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In Wire Arc Additive Manufacturing (WAAM), solidification grain morphology in titanium alloy tends to be columnar rather than equiaxed due to heat dissipation and repeated thermal cycles. This study demonstrates improved microstructure and anisotropic properties in Ti-6Al-4V specimens fabricated by WAAM and treated with hammer peening, resulting in a transition from columnar grains to fine equiaxed grains (~300 μm) in both single-pass and four-bead WAAM walls. The anisotropic elongation decreased by approximately 7%, and tensile strength along the building direction decreased by ~50 MPa for a single-pass wall. Additionally, small and large equiaxed prior-β grains appeared alternately due to the combined effect of hammer peening and welding deposition. The region can be categorized into three parts (MAX, MED, MIN) based on the degree of plastic strain characterized by KAM mapping of EBSD data. In current WAAM parameters, the ratio of strong (~1.5 mm) deformation field (MAX) is about 50% within one deposition layer (MAX+MIN), suggesting a new approach for producing equiaxed prior-β grains. We expect that this method will be applicable for transforming the prior-β grains from columnar to equiaxed. Furthermore, the distribution of plastic strain and phase transformation mechanisms offers innovative approaches to optimize the hammer peening process, with potential applications to optimize the process for more complex components in the aerospace and power plant industries. [ABSTRACT FROM AUTHOR]

Wire and arc additive manufacturing (WAAM) technique has introduced a novel approach for producing complex Ti–6Al–4V parts with metric dimensions. However, the produced part leads to the development of a strong texture and anisotropic mechanical properties due to the formation of large columnar β grains. To resolve this issue, the plastic deformation of each deposited track through hammer peening was developed as a means to refine these large β grains. In this study, we have investigated an innovative approach to further enhance the efficiency of β grain refinement by minimizing the arc heat input associated with previous deposited layer, which is achieved by employing a C-type filler wire. Our findings reveal a notable enhancement in grain refinement efficiency through the utilization of a C-type filler wire with peening process, as compared to available conventional commercial round shape filler wire. Specifically, the employment of the C-type filler wire results in a reduced melt pool penetration depth of WAAM Ti–6Al–4V (3.3 mm), compared to the commercially available round shape (R-Type) filler wire (4.48 mm). Within the plastically deformed region by peening, fine and randomly oriented β grains are observed, extending to a depth of deformation reaching 844 ± 32.65 μm. Peening WAAM Ti–6Al–4V with the C-type filler wire leads to the development of isotropic mechanical properties in both horizontal and vertical directions, offering high strength due to the presence of small equiaxed β grains and thin α laths (0.56 ± 0.18 μm), in contrast to the use of conventional commercial round shape filler wire.

In Wire Arc Additive Manufacturing (WAAM), solidification grain morphology in titanium alloy tends to be columnar rather than equiaxed due to heat dissipation and repeated thermal cycles. This study demonstrates improved microstructure and anisotropic properties in Ti-6Al-4V specimens fabricated by WAAM and treated with hammer peening, resulting in a transition from columnar grains to fine equiaxed grains (~300 μm) in both single-pass and four-bead WAAM walls. The anisotropic elongation decreased by approximately 7%, and tensile strength along the building direction decreased by ~50 MPa for a single-pass wall. Additionally, small and large equiaxed prior-β grains appeared alternately due to the combined effect of hammer peening and welding deposition. The region can be categorized into three parts (MAX, MED, MIN) based on the degree of plastic strain characterized by KAM mapping of EBSD data. In current WAAM parameters, the ratio of strong (~1.5 mm) deformation field (MAX) is about 50% within one deposition layer (MAX+MIN), suggesting a new approach for producing equiaxed prior-β grains. We expect that this method will be applicable for transforming the prior-β grains from columnar to equiaxed. Furthermore, the distribution of plastic strain and phase transformation mechanisms offers innovative approaches to optimize the hammer peening process, with potential applications to optimize the process for more complex components in the aerospace and power plant industries.

