Value Of Compressive Residual Stress Research Articles

Surface modification of fully austenitic stainless steel SMO 254 by laser shock peening to induce compressive residual stress

ABSTRACT The laser shock peening process was conducted with varying pulse densities on the SMO 254 material. The formation of an α martensitic layer from the austenitic structure was witnessed after conducting the laser shock peening process, with the migration of elements across the grains. The increase in the surface roughness value, measured by the Atomic force microscope and Mahr surface profilometer, is directly proportional to the rise in pulse density. An elevated value of compressive residual stress of −786 MPa and a higher Vickers micro hardness value of 365 HV were obtained in the specimen where a pulse density of 6000 pulse/cm2 was applied.

Development of Maximum Residual Stress Prediction Technique for Shot-Peened Specimen Using Rayleigh Wave Dispersion Data Based on Convolutional Neural Network

Shot peening is a surface treatment process that improves the fatigue life of a material and suppresses cracks by generating residual stress on the surface. The injected small shots create a compressive residual stress layer on the material’s surface. Maximum compressive residual stress occurs at a certain depth, and tensile residual stress gradually occurs as the depth increases. This process is primarily used for nickel-based superalloy steel materials in certain environments, such as the aerospace industry and nuclear power fields. To prevent such a severe accident due to the high-temperature and high-pressure environment, evaluating the residual stress of shot-peened materials is essential in evaluating the soundness of the material. Representative methods for evaluating residual stress include perforation strain gauge analysis, X-ray diffraction (XRD), and ultrasonic testing. Among them, ultrasonic testing is a representative, non-destructive evaluation method, and residual stress can be estimated using a Rayleigh wave. Therefore, in this study, the maximum compressive residual stress value of the peened Inconel 718 specimen was predicted using a prediction convolutional neural network (CNN) based on the relationship between Rayleigh wave dispersion and stress distribution on the specimen. By analyzing the residual stress distribution in the depth direction generated in the model from various studies in the literature, 173 residual stress distributions were generated using the Gaussian function and factorial design approach. The distribution generated using the relationship was converted into 173 Rayleigh wave dispersion data to be used as a database for the CNN model. The CNN model was learned through this database, and performance was verified using validation data. The adopted Rayleigh wave dispersion and convolutional neural network procedures demonstrate the ability to predict the maximum compressive residual stress in the peened specimen.

Enhancement of surface characteristics of additively manufactured γ-TiAl and IN939 alloys after laser shock processing

The enhancement in laser technology opened up new methods such as additive manufacturing (AM) of metals. While AM offers high design flexibility and reduced material usage, it can also produce problematic parts due to poor surface quality. A variety of post-processing techniques are available to address the drawbacks associated with the surface properties of AM. Laser Shock Processing (LSP) is one of the unique methods that induces compressive residual stress (CRS) on the surface and subsurface by creating severe plastic deformation. In this study, two critical aerospace alloys (γ-TiAl and IN939) were manufactured through two different methods called Powder Bed Fusion with Electron Beam (PBF-EB) and Powder Bed Fusion with Laser Beam (PBF-LB). Subsequently, AM samples were investigated to observe single layer LSP effects on the surface. The results of the laser peening process were determined by residual stress, microhardness and surface roughness measurements. The residual stress profiles showed that LSP significantly induces CRS on the surfaces of AM alloys. For the γ-TiAl and IN939 samples, the maximum values of CRS and depth of CRS were −460 MPa/1000 µm and −516 MPa/700 µm, respectively. Similarly, the microhardness of the materials was increased by 44.4 % for γ-TiAl and 18.2 % for IN939 by laser post-processing. In addition, a comparison of the roughness of the unground and ground AM samples was carried out. Depending on the surface condition of the AM samples, LSP had different outcomes. For example, the extreme roughness of the AM samples was partially reduced by the thermal effects of the high-energy laser shots. When comparing the roughness values in terms of Ra and Rz, there were decreases in the range of 14.7–21.3 % and 3.34–39.3 % for unground IN939 samples. However, for unground γ-TiAl samples, depending on the direction of measurement, roughness variations were observed as a 0.99 % decrease − 5.3 % increase for Ra and a 2.2 % decrease − 14.2 % increase for Rz. The roughness values for ground samples of both alloys were drastically increased, varying between 42.1 % and 7x increase. Sa values were recorded on unground AM samples. For IN939 and γ-TiAl samples these values decreased by 8.41 % and 15.8 % respectively.

