Shock Wave Loading Research Articles

SHOCK-WAVE INITIATION OF SYNTHESIS IN NI-AL POWDER MIXTURE INSIDE TITANIUM MATRIX

This study presents the results of studying the effect of shock-wave loading on the initiation of synthesis in Ni-Al powder mixture inside titanium matrix. X-ray phase analysis (XRD) and measurement of the microhardness of the intermetallic layer showed that this layer consists of a monophase product NiAl, which is formed directly during explosive loading at a given impact velocity of the plate. Thus, the use of shock-wave loading made it possible to obtain a layered material with a strengthening intermetallic layer. The results obtained are promising for the development of new structural materials with special performance properties.

STUDY OF STEEL BARRIER SURFACE AFTER HIGH-SPEED EXPOSURE OF W AND TIC POWDERS

The surface layer of an obstacle made of U8 steel is investigated after high-speed exposure to a flow of powder particles. After analyzing the frames of high-speed photography, the average velocities of movement of particles of tungsten and titanium carbide powders were determined. It is shown that the shock-wave loading of the barrier material and the effect of particles accelerated by the explosion energy provide a change in the physical and mechanical properties of the surface and the volume of the steel barrier material.

Damage effect of pile wharf under underwater explosion load

According to the relevant data of reinforced concrete pile test under underwater explosion load in the near-field range of the cooperative company, the corresponding numerical model is established through the explicit finite element analysis program AUTODYN. The accuracy of the required parameters and the calculation method in the numerical simulation process is verified by comparing shock-wave load with reinforced concrete pile damage. Considering the influence of charge quality on the dynamic response and damage mode of reinforced concrete single and group piles, the collapse conditions of the high-pile wharf are analyzed from static and dynamic aspects based on the reinforced concrete pile model of a typical high-pile wharf structure. Results show that the reflected pressure of shock wave is unevenly distributed along the pile with different explosive equivalents, that is, large in the middle and small on both sides. The damage modes of single piles can be divided into bending, bending shear, and shear failures. The study of the continuous collapse condition of piled wharf reveals that the concrete pile and the cap contact part of the first coagulant crushing failure.

Molecular dynamics simulation on spallation of [111] Cu/Ni nano-multilayers: Voids evolution under different shock pulse duration

Spalling behavior of multilayered materials has a tight correlation with shockwave loading conditions and heterointerfaces. Here, the dynamic response and spallation of [111] Cu/Ni nano-multilayered system under different shock pulse duration are investigated by molecular dynamics. Our work suggests that spallation occurs only in the Cu region instead of in Ni. Also, spalling mechanism transit from homogenous nucleation of voids within Cu layers to nucleation at Cu/Ni interfaces with growing shock duration, resulting in the drop of global spall strength. The recompaction result from the compressive wave is observed to blocks the cavitation’s aggregation, which proves the possibility of damage controlling by interface and impedance design at the atomic scale. Additionally, dislocation analysis shows a similar evolving process of dislocations in Cu and Ni. Longer shock duration is found to result in lower peak density of stair-rods.

Bioinspired diamond composites and their dynamic shock performance

The design of high-strength and high-toughness materials that can sustain high shock-wave loadings is crucial for both armor and civil applications. We propose a bioinspired diamond composite that mimics the brick-and-mortar arrangement of nacre from mollusk shells and evaluate its performance for different diamond brick contents using lattice-spring model. In this work, we present a systematic investigation elucidating the effects of volume fraction of diamond brick, on the shock compression response of bioinspired diamond composites. By comparing the nacre-like diamond composite with traditional diamond composite, it was found that the nacre-like diamond composite can reduce damage degree in diamond composite, and improve dynamic strength of diamond composite. More importantly, the damage evolution analysis of the impacted nacre-like diamond composite indicated that there is large-scale crack deflection, which is only cause slight damage to the diamond brick. The obtained numerical results may provide valuable insights into the preparation of superhard composites for numerous engineering applications.

Spallation Characteristics of Single Crystal Aluminum with Copper Nanoparticles Based on Atomistic Simulations.

