validate the simulations. It is concluded that the exit jet from the supersonic nozzle is marked by uniformity, better dynamic characteristics, and longer effective exit jet length compared with conical nozzle.

Акустические характеристики автоколебательного процесса, возникающего при взаимодействии сверхзвуковой недорасширенной струи с цилиндрической полостью

In high-pressure gas-jet emitters, the source of sound energy is kinetic energy of gas jet at supercritical pressure ratios between the working pressure and the atmospheric pressure. Under certain conditions, interaction of a supersonic jet with the resonator is accompanied by powerful self-excited oscillating process with the generation of acoustic waves into the environment and cavity resonator. A model of a self-excited oscillating process arising from the interaction of non-isobaric jet with semi-closed cylindrical cavities, allowing to distinguish typical elements of gas-dynamic structure of the forming flow, is considered. The physical pattern of the flow in the cavity of gas-jet emitter is discussed, and a study of the dependence of the characteristics of the self-excited oscillating process on the gas-dynamic and geometric parameters is performed.

Combined pulsed laser drilling of metal by continuous wave laser and nanosecond pulse train

In this paper, a new form of combined pulsed laser (CPL) consisting of continuous wave (CW) laser and nanosecond (ns) pulse train was proposed for drilling Q235B steel without high-pressure gas jet. The average power of CW laser ranged from 100 to 700 W, while the average power of the ns laser was fixed at 12 W. The experiments were carried out to study the influence of the average CW laser power on the drilling efficiency and quality of CPL. The results show that there were two completely different matching mechanisms between the CW laser and ns pulse train. Firstly, during the CPL drilling with the 100-200 W CW laser, the ns pulse train could be used to timely and periodically eject the central part of the molten metal, leaving a recast layer with a thickness of up to 200 μm. In addition, for the CPL drilling with the 550 W CW laser, a little part of molten metal was continuously ejected by the ns pulse train, and all of the remaining molten metal could be removed by the boiling of molten metal, thus leaving a recast layer with thickness less than 10 μm. The new CPL presented in this paper has an important guiding significance for improving the quality and making full use of the high efficiency of CW laser drilling.

Mechanical properties of supersonic-impacted Al6061 powder particles

The cold spray process utilizes a high-pressure gas jet to accelerate metallic particles to supersonic velocities, causing bonding to the substrate upon impact. The mechanical characterization of impacted particles is of great interest as their mechanical properties are strongly related to those of bulk cold-sprayed coatings. Here, in-situ micro-compression and tension results are presented from impacts in single-pass cold spray trials of as-atomized and heat-treated Al6061 powders. The effects of powder microstructure on the yield strength and ductility of individual impacts are discussed. Such observations contribute to a more fundamental understanding of the mechanical behavior of impacted metallic materials.