Laser-induced Plasma Shock Waves Research Articles

Laser Shock Peening: Fundamentals and Mechanisms of Metallic Material Wear Resistance Improvement.

With the rapid development of the advanced manufacturing industry, equipment requirements are becoming increasingly stringent. Since metallic materials often present failure problems resulting from wear due to extreme service conditions, researchers have developed various methods to improve their properties. Laser shock peening (LSP) is a highly efficacious mechanical surface modification technique utilized to enhance the microstructure of the near-surface layer of metallic materials, which improves mechanical properties such as wear resistance and solves failure problems. In this work, we summarize the fundamental principles of LSP and laser-induced plasma shock waves, along with the development of this technique. In addition, exemplary cases of LSP treatment used for wear resistance improvement in metallic materials of various nature, including conventional metallic materials, laser additively manufactured parts, and laser cladding coatings, are outlined in detail. We further discuss the mechanism by which the microhardness enhancement, grain refinement, and beneficial residual stress are imparted to metallic materials by using LSP treatment, resulting in a significant improvement in wear resistance. This work serves as an important reference for researchers to further explore the fundamentals and the metallic material wear resistance enhancement mechanism of LSP.

Lamb waves evaluation in CFRP plates with laser shock wave technique

Lamb waves, which are guided waves propagating along the surface of a thin plate structure, have been investigated to remotely perform nondestructive testing for aircraft or infrastructures made of carbon fiber reinforced plastic (CFRP) plates. CFRP plates are prone to internal damage such as delamination, which does not occur in metallic materials. Although nondestructive methods such as X-ray, flash thermography, etc. have been investigated in several studies, they may have some disadvantages such as risks of radiation exposure or limitation in terms of size of the structures to be tested for the former, and heat diffusion for the latter. Laser thermoelasticity can generate Lamb waves remotely and nondestructively. However, the generated Lamb waves have a small amplitude; therefore, hundreds of measurements must be averaged to achieve a sufficient signal-to-noise ratio. For these reasons, it has not yet been demonstrated as possible to detect damage in large CFRP structures within a short time using nondestructive, remote-controlled methods. As a first step towards performing nondestructive tests in CFRP plates, this paper demonstrates the generation of A0 mode Lamb waves in the experimental plate samples using laser-induced plasma (LIP) shock waves. The validity of the proposed system is verified by comparing the phase velocities of Lamb waves in the CFRP plates with three different layups obtained with the proposed system, with the theoretical values obtained analytically. This system can generate vibrations in CFRP plates in frequency ranges of a few hundred kHz and allow to determine the phase velocity of the experimental Lamb waves up to approximately 100 kHz.

Improving the Wear and Corrosion Resistance of Aeronautical Component Material by Laser Shock Processing: A Review.

Since the extreme service conditions, the serious failure problems caused by wear and corrosion are often encountered in the service process for aeronautical components. Laser shock processing (LSP) is a novel surface-strengthening technology to modify microstructures and induce beneficial compressive residual stress on the near-surface layer of metallic materials, thereby enhancing mechanical performances. In this work, the fundamental mechanism of LSP was summarized in detail. Several typical cases of applying LSP treatment to improve aeronautical components' wear and corrosion resistance were introduced. Since the stress effect generated by laser-induced plasma shock waves will lead to the gradient distribution of compressive residual stress, microhardness, and microstruture evolution. Due to the enhancement of microhardness and the introduction of beneficial compressive residual stress by LSP treatment, the wear resistance of aeronautical component materials is evidently improved. In addition, LSP can lead to grain refinement and crystal defect formation, which can increase the hot corrosion resistance of aeronautical component materials. This work will provide significant reference value and guiding significance for researchers to further explore the fundamental mechanism of LSP and the aspects of the aeronautical components' wear and corrosion resistance extension.

Review on Anti-Fatigue Performance of Gradient Microstructures in Metallic Components by Laser Shock Peening

Laser-shock-peening technology is an international research hotspot in the surface-strengthening field, which utilizes the mechanical effects of laser-induced plasma shock waves to effectively improve the fatigue performance of metallic components by introducing the gradient microstructures and compressive residual stress into the surface layer of processed materials. The fatigue failure caused by high-frequency vibrations in aeroengines during service is the most important threat to flight safety, and this case is more prominent for military aeroengines because their service situation is harsher. The present paper focuses on components such as high-temperature components, fan/compressor blade, and thin-walled weldments, and it systematically introduces the researching findings about surface nanocrystallization and compressive residual stress formation mechanism in typical aeronautical metallic materials treated by laser shock peening. The contents mainly involve the characteristics, formation process, fatigue resistance mechanism, thermal stability of residual compressive stress, and nanocrystallization generated by laser shock peening.

