Laser Shock Peening Research Articles

Numerical investigation of the effect of laser peen forming process parameters on 1060 aluminium sheets under preload

Abstract Laser peen forming process changes the shape of the metal sheet or plate by plastic deformation caused by laser induced mechanical shock wave. The bending behavior of 1060 aluminium sheets under laser peen forming (LPF) are studied numerically taking into account the various laser peening process parameters for two distinct cases; with and without preload. Modal analysis has been performed on 3D finite element model (FEM) to stop post-shock oscillations. A time-dependent and space-dependent pressure distribution is applied to the laser-peened area along with preload at the free end. The numerical comparison of bending angles and surface profile of 1060 aluminium sheets under laser peen forming are studied for both the cases, with and without preload. Preloading provides better surface profile for same bending angle for a no laser shock overlap.

Effect of Protective Coating Layer and Overlapping Factor on the Microstructure and Mechanical Properties of Rene-80 Ni-Based Superalloy in Laser Shock Peening Process

Effect of Protective Coating Layer and Overlapping Factor on the Microstructure and Mechanical Properties of Rene-80 Ni-Based Superalloy in Laser Shock Peening Process

Improvement of gradient microstructure and properties of wire-arc directed energy deposition titanium alloy via laser shock peening

Wire-arc directed energy deposition (WADED) technology has been widely used in the remanufacturing of titanium alloy structural components benefited from with the advantages such as high deposition efficiency and low cost. However, due to the coarse and anisotropic microstructure, the complex internal stresses and processing-induced rough surface significantly reduce fatigue performance and reliability of the remanufactured structural components. In this work, surface modification of titanium alloy WADED repair component was carried out via laser shock peening (LSP), and its gradient structure, microhardness, residual stress and fatigue performance and enhancement mechanism were systematically investigated. Results indicated that the different microstructure of each region led to different responses under the action of LSP, which was related to the change of dislocation density. LSP induced crystal defects such as high-density dislocations, twins and stacking faults on the surface. A variety of crystal defects gradually decreased with the depth from the strengthened surface, formed a gradient microstructure and significantly affected the microhardness and residual stress of the repaired components. The surface hardness and compressive residual stress of the repaired components were greatly increased after LSP and the hardened layer and compressive residual stress depth affected layer were 600 μm and 800 μm, respectively. The average fatigue life of the additive repair component increased by 197 % under the synergistic effect of compressive residual stress and gradient microstructure.

Study on the effects of laser shock peening on the microstructure and properties of 17-7PH stainless steel

To investigate the surface integrity of 17-7PH stainless steel welded structural components used in aviation, laser shock peening (LSP) with different power densities was applied to stainless steel welded joints. The microstructural morphology, structural features, full-width at half-maximum, microhardness, and surface roughness of the stainless steel welded joint specimens before and after LSP were characterized and measured using SEM, TEM, XRD, a microhardness tester, and a high-resolution confocal microscope. The effects of different laser power densities on the microstructure and properties of the stainless steel welded joints were explored. Results indicate that the stainless steel welded joints exhibit a typical BCC phase. Laser shock peening promotes grain refinement in the welded joints, leading to the phase transformation of residual austenite into martensite. The surface roughness of the specimen is positively correlated with laser power density. At a power density of 5.17 GW/cm2, the surface roughness increased to 1.919 μm, which is 117.08% higher than that of the non-peened specimen. The microhardness of the specimens shows a decreasing trend with increasing power density. When the power density is 2.79 GW/cm2, the microhardness of the specimen significantly increases to 462.94 HV0.5, which is 22.26% higher than that of the non-peened specimen.

Parameter Optimization for Laser Peen Forming on 6005A-T6 Aluminum Alloy Plates to Enhance the Constrained Deformation of Integral Stiffened Plates.

Multiscale parameter optimization for laser peen forming (LPF) on 6005A-T6 aluminum alloy plates was conducted through a combination of simulation and experimentation. By obtaining the optimal parameter, this study aims to explore the constrained deformation and forming laws of the integral stiffened plates. Detailed descriptions were provided regarding the dynamic response process and transient behavior of aluminum alloy plates under ultrahigh strain rates, along with an in-depth analysis of the stress evolution. The results reveal that laser beam diameter and laser beam energy can achieve large range forming, while the number of tracks facilitates the precise deformation adjustment. During the 12-track LPF process, there is an overall upward trend in deformation values accompanied by a dynamic increase in the bend curvature. After static relaxation, the deformation value recovers to 55.2% of the final bending curvature. The chord direction scanning of stiffened plates exhibits a larger bending curvature, indicating its greater forming capacity for large-sized single unfolding direction formation; whereas, the unfolding direction scanning of stiffened plates excels in achieving efficient integrated two-way forming.

