Laser-generated Shock Research Articles

Simultaneous laser sintering and embedding of silver nanoparticles for highly flexible embedded electrodes

In manufacturing electronic devices embedded in flexible substrates, persistent technical challenges include process complexity, substrate damage, high surface roughness, and low mechanical flexibility. To address these challenges, this study proposes a method that involves simultaneously sintering silver nanoparticles (Ag NPs) and embedding them in polyethylene terephthalate (PET) substrates to fabricate flexible embedded electrodes. The proposed technique uses laser-generated high-intensity shock waves to compress Ag NPs coated on a PET substrate heated to its glass-transition temperature. The mechanical impact of the shock wave embeds the Ag NPs into the substrate while simultaneously sintering the particles. The thin-film Ag electrode fabricated using the proposed method exhibited outstanding electrical and mechanical properties. The electrical resistivity measured as low as 7.8 μΩ·cm, with a minimal increase of approximately 5 % after 2000 bending cycles at a bending radius of 1 mm. Furthermore, the fracture strength of the fully embedded electrode, as assessed through adhesive tape-peel tests, significantly surpassed that produced through conventional sintering methods. The proposed method has the potential to revolutionize conventional sintering methods in flexible substrate applications, offering a more efficient and reliable method for fabricating flexible embedded electrodes.

Microstructural Evolution and Surface Mechanical Properties of the Titanium Alloy Ti-13Nb-13Zr Subjected to Laser Shock Processing.

As a progressive surface-hardening technology, laser shock processing (LSP) can enhance the mechanical properties and extend fatigue life for metallic components through laser-generated high-pressure plasma shock waves. In this work, LSP was used to treat titanium alloy Ti-13Nb-13Zr experimental coupons, and the microstructural response and surface mechanical properties of the Ti-13Nb-13Zr experimental coupons were investigated. After the LSP treatment, the X-ray diffraction (XRD) peaks were shifted without any new phase formation. The surface roughness of the experimental coupons increased, which can be explained by the LSP-induced severe plastic deformation. The LSP treatment effectively enhanced the surface compressive residual stress of Ti-13Nb-13Zr. Meanwhile, the microhardness of the Ti-13Nb-13Zr was also obviously increased after the LSP treatment. The experimental results also showed that the number of shocks times is an important factor in the improvement of surface mechanical properties. LSP treatment with multiple shocks can lead to more severe plastic deformation. The surface roughness, surface compressive residual stress and microhardness of the Ti-13Nb-13Zr experimental coupons shocked three times are higher than those after one shock. What is more, grain refinement accounts for the mechanical properties' enhancements after the LSP treatment.

Theoretical and Experimental Studies on Pyroshock Attenuation via Periodic Rods

Pyrotechnic releasing devices have been widely used in aerospace missions to separate subsystems from spacecraft. High-frequency transient pyroshock induced by pyrotechnic release devices may cause severe damage to electronic devices and involved systems. To mitigate the pyroshock, phononic crystals, as new artificial constructions with novel properties, are introduced for the first time. In the present study, the pyroshock propagation analysis in periodic composite rods consisting of two different materials is conducted both theoretically and experimentally by considering various geometry parameters. The band gaps, attenuation level, and dynamic responses of periodic rods are investigated by the differential quadrature method, and the simulation results are validated by finite element analysis. Using the established theoretical model and laser-generated shock experimental setups, the effect of geometry on wave propagation behaviors, dynamic responses, shock response spectrums, and pyroshock attenuation in periodic rods are investigated. The experimental and numerical results are in good agreement, demonstrating that effective shock attenuation may be achieved through periodic rods. The corresponding attenuation bands, attenuation trends, and turning points of shock response spectrums can be controlled by designing the geometry of periodic rods. The pyroshock attenuation effects in periodic rods can be predicted quantitatively by wave propagation analysis.

