Peening

About: Peening is a research topic. Over the lifetime, 5538 publications have been published within this topic receiving 73073 citations.

Improving the fatigue crack resistance of waspaloy by shot peening

Abstract: Four-point bending fatigue tests were conducted to study the effect of shot peening on the fatigue life of the nickel-base superalloy, Waspaloy. The influence of shot peening intensity on crack initiation, Stage I crack growth and the Stage I-to-Stage II crack growth transition phases, has been examined to identify the mechanisms by which shot peening improves fatigue resistance. The potential for extending the fatigue life of fatigue-damaged Waspaloy components has been explored by shot peening specimens which had been cyclic damaged to various degrees. The fatigue test was then continued after peening to ascertain the possibility of crack arrest or extending fatigue life. These experiments explore the possibility of ‘healing’ fatigue damage by a surface engineering treatment.

Microstructural characterization and mechanical behavior of ultrasonic impact peened and laser shock peened AISI 316L stainless steel

Abstract: The effects of ultrasonic impact peening (UIP) and laser shock peening (LSP) on 316L stainless steel were compared in terms of surface morphologies, microstructural evolutions and mechanical properties. The grain refinement mechanisms by mechanical and laser shock wave were subsequently analyzed. Experimental results showed that both UIP and LSP produced micro-grooves with the same depth (~48 μm) at the surface of 316L. The nano-grain size induced by double UIP treatment (10–90 nm) was much smaller than that by triple LSP treatment (>70 nm) because the impact numbers and total impact energy of UIP were much higher. The mechanical twinning was almost complete absence in the sample by UIP. On the contrary, the mechanical twinning was frequently observed in samples by LSP. The magnitude of peak pressure determined the transition from dislocation-dominated mechanism (~680 MPa for UIP) to twinning-dominated mechanism (~2200 MPa for LSP). The resultant dislocation cell size by UIP was much smaller than that by LSP due to the difference of dislocation density caused by different shock wave speed and impact numbers. Additionally, the compressive residual stress on the surface by UIP was higher than that by LSP in both measuring direction. Furthermore, both grain refinement and high dislocation density induced by UIP contributed to a significant increase in the hardness (~433 HV) and yield strength (~447 MPa). By contrast, the LSP induced mechanical twins which can act as dislocation blockers significantly improved the yield strength (~423 MPa).

The effect of shot peening on notched low cycle fatigue

Abstract: The improvement in low cycle fatigue life created by shot peening ferritic heat resistant steel was investigated in components of varying geometries based on those found in conventional power station steam turbine blades. It was found that the shape of the component did not affect the efficacy of the shot peening process, which was found to be beneficial even under the high stress amplitude three point bend loads applied. Furthermore, by varying the shot peening process parameters and considering fatigue life it has been shown that the three surface effects of shot peening; roughening, strain hardening and the generation of a compressive residual stress field must be included in remnant life models as physically separate entities. The compressive residual stress field during plane bending low cycle fatigue has been experimentally determined using X-ray diffraction at varying life fractions and found to be retained in a direction parallel to that of loading and to only relax to 80% of its original magnitude in a direction orthogonal to loading. This result, which contributes to the retention of fatigue life improvement in low cycle fatigue conditions, has been discussed in light of the specific stress distribution applied to the components. The ultimate aim of the research is to apply these results in a life assessment methodology which can be used to justify a reduction in the length of scheduled plant overhauls. This will result in significant cost savings for the generating utility.

Investigation of microstructures and residual stresses in laser peened Incoloy 800H weldments

Abstract: Laser Shock Peening (LSP) is an advanced surface enhancement technique to improve the mechanical properties of engineering materials. In the present study, LSP was performed on Incoloy 800H laser weldments. The microstructure and residual stress, two key factors for application of weldments, were investigated via optical and transmission electron microscopy and crystallographic and residual stress X-ray diffraction analysis. Micro-hardness tests were also used to evaluate mechanical properties. Results show that significant grain refinement occurs in the LSP-treated zone where original lath structures are refined to equiaxed grains, and dislocation density increases significantly. Because of the high strain rates produced by LSP, grain deformation by slip is limited, and therefore deformation by grain twinning occurs. The micro-hardness of weld joint increased after LSP with a hardened depth of about 1.2 mm. LSP processed welded joints exhibited high compressive residual stress, and the residual stress distribution was uniform. It is shown that LSP is an effective way to refine microstructure, increase strength and rebalance residual stress which will improve fatigue life and corrosion cracking resistance of Incoloy 800H weldments.