Effect of the Absorption Layer on the Microstructure and Mechanical Properties of M50 Steel by Laser Shock Peening

Effect of the Absorption Layer on the Microstructure and Mechanical Properties of M50 Steel by Laser Shock Peening

Effect of laser shock peening on the surface integrity and fretting fatigue properties of high-strength titanium alloy TC21

High-strength titanium alloy TC21 is often used to make aircraft load-bearing components in the aviation field. However, due to vibration, load-bearing components often suffer from fretting fatigue (FF), which greatly reduces their actual service life. Nowadays, laser shock peening (LSP) is being recognized as an effective strengthening process for many materials. Therefore, in this study, the effectiveness of LSP on the strengthening of high-strength titanium alloy TC21 is studied, in terms of surface integrity and FF properties. TC21 fretting specimens and tests are designed. Before fretting tests, the specimens are processed by LSP with varying laser pulse energies, number of shocks and overlap rate, and their surface integrity and FF properties are analyzed. It is found that the greater the laser pulse energy and number of shocks, the higher the surface hardness and compressive residual stress, the more the grain refinement, the greater the improvement in FF life. Under 32J-50%-T1, the FF life is improved by 191.3% compared with BM. But the overlap rate has little effect on surface integrity and FF life. Meanwhile, there forms amorphous structures, which tended to be transformed into nanograins during fretting process. This transformation is helpful for prolonging FF life due to its action of energy absorption. This study reveals the strengthening mechanism of LSP on TC21 and its effect on the FF properties of TC21 specimens.

Mitigating environmental assisted cracking in heterogeneous welds by laser peening without coating

In this work Laser Peening without Coating (LPwC) was applied underwater on heterogeneous weld joint made of P265GH and X6CrNiTi18-10 steel tubes to prevent Environmental Assisted Cracking on the weld/P265GH steel fusion boundary. Special laser head was designed to precisely deliver 200 mJ green laser beam on the centrally located weld interface on the inner surface of a pipe 76 mm wide and 420 mm long. Residual stress analysis revealed that the LPwC treatment led to generation of compressive residual stresses in the critical fusion boundary area with the magnitude of −168 MPa despite the absence of a protective layer in the peening process. The depth of compressive stresses reached up to 0.8 mm. Plastic deformation induced by LPwC led to grain refinement in the microstructure and improved hardness by 16 %. Samples sectioned from the treated pipe were subjected to accelerated corrosion-mechanical testing which showed more than 2.5x increase in cycles to failure after LPwC. Fractography analysis showed shorter length and decreased number of corrosion cracks after LPwC as well as formation of protective oxide layer on top of the treated surface. 3-point bend testing further showed more than 8x increase in corrosion fatigue life.

Application of impact-based and laser-based surface severe plastic deformation methods on additively manufactured 316L: Microstructure, tensile and fatigue behaviors

Applying post-processing methods can play a crucial role in addressing defects inherent in the as-built state of additively manufactured materials. This study comprehensively examined the effects of various post-processing techniques, including surface severe plastic deformation (SSPD) methods such as severe shot peening (SSP), ultrasonic shot peening (USP), ultrasonic nanocrystal surface modification (UNSM), and laser shock peening (LSP), combined with stress relieving (SR) on the tensile properties and fatigue behavior of laser powder bed fusion (LB-PBF) stainless steel AISI 316L specimens. Experimental characterization was carried out, focusing on microstructure, porosity, surface texture, hardness, residual stresses, monotonic tensile properties, and rotating bending fatigue behavior. The results demonstrated an excellent combination of enhanced strength and ductility after applying SR and SSPD treatments. Additionally, the post-processing methods significantly improved fatigue behavior by increasing strength, closing subsurface pores, surface layer nanocrystallization and hardening, inducing compressive residual stresses, and modifying the surface texture. Notably, in the high-cycle fatigue regime at the lowest stress amplitude, the SR + UNSM treated specimens exhibited the greatest improvement in fatigue life, followed by SR + USP, SR + SSP, SR + LSP, and SR, when compared to the as-built state.

