Rise Times Of Shock Waves Research Articles

Ultrafast measurement of laser-induced shock waves

We present measurements of laser-induced shockwave pressure rise time in liquids on a sub-nanosecond scale, using custom-designed single-mode fiber optic hydrophone. The measurements are aimed at the study of the shockwave generation process, helping to improve the effectiveness of various applications and decrease possible accidental damage from shockwaves. The developed method allows measurement of the fast shockwave rise time as close as 10 µm from an 8 µm sized laser-induced plasma shockwave source, significantly improving the spatial and temporal resolution of the pressure measurement over other types of hydrophones. The spatial and temporal limitations of the presented hydrophone measurements are investigated theoretically, with actual experimental results agreeing well with the predictions. To demonstrate the capabilities of the fast sensor, we were able to show that the shockwave rise time is linked to liquid viscosity exhibiting logarithmic dependency in the low viscosity regime (from 0.4 cSt to 50 cSt). Additionally, the shockwave rise time dependency on propagation distance close to the source in water was investigated, with shock wave rise times measured down to only 150 ps. It was found that at short propagation distances in water halving the shock wave peak pressure results in the rise time increase by approximately factor of 1.6. These results extend the understanding of shockwave behavior in low viscosity liquids.

Structure of shock waves in particulate composites

The shock compression response of particulate heterogeneous solids was investigated using normal plate impact experiments and numerical simulations. A model composite system of silica glass spheres embedded in a matrix of thermoplastic polymer, polymethyl methacrylate, was developed to mimic the impedance mismatch of structural and energetic heterogeneous materials. Shock wave profiles were measured at multiple points on the rear surface of the composite specimens to characterize shock dispersion and spatial heterogeneity in material response due to the random distribution of particles. Composites with single mode as well as bimodal bead diameter distributions were subjected to plate impact loading at ∼1000 m/s resulting in an average shock stress of ∼4 GPa. Shock rise times were measured for composites of 30% and 40% glass by volume, with spherical particles of diameters in the range of 100–1000 μm. In the case of single mode composites, the shock wave rise times were observed to scale linearly with particle diameter divided by the bulk shock wave speed. The addition of a second bead size to a base size in a 30% glass by volume composite mix resulted in significant increases in shock rise time. Numerical simulations were used to develop insights into scattering and the development of shock structure in particulate composites. Shock disruption mechanisms due to particles and matrix/interface damage effects are discussed.

Simulation guided experimental interface shock viscosity measurement in an energetic material

Experimental measurements of interface shock viscosity in hydroxyl-terminated polybutadiene (HTPB)-ammonium perchlorate (AP) material system are performed using mechanical Raman spectroscopy (MRS) combined with laser pulse shock loading. First, HTPB-AP interface level shock wave propagation is studied using the cohesive finite element method. The difference in the shock behavior of the analyzed HTPB-AP interfaces from that of the bulk AP and HTPB material is highlighted by numerical simulations of impacting a single AP particle in an HTPB-AP sample in three different ways: (1) a flyer plate is used to impact the whole HTPB-AP sample; (2) a flat impacter is used to impact the middle of AP particle embedded in HTPB matrix directly; and (3) a HTPB-AP interface is directly impacted with an impacter of radius 1 μm. Shock wave rise time at the interface is shown to differ for the three different impact modes. Based on the simulation results, a combined MRS and pulse laser-induced particle impact test is used for measuring shock viscosity at HTPB-AP interfaces. It is observed that by changing the chemical composition of the interface, shock viscosity can be altered. A modified finite element model with viscous stress based on shock viscosity values added to the stress equation is then used for the shock impact simulation of an HTPB-AP material system. A power law relation was obtained between shock wave rise time and the shock viscosity.

Experiment research on dynamic response of copper film at high strain rate by chirped pulse spectral interferometry

