The aim of this paper is to give a simple and accurate tool for prediction and comparison of residual stresses in laser shock peened and shot peen treated materials.
Abstract
Purpose
The aim of this paper is to give a simple and accurate tool for prediction and comparison of residual stresses in laser shock peened and shot peen treated materials.
Design/methodology/approach
This work applies finite element code ABAQUS in order to compare the residual stress state and plastic deformation in specimens in aluminium alloy 7050‐T7451, treated with shot peening (SP) and laser shock peening (LSP) processes. Both processes are simulated using the Hugoniot elastic limit (HEL) of the material in question, and the processes are modelled using same input parameters (pressure on the surface of the specimen and the duration of contact between the material and the peening medium).
Findings
By using the same approach in both the analyses, a sound comparison of two technologies can be made, by comparing the obtained residual stress profiles. In addition, surface pressure and contact time can be varied easily in a parametric analysis, allowing the calibration of the numerical results.
Research limitations/implications
Owing to simplicity of used numerical models, different process parameters relative to SP process have not been taken in consideration directly, but through their effect on pressure on the surface of the specimen and the duration of contact between the material and the peening medium.
Originality/value
Application of HEL material model, usually applied to LSP problems, to the analysis of SP process gives promising results, in spite of simplicity of used numerical model.
Details
Keywords
Kelly S. Carney, Omar Hatamleh, James Smith, Thomas Matrka, Amos Gilat, Michael Hill and Chanh Truong
The purpose of this paper is to present an analytical framework for predicting the residual stresses that result from the laser shock peening of a friction stir‐welded 2195…
Abstract
Purpose
The purpose of this paper is to present an analytical framework for predicting the residual stresses that result from the laser shock peening of a friction stir‐welded 2195 aluminum alloy sample, using the finite element software LS‐DYNA.
Design/methodology/approach
The pressures resulting from the laser peening are directly applied in an explicit transient analysis as forces. At the completion of the transient analysis, an implicit springback analysis is performed to determine the final residual stresses. This cycle is repeated for the appropriate number of peen applications, including the appropriate overlap of application areas. To validate the analytical framework, a comparison of residual stresses between analysis and a test specimen is made using laser‐peened base material which was not friction stir‐welded. Friction stir welding (FSW) causes residual stresses and material property variations. In this work, the varying material properties regions are simplified and defined as discrete, separate materials. The residual stresses resulting from the welding are introduced directly as initial conditions in the peening transient analysis and so are combined within the analysis with the residual stresses from the peening.
Findings
Comparisons made between the experimental and analytical residual stresses are generally favorable.
Originality/value
Analysis of the laser shock peening of FSW has not been accomplished previously.
Details
Keywords
Ulrike C. Heckenberger, Elke Hombergsmeier, Vitus Holzinger and Wolfgang von Bestenbostel
Laser shock peening (LSP) is a process capable of introducing compressive residual stresses into a metallic component. The residual compressive stress field can extend deeper…
Abstract
Purpose
Laser shock peening (LSP) is a process capable of introducing compressive residual stresses into a metallic component. The residual compressive stress field can extend deeper below the treated surface than that produced by conventional shot peening (SP). The effect of such deep compressive stress profile is expected to result in a significantly greater benefit in fatigue resistance after LSP compared to SP. The purpose of this paper is to examine this further.
Design/methodology/approach
Residual stress profiles have been determined by X‐ray diffraction and incremental centre hole drilling. They have been correlated with the respective LSP process parameters and the obtained fatigue behavior.
Findings
A significant improvement of the fatigue life was found for an R ratio of 0.1. SP leads to a fatigue improvement of about 15 percent. For the same specimen geometry, a fatigue life improvement of about 25‐35 percent, depending on the load level, can be obtained after LSP. However, not only for the positive R ratio, where it is quite obvious, but also for the negative R ratios, R=−1 and −3, an increase of the fatigue life is generated by SP and LSP.
Originality/value
A shown LSP has a high potential for extending the service life of metallic components at the design stage, but it may also be possible to apply this technique to in‐service aircraft to extend the service goals of existing structures.
