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Crack closure mechanisms in residual stress fields generated by laser shock peening: A combined experimental-numerical approach
摘要： Laser shock peening (LSP) is successfully applied to retard fatigue cracks in metallic lightweight structures by introducing specific, in particular compressive, residual stress fields. In this work, experiments and a multi-step simulation strategy are used to explain the fatigue crack retarding and accelerating mechanisms within these LSP-induced residual stress fields. Crack face contact is identified as main mechanism to retard the fatigue crack as the stress distribution changes and the stress intensity factor range decreases. Crack face contact is experimentally detected by load vs. crack opening displacement (COD) curves and scanning electron microscopy (SEM) of the crack faces, as well as during numerical simulations. The convincing agreement between experiment and simulation, especially regarding the specific crack face contact areas, allowed the proper evaluation of the stress intensity factors depending on the crack length. It is found that crack closure is indeed one of the main reasons for the efficient application of LSP for fatigue crack retardation. Furthermore, the occurrence of crack closure does not indicate a zero value stress intensity factor in complex residual stress fields, as the areas of crack face contact depend strongly on the LSP-induced compressive residual stresses.
关键词： Stress intensity factor,Laser shock peening,Residual stress,Fatigue crack growth,Crack closure
更新于2025-09-16 10:30:52
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Enhancement of oxidation resistance of modified P91 grade ferritic-martensitic steel by surface modification using laser shock peening
摘要： In this paper, effect of laser shock peening (LSP) on high temperature oxidation behavior of P91 steel has been studied. P91 samples were subjected to single and triple LSP treatments at a constant laser power density of 3.9 GW.cm?2. Single and triple LSP treatment led to the formation of ultrafine subgrains of sizes ~300 ± 30 and ~105 ± 10 nm respectively at near surface comparing to unpeened P91 sample (~1200 ± 120 nm). Further, unpeened and LSP treated samples were oxidized at temperatures of 600, 650 and 700 °C for time 5 to 200 h in air. Compare to unpeened sample, single and triple peened samples exhibited two and five fold reduction in weight gain after 200 h of oxidation at highest test temperature (700 °C). Improvement of oxidation resistance in LSP treated samples is attributed to the formation of continuous layer of protective oxides such as (Fe,Cr)2O3, Cr2O3 and MnCr2O4 due to enhanced diffusivity of Cr and Mn from bulk during early stage of oxidation. The enhanced diffusivity Cr and Mn in LSP treated samples have been further supported by reduction in apparent activation energy of oxidation, which is evaluated by modelling the time-temperature dependence of weight gain data in purview of kinetics theory.
关键词： Kinetic energy,Laser shock peening,Oxidation resistance,Diffusivity,P91 steel
更新于2025-09-16 10:30:52
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Finite Element Analysis of Surface Roughness Generated by Multiple Laser Shock Peening
摘要： Laser shock peening (LSP) is a novel surface processing technique for improving the fatigue properties of metal parts, and surface roughness is a critical parameter when fatigue strength resistance is concerned. In this paper, a three-dimensional (3D) finite element model was developed in order to assess the surface roughness evolution induced by multiple LSP. A modified finite element analysis (FEA) method was used to compute the vertical displacements profiles, and discrete data obtained from the numerical simulations were subsequently input to the proposed discretized formula to calculate the surface roughness Ra. The results obtained from the numerical simulations are in good agreement with the experiment data from open literatures, which validates the proposed approach. After the validation of the numerical model, a parametric study was conducted in order to predict the effects of overlap rates, number of impacts, and pulse energy on surface roughness Ra.
关键词： laser shock peening,surface roughness Ra,numerical simulation
更新于2025-09-16 10:30:52
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Raman spectroscopy of poly (methyl methacrylate) under laser shock and static compression
摘要： Time-resolved Raman spectroscopy for visualizing molecular fingerprint snapshots at nanosecond time scale is a useful tool for detailed understanding of in situ shock behaviour of materials. This technique was applied to study the changes in molecular vibrations of poly (methyl methacrylate) (PMMA) under laser driven shock compression up to ~1.9 GPa in a confinement geometry. A layered target configuration is used to enhance the shock pressure. The vibrational modes are measured as a function of dynamic shock and static compression. The Grüneisen parameters and bond anharmonicities in PMMA are determined using compression behaviour of Raman modes. The deduced shock velocity (~3.5 ± 0.4 km/s) in PMMA based on the time evolution of shocked Raman mode at 1.9 GPa is in agreement with the one calculated (~3.7 km/s) from 1-D radiation hydrodynamic simulations. A comparative study on shock experiment and static high pressure Raman spectroscopic measurements is done. Static pressure measurement up to ~16 GPa show rapid blue shifting of C–H stretching modes.
关键词： Raman spectroscopy,PMMA,confinement geometry,Raman shift,laser shock,diamond anvil cell (DAC),static experiment
更新于2025-09-16 10:30:52
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Surface dynamic deformation of LY2 aluminum alloy subjected to a laser shock wave planishing technique with different kinds of contacting foils
摘要： In this paper, a laser shock wave planishing technique (LSWP) was used to treat the LY2 aluminum alloy surface with corrugated structures, and the influence of contacting film material on the planishing effect was studied. The dynamic response characteristics of surface micro-features under different physical parameters of contacting foils were simulated by finite element simulation (FEM), and experimental verification was carried out. A close match between the experimental results with these simulation results in FEM was found. The planishing of surface micro-protrusions can reduce the surface roughness of treated sample, and the lifting of bottom materials can ensure the surface profile accuracy. The results demonstrate that the planishing effect on micro-protrusions improves with the density of the contacting foil decreasing; The lifting effect on the bottom material enhances with the strength of the contacting foil increasing. A high modulus of elasticity contacting foil also facilitates the bottom material bulging.