Cavitation Erosion Prevention Using Laser Shock Peening: Development of a Predictive Evaluation System.

Marine flow-passing components are susceptible to cavitation erosion (CE), and researchers have worked to find ways to reduce its effects. Laser Shock Peening (LSP), a material strengthening method, has been widely used in aerospace and other cutting-edge fields. In recent years, LSP has been used in cavitation resistance research. However, the current LSP research does not realize a comprehensive predictive assessment of the material's CE resistance. This paper uses m stresses to develop a comprehensive set of strengthening effect prediction models from LSP to CE using finite element analysis (FEA). Results show that the LSP-1 sample (4 mm spot, 10 J energy) introduced a compressive residual stress value of 37.4 MPa, better than that of 16.6 MPa with the LSP-2 sample (6 mm spot, 10 J energy), which is generally consistent with the experimental findings; the model predicts a 16.35% improvement in the resistance of LSP-1 sample to water jet damage, which is comparable to the experimental result of 14.02%; additionally, interactions between micro-jets do not predominate the cavitation erosion process and the final CE effect of the material is mainly due to the accumulation of jet-material interaction.

Enhanced high-temperature wear resistance of GCr15 steel balls by generating a Ti + Nb diffusion layer via mechanical alloying and NH3·H2O treatment

In this study, mechanical alloying and NH3·H2O treatmentGCr15 steel balls were used to strengthen GCr15 steel balls. The steel balls were first coated with a Ti + Nb coating using a ball mill equipped with a homemade grind jar, followed by a NH3·H2O treatment in a common jar to remove the Ti + Nb coating. Surprisingly, a Ti + Nb diffusion layer with a thickness of 5.1 μm was generated. The mechanical properties of both processed samples and unprocessed samples were investigated, including grains, dislocations, microhardness, residual stress, and friction properties at different temperatures. The results showed that the processed sample had obvious grain refinement and large dislocation density, with maximum microhardness and compressive residual stress values of 934 HV and − 490 MPa, respectively. Additionally, the processed samples exhibited exceptional high-temperature wear resistance, with a remarkable decrease in friction coefficient to 0.26 at 400 °C, which was 52.73 % less than that of unprocessed samples. These results highlight the potential of this method for improving the high-temperature resistance of various mechanical components, particularly steel balls.

Experimental investigation and estimation of compressive residual stress of ball burnished rare earth based magnesium alloy

The present study focuses on the experimental investigation and optimization of compressive residual stress on ball burnished Mg Ze41A alloy. The optimum compressive residual stress value of −182 MPa is obtained at burnishing force of 50 N, speed of 1200 r/min, feed of 150 mm/min and 4 number of passes. Burnishing force and speed are found to be the most sensitive parameters in affecting the compressive residual stress, followed by number of passes and burnishing feed. The demarcation lines in residual stress-burnishing maps of Mg Ze41A alloy are non-parallel and non-uniform, indicating significant interactions among burnishing parameters. Ball burnishing process imparted desired amount of work hardening, which resulted in homogenized ( σx1 = σx2) and isotropic stress ( σ1 = σ2) state. Additionally, the fuzzy logic model has been deployed to estimate the compressive residual stress values at different burnishing conditions. Fuzzy logic model estimated the results with an error of 6.11%. The results demonstrate that ball burnishing process is an effective method in inducing compressive residual stresses on Mg alloy. The outcome of this study can be of great help in enhancing the fatigue performance of small size products.

The Effect of Shot Peening on Residual Stress and Surface Roughness of AMS 5504 Stainless Steel Joints Welded Using the TIG Method.