In-silico experimentations of multimode shock response of polyurea

Computational studies can supplement existing ultrahigh strain rate experimental techniques in the absence of invasive full-field measurement and visualization. In this study, a computational model is employed to elucidate various phenomena accompanying the generation, propagation, and interaction of multimode shock waves in a viscoelastic material. Specifically, a 4 mm diameter polyurea plug with a thickness of 0.5 mm was modeled as a linear viscoelastic solid, where the relaxation behavior of the shear modulus was described using a Prony series while the bulk modulus was assumed to be linear elastic based on the Poisson's ratio of polyurea. The results are presented in three case studies, where a different type of shock wave was emphasized in each case while focusing on the regions at the leading and trailing edges of the shock wavefront. Generally, the wavefront interacted with the accompanying and reflected waves, resulting in compromising the purity of the sought-after loading condition, especially during the return trip of the wave upon approaching the free surface. In Case Study I, the propagation of laser-induced pressure wave remained pure during the forward trip towards the free surface but was compromised by the accompanying shear wave and side spherical patterned pressure waves. Case Study II simulated the generation of surface waves by incorporating a ring-shaped loading site, where the release of a surface displacement was found to be focused and amplified at the central point. In the final case study, Case Study III, the applied shear wave at ultrahigh strain rate generated secondary pressure and horizontal shear waves at the edges of the loading site, which complicated the loading scenario but provided new insight into the interaction of laser-generated shock waves within the solid. The results can be used to improve the analysis of experimental data to quantify the accompanying deformation and failure mechanisms of polymers subjected to hypervelocity impacts.

Propagation of laser-generated shock waves in metals: 3D axisymmetric simulations compared to experiments

This work aims at demonstrating the ability of an acoustic linear code to model the propagation of a shock wave created by a laser impact over a metallic surface. In this process, a high pressure surface level is reached using a ns laser pulse that heats the surface of the material and generates a dense plasma expansion. The pressure reaches few GPa so shock waves are generated and propagate into the bulk of the material. Currently, shock wave propagation is modeled using continuity equations and an ad hoc equation of state for the illuminated material, very limiting because it is numerically intensive. Here, we propose to model the shock wave bulk propagation using a linear acoustic code. A nonlinear surface pressure term, resulting from the laser–matter interaction, is used as a boundary condition. The applied numerical scheme is based on the Virieux scheme, including a fourth order finite difference discretization of the linearized elastomechanical equations. The role of longitudinal and transverse waves and their origins are highlighted. The importance of considering 3D geometries is pointed out. Simulations are finally confronted with experimental results obtained with the Hephaistos Laserlab facility (energy up to 14 J at 532 nm wavelength laser; pulse duration: 7 ns). Illuminations up to the optical breakdown in water are easily achieved with laser focal spots of 5 mm width. Excellent agreement between experiments and simulations is observed for several sets of experimental parameters for titanium, a material of high elastic limit, while limitations are founded for aluminum. The code is available in the MetaData.

In situ X-ray diffraction of silicate liquids and glasses under dynamic and static compression to megabar pressures

Properties of liquid silicates under high-pressure and high-temperature conditions are critical for modeling the dynamics and solidification mechanisms of the magma ocean in the early Earth, as well as for constraining entrainment of melts in the mantle and in the present-day core-mantle boundary. Here we present in situ structural measurements by X-ray diffraction of selected amorphous silicates compressed statically in diamond anvil cells (up to 157 GPa at room temperature) or dynamically by laser-generated shock compression (up to 130 GPa and 6,000 K along the MgSiO3 glass Hugoniot). The X-ray diffraction patterns of silicate glasses and liquids reveal similar characteristics over a wide pressure and temperature range. Beyond the increase in Si coordination observed at 20 GPa, we find no evidence for major structural changes occurring in the silicate melts studied up to pressures and temperatures exceeding Earth's core mantle boundary conditions. This result is supported by molecular dynamics calculations. Our findings reinforce the widely used assumption that the silicate glasses studies are appropriate structural analogs for understanding the atomic arrangement of silicate liquids at these high pressures.