Details
Keywords
Miguel Morales, Carlos Correa, Juan Antonio Porro, Carlos Molpeceres and José Luis Ocaña
Laser shock peening (LSP) is mainly a mechanical process, but in some cases, it is performed without a protective coating and thermal effects are present near the surface. The…
Abstract
Purpose
Laser shock peening (LSP) is mainly a mechanical process, but in some cases, it is performed without a protective coating and thermal effects are present near the surface. The numerical study of thermo‐mechanical effects and process parameter influence in realistic conditions can be used to better understand the process.
Design/methodology/approach
A physically comprehensive numerical model (SHOCKLAS) has been developed to systematically study LSP processes with or without coatings starting from laser‐plasma interaction and coupled thermo‐mechanical target behavior. Several typical results of the developed SHOCKLAS numerical system are presented. In particular, the application of the model to the realistic simulation (full 3D dependence, non‐linear material behavior, thermal and mechanical effects, treatment over extended surfaces) of LSP treatments in the experimental conditions of the irradiation facility used by the authors is presented.
Findings
Target clamping has some influence on the results and needs to be properly simulated. An increase in laser spot radius and an increase in pressure produces an increase of the maximum compressive residual stress and also the depth of the compressive residual stress region. By increasing the pulse overlapping density, no major improvements are obtained if the pressure is high enough. The relative influence of thermal/mechanical effects shows that each effect has a different temporal scale and thermal effects are limited to a small region near the surface and compressive residual stresses very close to the surface level can be induced even without any protective coating through the application of adjacent pulses.
Originality/value
The paper presents numerical thermo‐mechanical study for LSP treatments without coating and a study of the influence of several process parameters on residual stress distribution with consideration of pulse overlapping.
Details
Keywords
Yuji Sano, Koichi Akita, Kazuya Takeda, Rie Sumiya, Toshiyuki Tazawa, Toshiyuki Saito and Chihiro Narazaki
The purpose of this paper is to investigate the behavior of compressive residual stress induced by laser peening under external loading on an age‐hardened high‐strength aluminum…
Abstract
Purpose
The purpose of this paper is to investigate the behavior of compressive residual stress induced by laser peening under external loading on an age‐hardened high‐strength aluminum alloy A2024‐T3, a low‐carbon austenitic stainless steel SUS316L (Type 316L) and a nickel‐based alloy NCF600 (Alloy 600).
Design/methodology/approach
The surface residual stress was measured intermittently by X‐ray diffraction during cyclic uniaxial loading.
Findings
The compressive residual stress due to laser peening significantly decreased during the first few cycles at stress ratio of 0.1 with the maximum loading stress exceeding the 0.2 per cent yield stress. No remarkable decrease was observed afterward until the end of the loading cycles.
Originality/value
Under symmetric loading at the stress ratio of −1 to A2024‐T3, a major decrease took place in the compression side of the first loading cycle. The surface residual stresses remained in compression within all the extent of the present experiments, even if the maximum loading stress exceeded the yield stress of the materials.
Details
Keywords
Dennis J. Buchanan, Michael J. Shepard and Reji John
The purpose of this paper is to analyze the residual stress relaxation in laser shock‐peened and shot‐peened IN100 subject to thermal exposure.
Abstract
Purpose
The purpose of this paper is to analyze the residual stress relaxation in laser shock‐peened and shot‐peened IN100 subject to thermal exposure.
Design/methodology/approach
Shot peening (SP) is a commonly used surface treatment that imparts compressive residual stress into the surface of components. The shallow depth of compressive residual stresses, and the extensive plastic deformation associated with SP, has been overcome by modern approaches such as laser shock peening (LSP). LSP surface treatment produces compressive residual stress magnitudes that are similar to SP that extend four to five times deeper, and with less plastic deformation. Retention of compressive surface residual stresses is necessary to retard initiation and growth of fatigue cracks under elevated temperature loading conditions.
Findings
Results indicated that the LSP processing retains a higher percentage of the initial residual stress profile over that of SP.
Originality/value
The retained residual stresses after thermal exposure of these surface treatment processes can be incorporated into a life prediction methodology that takes credit for beneficial compressive surface residual stresses to delay initiation and retard fatigue crack growth.
Details
Keywords
Patrice Peyre, Neila Hfaiedh, Hongbin Song, Vincent Ji, Vincent Vignal, Wilfrid Seiler and Stephane Branly
The purpose of this paper is to conduct a comparative study of the surface modifications induced by two different lasers on a 2050‐T8 aluminum alloy, with a specific consideration…
Abstract
Purpose
The purpose of this paper is to conduct a comparative study of the surface modifications induced by two different lasers on a 2050‐T8 aluminum alloy, with a specific consideration of residual stress and work‐hardening levels.
