Strong Shock Loading Research Articles

Physically Evocative Meso-Informed Burn Model: Topology of Evolving Hotspot Fields

Reactive burn models for heterogeneous energetic material initiation must account for chemistry as well as microstructure to predict shock-to-detonation transition. Upon transient (strong) shock loading, the collapse of individual voids leads to ignition of hotspots, which then grow and interact to completely consume the surrounding material. This paper shows that a length scale measuring the perimeter of the evolving burn front in a field of hotspots, in combination with a topological function/form factor for the hotspot field, is a key input to a framework for constructing a meso-informed reaction rate model. The approach suggested in this paper provides a route to constructing reaction rate models with only two quantities of interest, viz., the burn front perimeter and burn front velocity, which are physically evocative of the underlying hotspot physics and can be quantified individually using meso-scale simulations. It overcomes the problem of calibrating many free parameters that appear in phenomenological burn models and therefore suggests a route to developing general frameworks for simulation-derived meso-informed burn models.

The homogeneity of multi-textured micro-pattern arrays in a laser shock surface patterning process and its effect on the surface properties of aluminum alloy

In this study, a laser shock surface patterning process was performed to effectively implement hundreds of micro-patterns on a metallic surface through a single laser beam irradiation. Micro-pattern arrays of rectangular, hexagonal, circular, and mesh shapes of various sizes were successfully transferred to the workpiece, and a multi-textured surface structure was realized. In order to improve the homogeneity of the micro-pattern array, it was most effective to increase the thickness of the ablation layer. In the case of the thicker ablation layer, it seems that more uniform pressure was transferred to the material because the ablation layer was in a relatively rigid state due to the reduced level of self-deformation. Since the laser shock surface patterning process exerts a strong shock loading along with plastic deformation on the material surface, the hardness value increased mainly around the area subjected to the shock load. The better the homogeneity of the micro-pattern array, the less the deviation in the hardness value. Therefore, it is important to ensure micro-pattern uniformity in order to achieve uniform surface properties. Changes in the contact angle were also observed under various process conditions. After surface patterning, the contact angle increased as the amount of air trapped in the bar region increased. As the laser intensity increased, it was observed that the geometric surface changes were sharp, and the surface structure changed. As a result, the contact between the air and the water droplets decreased, and the contact angle decreased.

Observation of ejecta tin particles into polymer foam through high-energy X-ray radiograpy using high-intensity short-pulse laser

Micron-scale fragment ejection of metal is a kind of surface dynamic fragmentation phenomenon upon shock loading. The study of ejecta is crucial in many fields, such as inertial confinement fusion and pyrotechnics. Due to the particular advantages of laser experiments, a lot of studies of ejecta by strong laser-induced shock loading have been conducted in recent years. The shapes, size and mass of particle can be obtained via static soft recovery technique with foam. However, the stagnation and succedent mixing of the ejecta in the foam could not be deduced by this technique. To study the mixing between the ejecta and foam, a radiography experiment is performed by using the X-ray generated through the irradiation of picosecond laser on the golden wire. This radiography technique has not only high spatial resolution but also high temporal resolution. Two kind of experiments are designed and performed. In the first one, the tin sample and the foam are close to each other while a vacuum gap is arranged between them in the other one. The mixing process is analyzed with the determined areal density and volume density, as well as the results of recovery. The areal density of the front mixing area is similar to the scenario in the case with a vacuum gap, suggesting that the ejecta have not underwent a secondary fragmentation due to the collision with foam. Furthermore, the static recovery results show a different characteristic of penetration depth for the ejecta in the foam. When the tin sample is not close to the foam, the penetration depth in the foam increases with the loading pressure increasing. However, the penetration depth begins to decrease at a critical pressure after a brief increase, which is attributed to the interaction between the shock and the foam before the ejecta coming, and also to the ejecta size and composition. The shock pressure is high enough to change the foam performance, thus enhancing the stagnation ability for ejecta penetration. Moreover, the size and composition vary with loading pressure, thereby leading to the momentum change of the ejecta related to the penetration depth. In the future work, we will improve the field of view of the X-ray radiography to achieve a direct comparison between the dynamic results and the recovery results. Moreover, we will arrange perturbations at the interface to study the mixing between the micro-jetting and the foam and the interface instability.