Shock Waves in Laser-Induced Plasmas

The production of a plasma by a pulsed laser beam in solids, liquids or gas is often associated with the generation of a strong shock wave, which can be studied and interpreted in the framework of the theory of strong explosion. In this review, we will briefly present a theoretical interpretation of the physical mechanisms of laser-generated shock waves. After that, we will discuss how the study of the dynamics of the laser-induced shock wave can be used for obtaining useful information about the laser–target interaction (for example, the energy delivered by the laser on the target material) or on the physical properties of the target itself (hardness). Finally, we will focus the discussion on how the laser-induced shock wave can be exploited in analytical applications of Laser-Induced Plasmas as, for example, in Double-Pulse Laser-Induced Breakdown Spectroscopy experiments.

Laser-Induced Damage on Fused Silica With Photo-Acoustic Spectrum Analysis

Laser-induced damage on fused silica is studied with photo-acoustic spectrum. The damage characteristics are evaluated with the spectral analysis of photo-acoustic signal. The experimental results show that the damage threshold of fused silica samples is about 20.9 J/cm2 at 1-ON-1 condition at the wavelength of 1064 nm and the pulse duration of 10 ns. The damage morphology observed with confocal microscopy is gray haze, and the diameter and depth of the largest crater in gray haze are $6.7~\mu \text{m}$ and 200 nm, respectively. The reproducibility of photo-acoustic spectrum analysis and the characteristic spectral peak is discussed. Compared to the photo-acoustic method judged by signal amplitude, the photo-acoustic spectrum is more sensitive, which may provide an effective support for the study on laser-generated thermal explosion and shock wave propagation. Moreover, the photo-acoustic spectrum may provide a clue for early-damage judgment.

Quantitative evaluation of the mechanical strength of titanium/composite bonding using laser-generated shock waves

Intense acoustic shock waves were applied to evaluate the mechanical strength of structural epoxy bonds between a TA6V4 titanium alloy and a 3D woven carbon/epoxy composite material. Two bond types with different mechanical strengths were obtained from two different adhesive reticulations, at 50% and 90% of conversion, resulting in longitudinal static strengths of 10 and 39 MPa and transverse strengths of 15 and 35 MPa, respectively. The GPa shock waves were generated using ns-scale intense laser pulses and reaction principles to a confined plasma expansion. Simulations taking into account the laser–matter interaction, plasma relaxation, and non-linear shock wave propagation were conducted to aid interpretation of the experiments. Good correlations were obtained between the experiments and the simulation and between different measurement methods of the mechanical strength (normalized tests vs laser-generated shock waves). Such results open the door toward certification of structural bonding.

Shock equation of state of LiH6 to 1.1 TPa

Using laser-generated shock waves, we have measured pressure, density, and temperature of LiH on the principal Hugoniot between 260 and 1100 GPa (2.6--11 Mbar) and on a second-shock Hugoniot up to 1400 GPa to near fivefold compression, extending the maximum pressure reached in non-nuclear experiments by a factor of two. We observe the onset of metal-like reflectivity consistent with temperature-induced ionization of the Li 2s electron, and no sign of additional changes in ionization up to the maximum pressure. Our measurements are in good agreement with gas gun, Z-machine, and underground test data and are accurately described by quantum molecular dynamics simulations. The results confirm the validity of equation of state models built on an average-atom description of the electron-thermal contribution to the free energy and a density-dependent Gr\uneisen parameter to describe shock response of LiH over this pressure range.

Amplitude-dependent shock wave propagation in three-dimensional microscale granular crystals

Ordered arrays of elastic spherical particles in contact, often referred to as granular crystals, have been used as a model system for understanding the dynamics of granular media and explored as a type of designer material for acoustic wave tailoring applications. Due to the Hertzian interactions between the particles, granular crystals composed of macroscale particles have been shown to support strongly nonlinear phenomena including shock and solitary waves. In this presentation, we will describe recent progress in our studies of laser-generated shock wave propagation in self-assembled three-dimensional microscale granular crystals, where adhesive forces between the particles play a major role. Specific features studied include the dependence of the shock wave velocities and absorption on excitation amplitude. Dynamic failure processes such as crater formation and spallation are also explored. The experimental measurements are compared with reduced-dimension discrete element model simulations. New under...

