Mid-plane forces during stress wave propagation through 1D granular chains of closed-cell PVC foams

The stress wave propagation and fracture formation in HMX-Estane polymer-bonded explosive under an impact loading were studied using material point method mesoscale simulation. The stress wave propagation, temperature localizations, and material fracture behaviors were analyzed for various impact velocities, porosities, and binder volume fractions. The peak value of local longitudinal stress, due to stress wave propagation and reflection upon impact loading, was found to be higher for a larger impact velocity but lower for a greater porosity or a binder volume fraction. A spall fracture was observed in the strong tensile zones formed by the reflected wave. Greater damage was observed for either a higher impact velocity or a larger porosity. The plastic dissipation, frictional dissipation, and viscoelastic dissipation were all found to be a lead for hotspots. This study provides mesoscale explanations for stress wave propagation, the fracture mechanism, and the formation of hotspots in energetic materials.

3D modeling of the influence of a splay fault on controlling the propagation of nonlinear stress waves induced by blast loading

The role of particle collisions for the dynamics in planetary rings

High chromium white irons (HCCIs) are used extensively throughout the mineral processing industry to handle erosive and corrosive slurries. This study is an investigation of the effect of impact angle and velocity on slurry erosion of HCCI. The tests were carried out using a rotating whirling-arm rig with particle concentration of 1 wt. %. Silica sand which has a nominal size range of 500–710 μm was used as an erodent. The results were obtained for angles of 30 deg, 45 deg, 60 deg, and 90 deg to the exposed surface and velocities of 5, 10, and 15 m/s. The highest erosion resistance of HCCI was at normal impact and the lowest at an angle of 30 deg, irrespective of velocity. The low erosion resistance at an oblique angle is due to large material removal by microcutting from ductile matrix and gross removal of carbides. The effect of velocity, over the studied range from 5 m/s to 15 m/s, on the increase in the erosion rate was minor. The change of impact velocity resulted in changing the slurry erosion mechanisms. At normal incidence, plastic indentation with extruded material of the ductile matrix was the dominant erosion mechanism at low impact velocity (5 m/s). With increasing impact velocity, the material was removed by the indentation of the ductile matrix and to smaller extent of carbide fracture. However, at high impact velocity (15 m/s), gross fracture and cracking of the carbides besides plastic indentation of the ductile matrix were the dominant erosion mechanisms.

The present study aims to address the effect of sphere temperature on water-entry cavity. For this purpose, an experiment on vertical water-entry cavity of a heated sphere is conducted by utilizing a high-speed video camera. The temperature of the sphere ranges from 17℃ to 800℃. The complex flow phenomena of water entry, produced by a change in temperature of a sphere, is obtained for the first time. According to the finding, cavity is not formed around the room temperature sphere under the condition of the impact velocity of 1.5 m/s. When the temperature of the sphere is 300℃, the cavity appears, while it disappears when the temperature reaches up to 400℃. Interestingly, cavity appears again as the sphere is heated to a temperature of 700℃. The degrees of drag reduction of the sphere are different in various temperature conditions. Based on the theory of heat transfer and fluid dynamics, we analyze the mechanism for the influences of temperature and velocity on the forming of cavitation. The results show that the heat-transfer efficiency and heat-transfer mode between sphere and water change with the increase of temperature. Meanwhile the turbulent characteristic around the sphere, the surface roughness and hydrophobicity of the sphere are affected by the bubbles and vapor layer. In consequence, these characteristics influence the formation of cavity. The results of the effect of impact velocity on water-entry cavity reveal that the heat transfer performance plays a significant role in the forming of cavity, while the heat transfer efficiency is improved by the increase of impact velocity. The water-entry characteristics are similar to those in flow field under high temperature at low impact velocity as well as under low temperature at high impact velocity. The flow field of water entry looks similar under 330℃ at high impact velocity as well as under 400℃ at low impact velocity. Thus, an abnormal phenomenon appears. That is to say, the cavity size first decreases, and then disappears with the increase of impact velocity for the sphere at 330℃. The heat transfer performance can determine whether a cavity forms under the conditions of the impact velocity ranging from 1.5 m/s to 3.8 m/s. Meanwhile, the impact velocity itself can merely affect the cavity shape. The pitch-off time of the 300℃ sphere is irrelevant to impact velocity, which shows a good consistency with the literature result. Also, this research will be conductive to gaining an insight into the complex flow of water-entry with a heated sphere.

