Value Of Compressive Residual Stress Research Articles

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.

Growth temperature effect on physical and mechanical properties of nitrogen rich InN epilayers

A set of N-polar InN epilayers has been grown at different temperatures by plasma–assisted molecular beam epitaxy (PA-MBE) on GaN/AlN/Al2O3(0001) templates. The purpose is to understand how the variation of crucial factor, such as the temperature, impacts the growth process and the resulting samples’ properties. The characterization of these InN samples using atomic force microscopy and scanning electron microscopy showed different island distributions and shapes by varying the growth temperature. High resolution-X-ray diffraction (HRXRD) enabled to identify a single crystalline phase (hexagonal wurtzite), whatever the growth temperature. Actually, the increase of growth temperature up to 560 °C has improved the crystalline quality; whereas for high temperature, the crystalline quality degrades. The dislocation density of the epilayer grown at this optimum temperature (around 560 °C) is about 1.9 × 1010 cm−2, which is determined using HRXRD spectra analysis. High compressive residual stress value of 0.54 GPa was derived using Raman spectroscopy. Room temperature photoluminescence (PL) displays a band gap energy around 0.69 eV. Besides, Burstein-Moss effect, the PL band gap energy measured at 10 K is dictated by the biaxial compressive residual stresses. Nanoindentation tests were carried out on InN epilayers. Only, the sample grown at 560 °C exhibited a pop-in event, for which the measured hardness and Young’s modulus are of 4.5 ± 0.5 GPa and of 171 ± 8 GPa, respectively. Accordingly, the growth temperature of InN epilayers influences the resulting physical and mechanical performances, thus a good compromise between physical and mechanical features permits to manufacture efficient devices.

Molecular modeling of Ti-6Al-4V alloy shot peening: the effects of diameter and velocity of shot particles and force field on mechanical properties and residual stress

Shot peening is a surface treatment process that is used for the improvement of the mechanical properties of metallic alloys. The effects of sphere particle diameter and impact velocity on residual stress and mechanical properties of Ti-6Al-4V as titanium alloy are investigated in this study using molecular dynamics simulation. In this research, titanium atoms are simulated as a surface layer and the carbon steel atomic structure is modeled as the impacting particle in the shot peening process. Two types of molecular potential functions including embedded atom method (EAM) and Lennard-Jones (LJ) are used for molecular modeling of colliding atoms and the effect of these force fields on residual stress, hardness, surface roughness is investigated. Moreover, the effects of impacting particle velocity and diameter on these parameters are studied. The results show the amount of residual stress in the titanium surface layer increased by increasing the particle diameter and velocity of particles. The diameter and velocity of particles in the shot peening process has a significant effect on the mechanical behavior of the simulated titanium surface layer. The value of maximum compressive residual stress is −413 MPa which occurs in depth of 10 Å from the surface layer for 1 Å fs−1 velocity and 10 Å diameter of shot particle. Furthermore, the results show that the Vickers hardness of the titanium is increased by increasing the size and velocity of the carbon steel particle in both EAM and LJ potential functions.

Influence of post-processing techniques on residual stresses of SLM processed HPNGV

Abstract In the present study, selective laser melting (SLM) technique employed to manufacture Inconel 718 high-pressure nozzle guide vane (HPNGV), an aero-engine component. The present work's focus is to investigate the influence of post-processing techniques on the residual stress of SLM fabricated HPNGV component. Two approaches for post-processing techniques such as standard post-processing (SPP) flow was compared with the customized post-processing (CPP) flow was investigated. Further, an attempt was also made to study the influence of component location on the baseplate and its effect on the magnitude of residual stress values in HPNGV components. The extensive residual stress measurements was carried out using X-ray diffraction technique. The results showed that the magnitude of compressive residual stress values obtained in the CPP technique was comparable with SPP technique. Further, HPNGV components fabricated on the build plate at different locations significantly affected the magnitude of residual stress values, which may be attributed to SLM processing and associated effects. The support structure removal sequence had a substantial contribution in controlling the distortion of the HPNGV component. The d-spacing value changes at different locations on the SLM processed samples due to changes in the chemical compositions due to inherent SLM processing characteristics.