Laser-generated shock wave attenuation aimed at microscale pyrotechnic device design

To meet the rising demand for miniaturizing the pyrotechnic device that consists of donor/acceptor pair separated by a bulkhead or a thin gap, the shock initiation sensitivity in the microscale gap test configuration is investigated. For understanding the shock attenuation within a gap sample (304 stainless steel) thickness of 10∼800 μm, the laser-generated shock wave in water confinement is adopted. The shock properties are obtained from the free surface velocity by making use of a velocity interferometer system for any reflector (VISAR). Analytical models for plasma generation in a confined geometry and for evolution and decay of shock waves during the propagation are considered. The shape and amplitude of the laser-driven initial pressure load and its attenuation pattern in the gap are effectively controlled for targeting the microscale propagation distance and subsequent triggering pressure for the acceptor charge. The reported results are important in the precise controlling of the shock strength during the laser initiation of microscale pyrotechnic devices.

Improving the forming capability of laser dynamic forming by using rubber as a forming medium

Laser dynamic forming (LDF) is a novel high velocity forming technique, which employs laser-generated shock wave to load the sample. The forming velocity induced by the high energy laser pulse may exceed the critical forming velocity, resulting in the occurrence of premature fracture. To avoid the above premature fracture, rubber is introduced in LDF as a forming medium to prolong the loading duration in this paper. Laser induced shock wave energy is transferred to the sample in different forming stages, so the forming velocity can be kept below the critical forming velocity when the initial laser energy is high for fracture. Bulge forming experiments with and without rubber were performed to study the effect of rubber on loading duration. The experimental results show that, the shock wave energy attenuates during the propagation through the rubber layer, the rubber can avoid the premature fracture. So the plastic deformation can continue, the forming capability of LDF is improved. Due to the severe plastic deformation under rubber compression, adiabatic shear bands (ASB) occur in LDF with rubber. The material softening in ASB leads to the irregular fracture, which is different from the premature fracture pattern (regular fracture) in LDF without rubber. To better understand this deformation behavior, Johnson–Cook model is used to simulate the dynamic response and the evolution of ASB of copper sample. The simulation results also indicate the rubber can prolong the loading duration.

The Investigation on Mask and Plasticine Laser Shock Forming

A novel technology called mask and plasticine laser shock forming (MAPLSF) was introduced to manufacture micro-features on the surface of pure copper foil with the thickness of 40μm. In this process, the laser-generated shock wave and plasticine are used to replace the conventional rigid punch and die. The result showed that the shape of laser beam can be roughly manufactured on the surface of the workpiece and this mold-free laser shock forming process is a fast method to fabricate controlled micro-feature on the metallic foils. In this damage-free forming process, the workpicec can keep good surface, because the plasticine is softer than metal foils.

A mold-free laser shock micro-drawing forming process using Plasticine as the flexible support

In this paper, a laser-generated shock wave was used to induce plastic deformation of metallic foils using Plasticine as a flexible support. In this new micro-drawing process, the laser-generated shock wave and the Plasticine are used to replace the conventional metal punch and mold. By undergoing large plastic deformation under the laser-generated shock wave, Plasticine accurately keeps the shape of the deformed workpiece, thereby improving the forming quality. Moreover, this is a damage-free forming process because the Plasticine is softer than metal foils. The feasibility of this new drawing process was conducted experimentally on aluminum, cooper, and titanium foils. The thickness distribution at the cross-section of the work piece was studied to evaluate the risk of crack. Meanwhile, the arrays of craters were fabricated on titanium foils. The results show that mold-free laser shock micro-drawing forming is an effective method to fabricate controlled micro-craters on metallic foils.

Development of x-ray radiography for high energy density physics

We describe an experiment performed at the LULI laser facility using an advanced radiographic technique that allowed obtaining 2D, spatially resolved images of a shocked buried-code-target. The technique is suitable for applications on Fast Ignition as well as Warm Dense Matter research. In our experiment, it allowed to show cone survival up to Mbar pressures and to measure the shock front velocity and the fluid velocity associated to the laser-generated shock. This allowed obtaining one point on the shock polar of porous carbon.