High-velocity bullet impact (velocity: 700 ± 15 m/s) is a significant concern during asymmetric warfare. Ballistic helmets for high-velocity bullet impact and associated biomechanical responses of the headforms are actively sought. Further, data on the performance of ballistic helmets against high-velocity impact are not available in the literature. Toward this end, we have evaluated the performance of Patka (helmet) against high-velocity bullet impact. Patka was mounted on various headforms to assess the perforation of the Patka by the bullet and to measure various biomechanical parameters such as back face deformation (BFD), head kinematics, brain simulant pressures, and neck loads. Bullet impact in front and oblique (30° right to the sagittal axis) orientations were considered. Our results suggest that the Patka was effective in mitigating the high-velocity bullet impact. Perforation of the Patka by the bullet was not observed. BFD in the witness material was negligible (<1 mm). Measured head kinematics and brain simulant pressures were comparable to the quantities typically reported during low- and medium-velocity bullet impacts. Further, most of the biomechanical responses, except angular acceleration and neck force, were below 50% injury risk for mild traumatic brain injury (mTBI). Despite these encouraging trends, the shattering of bullets into fragments was also observed. These fragments traveled a considerable distance at reasonable velocities. This work provides unique insights regarding the performance of Patka and associated biomechanical responses of the headforms against high-velocity bullet impact, with implications in the design and evaluation of futuristic ballistic helmets. TERMINOLOGIES Ballistic threat level: Ballistic threat levels are defined based on the impact velocity of the bullet. Different types of bullets are proposed to achieve the desired impact velocities corresponding to different ballistic threat levels. Ballistic helmet: Ballistic helmet is a type of protective headgear designed to protect the wearer head from potentially fatal impacts during combat operations. Ballistic performance: Ballistic performance of the helmet is evaluated based on the perforation resistance capacity of the helmet and back face deformation (BFD) of the helmet. Back face deformation (BFD): Back face deformation (BFD) of the helmet refers to the localized dent or bulge in the inner layer of the helmet due to ballistic impact. BFD is measured as a depth of indent in the witness material (e.g., Roma Plastilina #1 clay) of the cruciform cavity-based headform. Headform: Headform is a model of the human head replicating a few of the anatomical and material aspects. Headforms can vary in design and complexity based on the intended applications. Patka: Patka is a protective headgear designed to provide ballistic protection to the head against high-velocity threat (impact velocity: 700 ± 15 m/s). Patka is made up of hardened (armour) steel material. Head kinematics: Head kinematics refers to the motion of the head typically measured in terms of linear acceleration and angular velocity. Neck loads: Neck loads refer to the forces and moments experienced by the neck during a static or dynamic event. Brain simulant pressure: Brain simulant pressure is a hydrodynamic pressure generated within the brain simulant.

To investigate the relationship between stress wave propagation and the plasma discharge generated by a projectile high-velocity impact on solar array with 2A12 aluminum substrate structures at the incidence angle of 60°. Three sets of experiments about stress wave propagating and plasma discharge in composite structure of solar array have been performed by taking advantage of PVDF (polyvinylidene fluoride) film sensor, plasma characteristic parameter diagnostic system, discharge measurement system and two-stage light gas gun loading system established by ourselves. Experimental results showed that the duration of stress wave was about 30±5μs, and maximum stresses are about 1400±200MPa in experiments. Furthermore, the discharge phenomenon did happen and the duration of discharge current was also different in solar array at the different impact velocities. The basic consistency between stress wave propagation and discharge duration is also confirmed by experiments.