This article presents the influence of the Shot Peening (SP) process on residual stress and surface roughness of AMS 5504 joints welded using the Tungsten Inert Gas (TIG) method. Thin-walled steel structures are widely used in the aviation and automotive industries, among others. Unfortunately, the fatigue properties become worse during the welding process. Samples of 1 mm-thick AMS 5504 steel plates were first prepared using TIG welding and then strengthened by the Shot Peening (SP) process. The technological parameters of the SP process were changed in the range of time t from 2 min to 4 min and of pressure p from 0.4 MPa to 0.6 Mpa. The residual stresses were measured by X-ray diffraction in three zones: fusion zone (FZ), heat-affected zone (HAZ) and base metal (BM). The results showed that SP introduced compressive residual stresses in all of the zones measured, especially in the FZ. The greatest value of compressive residual stresses σ = -609 MPa in the FZ was observed for the maximum parameters of SP (p = 0.6 MPa, t = 4 min). The increase in value of residual stress is about 580% when compared to welding specimens without treatment. As a result of shot peening in the FZ, the mean roughness value Ra decreased in range 63.07% to 77.67% in the FZ, while in the BM increased in range 236.87% to 352.78% in comparison to specimen without treatment. Selected surface roughness parameters in FZ and BM were analyzed using neural networks. In FZ, it was demonstrated that the most correlated parameters with residual stresses are Rt and Rsk. On the other hand, in the BM zone, the most correlated parameters were Rv, Rt and Rq. This enables the estimation of stresses in the welded joint after SP on the basis of selected roughness parameters.

Effect of Residual Stress in Surface Layer on Plastic Yield Inception

This study aimed to acquire a comprehensive explanation on how the residual stress in the surface layer affects the contact behavior of solids. Plastic yield inception of residual stressed surface layer/substrate system during contact is simulated using the finite element method with the software ANSYS Workbench. The critical loads and locations for yield inception were acquired for contact systems with different residual stress levels and different surface layer thicknesses. Results show that the residual stress in the surface layer has little influence on the stress field in the substrate during contact. The influence of the residual stress on the critical yield load is mainly due to variations in the stress field in surface layer. A moderate compressive residual stress is preferable for increasing the critical yield load. An optimal value of compressive residual stress of 60% of the yield strength of surface layer was found to increase the critical yield load. The surface layer thickness and residual stress determine the yield inception location and the critical load of the contact system jointly.

Finite element analysis of stress-strain state of the deformation zone of a UFG TI Grade 4 workpiece subjected to abrasive-free ultrasonic finishing

An effective approach to increasing the fatigue resistance of metal products is to create compressive residual stresses on the surface of the product using surface plastic deformation (SPD) processing. One of the effective SPD methods is the process of abrasive-free ultrasonic finishing (AFUF). Another well-known approach to improving mechanical properties including fatigue resistance is to create an ultrafinegrained (UFG) structural state in the product. This research focuses on the finite-element study of the stress-strain state of a UFG workpiece subjected to SPD by the AFUF method. Commercially pure Grade 4 titanium in the UFG state obtained by the ECAP-Conform method was chosen as a workpiece material. In the course of the study, the stress-strain state of the deformation zone was analyzed after a single indentation with subsequent unloading under the elastic-plastic scenario. The effect of the indenter oscillation amplitude and its geometry on radial residual stresses including their depth of occurrence, average normal stress and strain intensity was analyzed. It was found that as the indenter radius increases, the strain intensity (e) value decreases. The e parameter distribution has a gradient nature with a decrease in values from the surface to the center of the workpiece. An analysis of simulation results shows that radial residual stresses in the deformation zone are predominantly compressive, and, accordingly, they will increase the fatigue resistance of the finished product. It was established that as the indenter oscillation amplitude increases, the values of compressive radial residual stresses also increase. Their maximum values reach 540 MPa at an amplitude of 75 μm with the depth of these stresses up to 0.3 mm. An increase in the indenter radius, i.e. in fact the contact area, leads to an increase in the magnitude of compressive radial residual stresses with an almost linear behavior.