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.

Spallation damage of 90W–Ni–Fe alloy under laser-induced plasma shock wave

Laser shock loading is a more promising technology for investigating spallation damage in materials under shock-wave loading. In this paper, shock-induced spallation in a 90W–Ni–Fe alloy at an ultrahigh tensile strain rate of 106 s−1 is investigated using a superintense ultrafast laser facility. The spallation of the 90W–Ni–Fe alloy was dominated by a transgranular fracture of tungsten(W) particles with a high spall strength of 6.46 GPa. Here, we found an interesting phenomenon that the formation of nanograins inside W particles leads to a new mode of transcrystalline fracture of W particles during the laser shock loading. Futhermore, most voids were nucleated inside the W particles rather than at the W/γ-(Ni, Fe) matrix-phase interface. This result contradicts the fracture theory under quasi-static loading, which posits that the W/γ-(Ni, Fe) matrix-phase interface is not the preferred site for the initial failure under shock loading.

Defect detection of concrete in infrastructure based on Rayleigh wave propagation generated by laser-induced plasma shock waves

Defects in large concrete structures, including critical infrastructure such as bridges and tunnels, are traditionally detected by hammering tests by inspectors. However, the results depend on the inspectors’ skills. Additionally, hammering tests are impractical to thoroughly inspect massive structures in a short time. Herein defect detection in concrete structures is realized by telemetry using shock waves generated by laser-induced plasma (LIP). LIP is generated by irradiating a Nd:YAG pulsed laser near the concrete surface. As LIP spreads to the surrounding area at an ultrafast speed, a spherical shock wave is generated. This shock wave realizes a non-contact, non-destructive impulse excitation force on a concrete structure. The response of the concrete structure is measured with a laser Doppler vibrometer (LDV). Applying this method to detect defects in an artificial concrete specimen can identify the natural frequencies and modes of the defects. By measuring the propagation of the Rayleigh waves generated by the LIP shock waves, defects and the approximate location of the boundary between the defective part and the defect-free part are detected.

Measurements of S0 mode Lamb waves using a high-speed polarization camera to detect damage in transparent materials during non-contact excitation based on a laser-induced plasma shock wave

The demand for transparent materials has been expanding due to their ubiquity in products such as solar panels, tablet terminals, and smartphones. To mass produce high-quality products, quickly detecting damage on the µm scale and evaluating the quality are critical. Herein an Nd:YAG pulsed laser with a nanosecond order is used to generate a shock wave by laser induced plasma, which is subsequently used as a non-contact, non-destructive excitation force for transparent materials. Then, a high-speed polarization camera measures the generated Lamb wave. In this experiment, an impulse input is generated via a laser-induced plasma shock wave and the phase velocity of the generated Lamb wave in the polycarbonate plate is measured by a high-speed polarization camera. We found that this Lamb wave was in the S0 mode. Observing its propagation can detect scratches on the order of several hundred µm on the surface of a transparent plate in a non-contact, non-destructive manner.

Spatio-temporal behavior of laser induced plasma shock wave probed by optical beam deflection technique

Spatio-temporal evolution of Nd:YAG laser induced shock wave generated from copper target under various pump laser power densities (0.8–2.38 GW/cm2) at atmospheric pressure is investigated. Using optical beam deflection method, a supersonic shock wave is detected, it propagates in air and progressively decays into an acoustic wave. The results show that neither the point-explosion blast wave model nor the drag force model is able to estimate the temporal evolution of the shock front. A power model considering the background pressure effect was suitable to fit the experimental data. The temporal behavior of the shock waves at different laser power densities is quite similar, but at higher laser power densities, a noticeable presence of reflected shock waves is seen. The effect of laser power density on the shock wave velocity is clearer near the target surface. A cooling wave with estimated velocity of 30 m/s is also detected.