In this study, the effects of Cu nanoparticle inclusion on the dynamic responses of single crystal Al during shockwave loading and subsequent spallation processes have been explored by molecular dynamics simulations. At specific impact velocities, the ideal single crystal Al will not produce dislocation and stacking fault structure during shock compression, while Cu inclusion in an Al–Cu nanocomposite will lead to the formation of a regular stacking fault structure. The significant difference of a shock-induced microstructure makes the spall strength of the Al–Cu nanocomposite lower than that of ideal single crystal Al at these specific impact velocities. The analysis of the damage evolution process shows that when piston velocity up ≤ 2.0 km/s, due to the dense defects and high potential energy at the interface between inclusions and matrix, voids will nucleate preferentially at the inclusion interface, and then grow along the interface at a rate of five times faster than other voids in the Al matrix. When up ≥ 2.5 km/s, the Al matrix will shock melt or unloading melt, and micro-spallation occurs; Cu inclusions have no effect on spallation strength, but when Cu inclusions and the Al matrix are not fully diffused, the voids tend to grow and coalescence along the inclusion interface to form a large void.

Insights from the MEDE program: An overview of microstructure–property linkages in the dynamic behaviors of magnesium alloys

Magnesium (Mg) and its alloys have been the subject of intensive scientific research and development in the communities of materials science and engineering, mechanical engineering and manufacturing. Considering their light weight and high specific strength, current and potential applications include the aerospace industry, automobiles, and vehicle and personnel armors. This range of applications demands a good understanding of the behavior under extreme conditions such as impact or high strain rate loading. The past two decades have witnessed a surge of studies of the mechanical responses of Mg and its alloys under impact loading, both experimentally and using simulations and modeling at different spatial and temporal scales. Experimental examinations at strain rates up to 107 s−1 (shock wave loading) have been published. In terms of simulations and modeling efforts, multi-physics, multi-scale investigations, from first principles calculations (density functional theory, DFT), molecular dynamics (MD), discrete dislocation dynamics (DDD), crystal plasticity (CP) and continuum mechanics have all been explored. To address the challenges in design, manufacturing and application of Mg alloys, the US Army Research Laboratory (US-ARL) created the Materials in Extreme Dynamic Environments (MEDE) Collaborative Research Alliance (CRA) in 2012. The goal of the Metals Program within the MEDE CRA has been to observe, understand, and design the mechanisms active within Mg and Mg alloys in these extreme conditions.In this paper, fundamental aspects of plastic deformation of Mg and Mg-alloys and the history of the research efforts in experiments, modeling, and simulations available in the literature are critically reviewed. Key findings and contributions from the Materials in Extreme Dynamic Environments (MEDE) Metals Collaborative Materials Research Group (CMRG) are presented, followed by summary and future perspectives.

Modeling of shock-wave loading of carbides as mixtures of components

The results of numerical experiments on the modeling of shock wave loading of solid and porous carbides with various stoichiometric compositions are presented. The model is based on the assumption that all the components of the mixture, including gas, have similar pressure, velocity and temperature. The model allows describing the behavior of porous materials and mixes in a wide range of porosity and pressures with precision of experiment. The behavior of complex materials such as carbides is considered as a mixture. The model accurately describes the behavior of the carbides with equal shares of the components of WC, TiC, TaC, NbC and the behavior of boron carbide B4C. Comparison for data of calculation and experimental data was held for carbides with different porosity.

Damage assessment of prefabricated prestressed channel slab under plane charge blast

The study of the mechanical properties of prestressed concrete channel slabs under different plane charge air blasts for applications in civil defense engineering is significant. For this reason, similar simulation tests were conducted on the anti-explosive performance of three 1:3 scale prestressed concrete channel slabs under 9 times plane charge air blast. The positive duration was more than 260 ms to simulate the uniform distribution load of a strong blast air shock wave on the prestressed concrete channel slab. The results showed that the designed prestressed concrete channel slab had good displacement ductility without brittle destruction, which significantly reduced the damage of the blasting impact on the structure. The channel slab could resist an air shock load of 0.467 MPa without damage. On the other hand, the positive duration was not only related to the quality of the overlying soil but also related to the air shock wave overpressure design value. The channel plate is regarded as a rigid-plastic component to calculate its plastic dynamic response under explosive load. In addition, the reliability of the theoretical calculation results and ABAQUS software simulation were verified by experimental data, which provided a feasible analytical method for calculation and simulation research in civil air defense engineering.