Combined peening composed of multiple peening processes or peening media is a surface treatment method for comprehensive control of the macro shape and performance of the part. Compared to combined peening, the impact kinetic energy of the combined hammering can be easier to control over a wide range, and the hammer tool head size is larger than the shot. This paper focused on investigating the effect of combined hammering treatment, 6 mm and 14 mm tool heads with peening density 3.7 to 4.2/mm 2 , on the variable scale evolution of titanium TA2. Three types of contact relation between the tool head and existing dimple were proposed for impacting at the same position. The size of the dimple of combined hammering varies in width or depth direction, resulting in nest morphology composed of different size dimples. The cross-section microstructure of the test plate was observed, and the gradient changes of dislocation, slip, and grain size are smoothed by combined hammering. The change in hammer tool head size makes the target plastic deform at different depths. The hammering sequence has a significant influence on the evolution of stress and strain fields. When the tool head is first large and then small, a large compressive residual stress near the surface is introduced, about 1000 Mpa; on the contrary, the compressive residual stress distributes uniformly in the depth direction, with an affected layer depth of about 4.4 mm. The measured dimple size and residual stress verified the reliability of the simulation results. [ABSTRACT FROM AUTHOR]

Inconel 718 is a widely used alloy in the aeronautic sector due to its excellent mechanical and corrosion wear resistance under high temperature conditions. However, its good mechanical properties can be a double edge sword in terms of manufacturing, especially in those processes based in mechanical principles, such as machining or forming. Considering that most aeronautic components are exposed to cyclic load and temperature, fatigue resistance becomes critical, and therefore, the finishing processes. The surface integrity of a component plays an important role on its fatigue behaviour, as the most common crack initiation area is usually the surface. The present work compares three different mechanical finishing processes that confer better surface properties to the component: polishing, burnishing, and hammer-peening. Each one achieves different degrees of roughness, and residual stress on the surface. The study is not only focused on the resultant mechanical properties, but also in productivity and process robustness. It is concluded that each technology excels in a different property.

Aerostructures withstand cyclic mechanical loads and therefore, their design must fulfil surface integrity and fatigue strength requirements. This paper studies the effect of pneumatic machine hammer peening on surface integrity of 7050-T7451 aluminium alloy. Specimens were hammer peened using two different stepover distances (0.07 and 0.35 mm) and initial offset (0.3 and 0.5 mm). A Kistler dynamometer was used to measure the forces generated by hammer peening. Then, the surface topography, residual stresses and microstructural damage of the specimens were characterised. The results demonstrate that the magnitude of residual stresses and the thickness of the affected layer increases when reducing the stepover distance, while surface roughness reduces. Additionally, none of the tested conditions produced microstructural defects. These findings suggest that pneumatic hammer peening is an additional process to manufacture thin-walled structural aluminium alloy components. [ABSTRACT FROM AUTHOR]

A number of surface modification processes have been developed over the past decades. Depending on the application in industry, different processes are selected to meet the needs. Shot peening is one of the widely adopted surface modification processes in various industries dedicated for improving the material properties. On the other hand, hammer peening is an emerging and promising surface modification process that can provide wide range of benefits, encompassing fatigue life enhancement, surface finish improvement and texturing, microstructural refinement, corrosion, and wear resistance. This technology has been extensively studied on its application as a post-welding treatment on metal alloys. However, there is limited information available for other applications such as additive manufacturing. This paper discusses how hammer peening has evolved into its current state today and the role it played in various industries. The variants of hammer peening technology and the standardized key process parameters are elucidated. In view of the rigorous research and development, the current state-of-the-art on different applications area also represented. Despite the proven capability by many studies, the gaps to the industrialization of this technology still exist which are identified in the final section of the paper. [ABSTRACT FROM AUTHOR]

