Characterization of nanocrystalline surface layer induced by shot peening and effect on their fatigue strength.

2004 ◽  
Vol 843 ◽  
Author(s):  
Hideo Mano ◽  
Kondo Satoru ◽  
Akihito Matsumuro ◽  
Toru Imura
Keyword(s):  
Residual Stress ◽  
Surface Layer ◽  
Fatigue Strength ◽  
Vickers Hardness ◽  
Shot Peening ◽  
White Layer ◽  
The Other ◽  
Fatigue Properties ◽  
Nanocrystalline Layer

ABSTRACTThe shot peening process is known to produce a hard layer, known as the white layer” on the surface of coil springs. However, little is known about the fatigue properties of this white-layer.In this study, coil springs with a white-layer were manufactured. The surface of these springs was then examined using micro Vickers hardness, FE-SEM etc. to test fatigue strength of the springs.From the results obtained, a microstructure of the white-layer with grain size of 50–100 nm was observed, with a Vickers hardness rating of 8–10 GPa.Tow category springs were manufactured utilizing a double-peening process. These springs had the same residual stress destruction and surface roughness. Only one difference was observed: one spring had a nanocrystalline layer on the surface, while the other did not. The results of the fatigue test realized an increase in the fatigue life of the nanocrystalline surface layer by 9%.

Characterization of Shot-Peened Surfaces by a Noncontacting Thermoelectric Method

2000 ◽  
Author(s):  
Hector Carreon ◽  
Peter B. Nagy
Keyword(s):  
Residual Stress ◽  
Surface Roughness ◽  
Surface Layer ◽  
Dislocation Density ◽  
Shot Peening ◽  
Compressive Residual Stress ◽  
Cold Work ◽  
Subsurface Layer ◽  
Thermoelectric Method

Abstract Shot peening is widely used in the aerospace and other industries to increase the damage tolerance of metal parts via producing a thin surface layer of compressive residual stress that prevents crack initiation and retards crack growth during service. Nondestructive evaluation of the prevailing compressive residual stress in the shallow subsurface layer is complicated by the adverse effects of shot peening, such as surface roughness and cold work that manifests itself through increased dislocation density and localized texture. Recent research efforts have revealed that conventional ultrasonic and eddy current NDT methods are simply too sensitive to surface roughness to quantitatively assess the subtle variations in mechanical and electrical properties that are caused by shot peening. On the other hand, noncontacting thermoelectric techniques are very unique among all other methods used in nondestructive materials characterization in that they are solely sensitive to intrinsic material variations regardless of the size, shape, and surface quality of the specimen to be tested. Noncontacting thermoelectric methods, based on magnetic detection of local thermoelectric currents around inhomogeneities in metals when a temperature gradient is established throughout the specimen, are especially well suited for the characterization of shot peened surfaces. Experimental evidence suggests that this method can reliably detect and quantitatively assess otherwise hidden variations in material properties within the shallow surface layer of shot peened specimens. The thermoelectric method is sensitive to all three “material” effects of shot peening, namely residual stress, local texture, and increased dislocation density, but it is entirely insensitive to its “geometrical” by-product, i.e., the rough surface topography. Further development of the thermoelectric method is necessary to study the underlying physical phenomena before it can be successfully adapted to practical inspection problems, but the preliminary results presented in this paper are very promising.

scholarly journals Contribution to Improvement of Fatigue Properties of Zr-4 Alloy: Gradient Nanostructured Surface Layer versus Compressive Residual Stress

Nanomaterials ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 3125
Author(s):  
Donghui Geng ◽  
Qiaoyan Sun ◽  
Chao Xin ◽  
Lin Xiao
Keyword(s):  
Residual Stress ◽  
Surface Layer ◽  
Fatigue Strength ◽  
Compressive Residual Stress ◽  
Fatigue Cracks ◽  
Coarse Grained ◽  
Fatigue Properties ◽  
Layer Versus ◽  
Mechanical Grinding ◽  
The Individual