Laser shock ignition of porous silicon based nano-energetic films

Nanoporous silicon films on a silicon wafer were loaded with sodium perchlorate and initiated using illumination with infrared laser pulses to cause laser thermal ignition and laser-generated shock waves. Using Photon Doppler Velocimetry, it was determined that these waves are weak stress waves with a threshold intensity of 131 MPa in the silicon substrate. Shock generation was achieved through confinement of a plasma, generated upon irradiation of an absorptive paint layer held against the substrate side of the wafer. These stress waves were below the threshold required for sample fracturing. Exploiting either the laser thermal or laser-generated shock mechanisms of ignition may permit use of pSi energetic materials in applications otherwise precluded due to their environmental sensitivity.

Two-temperature hydrodynamics of laser-generated ultrashort shock waves in elasto-plastic solids

Shock-wave generation by ultrashort laser pulses opens new doors for study of hidden processes in materials happened at an atomic-scale spatiotemporal scales. The poorly explored mechanism of shock generation is started from a short-living two-temperature (2T) state of solid in a thin surface layer where laser energy is deposited. Such 2T state represents a highly non-equilibrium warm dense matter having cold ions and hot electrons with temperatures of 1-2 orders of magnitude higher than the melting point. Here for the first time we present results obtained by our new hybrid hydrodynamics code combining detailed description of 2T states with a model of elasticity together with a wide-range equation of state of solid. New hydro-code has higher accuracy in the 2T stage than molecular dynamics method, because it includes electron related phenomena including thermal conduction, electron-ion collisions and energy transfer, and electron pressure. From the other hand the new code significantly improves our previous version of 2T hydrodynamics model, because now it is capable of reproducing the elastic compression waves, which may have an imprint of supersonic melting like as in MD simulations. With help of the new code we have solved a difficult problem of thermal and dynamic coupling of a molten layer with an uniaxially compressed elastic solid. This approach allows us to describe the recent femtosecond laser experiments.

Destruction of cancer cells by laser-induced shock waves: recent developments in experimental treatments and multiscale computer simulations.

In this emerging area article we review recent progress in the mechanical destruction of cancer cells using laser-induced shock waves. The pure mechanical damaging and destruction of cancer cells associated with this technique possibly opens up a new route to tumor treatments and the corresponding therapies. At the same time progress in multiscale simulation techniques makes it possible to simulate mechanical properties of soft biological matter such as membranes, cytoskeletal networks and even whole cells and tissue. In this way an interdisciplinary approach to understanding key mechanisms in shock wave interactions with biological matter has become accessible. Mechanical properties of biological materials are also critical for many physiological processes and cover length scales ranging from the atomistic to the macroscopic scale. We argue that the latest developments and progress in experimentation enable the investigation of the shock wave interaction with cancer cells on multiple time- and length-scales. In this way the integrated use of experiment and simulation can address key challenges in this field. The exploration of the biological effects of laser-generated shock waves on a fundamental level constitutes an emerging multidisciplinary research area combining scientific methods from the areas of physics, biology, medicine and computer science.

Ultrahigh strain-rate bending of copper nanopillars with laser-generated shock waves

An experimental study to bend FIB-prepared cantilevered single crystal Cu nanopillars of several hundred nanometers in diameter and length at ultrahigh strain rate is presented. The deformation is induced by laser-generated stress waves, resulting in local strain rates exceeding 107 s−1. Loading of nano-scale Cu structures at these extremely short loading times shows unique deformation characteristics. At a nominal stress value of 297 MPa, TEM examination along with selected area electron diffraction characterization revealed that twins within the unshocked Cu pillars interacted with dislocations that nucleated from free surfaces of the pillars to form new subgrain boundaries. MD simulation results were found to be consistent with the very low values of the stress required for dislocation activation and nucleation because of the extremely high surface area to volume ratio of the nanopillars. Specifically, simulations show that the stress required to nucleate dislocations at these ultrahigh strain rates is about one order of magnitude smaller than typical values required for homogeneous nucleation of dislocation loops in bulk copper single crystals under quasi-static conditions.