Subsurface hardening of Al irradiated with ultrafast infrared laser

The effect of femtosecond laser shock peening on a model Al-0.3Mn alloy was investigated experimentally and numerically by molecular dynamics. Micro-diffraction experiments performed at synchrotron source revealed the depth profiles of the residual stress and the stored energy of dislocations, a measure of local plasticity. The depth of the maximum compressive stress did not coincide with that of the maximum dislocation energy, which was found at the surface. The interaction between the laser and the metal was simulated with LAMMPS using a two-temperature molecular dynamics package. The model accurately described the equation of state of aluminum and showed nearly equal resolved shear stresses on all slip systems at the wavefront. The dislocation density at a depth of 1 μm, predicted by the Meyers' model [1], was higher than the experimental data, suggesting possible recovery due to the increased temperature of the sample after repeated shock loading.

Enhancing corrosion resistance of lightweight metal alloys through laser shock peening

In this study, we investigated the effects of laser shock peening (LSP) on the corrosion resistance of lightweight metal alloys, specifically AA6061 and AZ31. LSP was performed underwater, using a nanosecond pulse laser and without using a protective coating or layer on the workpiece. The corrosion behaviors of these alloys were analyzed through electrochemical tests, including open circuit potential, electrochemical impedance spectroscopy, and potentiodynamic polarization measurements. The results demonstrated that LSP significantly improved the polarization resistance, and higher laser power intensities led to increased corrosion resistance and reduced corrosion rates. This enhancement in anti-corrosion performance is attributed to the formation of a protective oxide layer on the surface, acting as a barrier against corrosion. The findings underscore the potential of laser surface treatment as a viable technique for enhancing the corrosion resistance of lightweight metal alloys.

Tribological behavior and surface characteristics of severe surface plastic deformed as-cast and 3D-printed SS316L using LSP

The effect of laser shock peening (LSP) on as-cast and three-dimensional (3D)-printed SS316L alloys was studied. The LSP process was found more dominant than the 3D-printing technique over as-cast alloy steel for enhancing the properties. The process of laser shock peening results in microlevel changes in the structure of the material. This, in turn, leads to grain refinement and the increase of compressive residual stresses. After LSP treatment, the surface microhardness value increased by 33% in both as-cast and 3D-printed SS316L alloys with the hardness gradient from surface to subsurfaces. The wear rate of as-cast specimens and 3D-printed specimens were reduced to 1.28 10−6 and 1.14 10−6 g/m, respectively, and tensile value increased up to 22% after LSP treatment. The scanning electron microscopy images on the wear track confirm the vulnerability of the untreated SS316L alloys with adhesion wear and surface delamination. This difference was because the wear rate of the 3D-printed specimens was lesser than the as-cast SS316L alloys due to their layer-by-layer high-temperature finishing. The samples were characterized by optical microstructure to identify the surface refinement, and confirmed by the transmission electron microscope images along with specified area electron diffraction pattern for the accumulation of dislocation and grain refinement after LSP treatment. The accumulated residual stress was measured by X-ray diffraction technique and it found the highest compressive residual stress after LSP treatment was accrued by 3D-printed SS316L alloy with 310 MPa.

The scaling of laser peen forming: A two-experiment finite similitude approach

Laser peen forming (LPF) utilizes laser-induced shock waves to bend and shape metal plates in what is effectively a non-thermal metal-forming process involving no hard tooling. A difficulty with the process, arising from the rapid localized physics involved, is the determination of process conditions for the establishment of desirable process outcomes. The nanosecond physical behaviors induced by the pulsed laser can make simulation impractical, effectively restricting investigations to experiments as the only practical recourse. This paper focuses on the use of scaled experimentation for LPF with the objective of making experimental outcomes more broadly applicable to a wider range of process conditions. Understanding how processes scale can in principle aid in the establishment of process parameters through timely and cost-effective experiments. Scaled experimentation has recently undergone a paradigm shift with the arrival of the finite similitude scaling theory. The theory provides extra degrees of freedom and facilitates the use of unlimited numbers of scaled experiments and allows for anisotropy in plate thickness. It is demonstrated in the work through experimental tests and simulation at two different scales, that geometric and loading similarities can be broken, yet the behavior of LPF can be quantified to good accuracy.