Several manufacturing processes are used to beneficially influence the surface and subsurface properties of manufactured parts. Different aspects such as the surface topography or resulting residual stresses are addressed using different manufacturing processes. This paper presents the first approach for pulsed mechanical surface treatment (PMST), a new manufacturing process aiming to combine the mechanics used in deep rolling and shot or hammer peening. The process can generate a defined surface topography while constantly impinging a mechanical impact on the workpiece. Two different tools (type 1 and type 2) have been designed to approach this new concept. Hardened carbide pins are used for type 1 to prove the concept using a simpler kinematic and resulting in a burnishing-like process. For type 2, hardened roller is used and results in an actual rolling process. Specimens made of S235 are processed in experiments with tool type 1 with varying pulse frequency and feeds. The resulting surface topography is described using optical measurement systems while micro-hardness measurements are used to describe the subsurface properties. The results in general show an increase of hardness in the surface and subsurface layer while the resulting surface topography can be directly controlled by the process parameters and therefore be designed for specific functional properties. [ABSTRACT FROM AUTHOR]

Asymmetric scallop cutouts on the sides of a U-rib caused by diaphragm splicing deviation were detected in a bridge. To study the possible effect of this phenomenon on fatigue performance, the stresses of the asymmetric scallop cutout and the diaphragm-to-rib weld were tested, and the influence was compared with that of the symmetric case. This and numerical simulation showed that, for the side of the U-rib with the smaller-radius scallop cutout, the position of stress concentration transferred from the scallop cutout to the diaphragm-to-rib weld, and the stress value of the weld was greater than that of the scallop cutout, resulting in more fatigue damage to the weld. To reduce the adverse effect caused by the asymmetric scallop cutouts, an application experiment with a hammer peening was carried out, and the stresses before and after hammering were monitored. The results showed that hammer peening could improve the fatigue performance by inducing compressive stress. [ABSTRACT FROM AUTHOR]

Several manufacturing processes are used to beneficially influence the surface and subsurface properties of manufactured parts. Different aspects such as the surface topography or resulting residual stresses are addressed using different manufacturing processes. This paper presents the first approach for pulsed mechanical surface treatment (PMST), a new manufacturing process aiming to combine the mechanics used in deep rolling and shot or hammer peening. The process can generate a defined surface topography while constantly impinging a mechanical impact on the workpiece. Two different tools (type 1 and type 2) have been designed to approach this new concept. Hardened carbide pins are used for type 1 to prove the concept using a simpler kinematic and resulting in a burnishing-like process. For type 2, hardened roller is used and results in an actual rolling process. Specimens made of S235 are processed in experiments with tool type 1 with varying pulse frequency and feeds. The resulting surface topography is described using optical measurement systems while micro-hardness measurements are used to describe the subsurface properties. The results in general show an increase of hardness in the surface and subsurface layer while the resulting surface topography can be directly controlled by the process parameters and therefore be designed for specific functional properties.

Inter-pass rolling is a cold-working technique to improve microstructure and associated mechanical properties in Ti-6Al-4V wire + arc additive manufacturing (WAAM) and other AM processes. Initially developed to eliminate residual stress and distortion in WAAM, rolling equipment is very cumbersome and the application is limited to simple features and geometries. To exploit the potential design freedom of AM processes, this study investigates the potential of novel machine hammer peening (MHP) tools to aid or replace rolling as inter-pass cold working technique, as these tools can be manipulated relatively easy with articulated robots. The MHP tool used in this study is the pneumatically powered FORGEfix XP by KWM tools GmbH. The cold working behaviour of the tool was assessed using a confocal microscope to measure the deformed surface geometry, EBSD plastic strain maps identify dislocations under the peened area, as well as hardness and residual stress profiles. After the tool characterisation, inter-pass peening was applied to Ti-6Al-4V WAAM walls. Residual stresses that typically occur in additive manufacturing seem to promote the potential of the tool, as the penetration depth was higher compared to the treatment of a stress-free specimen. The successfully achieved grain refinement has met the expectations and is reported in this study. [ABSTRACT FROM AUTHOR]