Comparative study of additively manufactured and reference 316 L stainless steel samples – Effect of severe shot peening on microstructure and residual stresses

The as-built selective laser melted (SLM) austenitic stainless steel 316 L components are characterized by presence of quality related concerns such as tensile residual stresses, poor surface finish, etc. These issues may prove to be detrimental during the actual usage of components and could result in poor mechanical performance. Therefore, it is important to perform the apt post processing such as heat treatment and shot peening to tailor such problems and facilitate improved mechanical performance. In the present work, additively manufactured (AM) 316 L samples were subjected to shot peening with different parameters including the severe shot peening (SSP) procedure. The identical shot peening protocol was also applied to reference samples to evaluate the comparable response. Both the shot peened reference and AM samples were studied for residual stresses, surface topography, microhardness, and the corresponding microstructure. The results indicated, that SSP induced higher values of compressive residual stresses deeper into the samples. This was accompanied by reduced surface roughness, increased grain refinement depth, and higher microhardness near the surface. The SSP resulted in transformation of original austenite to martensite near the surface in the reference samples.

Effect of laser peening without coating on mechanical and microstructural behaviour of SS 304 stainless steel

This present work investigates the influence of laser shock peening without coating (LPwC) of SS 304 stainless steel. To understand the effect of deformation behaviour, laser power densities of 3, 6 and 9 GW cm−2 were employed. The Residual stress and microhardness (HV) were investigated at surface and depth direction. The maximal value of compressive residual stress (−340 MPa) reached a depth of 50 µm for the laser intensity of 9 GW cm−2. Micro hardness significantly increased to 71.11% for 9 GW.cm−2 compared to the unpeened sample. To observe the mechanical twinning and grain refinement the Electron backscattered diffraction (EBSD) was carried out. A Transmission electron microscope (TEM) was also performed to know the nano twins and dislocation movement in the laser peened samples. Results showed that laser peening without coating process would cause a significant improvement on surface properties such as compressive residual stress, surface roughness, microhardness, and microstructure and grain refinement.

Investigation of wet shot peening on microstructural evolution and tensile-tensile fatigue properties of Ti-6Al-4V alloy

Ti–6Al–4V (TC4) alloy was treated by wet shot peening (WP) using ceramic beads compared with dry shot peening (SP). The effects of shot peening on surface integrity, microstructural evolution, fatigue crack initiation behavior and tensile-tensile fatigue performance were investigated applying multiple characterization techniques. The result exhibited that the surface plastic deformation caused by WP and SP treatment resulted in microstructure changes near the surface. Surface morphology was distinctly changed by shot peening treatment. The roughness value increased from 0.596 μm (Ra) to 1.594 μm (Ra). Microhardness gradients and compressive residual stress (CRS) distributions along the depth were induced by shot peening. The maximum hardness reached 373.5 HV, 407.8 HV and 445.3 HV. The maximum value of CRS reached 884 MPa, 1038 MPa and 1207 MPa with the corresponding depth at 21 μm, 25 μm and 40 μm. The fatigue life was significantly improved by shot peening treatment. Cracks tended to initiate at the subsurface layer instead of the treated surface after shot peening. The reason for crack initiation position altering was tentatively explained by the CRS stable zone. The competition mechanism between the surface stress concentration and local strengthening factors were discussed based on the analysis of stress concentration factor, Kt.

Tailoring the scratch adhesion strength and wear performance of TiNiN nanocomposite coatings by optimising substrate bias voltage during cathodic arc evaporation

The tribological properties of TiN-based coatings can be substantially influenced by the choice of substrate bias employed during physical vapor deposition. However, the effects of applied substrate bias voltages during cathodic arc evaporation on to the scratch adhesion strength and wear resistance of TiNiN coatings have not been previously studied. In this present work, a series of TiNiN coatings were fabricated onto tool steel (M2) substrates using the cathodic arc evaporation method by applying a range of bias voltages to the substrate. The aim of this study is to investigate the scratch response and wear performance of these coatings along with an investigation of the deformation mechanisms in operation during scratch and wear tests. The best scratch adhesion strength (i.e., greater LC1, LC2 and CPRs values) was noted for the coating prepared at a bias voltage of −100 V, which was ascribed to the synergistic responses arising from superior mechanical properties, the influence of a high compressive residual stress and a fine, equiaxed nanocomposite structure, that acted to promote effective resistance against cohesive and adhesive failure. Further, the failure mechanisms under progressive loading conditions were also investigated through observation of the complex crack patterns generated, compressive residual stress values and the coatings' hierarchical design. An approximately 85 % enhancement in wear resistance for these TiNiN coatings was achieved as the bias voltage was increased from 0 V to −100 V. This −100 V coating exhibited the highest values of H/Er (>0.1) and We (>60 %), as well as the highest Ni concentration (~ 4 at.%).