Design/methodology/approach
Two lasers have been used for Laser shock peening (LSP) treatment in water‐confined regime: a Continuum Powerlite Plus laser, operating at 0.532 mm with 9 ns laser pulses, and near 1.5mm spot diameters; a new generation Gaia‐R Thales laser delivering 10 J‐10 ns impacts, with 4‐6mm homogeneous laser spots at 1.06 mm. Surface deformation, work‐hardening levels and residual stresses were analyzed for both LSP conditions. Residual stresses were compared with numerical simulations using a 3D finite element (FE) model, starting with the validation of surface deformations induced by a single laser impact.
Findings
Similar surface deformations and work‐hardening levels, but relatively lower residual stresses were obtained with the new large 4‐6 mm impact configuration. This was attributed to a reduced number of local cyclic loadings (2) compared with the small impact configuration (4). Additionally, more anisotropic stresses were obtained with small impacts. FE simulations using Johnson‐Cook's material' behavior were shown to simulate accurately surface deformations, but to overestimate maximum stress levels.
Research limitations/implications
This work should provide LSP workers a better understanding of the possible benefits from the different LSP configurations currently co‐existing: using small (<2 mm) impacts at high‐cadency rates or large ones (>4‐5 mm). Moreover, experimental results and simulated data had never been presented on 2050‐T8 Al alloy.
Originality/value
An experimental (and numerical) comparison using two distinct laser sources for LSP, has never been presented before. This preliminary work should help LSP workers to choose adequate sources.
Details
Keywords
Thomas J. Spradlin, Ramana V. Grandhi and Kristina Langer
The purpose of this paper is to develop and implement a structural fatigue life estimation framework that includes laser‐peened (LP) residual stresses and then experimentally…
Abstract
Purpose
The purpose of this paper is to develop and implement a structural fatigue life estimation framework that includes laser‐peened (LP) residual stresses and then experimentally validates these fatigue life estimations.
Design/methodology/approach
A three‐dimensional finite element analysis of an Al 7075‐O three‐point bending coupon being LP was created and used to estimate the fatigue life when loaded. Fatigue tests were conducted to validate these estimations.
Findings
The framework developed for fatigue life estimation of LP‐processed coupons yielded estimates with goodness‐of‐fit between the log‐transformed experimental and analytical data of R2=0.97 for the baseline coupons and R2=0.94 for the LP‐processed coupons.
Research limitations/implications
Approximated ε‐life fatigue parameters were used to calculate the fatigue life resulting from the complex residual stress fields due to the simulated LP process.
Originality/value
A fatigue life estimation framework that considers LP residual stress fields has been developed for use on structural components.
Details
Keywords
Uroš Trdan, Sebastjan Žagar, Janez Grum and José Luis Ocan˜a
The purpose of this paper is to investigate the effect of shock waves and strain hardening effect of laser and shot peening on precipitation‐hardened aluminium alloy AA 6082‐T651.
Abstract
Purpose
The purpose of this paper is to investigate the effect of shock waves and strain hardening effect of laser and shot peening on precipitation‐hardened aluminium alloy AA 6082‐T651.
Design/methodology/approach
The hardened layer was evaluated by means of surface integrity with optical microscopy, scanning electron microscope (SEM), energy dispersive spectroscopy, analysis of microhardness and residual stress profiles. Corrosion anodic polarization tests in a 3.5 per cent NaCl water solution were carried out to express a pitting potential and the degree of pitting attack, which was verified on SEM and with 3D metrology.
Findings
Research results indicated significant differences between two treatment techniques which had an important influence on the final condition of the surface layer. Potentiodynamic polarization tests inferred that laser peening enabled shift of the pitting potential to more positive values, which ensures higher corrosion resistance.
Originality/value
Results confirmed that the higher corrosion resistance of the laser‐peened specimens against pitting corrosion depends on the modification of the surface, due to ablation during plasma generation. Despite increased surface roughness, laser‐peened specimen exhibits beneficial increase of the pitting/breakdown potential and in reduction of pitting attack degree at the specimen surface.