Low roughness of free-form surfaces represents a challenge in production of forming tools. In the industry, the free-form surface is grinded and polished manually. The technology of hammer peening has the capability to replace the time consuming handcraft by automated machining with high productivity and other positive effects, like increased hardness and compressive residual stress in the surface layer. This leads to a high wear resistance of the machined surface. The hammer peening can be conducted with a piezo-actuated tool. The high frequency of such a tool allows achieving higher productivity than other actuator principles used in hammer peening tools. In this paper, a piezo-actuated hammer peening tool working in its mechanical resonance is presented. Furthermore, a crossdomain model including the process, the mechanical and the electrical part of the tool is explained. This model is further used for optimization of the process and the tool. The functionality of the tool is demonstrated by machining results. [ABSTRACT FROM AUTHOR]

The increased usage of advanced high strength steels (AHSS) as material for car body parts leads to a continuous reduction of car weight and thus a lowering of CO 2 emissions. This weight reduction results from higher yield and tensile strength of AHSS than conventional steel grades. However, the higher strength of AHSS leads to higher loadings of the forming tools. To increase the wear resistance of the tool surfaces, mechanical surface treatments are used. In this work, the incremental forming of EN-JS2070 deep drawing tools by means of machine hammer peening (MHP) is investigated. In the past, small surface defects were observed after MHP of nodular cast iron EN-JS2070. The cause for the occurrence of these surface defects is unknown. The aim of this work is the investigation and description of the logical relationship between the cause and effect of MHP process parameters and the surface defects on nodular cast iron EN-JS2070. The surface defects occurred independent of the chosen MHP parameter setup at one critical zone on the hammered deep drawing tools and the investigated microstructure showed the existence of shrink holes, which were primarily responsible for the occurrence of the surface defects after MHP. [ABSTRACT FROM AUTHOR]

Austenitic stainless steel E309L is frequently used for welded repairs on 13%Cr-4%Ni martensitic stainless steel blade runners. However, very high tensile residual stresses are found in the upper layers of these repairs, thus reducing the fatigue resistance of the repaired area in comparison with the free of residual stress base material. The use of hammer peening to increase the fatigue life of E309L welded on UNS-S41500 base metal plates has been investigated using welded samples replicating in situ blade runner repairs. Residual stress measurements using the contour method on these samples have confirmed the high stresses caused by flux cored arc welding (FCAW) of E309L, leaving stress magnitudes close to the ultimate tensile strength of the base material. Hammer peening of the surface beads effectively creates high compressive stresses at the weld’s surface up to 3 mm depth. Alternating bending fatigue tests conducted on hammer peened samples have shown an average life increase of 5.8 times at S a = 330 MPa over unpeened samples. Fatigue tests have however shown diminishing returns when overpeening the samples. [ABSTRACT FROM AUTHOR]

The article provides information on the fundamentals of size reduction of materials used in chemical, mechanical and pharmaceutical industries. Particular focus is also given to types of grinding mills including hammer mills and jet mills referring to milling tests, characterization of feed materials, and size reduction application.

In this paper, the industrial hammer peening process is optimized using multi-objective, sequential approximate optimization, which is a mathematics- plus finite element- based algorithm. Since the number of design and objective variables is significant, the global optimization problem is split into two, more manageable multi-objective subproblems. The use of surrogate modelling together with an intensification and diversification strategy for solving the optimization subproblems allows for significant computational cost savings without loss of accuracy. Additionally, we propose a Bayesian inference criterion-based sensitivity approach for 'filtering-out' design variables which do not significantly affect objectives variables. Finally, guidelines for selecting appropriate Pareto optima are given using $N-1$ Pareto diagrams, where N is the number of objective variables. [ABSTRACT FROM AUTHOR]