Gradient microstructure and foreign-object-damaged fatigue properties of Ti6Al4V titanium alloy processed by the laser shock peening and subsequent shot peening

A dislocation-gradient microstructure layer with large depth and high compressive residual stress (CRS) value on the surface of Ti6Al4V titanium alloy is processed by laser shock peening and subsequent shot peening (LSP + SP). The microstructure evolution and its foreign-object-damaged fatigue properties were investigated by scanning electron microscope, transmission electron microscope, X-ray diffraction, microhardness tests, finite element numerical simulation and vibration fatigue tests. Foreign object damage (FOD) was introduced through the indentations of hardness testers, which can lead to the increase of stress concentration and redistribution of surface residual stress around craters. However, the dislocation-gradient microstructure layer can prolong crack initiation and propagation lives by 184% and 45% for specimens with FOD, respectively. The median fatigue life of (LSP + SP) specimens with FOD even shows longer than that of untreated specimens without FOD. Furthermore, a synergistic strengthening mechanism, involving dislocation strengthening, grain refinement and CRS, was clearly revealed.

Revealing the deformation mechanisms of the heterogeneous structured CrMnFeCoNi high entropy alloy with ameliorated mechanical and corrosion resistance properties

Developing high entropy alloy (HEA) with both high strength and ductility is a longstanding challenge as potential structural materials. The strength and ductility trade-off can achieve via tailoring heterogeneous structures. Herein, a gradient structure with grain size variation from surface to center was successfully introduced into the CrMnFeCoNi HEA by ultrasonic nanocrystal surface modification (UNSM) process. More importantly, the deformation mechanisms and strengthening mechanisms of the heterogeneous structured CrMnFeCoNi HEA during tension were also investigated. Experimental results demonstrated that the heterogeneous structured CrMnFeCoNi HEA shows excellent strength and ductility combination properties ascribed to the grain refinement strengthening, dislocation density strengthening, and twinning strengthening. Besides, the corrosion resistance properties are also simultaneously improved, resulting from the low surface roughness, small grain size, and large compressive residual stress value. During tensile deformation process, the deformation mode is the dislocation slip at low strain and the slip system of the alloy is mainly {111}〈110〉. With the increase of deformation amount, twin crossing occurs, and grain size gradually decreases. The deformation mode changes from dislocation slip to twinning at high strain. In conclusion, the UNSM process ameliorates the comprehensive mechanical and corrosion resistance properties of CrMnFeCoNi HEA.

Assessment of the surface integrity of ground cemented tungsten carbide cutting inserts and its influence on tool wear in turning of ferritic nodular cast iron

In order to improve surface finish, geometric and dimensional tolerances of cemented tungsten carbide cutting tools produced by powder metallurgy, grinding is commonly applied. Due to the high thermal and mechanical loads generated during this process, surface and metallurgical characteristics are directly affected and, as a result, tool performance. Within this context, the influence of grinding wheel characteristics on surface integrity parameters, like surface and edge roughness, hardness and residual stress, was investigated and cutting inserts ground under extreme conditions were applied in rough orthogonal turning of a ferritic nodular cast iron to evaluate their performance regarding tool life. The obtained results showed that higher compressive residual stress values, induced by a vitrified bonded diamond grinding wheel with grain size of 46 µm, contributed to increase tool life, as a protective layer of adhered material was formed on the cutting edge. Flank wear by abrasion was thus avoided and crack formation was the determining factor for the end of the tests. • Finishing process of cutting inserts significantly affects their performance. • Compressive residual stress contributes to increase tool life in rough turning. • Insert surface and edge roughness do not influence tool life in turning cast iron.