Molecular dynamics studies on energy dissipation and void collapse in graded nanoporous nickel under shock compression

We present systematic investigations on energy dissipation and void collapse in graded nanoporous nickel by non-equilibrium molecular dynamics simulations. It is found that void size gradient influences the time history path of the energy dissipation. Under strong shock loading conditions, when the voids are completely collapsed, the total energy dissipation is dependent only on the porosity, and is independent of the void size gradient in the shock direction. The total energy dissipation increases with the increase of porosity. However, when the porosity increases to a critical value of 6%, the total energy dissipation reaches an upper limit. Increasing the porosity beyond this critical value would not result in further increase in energy dissipation. The simulations show that voids collapse is attributed to the combined effect of transverse and longitudinal plasticity flow of void wall. Two mechanisms of voids collapse are revealed: the plasticity mechanism and internal jetting mechanism. Under relatively weaker shocks, the plasticity mechanism, which leads to transverse collapse of voids, prevails; while at the stronger shock strengths, the internal jetting mechanism, which leads to longitudinal flow, plays a more significant role. The earliest appearing dislocations in a void may either nucleate at the front half surface or on the back half surface, depending on the position of the void in the sample and the void size gradient. Moreover, the simulations provide quantitative descriptions about the effects of loading intensity on energy dissipation rate and void collapse rate. We show that the energy dissipation rate can be well represented by a quadratic polynomial function of the shock loading velocity, and the void collapse rate is a linear function of the shock loading velocity.

The Propagation of Stress Wave in the PZT-5H Composite Target and the Influence of Load Resistance on the Electrical Output Under the Strong Shock Loading

To introduce the application background the self-powered technology for Fuze bridge fire, high overload microthermal battery activation, rocket ignition, and the aircraft escape actual condition lifesaving system ignition power supply, which intends to use the high-speed impact of piezoelectric ceramic in the process of missile launching high overload pressure or missile and target intersection in the process of high overload stress wave of piezoelectric ceramics and the transformation of power, for closer to confession technology for Fuze bridge ignition, high overload microthermal battery activation, rocket ignition, and aircraft escape system engineering problems. The stress wave propagation in the PZT-5H piezoelectric ceramic composite target and load resistance effect to the electrical output characteristics is investigated under the strong shock loading; the experiments have been performed about cylindrical steel projectiles normal impact on PZT-5H piezoelectric ceramic composite target by using polyvinylidene fluoride stress test system and electrical output test system combining with one-stage light gas gun loading system. The experimental results show that the stress duration and peak stress are about $9~\mu \text{s}$ and 232 MPa, respectively, when the cylindrical projectile impacts on piezoelectric ceramic composite target at the impact velocity of 345 m/s. The outputs of current pulse peak, voltage pulse peak, and energy peak are 20 A, 734 V, and 11 mJ under the stress interactions of 200–300 MPa. At the near-impact stress conditions, the electrical output characteristics of piezoelectric ceramics are greatly affected by the load resistance. The output voltage pulse increases with the increasing of load resistance value, and the values of the load resistance have a significant effect on output energy; output energy conversion rate is up to 82% when the load resistance is $50~\Omega $ .