Propagation characteristics of nanosecond pulse laser-induced shock wave and the non-contact removal of particle

The evolution from propagation characteristics of nanosecond pulse laser-induced air plasma shock wave to the non-contact removal of particle is investigated theoretically and experimentally. The characteristic parameters of the plasma, electron number and temperature are discussed in detail. And the theoretical simulation analysis of the propagation characteristics of the plasma shock wave shows that the propagation velocity and pressure field are closely related to time and energy, and specially the pressure decreases with the increase in the propagation distance. Meanwhile, the motion state of driven particles under the pressure of shock wave is observed by means of high-speed photographic. Consistent with the pressure characteristics of the shock wave, the particles motion velocity is strongly dependent on laser energy and driving gap. On these foundations, a series of experiments are also carried out to demonstrate the removal of contaminated particles from the surface of the optical fiber ring by shock wave, where the fiber ring is detected without damage. This technology not only has the advantages of non-contact and high efficiency, but also realizes relatively larger cleaning region at microscale.

Soft Mango Firmness Assessment Based on Rayleigh Waves Generated by a Laser-Induced Plasma Shock Wave Technique.

Many methods based on acoustic vibration characteristics have been studied to indirectly assess fruit ripeness via fruit firmness. Among these, the frequency of the 0S2 vibration mode measured on the equator has been examined, but soft-flesh fruit do not show the 0S2 vibration mode. In this study, a Rayleigh wave is generated on a soft mango fruit using the impulse excitation force generated by a laser-induced plasma shock wave technique. Then, the flesh firmness of mangoes is assessed in a non-contact and non-destructive manner by observing the Rayleigh wave propagation velocity because it is correlated with the firmness (shear elasticity), density, and Poisson’s ratio of an object. If the changes in the density and Poisson’s ratio are small enough to be ignored during storage, then the Rayleigh wave propagation velocity is strongly correlated to fruit firmness. Here, we measure the Rayleigh wave propagation velocity and investigate the effect of storage time. Specifically, we investigate the changes in firmness caused by ripening. The Rayleigh wave propagation velocity on the equator of Kent mangoes tended to decrease by over 4% in 96 h. The Rayleigh wave measured on two different lines propagated independent distance and showed a different change rate of propagation velocity during 96-h storage. Furthermore, we consider the reliability of our method by investigating the interaction of a mango seed on the Rayleigh wave propagation velocity.

Laser-induced plasma shock wave excitation technique with acoustic lens

Laser-induced plasma shock wave excitation technique with acoustic lens

Research on the technical principle and typical applications of laser shock processing

Laser shock processing (LSP) is a novel surface hardening technology, utilizing the stress effect generated by laser-induced plasma shock waves, with the characteristics of better hardening effects, higher processing precision and strong controllability. Nowadays, LSP is widely applied in many fields such as the high-end equipment manufacturing industry. In order to further understand the LSP technology. In this work, the technical principle of LSP is reviewed through basic principle of LSP, enhanced mechanical properties, micro-structure evolution and simple process mechanism. In addition, some typical applications of LSP are introduced briefly from the aspect of aerospace industry, nuclear power industry, biomedical and material forming. This work will provide a theoretical guidance for researchers to further explore the mechanism of LSP and promote to the development of LSP.

Damage threshold of substrates for nanoparticles removal using a laser-induced plasma shockwave

With technological advancement, plasma shockwaves have become widely used as a novel cleaning method to remove nanoparticles. However, insufficient research has been conducted on their cleaning mechanism and application conditions, and the yield strength of substrates has been directly used as their damage threshold. we find that this definition is inaccurate. We treat clean and nanoparticle-coated silicon substrates with a laser-induced plasma shockwave to explore the effects of the presence of nanoparticles on the substrate during cleaning. We have confirmed the effect of nanoparticles on the substrate by simulating the mechanism of temperature and stress propagation between the particles and the substrate. This is because the yield strength of the substrate is greatly reduced by the increase of temperature under the action of shock wave. At the same time, the stress transferred by particles to the substrate increases, resulting in local high-pressure area and pit formation. Moreover, this study finds that the presence of nanoparticles increases the probability of damage to the substrate by an approximate factor of two. And the dependence of the damage threshold of the substrate on the size of the nanoparticles is demonstrated.

Laser-induced plasma shock wave excitation technique with acoustic lens

Laser-induced plasma shock wave excitation technique with acoustic lens

The New Technologies Developed from Laser Shock Processing.