Due to their outstanding properties, WC-WC iron-based cermet coatings are widely used in the field of wear protection. Regarding commonly used WC-WC reinforced coating systems, it has been reported that their tribological behavior is mainly determined by the carbide grain size fraction. Although the manufacturing route for arc-sprayed WC-WC cermet coatings is in an advanced state, there is still a lack of knowledge concerning the performance of cored wires with tungsten carbides as filling material and their related coating properties when post-treatment processes are used such as machine hammer peening (MHP). A major objective was to characterize WC-WC FeCMnSi coatings, deposited with different carbide grain size fractions as a filling using cored wires, with respect to their tribological behavior. Moreover, deposits derived from cored wires with a different amount of hard phases are investigated. According to this, polished MHP surfaces are compared to as-sprayed and polished samples by means of metallographic investigations. With the use of ball-on-disk and dry rubber wheel tests, dry sliding and rolling wear effects on a microscopic level are scrutinized. It has been shown that the MHP process leads to a densification of the microstructure formation. For dry sliding experiments, the MHP coatings obtain lower wear resistances, but lower coefficients of friction than the conventional coatings. In view of abrasion tests, the MHP coatings possess an improved wear resistance. Strain hardening effects at the subsurface area were revealed by the mechanical response using nanoindentation. However, the MHP process has caused a cracking of embedded carbides, which favor breakouts, leading to advanced third-body wear. [ABSTRACT FROM AUTHOR]

Existing design recommendations for the consideration of high frequency hammer peening (HFHP) are limited to steel grades of S960 and plate thicknesses of 5 mm and higher. The influence of HFHP treatment on the fatigue behaviour of welded ultra high strength steels with yield strengths of 960 MPa and higher – loaded in the upper finite and low cycle fatigue life region – has not been investigated sufficiently so far. For this reason, fatigue tests have been performed on four typical welded notch details of mobile crane structures made of S960, S1100 and S1300 to determine the influence of HFHP on the fatigue strength. The fatigue strength of HFHP treated specimens was at least twice the fatigue strength of the as welded toe condition. A fatigue life improvement due to HFHP treatment can be observed at load cycles of 10,000 and higher. In accordance with existing investigations, the slope of the S – N -line increases to approximately m ∼ 5 due to HFHP treatment if the fatigue cracks start from the treated weld toes. The classification of the test results for the HFHP treated toe condition shows, that fatigue classes (FAT) of existing design proposals are conservative. Further improvements of the proposed FAT classes are possible which shows the potential use of UHSS with steel grades higher than S960 in combination with HFHP treatment. [ABSTRACT FROM AUTHOR]

The effect of hammer peening on the fatigue resistance of high strength welded steel S690 has been investigated. Cyclic four points bending tests have been performed on butt weld samples, manually and automatically hammered. Microstructural and mechanical modifications induced by both methods and their subsequent influences on fatigue life have been studied using several characterization techniques. A comparison of residual stress measurements using X-ray diffraction shows also differences between methods. On the other hand, hardness profile of the strain hardened region is very similar for both types of samples. The ultra-fine grain microstructure of the heat-affected zone (HAZ) induced by the hammer peening process has been studied by Field Emission Scanning Electron Microscopy and Electron Back Scattered Technique (EBSD). In fatigue as expected, hammer peening increases the fatigue strength of weld structures in good agreement with the latest proposal of the International Institute of Welding (IIW). Compressive residual stresses play a key role. Microstructure does not seem to affect fatigue strength in spite of nanostructured layer. On the contrary to what is usually admitted, the local geometry of the weld toe is deteriorated because the process induces crack-like folds. In this paper, some recommendations are proposed for the hammer peening process in terms of sweeping strategy. [ABSTRACT FROM AUTHOR]