That the femtosecond laser pulses irradiate metallic materials thereby inducing ultrahigh strain rates, is an important experimental approach to studying the material behavior under extreme conditions. Femtosecond laser-generated shock waves in metal films have rise times of several picoseconds, the corresponding diagnostic technique is required to work with a higher time resolution, which makes the experimental measurements difficult. Chirped pulse spectral interferometry (CPSI) possesses capabilities of ultrafast time resolution and continuous measurement, thus it provides a diagnostic technique for studying the ultrashort shock wave. In this article, we carry out an experiment on femtosecond laser driven shock wave in copper film and the measurement by CPSI. Laser pulse of 25 fs duration at the central wavelength 800 nm is used, the tested samples are copper films of (5025) nm in thickness fabricated by electron beam sputtering deposition onto cover slip substrate of 180 m in thickness, pump beam focuses onto front surface of the copper film through the transparent substrate and this laser intensity is 2.31013 W/cm2. Chirped pulse spectral interferometry is used to detect the movements of the free rear surfaces of the copper films with temporal and spatial resolution. In the spectral interferometry, linearly chirped pulse is required and obtained by stretching the femtosecond laser pulse with a pair of gratings. The relation between frequency and time of the chirped pulse is accurately measured using asymmetric spectral interference method, which is required for explaining the experimental data. Since CPSI is a single shot diagnostic technique, we obtain the displacement and velocity history of the free rear surface with picosecond time resolution in a single measurement. From the results, the average shock velocity is calculated to be (5.60.2) km/s and the shock wave rise time is determined to be 6.9 ps. According to the shock wave relations, impact pressure and strain rate in the copper film are (57.18.8) GPa and 8109 s-1 respectively, the strain rate is so high that it is hard to achieve by long-pulse laser driven or other loading approaches. Additionally, experimental results also show that the free rear surface alternately experiences acceleration and deceleration, which indicates the spallation in the copper target. It is obvious that chirped pulse spectral interferometry is a reliable approach to studying ultrashort shock waves in metal films.

Shock Wave Structure in Particulate Composites

An experimental study of shock wave profiles in particulate composites of various compositions is undertaken to determine how shock width and rise times depend on the mean particulate size. The composites under examination serve as a model for concrete or polymer bonded explosives, based upon the impedance mismatch between the relatively stiff particulates and compliant matrix. Polymethyl Methacrylate (PMMA) and glass spheres ranging in size from 100μm to 1000μm are used in concentrations of 30% and 40% glass by volume for experiments with a single bead size, and up to 50% glass by volume for multi-mode particle size distributions. A linear change in shock wave rise time is observed as a function of mean particulate diameter.

Effect of wave-front width on micro-jet from a shocked aluminum surface

This work investigates the relation between shock wave risetime and the amount of micro-scale fragments ejected from a grooved aluminium surface under shock loading condition. Using smoothed particle hydrodynamics, we calculate the formation of micro-jet from the groove of metal surface, and analyze the dependence on the width of loading wave front. The simulation results compare well with the experiment ones, and reveal the dependence of the micro-jet on the wave front: both the mass and the maximal velocity of the ejection will decrease with the increasing of the width of wave front. It is also found that the micro-jet originates from the folium near the groove, which can acquire axial velocity and impact at axis when the shock wave releases at the metal/vacuum interface. The folium becomes smaller as the wave front widens. This is because some matter will satisfy the lock condition of jet strength and can eject no more.

Fundamental study of shock induced acceleration of cell growth by plane shock waves

This paper describes effects of shock waves on cells to certificate the angiogenesis by shock wave in the clinical application. Especially, the effects of plane shock waves without cavitation bubbles on the endothelial cells are investigated by experiments and computation. In the experiments, the plane shock waves using shock tube apparatus are applied to the endothelial cells. The peak pressure working on the cells in the test case is 0.4 MPa, which is under disintegration level for endothelial cells. After working shock waves on suspended cell, the disintegration and growth rate are measured. It is found that the initial growth rate of the shock‐worked cells are clearly higher than that of control ones. As for the effect of rise time of working shock waves, to change the rise time of shock wave, Air and He gas are used as driver gas in the shock tube. As a result, the shorter rise time brings higher growth rate. In the computation, to check the effects of rise time on the pressure and stress distribution on the cells, fluid and structural interaction model are analyzed. The result shows that shorter rise time makes high stress level distribution on the cell membrane.

Ultrafast studies of shock waves using interferometric methods and transient infrared absorption spectroscopy

During the past few years, we have set up two ultrafast laboratories to study laser-induced shock waves with picosecond (or better) temporal resolution. In this paper, we provide an overview of our laboratories and the diagnostics we have developed to study the dynamic processes of matter being shocked to extreme conditions. Results are presented on the measurement of the shock wave rise time in aluminium and nickel, the effects of dynamic pressure on the complex index in aluminium, the measurement and characterization of the shock velocity, particle velocity, and index of refraction in shocked polymethylmethacrylate (PMMA), and our initial studies of transient infrared vibrational spectroscopy of shocked energetic polymers (nitrocellulose and poly-vinyl nitrate).