Numerical Investigation on the Formation and Penetration Behavior of Explosively Formed Projectile (EFP) with Variable Thickness Liner

Explosively formed projectiles (EFPs) are widely used in civil applications and the military field for their excellent impact performance. How to give full play to the energy accumulation effect of explosives and improve the penetration performance has become the main problem of EFP design. The aim of the present study was to investigate the effect of liner structure on EFP formation and its penetration behavior. In order to achieve this, a finite element (FE) model was first established on the basis of the Lagrange and ALE method. Then, formation and penetration performance tests of EFP were performed to verify the validity and feasibility of the proposed FE model, where the configuration, velocity of EFP, and penetration diameter left on the target plate were compared. Finally, by using the proposed FE model, the entire process of the formation and penetration behavior of EFP with axial symmetrical variable thickness liners were analyzed, where spherical-segment liners with uniform and non-uniform thickness were developed. The results were drawn as follows: the numerical simulation error of EFP velocity was less than 5%, and the simulated penetration diameter was compared to the 8.6% error obtained from the experimental method. It demonstrated that the proposed FE model had higher prediction precision. After the explosive was detonated, a forward-folding EFP was formed by the liner with a thin edge thickness, while the EFP formed by the liner with uniform thickness had a backward-folded configuration. It was also found that the liner with a thin edge thickness gave the largest steady velocity of EFP, and it was the lowest by using the liner with uniform thickness. There were two types of loads generated after the formation of an EFP, those were shock wave loading and an EFP, both causing damage in the target plate during the process of an EFP’s penetration into it. The shock wave induced by liners with non-uniform thickness caused higher damage in the target plate, the maximum value of stress was reached at about 4.0 GPa. The forward-folding EFP formed by the liner with the thinnest edge thickness had the largest penetration ability. The backward-folded EFP, owing to the hollow structure, had the worst penetration ability, which failed to penetrate the target plate.

Spall damage in single crystal tin under shock wave loading: A molecular dynamics simulation

Using molecular dynamics methods, we investigated the spall damage in single crystal tin under different shock pressures. The results show that release melting and shock melting occur when the shock velocities increase in the metallic tin. The spall strengths in the molten tin are ~1.5–2.0 GPa lower than that in solid. When release melting occurs, the spall strength drops rapidly, whereas the downtrend of the spall strength becomes gentle during shock melting. The results also show that the spall strength is affected by not only the shock pressure and phase state, but also the temperature and strain rate. By visualizing the development of spall damage, we find that it forms a spall layer in the solid. In molten tin, a cavitation region with a large volume is formed. The maximum number of voids increases with an increase in the shock pressure. The growth rate of the void volume fraction slows down after reaching the initial time of void growth at different impact pressures. We elucidated the variation trend of spall strength between solid and molten tin under different shock pressures. The relevant results can provide a reference for future studies on spall damage investigations.

Atomic-level mechanism of spallation microvoid nucleation in medium entropy alloys under shock loading

Spallation, rupture under impulsive tensile loading, is a dynamic failure process involving the collective evolution and accumulation of enormous microdamage in solids. In contrast to traditional alloys, the spallation mechanism in medium entropy alloys, the recently emerged multiprinciple and chemically disordered alloys, is poorly understood. Here we conduct molecular dynamics simulations and first principle calculations to investigate the effects of impact velocities and the local chemical order on spallation microvoid nucleation in a CrCoNi medium entropy alloy under shock wave loading. As the impact velocity increases, the microvoid nucleation site exhibits a transition from the grain boundaries to the grains to release redundant imposed energy. During the intragranular nucleation process, microvoids nucleate in the poor-Cr region with a large local nonaffine deformation, which is attributed to the weak metallic bonds in this position with sparse free electrons. For intergranular nucleation, a Franke-like dislocation source forms through the dislocation reaction, leading to enormous dislocations piling up in a narrow twin stripe, which markedly increases the local stored energy and promotes microvoid nucleation. These results shed light on the mechanism of spallation in chemically complexed medium entropy alloys.