The overall dynamic mechanical behavior of a double-scale discontinuous rock mass with a nonlinear deformational macrojoint was investigated. A method of combining the split three characteristic lines with the piecewise linear displacement discontinuity model (DDM) was proposed. The method was applied to investigate the transmission coefficient of P-wave propagation normally through a double-scale discontinuous rock mass with a nonlinear deformational macrojoint. The results were verified by comparison with the results of P-wave propagation normally through a double-scale discontinuous rock mass with a linear deformational macrojoint. The results showed that for a small amplitude stress wave, the nonlinear deformational macrojoint can be simplified as a linear deformational form to study the stress wave propagation, whereas for a large amplitude stress wave, the effects of the nonlinear deformational behavior of the macrojoint must be considered. The difference of the effects of nonlinear and linear deformational macrojoints on large amplitude stress wave propagation can be overlooked in the low-frequency or high-frequency regions. In addition, when the incident stress wave amplitude and initial macrojoint stiffness are sufficiently large, the effects of the nonlinear deformational macrojoint on stress wave propagation can be overlooked, and the effects of microdefects must be considered. The influence degree of microdefects on the stress wave propagation increases with the increase of incident stress wave frequency.

Research of the different impact velocity influences on the efficacy of Penetration with Enhanced Lateral Efficiency (PELE) ammunition was performed using numerical simulations, where several conclusions were drawn. Namely, the average mass of fragments decreases as impact velocity rises. The mass of the residual projectile drops as impact velocity rises. At higher impact velocities, the casing and core of the projectile fracture more, and more fragments are formed. At higher impact velocities, the dispersion of fragments is greater, and bigger holes in the target are present. The fragment velocity rises linearly with the increase of impact velocity. Research on different target material influences on terminal ballistics of PELE is also conducted, where one target material from experimental research was also compared with numerical simulation. Several conclusions were made. Namely, the harder the target, the more fragments are created. The radial velocity of fragments is higher behind the steel target than behind the aluminum one. The aluminum target fragments the most and gives the highest residual velocity of the projectile. The highest fragmentation of the projectile jacket was recorded for the case of the hardest target (Nanos-BA). Nanos-BA steel target deformed the least upon impact, has the smallest hole, and gives the smallest number of fragments (from the target itself). The Nanos-BA steel target produces the largest number of fragments from the projectile jacket.

This paper presents a theoretical study of the heat transfer during particles colliding with a surface considering the material elastoplastic properties and adhesion forces of particles. The model divides the impact processes into three stages, the elastic stage, the elastic-plastic stage, and full plastic stage, and assumes that the recovery stage is fully elastic. The rebound velocities of particles are obtained by the comparison of initial kinetic energy and total energy losses, and the major loss mechanisms in the form of adhesion forces and plastic deformation of particles. During each stage of the collision, the impact duration of collision is predicted numerically by integrating the differential equations of contact forces and particle motion. Elastic impact duration and heat transfer of a 4.76 mm stainless steel particle with 304 stainless steel surface agrees well with a previous analytical model. The result shows that at higher impact velocity, a larger percentage of time is spent in the compression stage. Sand particles under 50 μm impacting a nickel based super alloy surface (DD3) from room temperature to 1273 K are evaluated. Time duration decreases with an increase in impact velocity and a decrease in particle size. Heat transfer at particle impact is determined primarily by the contact area and time duration, besides the temperature difference and thermal conductivity. Heat transfer of plastic impact is noticeably smaller than the Sun and Chen’s analytical model, and the difference increases with increase in impact velocity. Adhesion forces affect the time duration significantly at low impact velocity. Heat transfer for 20 μm sand particles at 1073 K, 1173 K and 1273 K is about 1.12, 1.15 and 1.25 times that at room temperature, and about 1.07, 1.08 and 1.15 times the impact duration at room temperature.