关键词： Micro-features,Aluminum alloy,Finite element modeling,Surface topography,Laser shock wave,Dynamic response
更新于2025-09-16 10:30:52
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Femtosecond laser shock peening of galvanized stainless steel
摘要： In this paper a SUS316L stainless steel was electroplated with metallic layers and coated with polymer films. A sub-100fs ultrashort laser pulse with a central wavelength of λ=800nm was utilized to process the layer. The aim was to generate shock waves due to ablation of the deposited sacrificial layers. Generated shockwaves propagate and penetrate the lower stainless-steel sample and increase its mechanical hardness (Laser Shock Peening). The sacrificial layer protects the sample from ablation damage and determines the shock wave coupling. To achieve maximal peening, we compare different sacrificial layers and laser processing parameters.
关键词： Ultrashort Laser Peening,Shock hardening,LIPSS,Laser Shock Peening
更新于2025-09-12 10:27:22
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Dynamic analysis of laser shock response: Experimental and numerical studies
摘要： Laser is an excellent shock source with the advantages of non-contact, high controllability and broadband frequency, which has great potential to replace traditional mechanical impact and simulate pyroshock. In this paper, the dynamic response induced by laser shock is studied both experimentally and numerically. Firstly, laser shock tests are conducted. The general characteristics of laser shock response are experimentally investigated, where the effects of transparent overlays and absorbent coatings are evaluated in terms of shock response spectrum. Furthermore, a finite element (FE) model is developed and validated by comparing simulation and experimental results. Based on FE model, the effects of power density, pulse duration, and spot size of laser on the dynamic response are evaluated. The results demonstrate that laser shock response has fantastic high-frequency and broadband-frequency characteristics and shock response spectrum amplitude of laser shock can be obviously improved by adding transparent overlays and absorbent coatings. The amplitude of shock response spectrum is in quadratic correlation with laser power density. Laser pulse duration significantly influences the slope of shock response spectrum, but power density and spot size of laser have little effect on the slope.
关键词： Laser shock,Dynamic response,Shock response spectrum,Pyroshock
更新于2025-09-12 10:27:22
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AIP Conference Proceedings [AIP Publishing XLIII ACADEMIC SPACE CONFERENCE: dedicated to the memory of academician S.P. Korolev and other outstanding Russian scientists – Pioneers of space exploration - Moscow, Russia (28 January–1 February 2019)] XLIII ACADEMIC SPACE CONFERENCE: dedicated to the memory of academician S.P. Korolev and other outstanding Russian scientists – Pioneers of space exploration - Laser shock peening with low-energy laser sources: Techniques and prospects
摘要： The first part of the article considers practical prospect of using laser shock peening technology. There are presented prerequisites of solving several technological tasks related to local impact with laser shock processing. The second part of the article is devoted to analysis and parameter optimization that permit to apply low-energy sources for laser shock processing. The influence of various absorbing and tamping coatings used in the process of laser shock peening on the properties of the processed material was researched. Physical and technological properties of viewed coatings were evaluated. The results were evaluated by the treated material microhardness, due to its linear relationship with the stresses in material. Conducted research enables the selection of the optimal environments combination to achieve the most effective results in the process of laser shock peening.
关键词： laser shock peening,surface modification,low-energy laser sources,tamping coatings,absorbing coatings,microhardness
更新于2025-09-12 10:27:22
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Effective femtosecond laser shock peening on a Mg–3Gd alloy at low pulse energy 430?μJ of 1?kHz
摘要： In this paper, microstructure evolution and hardness of Mg-3Gd alloy treated by femtosecond (fs) laser shock peening (LSP) with direct and con?ned ablation modes were investigated in detail. Under a relatively low pulse energy of 430 μJ with a repetition of 1 kHz, the surface hardness of sample has been enhanced by 70% effectively. Compared with ns-LSP with pulse ?uence of 71.7 J/cm 2 , fs-LSP with pulse ?uence of 34.2 J/cm 2 is superior in the hardness increment, both of which are in the same order of magnitude. A distinct grain re?nement of surface layer has been discovered and results in the increase of hardness. Nonuse of absorption and con?ning layers and the employment of the industry commercial fs laser with high repetition can inspire big potential LSP application in special metal material.
关键词： Mg–3Gd alloy hardness,Laser shock peening,Surface treatment,Femtosecond laser
更新于2025-09-12 10:27:22
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Surface modification methods for fatigue properties improvement of laser-beam-welded Ti-6Al-4V butt joints
摘要： Surface and internal defects formed upon laser beam welding (LBW) have been recognized as a serious problem because they cause stress concentration leading to premature failure of a welded component. This paper seeks to remedy these weld imperfections by applying various post-weld treatments and analyzing their effect on the high cycle fatigue (HCF) performance of welded joints. High efficiency of laser-based post-processing techniques after welding such as laser surface remelting (LSR) and laser shock peening (LSP) was demonstrated and compared with conventional approaches. The study reveals that welding porosity determines the internal crack initiation of the surface-treated weldments. Influence of process parameters on porosity level and the HCF properties is presented in detail. Based on an extensive experimental study, practical guidelines needed to mitigate the notch effect from defects and to maximize the fatigue performance of the laser-welded Ti-6Al-4V butt joints are given.
关键词： laser shock peening,Laser beam welding,high cycle fatigue,porosity,defects
更新于2025-09-12 10:27:22