Effect of plasma interface treatment on the microstructure, residual stress profile, and mechanical properties of PVD TiN coatings on Ti-6Al-4V substrates

Interface engineering is essential to enhance and to maintain the performance of protective coatings on metallic substrates. Plasma pre-treatments and coating deposition processes have shown to be an ideal solution to improve Ti-6Al-4V alloy mechanical and tribological properties, while enhancing components' durability. In the present work, we study model Titanium Nitride (TiN) coatings with three interface engineering surface treatment approaches using: a) Argon plasma, b) Titanium implantation, and c) plasma surface nitriding. In particular, we investigate the influence of the plasma pre-treatments on the microstructure, mechanical properties, especially residual stress (RS) and adhesion, of TiN coatings on Ti-6Al-4V substrates. X-Ray Diffraction, Transmission Electron Microscopy, and Transmission Kikuchi Diffraction were used as complementary techniques to evaluate the crystallographic and microstructural properties of the interfaces created by the three pre-treatment methods in order to elucidate their effect on the evolution of microstructure, hardness, RS and adhesion. The RS study involved surface and depth profiles through the coating-substrate system. Compressive RS values were found to vary between −1 GPa and −4 GPa throughout the TiN coatings, and from −0.2 to −0.8 GPa across the different interfaces. In addition, a strong RS anisotropy in dependence on the way how the substrate has been fixed to the holder (rigidly clamped or freely attached) shows a significant difference in the RS with a deviation of >100% in dependence on the orientation of coated samples during the XRD measurements. Experimental results show that Ar plasma and Ti implantation form interfaces with (200) and (111) preferential orientations within the TiN layers that exhibited a hardness of up to ~29 GPa and a Young's modulus of ~350 GPa.

Effect of Grit Blasting Parameters on Surface and Near-Surface Properties of Different Metal Alloys

In thermal spray, grit blasting is the standard method used to prepare the substrate surface before coating deposition. This study examines the effect of the grit blasting parameters on the residual stresses, roughness and hardness of three metal alloys with widely different mechanical properties: low-carbon steel, Ti-6Al-4V and Inconel 718. It also estimates the density of dislocations using the Williamson–Hall method. The dislocation structures of low-carbon steel grit blasted at different grit impingement angles were observed under a transmission electron microscope. The surface dislocation density was found to increase with the blasting time and angle of impact. Moreover, the depth profile of the dislocation density was in good agreement with that of the hardness profile of the blasted specimen. The residual stress depth profiles of each material at different blasting pressure showed an increase in the value and depth of maximum compressive residual stresses. Both surface residual stresses and roughness were found to increase with the grit blasting pressure, angle and, to some extent, with time and stand-off distance. The mechanisms of material erosion were found to be microcutting and indentation at lower and higher angles of abrasive impingement, respectively. The extent of damage of the materials was explained on the basis of the Johnson–Cook flow strength model.

Residual Stresses on Various PVD Hard Coatings on Tube and Plate Substrates

In this study, the average residual stresses were determined in hard PVD nACRo (nc-AlCrN/a-Si3N4), nACo (nc-AlTiN/a-Si3N4), AlCrN, TiAlN, and TiCN commercial coatings through the deflection of the plate substrates and the simultaneous measurement of length variation in thin-walled tubular substrates. The length measuring unit was used for the measurement of any length change in the tubular substrate. A change in tube length was reduced to the deflection of the middle cross-section of the elastic element for which deformation was measured using four strain gauges. The cross-sectional microstructure and thickness of the coatings were investigated by means of scanning electron microscopy (SEM), and a determination was made of the chemical composition of the coatings and substrate by means of energy dispersive X-ray spectroscopy (EDS). The values of average compressive residual stresses, as determined by both methods, were very high (with a variation of between 2.05 and 6.63 GPa), irrespective of coating thickness, but were dependent upon the shape of the substrate and on its position in relation to the axis of the rotating cathode. The thicknesses of the coatings that were deposited on the plates with two parallel fixings (such as the nACRo coatings on the front surface at 6.8 μm and on the rear surface at 2.9 μm) and on the tubular substrates (10.0 μm) were significantly different. The higher average compressive residual stresses in the coating correlate to the higher average relative wear resistance that was obtained during field wear testing.