The gradient nanostructured (GNS) layer forms beneath the surface of Zr-4 samples by the surface mechanical grinding treatment (SMGT) process, which increases the fatigue strength apparently due to the synergistic effect of the gradient nanostructured layer and compressive residual stress. The SMGTed Zr-4 samples are subjected to annealing to remove residual stress (A-SMGT) and the individual effect of the GNS layer and compressive residual stress can be clarified. The results show that the gradient nanostructure in the surface is stable after annealing at 400 °C for 2 h but residual stress is apparently removed. Both SMGTed and A-SMGTed Zr-4 samples exhibit higher fatigue strength than that of coarse-grained (CG) Zr-4 alloy. The fatigue fracture of Zr-4 alloy indicates that the hard GNS surface layer hinders fatigue cracks from approaching the surface and leads to a lower fatigue striation space than that of CG Zr-4 samples. The offset fatigue strength of 106 cycles is taken for SMRT-ed, A-SMRT-ed, and CG Zr-4 samples and the results indicate clearly that the GNS surface layer is a key factor for the improvement of fatigue strength of the Zr-4 alloy with surface mechanical grinding treatment.

Effect of Pre-Strain and Roller Working on Torsional Fatigue Properties of a Structural Steel

2011 ◽  
Vol 295-297 ◽  
pp. 2227-2230
Author(s):  
Cong Ling Zhou
Keyword(s):  
Residual Stress ◽  
Fatigue Limit ◽  
Work Hardening ◽  
Compressive Residual Stress ◽  
Strain Ratio ◽  
Fatigue Tests ◽  
The Other ◽  
Fatigue Properties ◽  
Torsional Fatigue ◽  
Stress Work

In this study, fatigue tests have been performed using two kinds of specimens made of 25 steel. One is pre-strained specimen with pre-strain ratio changing from 2% to 8% by tension, the other is roller worked with deformation of 0.5 mm and 1.0 mm in diameter direction. In the case of pre-strained specimen, the fatigue limit increases according to increase of tensile pre-strain, the fatigue limit of 8% pre-strained specimen is 25% higher than that of non-pre-strained one; in the case of roller worked specimen, the fatigue limit of R05 and R10 is 126% and 143% to that of non-roller worked specimen, respectively. These remarkable improvements of fatigue limit would be caused by the existence of compressive residual stress, work-hardening and the elongated microscopic structures.

Surface Modification Analysis after Shot Peening of AA 7075 in Different States

2013 ◽  
Vol 768-769 ◽  
pp. 519-525 ◽  
Author(s):  
Sebastjan Žagar ◽  
Janez Grum
Keyword(s):  
Residual Stress ◽  
Surface Layer ◽  
Residual Stresses ◽  
Aluminium Alloy ◽  
Shot Peening ◽  
Fatigue Testing ◽  
Stress Profile ◽  
Treatment Conditions ◽  
Stress Profiles ◽  
Compressive Residual Stresses

The paper deals with the effect of different shot peening (SP) treatment conditions on the ENAW 7075-T651 aluminium alloy. Suitable residual stress profile increases the applicability and life cycle of mechanical parts, treated by shot peening. The objective of the research was to establish the optimal parameters of the shot peening treatment of the aluminium alloy in different precipitation hardened states with regard to residual stress profiles in dynamic loading. Main deformations and main residual stresses were calculated on the basis of electrical resistance. The resulting residual stress profiles reveal that stresses throughout the thin surface layer of all shot peened specimens are of compressive nature. The differences can be observed in the depth of shot peening and the profile of compressive residual stresses. Under all treatment conditions, the obtained maximum value of compressive residual stress ranges between -200 MPa and -300 MPa at a depth between 250 μm and 300 μm. Comparison of different temperature-hardened aluminium alloys shows that changes in the Almen intensity values have greater effect than coverage in the depth and profile of compressive residual stresses. Positive stress ratio of R=0.1 was selected. Wöhler curves were determined in the areas of maximum bending loads between 30 - 65 % of material's tensile strength, measured at thinner cross-sections of individual specimens. The results of material fatigue testing differ from the level of shot peening on the surface layer.

