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In metallurgy, peening is the process of working a metal's surface to improve its material properties, usually by mechanical means, such as hammer blows, by blasting with shot (shot peening), focusing light (laser peening), or in recent years, with water column impacts (water jet peening) and cavitation jets (cavitation peening). With the notable exception of laser peening, peening is normally a cold work process tending to expand the surface of the cold metal, thus inducing compressive stresses or relieving tensile stresses already present. It can also encourage strain hardening of the surface metal. Residual stress Plastic deformation from peening induces a residual compressive stress in a peened surface, along with tensile stress in the interior. This stress state resembles the one seen in toughened glass, and is useful for similar reasons. Surface compressive stresses confer resistance to metal fatigue and to some forms of corrosion, since cracks will not grow in a com

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Bragg edge tomography characterization of additively manufactured 316L steel

Nikola Kalentics, Christian Leinenbach, Roland Logé, Efthymios Polatidis, Markus Strobl

In this work we perform a neutron Bragg edge tomography of stainless steel 316L additive manufacturing samples, one as built via standard laser powder bed fusion, and one using the novel three-dimensional (3D) laser shock peening technique. First, we consider conventional attenuation tomography of the two samples by integrating the signal for neutron wavelengths beyond the last Bragg edge, to analyze the bulk density properties of the material. This is used to map defects, such as porosities or cracks, which yield a lower density. Second, we obtain strain maps for each of the tomography projections by tracking the wavelength of the strongest Bragg edge corresponding to the {111} lattice plane family. Algebraic reconstruction techniques are used to obtain volumetric 3D maps of the strain in the bulk of the samples. It is found that not only the volume of the sample where the shock peening treatment was carried out yields a higher bulk density, but also a deep and remarkable compressive strain region. Finally, the analysis of the Bragg edge heights as a function of the projection angle is used to describe qualitatively crystallographic texture properties of the samples.

AMER PHYSICAL SOC2022

Analysis of results on improved welded joints

Alain Nussbaumer

Recents studies have shown that the use of improvement techniques on welds allows an increase in the level of admissible fatigue strength (even more than 100%). The aim of this study was to collect and validate literature data, create a data base containing the joint characteristics and fatigue results, make a statistical analysis of the data in order to quantify the effect of parameters influencing the fatigue strength and propose new S-N curves which are compared to those given in Eurocode 3. Four improvement techniques (grinding, TIG dressing, hammer peening, shot peening) and four joint types (butt, T joints, cruciform and longitudinal joints) were taken into account. Joint thicknesses less than 25 mm loaded in air with a stress ratio R between 0 and 0.1 were selected. Three classes of yield strength for the base metal were considered: 600. All S-N curves were above those of as-welded assemblies. The best results were obtained with hammer peening. The larger increase in the fatigue strength due to the use of improvement techniques was due to the occurrence of an initiation phase in addition to the crack propagation phase. During the initiation phase, the extension of existing crack-like defects is slowed down or even stopped. The duration of this phase increases with the total fatigue life.

1997

Peening methods for improvement of fatigue strength

Ian Smith

EPFL, ICOM - Construction métallique1990

MSE-101(a): Materials:from chemistry to properties

Ce cours permet l'acquisition des notions essentielles relatives à la structure de la matière, aux équilibres et à la réactivité chimique en liaison avec les propriétés mécaniques, thermiques, électriques et magnétiques des matériaux.

MSE-422: Advanced metallurgy

This course covers the metallurgy, processing and properties of modern high-performance metals and alloys (e.g. advanced steels, Ni-base, Ti-base, High Entropy Alloys etc.). In addition, the principles of computational alloy design as well as approaches for a sustainable metallurgy will be addressed

MICRO-301: Manufacturing technologies

This course gives an introduction to production methods and manufacturing technologies used in microengineering. The focus is given on the understanding of physical phenomena underlying the processes, the relation between materials, manufacturing processes and design, as well as economical aspects.

Shot peening

Shot peening is a cold working process used to produce a compressive residual stress layer and modify the mechanical properties of metals and composites. It entails striking a surface with shot (rou

Fatigue (material)

In materials science, fatigue is the initiation and propagation of cracks in a material due to cyclic loading. Once a fatigue crack has initiated, it grows a small amount with each loading cycle, t

Laser peening

Laser peening (LP), or laser shock peening (LSP), is a surface engineering process used to impart beneficial residual stresses in materials. The deep, high-magnitude compressive residual stresses indu