Peening

About: Peening is a(n) research topic. Over the lifetime, 5538 publication(s) have been published within this topic receiving 73073 citation(s).

Laser shock processing and its effects on microstructure and properties of metal alloys: a review

Abstract: The current status of research and development on laser shock processing of metals, also known as laser peening, using Q-switched high power lasers is reviewed. The influence of processing parameters on the laser-induced shock waves in metal components are discussed and analyzed. Special attention is paid to the residual stresses and improved fatigue performance from laser peening, which are compared with conventional shot peening results. Modification of microstructure, surface morphology, hardness, and strength by laser peening is also discussed. Finally, applications of laser peening are addressed. Results to date indicate that laser peening has great potential as a means of improving the mechanical performance of components.

A new method for estimating residual stresses by instrumented sharp indentation

Abstract: A general methodology is proposed for the determination of surface residual stresses and residual plastic strains using instrumented sharp indentation. The residual stresses and the residual plastic strains are assumed to be equibiaxial and uniform over a depth (beneath the indented surface) which is at least several times larger than the indentation contact diameter. The indenter load and geometry can be so chosen as to minimize or maximize the contact radius to seek the broadest range of applicability and validity of the proposed method by recourse to macro-, micro- and nanoindentation of elastoplastic materials. Invoking the invariance of contact pressure in the presence of an elastic residual stress, or the change in the instantaneous yield strength of a strain-hardening elastoplastic solid in the presence of a residual plastic strain, a step-by-step method is outlined here to estimate pre-existing residual stress/strain fields. The technique can be directly used for residual stress measurements in such applications as thin films for microelectronics and optoelectronics, structural coatings, and engineered surfaces whose properties are altered by such methods as mechanical working, etching, ion implantation, case hardening, laser treatments, shot peening or laser shock peening. The predictions of the proposed analytical method for determining residual stresses have been shown to compare favorably with finite element predictions as well as available experimental results.

Intrinsic stress in sputter-deposited thin films

Abstract: A review of the sputtered film stress literature shows that the intrinsic stress can be tensile or compressive depending on the energetics of the deposition process. Modeling studies of film growth and extensive experimental evidence show a direct link between the energetics of the deposition process and film microstructure, which in turn determines the nature and magnitude of the stress. The fundamental quantities are the particle flux and energy striking the condensing film, which are a function of many process parameters such as pressure (discharge voltage), target/sputtering gas mass ratio, cathode shape, bias voltage, and substrate orientation. Tensile stress is generally observed in zone 1-type, porous films and is explained in terms of the grain boundary relaxation model, whereas compressive stress, observed in zone T-type, dense films, is interpreted in terms of the atomic peening mechanism. Modeling of the atomic peening mechanism and experimental data indicate that the normalized moment...

An evaluation of shot peening, residual stress and stress relaxation on the fatigue life of AISI 4340 steel

Abstract: Shot peening is a method widely used to improve the fatigue strength of materials, through the creation of a compressive residual stress field (CRSF) in their surface layers. In the present research the gain in fatigue life of AISI 4340 steel, used in landing gear, is evaluated under four shot peening conditions. Rotating bending fatigue tests were conducted and the CRSF was measured by an X-ray tensometry prior and during fatigue tests. It was observed that relaxation of the CRSF occurred due to the fatigue process. In addition, the fractured fatigue specimens were investigated using a scanning electron microscope in order to obtain information about the crack initiation points. The evaluation of fatigue life, relaxation of CRSF and crack sources are discussed.

On the influence of mechanical surface treatments—deep rolling and laser shock peening—on the fatigue behavior of Ti–6Al–4V at ambient and elevated temperatures

Abstract: It is well known that mechanical surface treatments, such as deep rolling, shot peening and laser shock peening, can significantly improve the fatigue behavior of highly-stressed metallic components. Deep rolling (DR) is particularly attractive since it is possible to generate, near the surface, deep compressive residual stresses and work hardened layers while retaining a relatively smooth surface finish. In the present investigation, the effect of DR on the low-cycle fatigue (LCF) and high-cycle fatigue (HCF) behavior of a Ti–6Al–4V alloy is examined, with particular emphasis on the thermal and mechanical stability of the residual stress states and the near-surface microstructures. Preliminary results on laser shock peened Ti–6Al–4V are also presented for comparison. Particular emphasis is devoted to the question of whether such surface treatments are effective for improving the fatigue properties at elevated temperatures up to ∼450 °C, i.e. at a homologous temperature of ∼0.4 T/T m (where T m is the melting temperature). Based on cyclic deformation and stress/life ( S / N ) fatigue behavior, together with the X-ray diffraction and in situ transmission electron microscopy (TEM) observations of the microstructure, it was found that deep rolling can be quite effective in retarding the initiation and initial propagation of fatigue cracks in Ti–6Al–4V at such higher temperatures, despite the almost complete relaxation of the near-surface residual stresses. In the absence of such stresses, it is shown that the near-surface microstructures, which in Ti–6Al–4V consist of a layer of work hardened nanoscale grains, play a critical role in the enhancement of fatigue life by mechanical surface treatment.