Fabrication and Characterization of Bulk Nanocrystalline Layer in Steel and Aluminum Alloys Formed by Shot Peening

2009 ◽  
Author(s):  
R. Waikar ◽  
Y. B. Guo ◽  
Keith A. Woodbury
Keyword(s):  
Aluminum Alloys ◽  
Shot Peening ◽  
Martensitic Steel ◽  
Bulk Material ◽  
Lower Surface ◽  
Martensitic Steels ◽  
Cross Sectional ◽  
Bulk Nanocrystalline ◽  
Nanocrystalline Layer

The formation of bulk nanocrystalline (NC) layers in AISI 1075 pearlitic and martensitic steels and aluminum alloys 6061-T6 and 7075 using air blast shot peening was studied. The cross-sectional microstructure of the samples showed a gradual reduction of the grain size near the surface. The NC layers were characterized using optical and scanning electron microscopy and nanohardness measurements. 2D surface topography of the top surface was also carried out. The roughness of the peened surfaces depends on sample hardness. The hardened AISI 1075 martensitic steel had lower surface roughness value. NC layers of 5 to 15 μm thickness were observed in the steels whereas the aluminum alloys 6061 and 7075 yielded NC layers up to 20 to 25 μm thick. The measured nanohardness in the NC layers confirmed the higher hardness of the NC layer compared with the bulk material.

Effect of Fine-Grained Microstructure Induced by Induction-Heating Fine Particle Peening Treatment on Fatigue Properties of Structural Steel (0.45%C)

2014 ◽  
Vol 891-892 ◽  
pp. 1482-1487
Author(s):  
Kazue Murai ◽  
Ryota Toyama ◽  
Jun Komotori ◽  
Kengo Fukazawa ◽  
Yoshitaka Misaka ◽  
...  
Keyword(s):  
Residual Stress ◽  
Fatigue Strength ◽  
Structural Steel ◽  
Grain Refinement ◽  
Induction Heating ◽  
Fine Particle ◽  
Optical Microscope ◽  
Treatment Temperature ◽  
Fatigue Properties ◽  
Fine Grained

To improve the fatigue properties of structural steel, a novel surface modification process which combines high-frequency induction heating (IH) with fine particle peening (FPP) was developed. IH-FPP treatment was performed on the surface of structural steel specimens (0.45%C) at temperatures from 600 to 750 °C, with peening times of 60 and 120 s. To determine the characteristics of the treated surfaces, the microstructure was observed using an optical microscope and a scanning electron microscope. Vickers hardness and residual stress distributions were also measured. The characteristics of fine-grained microstructures were examined by electron backscatter diffraction. Furthermore, in order to investigate the effect of the grain refinement achieved by IH-FPP treatment, rotational bending fatigue tests were performed on treated specimens. Results showed that IH-FPP treatment created fine-grained microstructures beneath the surfaces of steel samples. The average ferrite grain size was 4.06 μm for a treatment temperature of 700 °C, and finally 0.76 μm for 600 °C . This was due to dynamic recrystallization in the processed region. IH-FPP treated specimens exhibited a higher fatigue strength than untreated specimens. As almost no compressive residual stress was measured in the treated or untreated specimens, the increase in fatigue strength resulting from IH-FPP treatment was due solely to grain refinement.

Numerical Simulation of Residual Stresses Induced from Shot Peening with Finite Element Method

2013 ◽  
Vol 433-435 ◽  
pp. 1898-1901
Author(s):  
Li Juan Cao ◽  
Shou Ju Li ◽  
Zi Chang Shangguan
Keyword(s):  
Numerical Simulation ◽  
Finite Element Method ◽  
Residual Stress ◽  
Surface Layer ◽  
Residual Stresses ◽  
Shot Peening ◽  
Target Material ◽  
Residual Stress Field ◽  
State Of Stress ◽  
Compressive Residual Stresses

Shot peening is a manufacturing process intended to give components the final shape and to introduce a compressive residual state of stress inside the material in order to increase fatigue life. The modeling and simulation of the residual stress field resulting from the shot peening process are proposed. The behaviour of the peened target material is supposed to be elastic plastic with bilinear characteristics. The results demonstrated the surface layer affected by compressive residual stresses is very thin and the peak is located on the surface.

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