The propagation of stress waves in filled jointed rocks involves two important influencing factors: transmission‐reflection phenomena and energy attenuation. In this paper, the split Hopkinson pressure bar (SHPB) test is used to shock the filled rock with joint angles of 0, 30, and 45° and the thickness of 4 mm and 10 mm, respectively, in three different velocities. The wave curves of the incident wave, reflected wave, and transmission are obtained. The effects of the filling angle and joint thickness on wave propagation are analyzed. Based on the propagation characteristics of stress waves in joints, the stress expression of oblique incident stress waves propagating in filling joints is derived, and the energy coefficient of transmission and reflection is calculated. The results show that the propagation of stress wave in filling joints is related to the impact rate. The larger the impact rate is, the larger the maximum voltage amplitude of the three waves is. And the increasing amplitude of the incident and reflected waves is larger than the transmitted wave; the greater the impact velocity is, the smaller the stress‐strain curve gap of the three dip joints is, and the fracture strength of the specimen decreases with the increase of the joint dip angle. The larger the joint dip angle is, the smaller the deformation of the rock‐like specimen is. The change of the transmission coefficient is related to the joint angle, and the larger joint angle weakens the influence of the joint width on the transmission of the transmitted wave; under each impact velocity, the theoretical and experimental stress peaks are approximately the same, and the transmission coefficient maintains a good consistency with the oblique incident angle.

A series of experiments has been performed on the Sandia Hypervelocity Launcher to impact a 1.25‐mm thick aluminum bumper by an aluminium flier plate 17‐mm diameter by 0.092‐mm thick over the velocity range of 5 km/s to 11 km/s. Radiographic techniques were employed to record the debris cloud generated upon impact. The shape of the debris cloud is found to depend on the flier plate tilt. Generally—the data indicate a central core of high desity surrounded by a diffused layer. These experiments allow measurements of debris cloud expansion velocities as the material undergoes a phase change from solid fragments at impact velocities of 5 km/s to a mixture of liquid and vapor phase at higher impact velocities. The expansion velocity of the debris cloud increases with increasing impact velocity, with the high‐density leading edge traveling faster than the impact velocity. There is a difference between the X‐ray and photographic measurements of expansion velocities at higher impact velocities. This is believed to be due to the presence of very low‐density vapor in the photographic records that are not detected using X‐ray techniques.

Study on the impact damage behavior and infrared radiation evolution characteristics of rock under different drop hammer velocities

Supersonic impact of metallic microparticles onto metallic substrates generates extreme interfacial deformation and high contact pressures, enabling solid-state metallic bonding. Although higher impact velocities are generally believed to improve bond quality and mechanical properties in materials formed by supersonic impact deposition, here we report a peak in bond strength for single microparticle impact bonding, followed by a decline at higher impact velocities. Our in situ micromechanical measurements of interfacial strength for Al microparticles bonded to Al substrates reveal a three-fold increase from the critical bonding velocity (800 m/s) to a peak strength around 1,060 m/s. Interestingly, further increase in impact velocity results in a rapid decline in local interfacial strength. The decline continues up to the highest velocity studied, 1,337 m/s, which is well below the threshold required to induce melting or erosion. We show that a mechanistic transition from material strengthening to intensified elastic recovery is responsible for the peak strength in impact-induced bonding, with evidence linking the intensified elastic recovery to adiabatic softening at high impact velocities. Beyond 1,000 m/s for Al, interfacial damage induced by the intensified elastic recovery offsets the strength gain from higher impact velocities, resulting in a net decline in interfacial strength. This mechanistic understanding shall offer insights into the optimal design of processes that rely on impact bonding.

the stress wave speed is the necessary condition to make sure pile length and pile defects position in low strain integrity testing of foundation pile with the stress wave echo method. Quantifying the stress wave speed is very difficult, because it is affected by multi- factors. This has been choke point developing test technology of foundation pile. In the paper, some factors influencing the stress wave speed were analyzed according to stress wave theory and experiment results, the quantity relations of the stress wave speed in pile and time and concrete age were made sure. lastly, five brief methods to quantifying the stress wave speed in pile were presented to control pile quality for test engineers according engineering practice.