The Effect of Material Heterogeneity on the Shock Response of Layered Systems in Plate Impact Tests

In the study of shock wave propagation in solids, scattering, dispersion, and attenuation play a critical role in determining the thermomechanical response of the media. These phenomena can be attributed to a number of nonlinearities arising from the wave characteristics, loading conditions, material heterogeneity (measured at various spatial scales ranging from nanometers to a few millimeters). The nonlinear effects in general can be ascribed to impedance (and geometric) mismatch present at various length scales as often encountered in composite material systems, apart from material nonlinearities arising from inelastic effects, void nucleation and growth, cracking, and delamination. However, in nearly brittle material systems, elastic effects dominate and is the only effect considered here. Uniaxial strain experiments on the S-2 glass/polymer composite system display markedly different behavior than that observed in monolithic metallic systems [6] and this motivated the present work. Stress profiles measured at various locations along the direction of wave propagation in the plate impact experiments showed that the shock wave rise time increased with propagation in addition to the reduction of peak stress. In this work, we specifically address the issue of shock wave rise time in a simplified multi-layered system. A careful analysis of wave propagation in heterogeneous medium is performed by considering the elastic/acoustic properties of individual lamina in a layered system. An analytical model has been developed to describe the scattering process (reflection/transmission) at various layer interfaces of multilayer composite system. FEM results are then used to compare with the analytical predictions. These results show that the rise time can be a consequence of multiple internal reflections and transmissions occurring at the heterogeneous interfaces, it is further shown that the rise time depends on the magnitude of impedance mismatch and the number of layers.

State of the art of sonic boom modeling.

Based on fundamental theory developed through the 1950s and 1960s, sonic boom modeling has evolved into practical tools. Over the past decade, there have been requirements for design tools for an advanced supersonic transport, and for tools for environmental assessment of various military and aerospace activities. This has resulted in a number of advances in the understanding of the physics of sonic booms, including shock wave rise times, propagation through turbulence, and blending sonic boom theory with modern computational fluid dynamics (CFD) aerodynamic design methods. This article reviews the early fundamental theory, recent advances in theory, and the application of these advances to practical models.

Improvement of Prediction Method of Shock Wave Rise Times Using Thermoelastic Stress.

In the present study, improvement of numerical simulation code for the prediction of shock wave rise times developed by Swegle and Grady is carried out using equilibrium (thermoelastic) stress. The thermoelastic stress is obtained from Inside Temperature (IT) method for estimating temperatures in steady shock wave fronts established by Sano and Abe. In addition, use of the artificial viscous stress is limited conditionally in order to examine effects of the real shock viscous stress in our numerical calculation. The results of our improved simulation for 6061-T6 Al shocked below 9 GPa are compared with experimental results, and obtained good agreements. While, the effect of the viscous stress determined from the thermoelastic stress in the present method shows little differences from the Swegle-Grady method.

Effects of Shock Waves on Living Tissue Cells and its Deformation Process Using a Mathematical Model.

In this study, damage of living tissue cells (red blood cells and cancer cells) and experimental cell models (microcapsules) by plane shock waves is carried out experimentally. In addition, the effects of physical condition on the degree of damage are evaluated by constructing an appropriate mathematical model. To explain these phenomena, the red blood cells and the microcapsules are modeled mathematically as two spherical elastic shells filled with liquid. The fundamental equations express the oscillation of the spherical elastic shell in response to the incident pressure wave in the surrounding fluid. Frequency responses of the elastic shell model of two living tissue cells with mutual interaction in water are analyzed. From the results of this analysis, the effects of (1) the rise time of shock waves, (2) the distance between cells on shock-induced damage, (3) the concentration of suspended cells and (4) the incideuce angle of shock waves are discussed. It is found that effects of these parameters are large in certain cases.

Shock viscosity and the prediction of shock wave rise times

The present study is focused on viscouslike behavior of solids during large-amplitude compressive stress-wave propagation. Maximum strain rate in the plastic wave has been determined for 30 steady- or near steady-wave profiles obtained with velocity interferometry methods. The materials include six metals, aluminum, beryllium, bismuth, copper, iron, and uranium, and two insulating solids, magnesium oxide and fused silica. A plot of Hugoniot stress versus maximum strain rate for each material is adequately described by η̇=aσmh. The exponent m is approximately 4 for all materials while the coefficient a is material dependent. A model is developed which incorporates the observed trends of the shock viscosity data in a three-dimensional framework. Finite-difference calculations using the model reproduce the experimental wave profile data.

Effect of vibrational relaxation on rise times of shock waves in the atmosphere

The effect of atmospheric absorption including vibrational relaxation absorption of N2 and O2 on shock wave rise times was presented in an earlier paper [J. Acoust. Soc. Am. 64, 1208–1210 (1978)]. In this paper, velocity dispersion due to these same relaxation mechanisms is included. The added effect of dispersion is to lengthen predicted rise times except for large amplitude (peak pressure greater than 100 Pa) shocks. The rise times computed with both absorption and dispersion are in excellent agreement with experimental data. This finding suggests that atmospheric turbulence has little or no effect on measured rise times.