Behaviour of rippled shocks from ablatively-driven Richtmyer-Meshkov in metals accounting for strength

While numerous continuum material strength and phase transformation models have been proposed to capture their complex dependences on intensive properties and deformation history, few experimental methods are available to validate these models particularly in the large pressure and strain rate regime typical of strong shock and ramp dynamic loading. In the experiments and simulations we present, a rippled shock is created by laser-ablation of a periodic surface perturbation on a metal target. The strength of the shock can be tuned to access phase transitions in metals such as iron or simply to study high-pressure strength in isomorphic materials such as copper. Simulations, with models calibrated and validated to the experiments, show that the evolution of the amplitude of imprinted perturbations on the back surface by the rippled shock is strongly affected by strength and phase transformation kinetics. Increased strength has a smoothing effect on the perturbed shock front profile resulting in smaller perturbations on the free surface. In iron, faster phase transformations kinetics had a similar effect as increased strength, leading to smoother pressure contours inside the samples and smaller amplitudes of free surface perturbations in our simulations.

Shock response of Cu/graphene nanolayered composites

Shock response of Cu/graphene nanolayered composites is investigated with molecular dynamics simulations, including deformation and spall damage of Cu, and delamination of the nanolaminates, as well as wrinkling, fracture and perforation of graphene, for parallel and normal shock loading. The Cu (111)/graphene interface is the source of dislocations in Cu and barrier to their propagation, and nucleation sites follow the Moiré pattern. Direct transmission of dislocation across graphene is not observed. Spallation occurs at the Cu/graphene interface with a reduced tensile strength. Under strong shock loading, graphene forms wrinkles and folds upon compression, and fractures upon release and tension for parallel shocks, while it is perforated by Cu atoms for normal shock loading via defect formation in graphene at high temperatures.

Effects of vacancy point defects and phase transitions on optical properties of shocked Al2O3

The velocity interferometer system for any reflector (VISAR) and pyrometric measurements in dynamic highpressure experiments require the use of an optical window, and Alumina (Al2O3) or sapphires is often considered as a window material due to its high shock impedance and excellent transparency. Consequently, understanding the characteristics of its transparency and refractive index change under shock loading is crucial for explaining such experimental data. Experimental studies indicate optical transparency loss in shocked Al2O3. The mechanisms for the phenomenon are some interesting issues. A first-principles study suggests that shock-induced VO+2 (the +2 charged O vacancy) defects in Al2O3 could be an important factor causing the transparency loss. Recently, the red shift of the extinction curve (i.e., the wavelength dependence of the extinction coefficient) with increasing shock pressure has been observed. It is needed to ascertain whether this behavior is also related to shock-induced vacancy point defects. In addition, up to now, information about Al2O3 refractive index at a wavelength of 532 nm under strong shock compression (the optical source wavelength in VISAR measurement is usually set at 532 nm) has been unknown, and neither the effects of structural transitions nor vacancy point defects on the refractive index of shocked Al2O3 are determined. Here, to investigate the above-mentioned questions, we perform first principles calculations of optical absorption and refractive index properties of Al2O3 crystal without and with VO+2 and VAl3 (the -3 charged Al vacancy) defects in a pressure range of 180 GPa (the calculations in CASTEP are carried out by the plane-wave pseudo potential method in the framework of the density functional theory). Our absorption data show that the observed optical extinction in shocked Al2O3 cannot be explained by only considering pressure and temperature factors, but shock-induced VO+2 should be an important source for this behavior. On the basis of these results, we may judge that 1) the transparency loss explanation for shocked Al2O3 in the view of vacancy point defects is reasonable; 2) the absorption extinction should dominate the extinction phenomenon observed in shocked Al2O3. Our calculations find that high-pressure structural transition in Al2O3 causes an obvious enhancement of its refractive index. The refractive index decreases with increasing shock pressure in corundum and Rh2O3 regions, and decreases slightly below 172 GPa and increases slowly above 172 GPa with increasing shock pressure in CalrO3 region. The VO+2 and VAl3 defects in Al2O3 have apparent influences on the shock pressure dependence of its refractive index. These results mean that the information about Al2O3 refractive index under strong shock loading cannot be obtained simply by extrapolating its low pressure data. Our prediction could be of importance for future experimental study and new window-material development.

