Experimental study of shot peening effect on the surface of austenitic stainless steels :
roughness, residual stresses and work hardening
Mohamed Chaiba, Mohamed Belhamianib, Abdelkader Meguenia, Abdelkader Ziadib, F. Javier Belzuncec
*LMechanic of structures and solids laboratory/DGRSDT, University of Sidi Bel Abbes, 22000, Algeria.
*Smart Structures Laboratory/DGRSDT, Ctr Univ. Ain Témouchent, BP 284, 46000,Algeria.
cMaterials Science and Metallurgical Engineering Department, University of Oviedo, campus universitario, 33203 Gijón, Spain
E-mail : pro19moh@hotmail.com
Abstract- Shot peening is a mechanical surface treatment widely used in automotive and aerospace industries to enhance the fatigue life of mechanical parts. In this process, many small and hard particles, called shots, are projected at high velocities on to the sample. The multiple impacts plastically deform the material surface and induce an in-plane compressive residual stress field near the surface. Roughness, compressive residual stress and work hardening of an AISI 304 austenitic stainless steel was studied to explain it evolution according to the Almen intensity and mechanical properties. Shot peening increases surface hardness levels. We can confirm in case of CSP the highest microhardness observed at topmost surface. According to these results it can be considered, that after CSP application, the
microhardness in depth of 0.025 mm increased from about 220 HV to 350 HV.
Keywords-shot peening, residual stresses, work hardening, Almen intensity, roughness, FWHM.
I. Introduction
The mechanical strength of a surface is a decisive factor in the strength of the part to fatigue life of the parts. This improvement is mainly due to the hardening of the surface layer [1] and the introduction of residual compressive stress which locally reduce the load [2] The tribological properties can also be improved by appropriate surface treatments [3], [4]. They have the further advantage of generating gradient conferring properties of a good compromise between a hard surface material, and relatively ductile heart.
Shot peening is a surface treatment commonly used to improve the fatigue performance of various metallic parts [5-7], it is a hybrid process involving many disciplines of static and dynamic elasticity and plasticity. This process consists of projecting a large number of tiny particles at high velocity onto the surface of a component. Each impact plastically deforms the material and repeated impacts lead to a beneficial compressive residual stress state near the surface. In addition, shot peening alters both the local mechanical properties and microstructure [8].
On the other hand, it also generates increased surface roughness [9] and possible damage. Its influence on fatigue life therefore arises from a combination of multiple effects.
Residual stresses in a work piece can be divided into macro and micro stresses [10-12]. By definition the macrostresses are the same in all phases present at the same depth in the material. Consider the plastic deformation occurring at the surface during machining operations where the deformation of the surface layer will be constrained by the bulk where the plastic deformation is minimal, if existing. The magnitude of these residual stresses and the depth
of the layer containing these stresses are function of the process parameters[13–16].
Macrostresses are self-equilibrated through the cross-section of the work piece. In multi-phase materials the differences in yield point and possible response to mechanical load results in inhomogeneous strains in the material volume.
Strong phases constraining the weaker ones and giving rise to stresses on a microscale level, these are the microstresses.
Therefore, the investigation of this process requires a thorough understanding of mechanical behavior of the shot and the target, the two main elements in shot peening, at both low and high strain rates.
Al-Obaid [17] studied the residual stress distribution in the target and developed a number of theoretical expressions for the parameters of the process based on a new model of spherical cavity expansion. However, Al-Obaid states at the end that there is still a huge lack of knowledge and that we are only just entering the area of mechanics of shot peening.
Kobayashi et al. [18] investigated the mechanism of compressive residual stress by shot peening. They performed static compression tests and dynamic impact tests using a single steel ball against a flat steel plate. In the static tests, compression residual stress was created near the center of the ball indentation mark. In the dynamic tests, however, tensile stress was created near the center of the ball indentation mark and compression residual stress was created outside of the indentation.
Coombs et al [19] made an attempt to measure the most effective peening affected depth for several different shot peening conditions. To find this depth they removed some material of the specimens and then determined the fatigue life.