Investigation of Shock Initiation in Covered Charges under Shock Wave and Fragment Impacts

In the current work, a series of step-by-step research methods have been applied to address the damaging effects of near-field strong shock waves and high-speed fragments on covered charge. In the first step, the defects of covered plates due to high-speed fragments were simplified to penetrated notches, and then, these notches were used to evaluate the impact of shock wave loads on charges covered with metal plates. In the next step, we developed a theoretical model to take into account the shock initiation of charges covered with defected metal plates. Explosive initiation standards coupled with shock wave evolution characteristics were applied to specify the crucial conditions of explosive detonation. Finite element program, for instance, was applied for the simulation of shock initiation processes in pressed charges (when TNT was covered with a steel plate containing a penetrated notch), and then, numerical simulations were validated by experimental findings. Finally, the results obtained from the numerical simulations and theoretical model were applied to evaluate the impacts of shock wave intensity, the thickness of covered metal plate, and the geometrical features of penetrated notch on pressed charge shock initiation. The least squares method was applied to determine critical initiation criteria (n and K). Theoretical calculation results were found to be highly consistent with those obtained from numerical simulations, indicating that covered metal plates significantly contributed to charge protection. The results also revealed that notches could undermine the protective function of covered plates and the size and shape of notch significantly affected charge critical detonation distance. Critical detonation distances of noncontact explosions were found to be 25 and 81 mm for a 3 mm thick pressed TNT in the presence and absence of 45# steel-covered plate, respectively. According to the results, increase in the diameter of covered plates containing a cylindrical notch increased pressed TNT critical detonation distance. When dealing with a covered plate containing a normally reflected frustum notch, however, we figured out that any increase in normal reflection slope could decrease pressed TNT critical detonation distance.

Numerical Study of Shock-Wave Loading of the W- and WC-Based Metal Composites

Numerical Study of Shock-Wave Loading of the W- and WC-Based Metal Composites

Measurement and characterization of nanosecond laser driven shockwaves utilizing photon Doppler velocimetry

Laser driven shockwaves from nanosecond pulsed lasers were evaluated for pressure magnitude and duration using photon Doppler velocimetry (PDV). Specific investigations were performed on Ti-6Al-4V alloys and 7085-T7651 aluminum alloys with laser full-width half-max pulse lengths ranging from 6 to 20 ns and laser intensities of 2–10 GW/cm2. The rear surface velocity data obtained using a heterodyne PDV system and an automated signal processing algorithm are demonstrated and utilized to capture rear surface velocity profiles. Peak shockwave pressures measured under bare surface water confinement reached approximately 6 GPa. Shockwave loading durations were observed to correspond with laser pulse durations with impulse loading times on the order of 2×–4× the laser pulse duration.

Coupling effects of the explosion shock wave and heat radiation on the dynamic response of a fixed-roof tank

The occurrence of leakage in large tank farms or oil deposits can lead to fire or explosion accidents. Coupling effects of fire and explosion loadings can cause considerably more damage to adjacent tanks or buildings than either loading individually does. In this study, the combined loadings of the explosion shock wave and heat radiation from a pool fire on a neighboring empty fixed-roof tank were numerically investigated. The effects of the explosion shock wave intensity and relative height of the explosion center [the ratio of the height of the explosion center to the height of the tank (hr)] were analyzed. The results indicate that tanks damaged by explosion shock waves have decreased fire resistance and critical buckling temperature. Moreover, the thermal buckling deformation of the predamaged tank largely depends on the explosion shock wave. With an increase in the explosion shock wave intensity or a decrease in hr, the explosion shock wave has greater influence on the fire resistance of the tank, and the critical buckling temperature decreases. This paper can provide an understanding of the dynamics of a tank under explosion shock wave loading, and of the critical failure criterion and failure modes of a target tank under the coupled loading of the explosion shock wave and an adjacent pool fire.