Influence on micro-geometry and surface characteristics of laser powder bed fusion built 17-4 PH miniature spur gears in laser shock peening

Micro-geometrical errors, surface roughness, and surface integrity (microstructure, residual stresses, microhardness) play an important role in defining the quality of the gears as they directly affect their noise, vibration characteristics and service life during their use. In the present work, underwater laser shock peening (LSP) is employed to improve the quality of the laser powder bed fusion built 17-4 PH small-size spur gears (12 mm outside diameter). LSP was employed near the spur gear root, and effects were measured in terms of residual stresses, variation in microgeometry errors, surface roughness, porosity, microstructure, and microhardness. It was observed that LSP could impart compressive residual stresses up to 0.4 mm of measured depth, while the surface roughness has improved by 32%. Microgeometry and microhardness of gears showed minor variations. Additionally, LSP has shown an impact on the microstructure as the grain orientation was altered and grain size reduced by 15.6% due to shock wave transmission. The study paves the way to use LSP as a post-processing technique to modify the surface characteristics of LPBF-built miniature spur gears with minimal impact on the gear microgeometry.

Achieving high strength and ductility of Al-Zn-Mg-Cu alloys via laser shock peening and spray forming

In order to further enhance the strength and ductility of ultra-high strength aluminum alloys, the laser shock peening technology was applied to ultra-high strength Al-Zn-Mg-Cu alloy. The ultimate tensile strength, elongation and hardness can reach to 751 MPa, 11 % and 208.3 HV by combining spray forming, secondary extrusion, solid solution, retrogression and reaging as well as laser shock peening. The high strength and hardness of the alloys is mainly attributed to the fine-grained layer on surface as well as new grain boundaries, dislocation cells and high-density dislocations introduced by laser shock peening, uniform nano-sized strengthening phases with high density precipitated during heat treatments. The excellent ductility of the alloys is mainly ascribed to multiple structures including fine-grained layer on surface and slip lines inside different grains introduced by laser shock peening, smaller size of fibrous grains and Al7Cu2Fe phase produced by secondary extrusion and spray forming. The aging treatment after laser shock peening can lead to the annihilation of high-density dislocations as well as significantly promote the formation of stable and coarse η phase, which can greatly reduce the strength of the studied alloys.

Deciphering laser shock peening quality monitoring: Wavelet-driven network with interpretability

Quality monitoring of laser shock peening based on acoustic emission technology is a topical multidisciplinary issue that has received much attention in recent years. To acquire complex time-varying information in acoustic emission signals, convolutional neural networks with powerful learning capabilities have shown potential for a wide range of applications. However, the black-box property of the network imposes limitations on its further development and decision credibility. Therefore, this study proposes a wavelet-driven network with theoretical basis and physical significance. This network can cyclically utilize discrete wavelet packet transform to map input features to the wavelet domain during the learning process, thereby obtaining more robust and valuable information. This paper also constructs a novel wavelet attention mechanism that takes into account the difference between low-frequency and high-frequency information, and is able to allocate resources in both the decomposition component and the time-domain dimension. The proposed method can be seen as a multiresolution analysis technique that combines existing physical knowledge with nonlinear feature processing and feature selective enhancement. The results of the two laser shock peening cases show that the proposed method not only outperforms current state-of-the-art models in terms of monitoring performance, but also has better physical interpretability. Importantly, the proposed method has the potential to be further extended to other interpretable structural health monitoring.

Quantitative analysis of deformation characteristics and corrosion properties of high energy laser shock peened Ni-based superalloy

This study examines the influence of high-energy laser shock peening (LSP) using 7 J and 10 J pulse energies on the sub-surface deformation characteristics of Inconel 718 superalloy. High-magnitude compressive residual stresses were induced into the samples after LSP with large residual stress depths of the order of 2 mm – the experimental observations were in good agreement with finite element analyses of the LSP process. The propagation of intense shock waves led to increased strain hardening and dislocation densities that were experimentally quantified by synchrotron diffraction and transmission electron microscopy. Microscopic analyses revealed highly refined grain structure only at the surface without much refinement observed in the residual depth region. Alongside a high degree of strain hardening, profuse amount of adiabatic shear bands was observed in the hardened depth, indicative of simultaneous strain localisation under such high laser pulse energy. These bands occurred along common slip planes in the Ni γ-matrix and could be potential areas of instability leading to failure. The LSP-treated samples exhibited improved corrosion resistance, with higher laser pulse energy peened samples performing better.