What they found was at a certain depth (when some material had been removed) the maximum cycles to failure were found for all the test conditions. Their
explanation to this phenomenon was that at a certain depth below the shot peened surface, there exists a maximum compressive residual stress peak.
Today it is considered that shot peened steels have a maximum compressive stress peak just below the peened surface. By screening the literature dealing with shot peening of different steels and its effects on different loadings [20-24] it becomes clear that shot peening is a very effective and cost efficient post treatment to increase the fatigue strength of steels. To find the optimum shot peening conditions for the steel might be impossible without narrowing down the problem to specific steel under specific loadings [25].
Other works have used the width of the X-ray diffraction peak, generally the full width at half maximum (FWHM), to evaluate the dislocation density and micro-residual stresses and assess the degree of strain hardening Pariente et al [26], Turski et al [27] used crystallographic orientation data acquired with electron backscatter diffraction (EBSD) mapping to evaluate the average orientation spread within each grain as an indicator of strain- hardening.
Mylonas and Labeas [28] noted that knowledge of the degree of cold work is important since the work- hardened material may exhibit different properties than the base material. It should be noted that work- softening effects have also been observed after shot peening for some materials [29].
Turski et al [27] also reported high dislocation densities near the surface of nickel super alloy Udimet 720Li peened with a high intensity (8-10A) using ion beam induced secondary electron imaging. In addition, complex phenomena can occur in some material types. For instance, shot peening of steel with specific composition and heat treatments can lead to phase transformation of austenite into martensite [27] and [29] also studied the crystallographic texture of C 45 steel before and
after shot peening. It was found that peening significantly altered the texture near the surface by aligning the slip planes with the surface.
K. Dai et al [30] examine the exact effect of the kinetic energies on the surface nanocrystallization with a finite element modeling to provide quantitative description of the difference between surface nanocrystallization and hardening (SNH) and shot peening (SP), it was assumed that SNH has the potential to improve the fatigue resistance more than SP does.
In the present paper, the AISI 304 was treated by using the conventional air blast shot peening device.
Treated specimens surfaces have been characterized using roughness, microhardness, X-ray diffraction (XRD) measurements and microscopy observations.
The results are critically discussed.
II. Materiel and experimental procedure The austenitic stainless steel AISI 304 (X5CrNi18- 10, UNI EN 10088) was considered in this study.
The nominal chemical composition of the steel and its mechanical properties are shown respectively in tables 1 and 2. Shot peening experiments, the X-ray diffraction and roughness measurement were conducted in the laboratory Oviedo of Spain. The results of hardness also the analysis optical microstructures and scanning electronic (SEM) have been made in mechanical laboratory of Polytechnic in Milan (Italy).
Table 1: Nominal chemical composition of AISI 304 austenitic stainless steel in mass density.
C≤ % Si
≤ % Mn
≤ % P
≤ % S
≤ % Cr
% Mo
% Ni
% V
%
0,07 1,0 2,0 0,045 0,015 17,0-19,5 8,0-10,5
Table 2 Mechanical properties of AISI 304 austenitic stainless steel.
0.2 Yield strength
(Mpa) Tensile strength
(MPa) Elongation % Reduction of area
(%) Hardness HV
541 748 39.0 70.0 210
The specimens are subjected to air blast shot peening, we are focused to the conventional shot peening (CSP). Almen intensity [31] and surface coverage [32], presented in table 3, are the important measuring parameters of shot peening
that indicate the total kinetic energy of the process and are related to the total accumulated plastic strain.
Table 3:aspects of the series of specimens.
Treatment Shot diameter
(mm) Almen intensity Pressure (MPa)
Coverage (%)
Not peened (NP) - - - -
Conventionally shot
peened (CSP) 0.3mm (zirconium) 10A 0.4 100
(CSP) 0.3mm (zirconium) 10A 0.4 200
The measurement of the surface residual stress were performed using a computer STRESSTECH X- Stress G3R 3000. We used the wavelength corresponding to the Kchromium (= 0.2291 nm) line generated low voltage 30 kV and a current of 6.7 mA and measures have been carried out on the planes (220) of austenite, which themselves have a
diffraction angle (2, approximately 128, 8º, the settings summary measures are presented in table 4.