Spall strength of aluminium single crystals under high strain rates: Molecular dynamics study

The spall process of single crystal aluminium under triangular waves loading has been performed with molecular dynamics simulations. The variation of spall stress with shock strength is directly calculated using the virial formula. Our simulations show that the spall strength keeps a linear reduction with the spall temperature before melting, whose occurrence will weaken this reduction tendency. This result is qualitatively different from the acoustic approximation, for the latter is out of work under such strong shock loading. We observe the increase of plastically deformed zones with impacting velocity before release melting and also the transition from plastic deformation to disordered state after melting. The microscopic views of voids nucleation and growth are also presented. The void nucleation is found primely along the close-packed plane {111}, and with increasing impacting velocity the void shape tends to spherical. After melting, the voids nucleate in complete disordered state, and the void number increases apparently, where the temperature effect is no more remarkable as in solid state.

Numerical Simulation on Penetration Properties of Concrete Based on Random Particle Model

As an important building material, concrete is widely used in military and civil areas for its superiorities, such as civil engineering, hydraulic engineering, protection engineering and so on. It is necessary to research its dynamic mechanical properties under strong shock loading. The concrete is considered as a composite material which is made of aggregate particles and cement paste from micromechanical angle. This paper uses random function to establish random particle model and simulates dynamic mechanical responses of concrete under strong shock loading based on random particle model using ANSYS/LS-DYNA.

Optimum Operating Conditions Confirmation and Effectiveness Analysis Based on Research of the Coagulation and Precipitation Integrated Process

Abstract Aiming at the increasing small-scale water supply projects, the increasingly serious pollution of the water resource and stringent water quality standards, the coagulation and precipitation integrated process on the basis of quiescent precipitation was proposed in this study. By experiments in the integrated reactor, the optimum process operating conditions were confirmed. It is verified that the optimal dosage of PAC was 16 mg/L in the optimum temperature and pH range. The repeated utilization volume of the floc mud from the former precipitation period was the same as 6% of the water volume in the next processing period, and the corresponding optimal dosage of PAC was 8 mg/L with 50% reduction of the flocculants dosage, while the residual turbidity was less than 1.0NTU, which could reach the standard after simple filtration and disinfection procedure. With low energy consumption, little land occupation, low cost, high efficiency of the water production and strong anti shock loading capability, this process could guarantee the safety of drinking water supply, and deserve popularization and application.

Dynamical similarity in shock wave response of porous material: From the view of pressure

Under strong shock loading, the pressure distribution in porous material is very complicated. We simulate such a system using a mesoscopic particle method. Morphological analysis is used to characterize the high pressure regimes defined by P ≥ P th , where P is the local pressure and P th a threshold value. The mean size of the voids embedded is about 10 μm. It is found that, the geometrical and topological properties of the high pressure regimes show high structure similarity S ( t ) and process similarity S P if the threshold P th , porosity Δ and shock strength v init 2 are appropriately controlled. For dynamical similarities in the same material, when the shock becomes stronger, the required pressure threshold P th increases, but the increasing rate decreases; when the porosity becomes higher, P th has a wider spectrum. For the dynamical similarities in different materials, in a wide range, the required P th linearly decreases when the porosity Δ becomes larger.

Mass-Spectroscopic Observations of Glycine Subjected to Strong Shock Loading

We have made time-of-flight mass-spectroscopic observations of 85/15 wt % water/glycine solutions and of crystalline alpha-glycine subjected to strong shock loading. The shockwaves were produced by placing the materials in contact with detonating solid explosives. In the solution observations, we have done experiments with glycine molecules composed of ordinary isotopes and with molecules labeled with (13)C, (15)N, and D atoms. The primary reason for conducting this research was to examine whether glycine molecules can survive exposure to strong shock loading, e.g., as might occur in the entry of a meteor into the earth's atmosphere. Our results show that glycine molecules can withstand the rigors of shock environments that generate pressure and temperature up to 180 kbar and 3200 K. Glycine in a 85 H(2)O/15 glycine wt % solution (i.e., one molecule of glycine to ca. 24 H(2)O molecules) exists primarily in its zwitterionic form. In both the solution and crystal experiments, we observed zwitterionic dimers, trimers, and, possibly, tetramers, after the materials were shocked. This implies that the solvating water molecules in the solution experiments must reside on the exterior of groups of solvated glycine molecules. We report quantum-chemical calculations, using density functional theory, that predict that two glycine zwitterions are bound together by ca. 15.72 kcal when immersed in an Onsager model of water. Our observations allow us to place lower-bound estimates on the lifetime of glycine zwitterions under our conditions. We have examined our data to determine whether dipeptide formation has occurred and found no evidence that it has. Compressible fluid-mechanical calculations were performed to estimate the pressures, temperatures, and the time scales present in the experiments.