Evaluation of laser shock peening process parameters incorporating Almen strip deflections

Engineering of component surfaces using Laser Shock Peening (LSP) requires optimisation of key process parameters to enhance performance through the generation of beneficial compressive residual stresses. Quantification of residual stress fields typically requires considerable experimental resources involving multiple complementary techniques to obtain reliable measurements through the depth of the target material. LSP induced plastic strains lead to the formation of residual stresses and cause deformation of thin components. This effect is routinely used in the assessment of mechanical Shot Peening (SP) where distortion coupons, called Almen strips, correlate the peening intensity to process parameters. This study explores the extension of this Almen strip concept to facilitate the quick assessment of LSP parameters for aluminium alloy 6056-T4 aeronautical structural applications. Direct measurements of the resulting LSP residual stresses have been performed using Synchrotron X-Ray Diffraction, Neutron Diffraction, and Incremental Hole Drilling, complemented by analyses of surface integrity and sub-surface modifications. It has been found that the attained near-surface compressive residual stress values and depths are strongly dependent on laser power intensity and spot coverage, whilst surface roughness and microhardness are mostly independent of the LSP parameters. Optimal parameter selection should therefore be primarily focused on the required residual stress field. A direct correlation has been observed between the magnitudes of LSP Almen distortions and the residual stresses. This qualifies extending the deflection based approach to be used as a quick, simple and effective qualitative screening technique of LSP process parameters, such as the laser power intensity saturation.

Technology development for in-situ measurement of residual stress in arc welded joints of MDN 250 by portable Cosα X-ray diffraction method

Residual stresses are inherent stresses that exist in engineering components even though no external load is applied. They are caused by the non-uniform volumetric shift of the metallic component during manufacturing processes. Welding is a key manufacturing technique that has a substantial impact on the economy since it is required for the production of a diverse variety of products used in the engineering sector. The residual stress primarily affects the stability, durability and performance of the welded joints. Hence its determination is of utmost importance. X-ray diffraction (XRD) is the most commonly used method for residual stress analysis. There are mainly two approaches for measuring residual stress using XRD; one is the sin2ψ method and the other is the cosα method. The residual stress measurements using the cosα method are handy, quick and convenient compared to the sin2ψ method. This method is well suited for welded joints, as it provides flexibility for testing immediately after the welding operation. Apart from residual stress measurements, the cosα method also gives valuable insights in the form of Debye-Scherrer (DS) rings and full width at half maximum. The present study focuses on the development of a novel technique that not only enables residual stress measurement but also provides a quantitative estimation of hardness and qualitative estimation of grain size without performing metallurgical or mechanical characterization. The material used for the present study is an arc-welded joint of MDN 250 grade maraging steel. The residual stress results show a compressive profile throughout the weldment, with a maximum value of compressive residual stress of 428 MPa at the fusion zone.

THE INFLUENCE OF CUT’S DEPTH ON RESIDUAL STRESSES DISTRIBUTION AND AN ENDURANCE LIMIT OF SPECIMENS UNDER SURFACE HARDENING

The influence of cuts depth on residual stresses distribution and an endurance limit under bending of hollow cylindrical specimens made of steel 20 with external diameter 50 mm and interior diameter 40 mm after outstripping superficial plastic deforming by roller strengthening of two regimes has been examined. Its been stated that the value of compressive residual stresses in a dangerous section of specimens decreases on cuts depth increase. As a result, an endurance limit increment of hardened specimens with cuts diminishes. In order to preserve the effect of hardening by increasing the endurance limit under outstripping superficial plastic deforming with an increase in a cuts depth, it is necessary to increase the thickness of a smooth part with compressive residual stresses layer. Its been shown that in order to estimate the increase in the endurance limit of hardened specimens, one should use not residual stresses at the bottom of a cut, but average integral residual stresses through the parts dangerous section surface layer thickness that equal a critical depth of a non-propagating fatigue crack.

The effect of laser shock peening, shot peening and their combination on the microstructure and fatigue properties of Ti-6Al-4V titanium alloy

In this work, the effect of a novel post process integrating laser shock peening (LSP) with shot peening (SP) on the fatigue property of Ti-6Al-4V titanium alloy is investigated. The fatigue life can be improved (up to 9.3 times) by this post-process. The compressive residual stress (CRS) distribution and dislocation-gradient microstructure obtained were found to be responsible for the improvement. The fatigue crack initiation was hindered by the high-density dislocation layer with high CRS value on the surface and maximum CRS in the sub-surface, while the crack propagation was retarded by the dislocation proliferation layer with large CRS gradient.