Table 4: Experimental parameters employed in the X-ray diffraction analysis
Wavelength Kα (Cr) 0.2291 nm Filter Vanadium
Exposure time (s) 30 Ø collimator (mm) 2
Tilt ψ (º) 9 points between -45/+45 Rotation angle, φ (º) -45, 0 and 45
Background Parabolic Fit Pseudo-Voigt
Measuring mode χ-modified Diffraction angle 128,8º
Miller indices (hkl) (220) [33] Elastic constant, E/(1+ν)
(GPa) 139,2 [33]
It was used sin2 technique which the residual stress is calculated by the following expression:
( ) 0 2
1
1
hklsin
E d
d
(1)E and are the elastic constants of AISI 304 crystallographic direction corresponding to the action (elastic modulus and Poisson's ratio), d is the interplanar distance of the plane of diffraction selected (hkl), the rotation angleand the angle in the specimen plane. The spring constant E / (1 +
) corresponding to the family of planes used in the calculations (220), was 139.2 GPa (table 04).
The effective depth of penetration of radiation is approximately 5.4 µm [34]. Measurements have been carried out in depth step by step removing a very thin layer of material (0.01–0.02 mm) using an electro-polishing device in order to obtain the in- depth profile of residual stresses. A solution of Acetic acid (94%) and Perchloric acid (6%) has been used for electro-polishing. On each specimen, material removal has been carried on up to the
depth showing insignificant compressive residual stress values. The results of the in-depth residual stress measurements were corrected by using the method described by Moore and Evans[35]in order to account for the removed material.
It is important to prepare the specimen before observation and microscopic analysis which leads to group all the means to observe and give a good interpretation of the micrograph. The sawed samples were firstly mounted into epoxy resin, then ground by abrasive paper after they were solidified and finally the sawed samples polished by a 0.1 μm diamond polish agent.
In order to investigate the microstructure evolution after ABSP treatment, the cross sections of the AISI 304 specimens were prepared for metallographic examination using standard procedures, the specimens have been first wet ground with 1200 grit sandpaper and polycrystalline diamond water base suspension with average scratch size of 1 µm after that the last one will be soaked and etched in a chemical solution with 10% C2H2O4 and 90%
H2O for about 30 seconds room temperature with
1.6 A and 15 V. Grain size measurement have been performed by an in situ high energy synchrotron X- ray diffraction device. The microstructures were observed by using a Zeiss EV050 scanning electron microscope (SEM) with thermionic source.
The curves of hardness and roughness are important elements regarding the characterization of treatments performed. The hardness is expressed in our case, in Vickers. The surface roughness was measured in six different locations to obtain the average roughness by using a MARSURF M300.
III. Results and discussion A. Microscopy observations
To gain a better understanding on the material behavior and order to characterize the surface layers after shot peening the optical microscopy and the scanning electron microscopy (SEM) ( fig. 1, 2) have been done.
The description of a microstructure requires two steps:
1- A general observation for:
- locate defects and the different areas - judge the homogeneity of the structure 2- A detailed observations at higher
magnification and description of different zones:
- Analyze the nature and the phase topography (present)
- Measure or judge the size of the components,
The multiple impacts of shot have influence on the surface integrity of shot peened samples, representing many dimples. Surface optical observations of non-peened, shot peened specimens were shown in figure 1. Figure 1(a) shows the surface morphology of not peened stainless steel, the surface is smooth and the material flow direction of fiber texture can be seen. Figure 1(b) shows the surface morphology of shot peened stainless steel, there is a certain increase on surface
roughness. There is a certain degree of damage in the surface of stainless steel after shot peening, chapped phenomenon appear around craters.
Although shot peening can improve the mechanical properties of the material, but also can affect the integrity of the material surface. Also we can observe different dimples of impacts due to the limitations of the shot peening equipment, the speed of each shot was different, so each shot carried different energy, so the craters emerged irregular distribution and the size of craters was not the same with each other.