Deformation of an airfoil-shaped brain surrogate under shock wave loading

Improvised explosive devices (IEDs), during military operations, has increased the incidence of blast-induced traumatic brain injuries (bTBI). The shock wave is created following detonation of the IED. This shock wave propagates through the atmosphere and may cause bTBI. As a result, bTBI research has gained increased attention since this injury's mechanism is not thoroughly understood. To develop better protection and treatment against bTBI, further studies of soft material (e.g. brain and brain surrogate) deformation due to shock wave exposure are essential. However, the dynamic mechanical behavior of soft materials, subjected to high strain rates from shock wave exposure, remains unknown. Thus, an experimental approach was applied to study the interaction between the shock wave and an unconfined brain surrogate fabricated from a biomaterial (i.e. polydimethylsiloxane (PDMS)). The 1:70 ratio of curing agent-to-base determined the stiffness of the PDMS (Sylgard 184, Dow Corning Corporation). A stretched NACA 2414 (upper airfoil surface) geometry was utilized to resemble the shape of a porcine brain. Digital image correlation (DIC) technique was applied to measure the deformation on the brain surrogate's surface following shock wave exposure. A shock tube was utilized to create the shock wave and pressure transducers measured the pressure in the vicinity of the brain surrogate. A transient structural analysis using ANSYS Workbench was performed to predict the elastic modulus of 1:70 airfoil-shaped PDMS, at a strain rate on the order of 6 × 103 s−1. Both compression and protrusion of the PDMS surface were found due to the shock wave exposure. Negative pressure was found in a semi-ring area, which was the cause of protrusion. Oscillation of the brain surrogate, due to the shock wave loading, was found. The frequency of oscillation does not depend on the geometry. This work will add to the limited data describing the dynamic behavior of soft materials due to shock wave loading.

A phase-field model for spall fracture

As a kind of dynamic tensile failure, the spall fracture usually happened in ductile metals under shock wave loading. Also, its macroscopic softening behavior on the stress caused by the damage is complicated due to the micro-voids nucleation, growth, and coalescence, and finally forming macro-cracks in the material. In addition, the simulated results are often mesh-dependent. Recently, the phase-field model of fracture (PFM) gains popularities in modeling fracture and damage problems. One of its advantages is that the simulated results are mesh independent. The PF-CZM by Wu [J. Mech. Phys. Solids 103, 72–99 (2017)], which is a cohesive zone model regularized by the PFM, can account for different softening behaviors via characteristic functions and proves to be suitable for spall fracture modeling. In this paper, we used the PF-CZM to conduct spall fracture modeling in consideration of constitutive description of elastic-plastic-hydrodynamics (refer to the LS-DYNA theory manual). The free surface velocity profile for plate impact experiments, including the pullback signal, pullback slope, and the first velocity peak after pullback, were simulated and well matched the experimental results. Furthermore, the results show mesh independency. Different softening behaviors were assessed for their accuracy to model the spall fracture, and parameters in this model were discussed in detail. Besides, we directly extended this model to 3D simulation, showing potential engineering applications.

Experimental Study of Whisker Formation and Properties of Spheroplastic under Shock-Wave Loading

Experimental Study of Whisker Formation and Properties of Spheroplastic under Shock-Wave Loading

Interaction of a Shock Wave with an Increased-Density Gas Bubble in the Neighborhood of the Wall

The problem of the interaction of a shock wave with an increased-density gas bubble in the neighborhood of the wall is investigated on the basis of numerical simulation of Euler’s equations in the two-dimensional plane formulation. The process of shock wave refraction and focusing, namely, reflection of transverse shocks from the plane of symmetry of flow and the wall, is described. It is found that qualitatively different flow regimes, in which the wave is focused in the plane of symmetry before or after the beginning of wave reflection from the wall, can be implemented depending on the constitutive parameters of the problem. It is shown that the presence of a heavy bubble in the neighborhood of the wall strengthens multiply the pulse shock-wave loading on the wall. The maximum pressure reached on the wall is found as a function of the impinging wave Mach number, the bubble gas density, and the initial distance between the bubble and the wall. In some cases such a dependence is essentially nonmonotonic with respect to the bubble gas density and the distance between bubble and wall.