Krankonstruktionen sind im Allgemeinen hohen Beanspruchungen mit vergleichsweise geringen Lastspielzahlen ausgesetzt. Im Bereich der Kurzzeitfestigkeit, bekannter unter dem englischen Begriff Low-Cycle Fatigue (LCF), bieten höchst- und ultrahochfeste Stähle erhebliche Vorteile. Im Folgenden wird über Ergebnisse von Ermüdungsversuchen an höchst- und ultrahochfesten stumpfgeschweißten Blechen und höchstfesten Rundhohlprofilen mit aufgeschweißten Längssteifen berichtet. Hierbei wurden Versuchsserien mit WIG-Decklagen, geschliffenen Nahtwurzeln und hochfrequenten Hämmerverfahren (HFH) untersucht. Die Untersuchungsergebnisse werden zusammengefasst und mit Bezug auf die Kerbklassen des Eurocode 3 bzw. auf die FAT-Klassen der aktuellen IIW-Richtlinie ausgewertet. Low-cycle fatigue of welded joints made of high and ultra-high strength steels. Crane structures are exposed to very high loading but with rather low number of load cycles. In the so called low cycle fatigue (LCF) domain the use of high- and ultra-strength steels offer considerable advantages. In this paper, fatigue tests on butt welded ultrahigh-strength plates and circular hollow sections with longitudinal attachments and post weld treatment by means of TIG-dressing, high frequency hammer peening (HFHP) and grinded roots are presented. A summarized evaluation and discussion of results referring to fatigue class classification of Eurocode 3 and the recent IIW guideline is given. [ABSTRACT FROM AUTHOR]

Abstract: The effect of hammer peening on the fatigue resistance of high strength welded joints in high strength structural steel S690 has been investigated. Cyclic four points bending tests have been performed on butt weld samples, manually and automatically hammered. Microstructural and mechanical modifications induced by both methods and their subsequent influences in fatigue life have been studied using several characterization techniques. It was found that the roughness of manually hammered samples is different than that of automatically hammered samples for which a lack of correct treatment in some regions of the weld cordon has been observed. A comparison of residual stress measurements using X-ray diffraction shows also differences between both methods. On the other hand, hardness profile of the strain hardened region is very similar for both types of samples. The ultra-fine grain microstructure of the heat-affected zone (HAZ) induced by the hammer peening process has been studied by Field Emission Scanning Electron Microscopy and Electron Back Scattered Technique (EBSD). The strain-hardened depth determined by Kernel Average Misorientation (KAM), microhardness and residual stress are compared. [Copyright &y& Elsevier]

Abstract: This paper presents the results of the development process for a Finite Element Analysis of the Hammer Peening Fatigue Life Improvement Technique. The Fatigue Life of welded structures is still in need for improvement. The sheer number of Fatigue Live Improvement Techniques parameters leads to the need of simulating and predicting their results. For this study, two different materials were used, an Austenitic Stainless Steel and a Duplex Stainless Steel. Non-load carrying cruciform weld joints were produced and fatigue tested, with and without the Hammer Peening treatment. Finally a FEA code (ABAQUS®) was used to simulate the Hammer Peening technique. A fully dynamic model was used, combined with the Chaboche Kinematic-hardening material model and different Hammering parameter experimentally determined. Alongside the residual stresses introduced by the Hammer Peening Technique, the predicted Fatigue Life using the FEA model were compared with the experimental results, showing a very good agreement between them. Also the effect of several parameters, like the hammering impact load, the hammer positioning or the number of hammering passages, were analysed as a way to validate the FEA model. The most important result was of course the Fatigue Strength Gain factor, for the Hammer Peening Technique, that in both cases was found to be superior to 1.3. [Copyright &y& Elsevier]