It clearly distinguished in figure 2a a white residual austenite, in relatively large amounts. This can significantly reduce the surface hardness and change the distribution of residual stress [35]. It may be tolerable or even desirable, depending on the type of stress. A rate of 20 to 25% is generally favorable for fatigue. Its distribution in the room also affects the fatigue strength in a regular gradient depth, and beneficial for bending and contact fatigue [36]. Stable austenite depends on the chemical composition.
This phenomenon concerns only a superficial depth.
It reduces the hardness and causes fatigue microcracks. The compressive stress introduced by peening reducing stress in crack tip, tend to close the microcracks. Thus they slow down their growth and increases the lifetime of the parts. Plastic deformation in the material results in clear contrast in the image, as shown in the upper of specimen nearest than the epoxy resin of figure 2a.
The surface layer with indistinguishable grain boundaries is considered to be ultrafine grain layer (fig.2b) as reported by Darling et al [37]. The microstructure in the surface layer differs obviously from that in the matrix and changes gradually from ultrafine grains to the undeformed grains in the matrix. Literatures [38] reported that the grain size noticeably increases with the depth from the treated surface. These results are similar to the present study.
Figure 1: Surface morphology of AISI 304: (a) not peened; (b) shot peened.
(a) (b)
Figure 2: Cross section microscopy of specimens CSP: (a) optical microscopy observations
(b) SEM observation (500 X) of CSP
B. Hardness measurement
Microhardness measurement was done on the cut section of the specimen with load of 200 gf (1.96N) and a 15s dwell time, spacing between indentations was 0.025 mm. For hardness measurements, the specimens were mounted and polished using standard techniques (ASTM E3).
Three series of measurements were performed for each specimen and the average value is reported to account for materiel’s heterogeneity. The first point of microhardness obtained at depth 0.025 mm was not measured in the same row as the rest of the values, because it might be affected by the other indentation and also there is an influence of free surface, so the first point does not fulfill the requirements of mentioned standard.
In general, shot peening increases surface hardness levels. We can confirm in case of CSP the highest microhardness observed at topmost surfaces, according to these results it can be considered, that after CSP application, the microhardness in depth of 0.025 mm increased about from 220 HV to 350 HV (fig. 3). Going further in depth, the microhadness
values stabilize around 215 HV at 0.25 mm of depth, the same value observed for NP specimen.
This can be considered as the first mark of the presence of work hardened layer induced by CSP and explain the presence of residual stress field. The same behavior has been observed by [39].
Figure 3: Microhardness profiles for all series of specimens
C. Analysis of residual stress profile To obtain the residual stress profile with x-rays diffraction, material needs to be removed in small steps since the penetration depth of the x-rays. This should be done without introducing any new residual stresses, like those obtained from polishing.
To remove material without introducing new residual stresses, electrolytic polishing is the best method to use and the one conducted in this project.
Even though it is practically impossible to remove material without affecting the stress field. With the electrolytic polishing the residual stress distribution will be minimum affected.
After machining a polishing (NP) the strengthened layer of material is very thin and the compressive residual stress disappears at 0.045 mm from the surface.
XRD measurement results show that a considerable depth of materiel is characterized with high compressive residual stresses (fig. 4), this is verified by comparison in the depth residual stress profile
for CSP and NP specimens shown in figure 4, a notable increase is observed for CSP specimen, the compression residual stress after CSP application leads to maximum at this depth and then slightly decreases until depth of 0.12 mm, then it starts rapidly dropping and meets the value of NP material in the depth of 0.37 mm.
Figure 4: Residual stress profiles for all series of specimens
In this study, the experimental run was randomized in order to reduce errors arising from the experimental process. The residual stress profile (fig. 4) in the shot peened sample can be fitted by the following equation:
y = -1E+06x5+ 2E+06x4- 809923x3+ 161300x2- 10370x - 564, 23 (2)
The expression shown in equation (2) was obtained by nonlinear regression and statistical analysis (R2=0, 92).