Extending cutting tool remaining life through deep learning and laser shock peening remanufacturing techniques

Predicting and extending the remaining life of cutting tools during machining processes is crucial for sustainable manufacturing. Traditional prognosis methods often struggle to adapt to diverse working conditions throughout the machining process lifecycle. This paper introduced a comprehensive framework that effectively addressed the challenges by integrating multi-source data and using deep learning techniques. The system integrated power and vibration data collected from LGMazak VTC-16A and IRON MAN QM200 machines with the following innovations: (1) A standardized data fusion method was developed to integrate multi-source data sources, the hybrid graph convolutional network (GCN) with attention mechanisms was employed to improve the prognosis accuracy of cutting tool remaining life, best accuracy of 98.56% and average accuracy of 97.71% were achieved. (2) The optimization of laser shock peening (LSP) remanufacturing parameters using the bees algorithm showed good performance, a fitness value of 0.95 was achieved with convergence within 15 iterations. (3) Monitoring of the LSP remanufacturing process was designed based on sound and vibration data for optimal remanufacturing performance. (4) The remanufacturing approach in extending the remaining life of cutting tool was validated through FEA analysis and experimental testing, cutting tool life was extended by 29.32% to achieve a sustainable manufacturing process.

Control and Modelling of Laser Shock Peening without Coating (LSPwC) Texture of AISI 9310 Steel.

LSPwC is an important development of Laser shock peening (LSP) technology, and surface texturing is an effective method to improve tribological properties. The combination of these is expected to innovate a new surface texturing technology with a strengthing effect, but no one has attempted it. In this paper, a new LSPTwC technology combining them is innovatively proposed and validated on AISI 9310 steel, which is commonly used in helicopter transmission components for surface texturing. The LSPTwC surface was studied using an optical microscope, electron microscope, energy dispersive spectrometer, and so on. The results proved that LSPTwC is an effective texturing method of AISI 9310 steel, which modulates the texture and improves the properties, such as the microhardness increased by more than 10%. A model for calculating the texture and process parameters is also constructed on a statistical basis, and a modeling method for textured surfaces is proposed. It is verified that the calculation results and the constructed model are highly consistent with the test, with a diameter deviation <3% and depth deviation <4%. The above results can provide the experimental basis, process design method, and calculation model for single-point LSPwC texturing of AISI 9310 steel parts for helicopters, which have application value.

Accelerable adaptive cepstrum and L2-Dual Net for acoustic emission-based quality monitoring in laser shock peening

Acoustic emission monitoring in laser shock peening facilitates real-time detection of potential quality issues arising from variations in industrial parameters, enabling iterative optimization of the manufacturing process through material behavior analysis. However, existing research still lacks a comprehensive understanding of the time-varying time-frequency characteristics in dynamic acoustic emission and efficient corresponding models. Therefore, this study proposes an innovative monitoring approach that integrates accelerable adaptive cepstrum (AAC) and L2-Dual Net. Specifically, AAC first employs variable frames and filters to map time-varying features in the signal, and then obtains representative frame length distributions and filter weights for different operating conditions based on statistical information. AAC not only unveils time-varying features in signals but also boasts an efficient computational process. L2-Dual Net is a novel quality assessment model with robust feature extraction and local spatial feature interactions. The incorporation of L2 norm equips the model with robust interference immunity, while the dual spatial attention mechanism helps the model to interact with spatial features exhibiting different time-frequencies. Variable process parameter experiments for aluminum alloy 7075 and titanium alloy TC4 were conducted to validate the reliability of the proposed method. Results demonstrate that AAC showcases optimal computational efficiency and higher feature resolution. When compared with state-of-the-art network architectures, L2-Dual Net exhibits superior information flow, along with higher recognition accuracy and robustness. Moreover, various variants of L2-Dual Net are explored and the code is accessible at https://github.com/Qinr1026/L2-Dual-Net. The proposed method holds promising potential for application in other areas of acoustic emission monitoring.