Welded components suffer from high tensile residual stresses close to the weld beads. These stresses seem to be the origin of premature cracking which could result in a catastrophic rupture during operation and a reduction of the lifespan of these components. In this context, the Hydro-Québec’s Research Institute (IREQ) developed a technique of residual stresses relaxation by robotized hammer peening which makes it possible to release stresses close to surface and preserve the mechanical and dimensional properties of manufactured components. Robotized hammer peening was used to induce compressive residual stresses on initially stress free samples of austenitic stainless steel 304L. Hammer peening layers from one to nine were performed and the resulting residual stresses were evaluated thanks to the contour technique. Complete 2D residual stress fields on samples cross sections were obtained. The ability of hammer peening to relax residual stresses within welded plates was then quantified on austenitic stainless steel 304L plates welded with a 308 steel and hammer peened. These tests show the efficiency of hammer peening as a method to relax tensile residual stresses and induce compressive ones to a depth of a few millimetres. Process parameters were optimized such as the number of hammer peening layers to be applied to reduce processing time and maximization of the intensity and spatial distribution of the compressive residual stresses. [ABSTRACT FROM AUTHOR]

Abstract: In this study, a series of tests were conducted in aluminum alloy 2A12-T4 to investigate the effect of hammer peening process on the fatigue behavior of holes in specimens. The fracture surfaces of the specimens were observed by means of an optical microscope in order to disclose the mechanism of fatigue failure. The finite element method (FEM) was used to analyze the distribution of residual stress around the holes which were preliminarily treated with hammer peening. The results revealed that the crack of a hammer peened hole always initiated at the peened face. The fatigue life of these hammer peened holes significantly was prolonged five fold compared to non-hammer peened holes. Their fatigue life showed a positive correlation with the residual plastic strain which was induced by hammer peening process. The longest fatigue life was found in cases in which the residual plastic strain surrounded the whole bore of the hole but did not emerge at the fix face. [Copyright &y& Elsevier]

Abstract: Residual stresses induced by welding may reach the yield strength of the material and decrease the life of the components by premature cracking. The hammer peening process has been used to improve the fatigue resistance in welded components, especially at the weld toe. It is expected that the powerful hammer peening process produces a deeper compressive layer than other currently used processes and thus a better improvement in fatigue life for heavy welds. To better understand residual stress relaxation by hammer peening, this study evaluates the effect of each hammer blow on the residual stresses field under the treated surfaces. An impact machine was used for hammering and generating unitary impacts at the same location. 304L steel plates were tested under 10-impact with various energy levels. Both initial stress free plates and plates with residual stresses were tested. Strain gages were used for recording strains at the surface in the near field of the impact, whereas in-depth residual stresses at 8mm from the impact center were measured using the hole-drilling technique. The micro-hardness profiles were also measured to evaluate the hardening affected zone of the hammer peening. It was found that in initial stress free plates, hammer peening introduces compressive residual stresses. In plates with initial tensile residual stresses, hammer peening either released them or turned them into compression. It was found that increasing energy improves the hammer peening efficiency and that the first three or four hammer blows were the most effective. It was also found that the extent of the hammer-peening induced compression was around 1mm. Microscopic observations of samples from the tested plates did not reveal cracks on the treated surfaces. [Copyright &y& Elsevier]

The existing methods of assessing the fatigue life of welded joints fail to consider local strain ranges and mean stress at the weld toe. The present work proposes a novel approach to assessing the fatigue life of welded joints by conducting measurements with digital image correlation (DIC) and X-ray diffraction (XRD) in combination. Local strain ranges at the weld toe of gusset welded joints were measured by DIC. Hammer peening was conducted on the welded joints to introduce different initial stresses. The influence of mean stress was investigated by considering initial residual stress measured by XRD and a perfect plastic material model. The fatigue experiment was carried out on specimens with and without hammer peening. The results showed that hammer peening could offset adverse welding deformation effectively, and introduce significant residual compressive stress. The fatigue failure life increased by more than 15 times due to hammer peening. The fatigue initiation life assessed by the proposed method was close to that based on nominal stress, indicating that the proposed method is reliable for predicting the fatigue initiation life of welded joints. [ABSTRACT FROM AUTHOR]