The prediction R square indicates how well the model predicts the response for new observations. A larger prediction R square means that the model has a greater predictive ability.
D. Surface work hardening
Figure 5 shows the XRD analysis of the unpeened and shot-peened samples at angles ranging from 113 to 142, the results show several peaks in the
two cases, we can observe than after shot peening the intensity decreases but there is no phase change due to shot peening.
Figure 5: XRD analysis of unpeened and shot- peened samples
However, as shown in figure 6, the full width at half maximum (FWHM) of the measured X-ray diffraction peaks can also be used to assess work- hardening. It is defined as the width of the diffraction peak in half of its height and it is related both to residual microstrain in the material and the grain size [40]. A larger width indicates a greater dislocation density that can be correlated with a more work-hardened state and higher strength.
According to FWHM profile, it can be noted a strong surface hardening after CSP and that the CSP tend to the FWHM profile of NP rod at a depth of 0.22 mm (fig. 6).
Figure 6: FWHM profile obtained by XRD for different shot peened series
XRD analysis shows clearly that, in all the shot- peened samples, new phases are not formed and the original phases are maintained during the shot peening process. Meanwhile, it is observed that there is an evident broadening of FWHM after shot peening treatment comparing with unpeened sample, which can be attributed to the grain refinement and dislocation arrangement. Similar results were observed [41-42].
E. Roughness measurements
Surface roughness is one of the important properties that are usually required for the shot peening. It was evaluated before and after shot peening with 100 and 200 % of coverage with a Mahr profilometer PGK, an electronic contact instrument, equipped with MFW-250 mechanical probe and a stylus with tip radius of 2 lm was used to trace the surface profiles with a speed of 0.5 mm/s. The acquired signal was then elaborated by Mahr Perthometer Concept 5 software to obtain the standard roughness parameters (fig. 7).
Figure 7: Surface roughness profile
However, a single roughness value may not be so informative to describe the topography of a surface and additional parameters shall be used to characterize the surface state [43]. The measurement have been performed on six different location of each specimen’s surface, table 5 presents surface roughness parameters as a function of
coverage, where the parameters are defined in ISO 4287 [44].
Table 5: Roughness parameters, measurements and calculated average values of shot peened samples.
Firstly, the results indicated that the difference in the surface roughness parameters for the six locations was found to be around 10%. Clear fluctuations of the measured roughness values on the surface of shot peened specimens, are reported also by Clausen andStangenberg [45].
Surface roughness increases when coverage increases. In case of the arithmetic-mean value Ra, this value increases rapidly from 0,126333 µm to 3.995 µm when coverage change from 0% to 100 % and then increases slightly to 4.547 µm at 200 % of coverage. The surface roughness does not exhibit a significant increment at the 200 % of coverage and seems to generate roughness saturation at 4 µm.
However, the surface roughness of treated surface is rougher than the initial one. Katarina et al [46]
observe the similar phenomenon.
A considerable increase in surface roughness parameters is observed in comparison with unpeened sample due to very high kinetic energy of impact in shot peening treatment [47].
Coverage LT(mm) Lm(mm) Parameters Scan 1 Scan 2 Scan 3 Scan 4 Scan 5 Scan 6 Average
Unpeened 5.60 2.5 Ra (µm) 0.122 0.119 0.138 0.086 0.1 0.193 0,126333
Rz (µm) 1.503 1.183 1.641 1.001 1.024 2.086 1,406333 Rt (µm) 2.289 1.502 3.015 1.44 1.373 3.235 2,142333
100 % 5.60 2.5 Ra (µm) 4.014 3.659 3.58 4.302 3.854 4.565 3.995666
Rz (µm) 24.21 21.42 20.78 21.38 20.54 26.48 22.46833
Rt (µm) 42.35 27.09 26.54 28 30.01 32.6 31.09833
200 % 5.60 2.5 Ra (µm) 4.562 4.864 4.368 4.199 5.228 4.061 4.547000
Rz (µm) 26.34 25.16 25.77 22.47 27.02 24.29 25.17500 Rt (µm) 32.5 35.49 33.82 28.47 35.09 30.09 32.57660
IV. Conclusion
The shot peening treatment is a complex technology which produces different effects on the surface of the treated components, the most important being the modification of surface appearance, work hardening and residual stresses. In this paper, we select the stainless steel as the research material to study the variations in the microstructure and residual stress distribution after shot peening. The most relevant results obtained using an AISI 340 steel submitted to shot peening in order to obtain a wide range of mechanical properties are reported below:
-After shot peening, a compressive residual stress below the surface is created and the surface topography is changed. Compressive residual stresses have beneficial effect for the improvement of mechanical behavior of the peened component.