Treatment and hydraulic performances of the NiiMi process for landscape water

This paper describes the NiiMi process designed to treat landscape water. The main aim of the research was to investigate the feasibility of NiiMi for removing organic and nutriment materials from landscape water. During the batch-scale NiiMi operation, the removal rates of color ranged from 66.7%–80%, of turbidity from 31.7%–89.3%, of chemical oxygen demand (COD) from 7%–36.5%, of total phosphor (TP) from 43%–84.2%, of soluble phosphate from 42.9%–100%, of total nitrogen (TN) from 4.2%–46.7%, and of NH4+-N from 39.3%–100% at the hydraulic loading of 0.2 m3/(m2·d). Results showed that the removal efficiencies of COD, TP, soluble phosphate and TN decreased with the decline in the temperature. The NiiMi process had a strong shock loading ability for the removal of the organics, turbidity, TP, soluble phosphate, TN and NH4+-N. Three sodium chloride tracer studies were conducted, labeled as TS1, TS2, and TS3, respectively. The mean hydraulic retention times (mean HRTs) were 31 h and 28 h for TS1 and TS2, respectively, indicating the occurrence of a dead zone volume of 12% and 20% for TS1 and TS2, respectively. TS1 and TS2 displayed the occurrence of short-circuiting in the NiiMi system. The comparison results between TS1 and TS2 were further confirmed in the values obtained for some indicators, such as volumetric efficiency (e), short-circuiting (S), hydraulic efficiency (λ) and number of continuously stirred tank reactors (N).

A virtual test facility for the efficient simulation of solid material response under strong shock and detonation wave loading

A virtual test facility (VTF) for studying the three-dimensional dynamic response of solid materials subject to strong shock and detonation waves has been constructed as part of the research program of the Center for Simulating the Dynamic Response of Materials at the California Institute of Technology. The compressible fluid flow is simulated with a Cartesian finite volume method and treating the solid as an embedded moving body, while a Lagrangian finite element scheme is employed to describe the structural response to the hydrodynamic pressure loading. A temporal splitting method is applied to update the position and velocity of the boundary between time steps. The boundary is represented implicitly in the fluid solver with a level set function that is constructed on-the-fly from the unstructured solid surface mesh. Block-structured mesh adaptation with time step refinement in the fluid allows for the efficient consideration of disparate fluid and solid time scales. We detail the design of the employed object-oriented mesh refinement framework AMROC and outline its effective extension for fluid–structure interaction problems. Further, we describe the parallelization of the most important algorithmic components for distributed memory machines and discuss the applied partitioning strategies. As computational examples for typical VTF applications, we present the dynamic deformation of a tantalum cylinder due to the detonation of an interior solid explosive and the impact of an explosion-induced shock wave on a multi-material soft tissue body.

A large deformation elastic-plastic dynamic analysis of square plate and spherical shell subjected to shock loadings

Based on Bathe's methodology and Yuan's formulation, a large deformation elastic-plastic transient dynamic finite element method is proposed for shock loading dynamic analysis on simple local structure, such as square plate and spherical shell. The verification of the adopted method shows good agreement with related literature. The proposed method is then extended to study strong shock loading problems on local structure. The displacement/acceleration time histories with plastic zone spread phenomenas are shown in several interesting figures.