Laser shock processing (LSP) is an advanced material surface hardening technology that can significantly improve mechanical properties and extend service life by using the stress effect generated by laser-induced plasma shock waves, which has been increasingly applied in the processing fields of metallic materials and alloys. With the rapidly development of modern industry, many new technologies developed from LSP have emerged, which broadens the application of LSP and enriches its technical theory. In this work, the technical theory of LSP was summarized, which consists of the fundamental principle of LSP and the laser-induced plasma shock wave. The new technologies, developed from LSP, are introduced in detail from the aspect of laser shock forming (LSF), warm laser shock processing (WLSP), laser shock marking (LSM) and laser shock imprinting (LSI). The common feature of LSP and these new technologies developed from LSP is the utilization of the laser-generated stress effects rather than the laser thermal effect. LSF is utilized to modify the curvature of metal sheet through the laser-induced high dynamic loading. The material strength and the stability of residual stress and micro-structures by WLSP treatment are higher than that by LSP treatment, due to WLSP combining the advantages of LSP, dynamic strain aging (DSA) and dynamic precipitation (DP). LSM is an effective method to obtain the visualized marks on the surface of metallic materials or alloys, and its critical aspect is the preparation of the absorbing layer with a designed shape and suitable thickness. At the high strain rates induced by LSP, LSI has the ability to complete the direct imprinting over the large-scale ultrasmooth complex 3D nanostructures arrays on the surface of crystalline metals. This work has important reference value and guiding significance for researchers to further understand the LSP theory and the new technologies developed from LSP.

Selenium nanoparticle prepared by femtosecond laser-induced plasma shock wave.

A novel approach for the production of both amorphous and crystalline selenium nanoparticles (SeNPs) using femtosecond laser-induced plasma shock wave on the surface of Bi2Se3 topological insulators at room temperature and ambient pressure is demonstrated. The shape and size of SeNPs can be reliably controlled via the kinetic energy obtained from laser pulses, so these are applicable as active components in nanoscale applications. Importantly, the rapid, low-cost and eco-friendly synthesis strategy developed in this study could also be extendable to other systems.

Particle removal is explored by the motion of individual particles based on laser-induced plasma shock wave

Removing particles from the device is a challenging in the micro-field. The traditional method is easy to often result in device damage. Therefore, developing an alternative method to resolve the shortcomings is necessary for micro-contamination removal. In this study, a non-contact method is presented, which is based on the shock wave for removal of particles from substrate surface. A series of experiments of particle removal and simulation mode of shock wave characteristics was performed to investigate the removal mechanisms, particle removal modes, and the influence of relevant parameters (laser energy, particle properties, and gap distance d) on particle removal. By analyzing the experimental and simulation results, the particle removal mechanism is dominated by the shock wave ejection mechanism, which is owned to its strong pressure. The particle removal velocity is closely related to the gap distance d and the laser energy, and the maximum velocity was approximately 0.0138Mach for gap distance d is ∼1.45 mm at the energy of 9.32 mJ. Moreover, it is considered that the detachment will be obtained by the combination of lifting, rolling and sliding modes. Our basic research contributes to a better understanding of the particle removal.

Evaluating methods for quality of laser shock processing

Laser shock processing is an advanced surface modification technology that can effectively enhance the mechanical properties of alloy and metallic materials, such as micro-hardness, fatigue resistance and corrosion resistance, by using laser-induced plasma shock waves, and it has a wide applications in the field of aerospace industry. In this work, the development of laser shock processing is introduced briefly, the research of evaluating methods for quality of laser shock processing is summarized emphatically, and the study necessary of online measuring methods for quality of laser shock processing is indicated.

Regional effects and mechanisms of nanoparticle removal from Si substrate by laser plasma shock waves

We use laser-induced plasma shock waves to remove Al nanoparticles from a smooth silicon substrate. Our experimental results show that the removal mechanism varies for different substrate regions. We examine the factors influencing particle removal by evaluating the shock-wave spatial distribution and the removal mechanisms. Further, we evaluate the influence of the gap between the laser focus and substrate on the removal results. The effects of the laser focus and substrate particle sizes are also investigated, and the optimum removal conditions are obtained. Our study can aid in better understanding the mechanisms of particle removal from surfaces.