The residual stress distribution as well as the surface morphology have been experimentally measured and presented.
– A compressive residual stress field in the surface layer together with high surface hardness are also observed after the treatment.
-The microhardness values of the central zone are lower than those of the surface layer in the sample.
The increase of microhardness of AISI 304 steel is due to grain refinement and work hardening. Large elongated grains were transformed into small grains in the surface layer.
-Shot peening induces plastic deformation, increases surface hardness, and introduces significant levels of compressive residual stress.
Similar results were presented in Mhaede et al [48].
-The maximum hardness is directly related to the amount of plastic deformation in the material such as the dislocation density in the material.
-Shot peening does not cause a phase change, but makes the FWHM to become broader, which can be attributed to the grain refinement and dislocation arrangement. This result is consistent with that of Kumar et al [41]. Surface roughness parameters increase and then stabilize with respect to the peening time.
-Microscopy observations and X-ray diffraction XRD grain size measurements, confirm that a NC nanocrystallized layer has been created on the surface of the specimens.
- Surface of not peened stainless steel is smooth and the material flow direction of fiber texture can be seen, however there is a certain degree of damage in
the surface of stainless steel after shot peening, chapped phenomenon appear around the crater.
-Obvious defects were observed on the surface of the conventional shot peened specimens, generated by the kinetic impacts during the process.
-Roughness increases with increasing coverage; this change is attributed to the greater number of impacts that modify the surface topography due to very high kinetic energy of impact in CSP treatment.
-A single roughness value is not so informative to describe the general surface state; additional parameters should be used in order to provide reliable data on surface topography, that is why different roughness parameters including Ra, Rz and Rt, show diverse evolution trends during the process time.
-Work hardening after shot peening also induces an increase of the hardness of the surface region which can be easily quantified by means of the FWHM parameter. It was seen that the FWHM of the steel, being a hardening parameter, is linearly related to its hardness.
-This work showed that the material state arising from shot peening is not uniform on the surface plane in terms of residual stresses, local mechanical properties, roughness, and surface damage.
References
[1] B. SELÇUK, R. IPEK, M.B. KARAMIȘ, "a study on friction and wear behavior of carburized, carbonitrided and borided AISI 1020 and 5115 steels”. Journal of Materials technology 141 187- 197. -2003.
[2] Inés Fernández Pariente, Mario Guagliano,
"About the role of residual stresses and surface work hardening on fatigue ΔKth of a nitrided and shot peened low-alloy steel" Surface & Coatings Technology 202 (2008) 3072–3080
[3] M.B. KARAMIS, R. IPEK, "An evaluation of using possibilities of carbonitrided simple steels instead of carburizing low alloy steel (wear properties)" Applied Surface Science 119 25-33. - 1997 .
[4] J.L. ARQUES, J.M. PRADO, "The dry wear resistance of carbonitrided steel". Wear 103 321- 331. - 1985.
[5] H.O. Fuchs, Shot-peening, Mechanical EngineerÕs Handbook, Wiley, Cincinnati, OH, 1986, pp. 941-951.
[6] J. Harrison, Controlled shot-peening: cold working to improve fatigue strength, Heat Treatment 19 (1987) 16-18.
[7] S.A. Meguid, E¤ect of partial coverage upon the fatigue fracture behaviour of peened components, Fatigue Fracture Eng. Mater. Structures 14 (5) (1991) 515-530.
[8] S. Bagherifard, "Fatigue behavior of notched steel specimens with nanocrystallized surface"
obtained by severe shot peening". Materials and Design 45 (2013) 497–503.
[9] S. Bagherifard, "Numerical and experimental analysis of surface roughness generated by shot Peening". Applied Surface Science 258 6831–
6840.- 2012.
[10] I.C. Noyan, J.B. Cohen, Residual Stress Measurement by Diffraction and Interpretation, Springer-Verlag, New York, 1987.
[11] V. Hauk, Structural and Residual Stress Analysis by Nondestructive Methods, Elsiver, Amsterdam, 1997.
[12] P.J. Withers, H.K.D.H. Bhadeshia, Residual stress Part 2 - Nature and origins, Materials Science and Technology. 17 (2001) 366-375.
[13] Marsh KJ. Shot peening: techniques and applications. London: EMAS; 1993.
[14] Schulze V. Modern mechanical surface treatment, states, stability, effects. Weinheim:
WILEY-VCH Verlag GmbH & Co. KGaA; 2006.
[15] Gao YK, Yao M, Shao PG, Zhao YH. Another mechanism for fatigue strength improvement of metallic parts by shot peening. J Mater Eng Perform 2003;12:507–11.
[16] Gao YK, Wu XR. Experimental investigation and fatigue life prediction for 7475–T7351 aluminum alloy with and without shot peening- induced residual stresses. Acta Mater 2011;59:3737–47.
[17] Y.F.Al-Obaid, Shot peening mechanics:
experimental and theoretical analysis, Mech. Mater.
19 (1995) 251–260.
[18] M. Kobayashi, T. Matsui, Y. Murakami, Mechanics of creation of compressive residual stress by shot peening, Int. J. Fatigue 20 (1998) 351–357.
[19] A.G.H. Coombs, F. Sherratt, J.A. Pope, An analysis of the effects of shot peening upon the fatigue strength of hardened and tempered spring steel. Int. Conf. in Fatiuge of Metals. (1956).
[20] V. Schulze, Modern Mechanical Surface Treatments, First ed., WILEY-VCH Verlag GmbH
& Co. KGaA, Weinheim, 2005.
[21] F.P. Smaglenko, B.A. Gryaznov, S.S.
Gorodetskii, Influence of machining methods on the
residual-stress distribution and fatigue strength of steel ShKh15 specimens, Strength of Materials. 9 (1977) 145-150.
[22] K. Dalaei, B. Karlsson, L.-. Svensson, Stability of residual stresses created by shot peening of pearlitic steel and their influence on fatigue behaviour, Procedia Engineering. 2 (2010) 613-622.
[23] M.A.S. Torres, H.J.C. Voorwald, An evaluation of shot peening, residual stress and stress relaxation on the fatigue life of AISI 4340 steel, Int.
J. Fatigue. 24 (2002) 877-886.
[24] A.M. Eleiche, M.M. Megahed, N.M. Abd- Allah, The shot-peening effect on the HCF behavior of high-strength martensitic steels, J. Mater.
Process. Technol. 113 (2001) 502- 508.
[25] B. Bhuvaraghana, S.M. Srinivasanb, B.
Maffeoc, Optimization of the fatigue strength of materials due to shot peening: A Survey,
INTERNATIONAL JOURNAL OF
STRUCTURAL CHANGES IN SOLIDS. 2 (2010) 33-63.
[26] PARIENTE, I. F. and GUAGLIANO, M.
(2009). Infuence of shot peening process on contact fatigue behavior of gears. Mater. Manuf. Process., 24, 1436-1441.
[27] TURSKI, M., CLITHEROE, S., EVANS, A.
D., RODOPOULOS, C., HUGHES, D. J. and WITHERS, P. J. (2010). Engineering the residual stress state and microstructure of stainless steel with mechanical surface treatments. Appl. Phys. A, 99, 549-556.
[28] MYLONAS, G. I. and LABEAS, G. (2011).
Numerical modelling of shot peening process and corresponding products: Residual stress, surface roughness and cold work prediction. Surf. Coat.
Technol., 205, 4480-4494.
[29] VÖHRINGER, O. (1987). Changes in the state of the material by shot peening. Proc. 3rd conf. shot peening (ICSP3). Garmisch-Partenkirchen, Germany, 185-204.
[30] CAO, W., FATHALLAH, R. and CASTEX, L.
(1995). Correlation of Almen arc height with residual stresses in shot peening process. Mater. Sci.
Technol., 11, 967-973.
[30] K. Dai et al, Comparison between shot peening and surface nanocrystallization and hardening processes, Materials Science and Engineering A 463 (2007) 46–53
[31] Almen JO, Black PH. Residual stresses and fatigue in metals. McGraw-Hill Publ.; 1963.
[32] Bagherifard S, Ghelichi R, Guagliano M. On the shot peening surface coverage and its assessment by means of finite element simulation: a critical review and some original developments.
Appl Surf Sci 2012;259:186–94.
[33] Prevey. P.S. (1977).Adv, X-Ray Anal. 20,345- 354.[34] Noyan IC, Cohen JB. Residual stress measurement by diffraction and interpretation. New York: Springer; 1987.
[35] Moore MG, Evans WP. Corrections for stress layers in X-ray diffraction residual stress analysis.
SAE Trans 1958;66:340–5.
[36] A. DIAMENT, R. EL HAIK, R. LAFONT, R.
WYSS, "Tenue en fatigue superficielle des couches carbonitrurées et cémentées en liaison avec la répartition des contraintes résiduelles et les modifications du réseau cristallin apparaissant en cours de fatigue". - 1974.
[37] Darling KA, Tschopp MA, Roberts AJ, Ligda JP, Kecskes LJ. Enhancing grain refinement in polycrystalline materials using surface mechanical attrition treatment at cryogenic temperatures.
Scripta Mater 2013;69:461–4.
[38] Aymen A. Ahmed et al The effect of shot peening parameters and hydroxyapatite coating on surface properties and corrosion behavior of medical grade AISI 316L stainless steel Surface &
Coatings Technology 280 (2015) 347–358.
[39] G. Fargas et al. "Effect of shot peening on metastable austenitic stainless steels", Materials Science & Engineering A 641(2015)290–296.
[40] Farrahi GH, Lebrun JL. Surface hardness measurement and microstructural characterisation of steel by X-ray diffraction profile analysis. J Eng 1995;8(159):67.
[41] S. Kumar, G.S. Rao, K. Chattopadhyay, G.S.
Mahobia, N.C. Santhi Srinivas, V. Singh, Effect of surface nanostructure on tensile behavior of superalloy IN718, Mater. Des. 62 (2014) 76–82.
[42] yong et al "Enhancing surface layer properties of an aircraft aluminum alloy by shot peening using response surface methodology", Materials & Design 83 (2015) 566–576.
[43] K. Anselme, P. Davidson, A.M. Popa, M.
Giazzon, M. Liley, L. Ploux, Review: the interaction of cells and bacteria with surfaces structured at the nanometer scale, Acta Biomater. 6 (2010) 3824–3846.
[44] ISO 4278, Geometrical product specifications (GPS)–surface texture: profile method–terms, definitions and surface texture parameters, 1st ed., 1997.
[45] R.CLAUSEN et al. Roughness of shot-peened surfaces - definition and measurement. Proc. 7th conf. shot peening (ICSP7). Warsaw, Poland, 69- 77.[46] Katarina et al, Fatigue behavior of X70 microalloyed steel after severe shot peening, International Journal of Fatigue 55 (2013) 33–42.
[47] BN.Mordyuk et al. Ultrasonic impact peening for the surface properties’ management. J Sound Vib 2007;308:855–66.
[48] M. Mhaede, Influence of surface treatments on surface layer properties, fatigue and corrosion fatigue performance of AA7075 T73, Materials and Design 41 (2012) 61–66.