Research on microstructure and mechanical properties of HIP Ti-6Al-4V treated by surface rolling at low-heating temperatures

This paper was to research the effects of surface rolling at low-heating temperatures (SRLT) on microstructure and mechanical properties of HIP Ti–6Al–4V alloy. An obviously plastic deformation emerged in surface modification layer and accompanied with the grain refinement and dense dislocations. The values of compressive residual stress and surface microhardness were also increased. The fretting friction tests were further compared without lubrication. The sample treated by surface rolling (SR) at 160 °C had the smaller steady-state CoF and less material loss relative to the untreated sample. But it still had the higher steady-state Coefficient of friction (CoF) and more material loss than surface-rolled sample at room temperature. On the one hand, the comparatively low microhardness and residual stress would damage the mechanical properties. On the other hand, the material’s friction would be increased by the high surface roughness and the absence of cold work strengthening would decrease the wear resistance. In addition, the low-heating temperature would also increase material deformation mechanism and decline the friction properties.

Laser shock peening-induced surface gradient stress distribution and extension mechanism in corrosion fatigue life of AISI 420 stainless steel

Surface gradient stress distribution was prepared on AISI 420 martensitic stainless steel (MSS) by massive laser shock peening treatment (MLSPT) with different pulse energies, and effects of MLSPT on residual stress and corrosion fatigue properties in NaCl solutions with different pH values were investigated by microstructural observation, residual stress measurement, corrosion fatigue test, and fractural morphology. Results showed that the coupling effect of MLSPT-induced surface microstructural evolution and gradient stress distribution effectively contributed to an extension in corrosion fatigue properties. Furthermore, the corrosion fatigue crack growth rate equation considering both gradient compressive residual stress and pH value was developed.

Influences of particle collision treatments on surface characteristics and fatigue strength of Ti-6Al-4V alloy

In this study, the particle collision treatments (fine particle bombarding (FPB) and conventional shot peening (SP)) were performed for Ti–6Al–4V alloy in order to comprehensively investigate the influences of their treatment conditions on the surface conditions, microstructures, hardness distributions and residual stress. Moreover, we examined the relationship between the surface characteristics of the treated materials and their mechanical properties including fatigue strength in detail. According to the obtained experimental results, the values of the maximum height waviness increased with increasing in the size of collision particles and injection pressure. Among all the treated materials, the differences in hardness distribution were relatively small because the work hardening exponent of Ti–6Al–4V alloy is low and the degree of work hardening is insensitive to the amount of plastic deformation. The absolute values of compressive residual stress generated at the surfaces became higher when finer particles were used as collision particles. The increase in injection pressure increased the surface temperature and released the introduced residual stress. As the particle collision treatments affected only the surface regions, the mechanical properties of the treated materials were almost the same as those of the annealed one. In the range of the conditions examined in this study, the most effective treatment to improve the fatigue strength of Ti–6Al–4V alloy was FPB under a relatively low injection pressure. This was because the value of the maximum height waviness was the smallest and the highest compressive residual stress was introduced at the same time.

Microstructure and mechanical properties of laser shock peened 38CrSi steel

Laser shock peening (LSP) induces severe plastic deformation and high compressive residual stress in the metal surface, which can effectively enhance mechanical properties. In this work, the effects of LSP on the microstructure, microhardness, residual stress, tensile and fatigue properties of 38CrSi steel were investigated. After LSP, high-density dislocations such as dislocation walls, dislocation cells, and deformed cementite lamellae structures were observed in the surface layer. The dislocation density was roughly calculated by TEM images. Surface microhardness strengthened by dislocations increased by 24%. The maximum value of compressive residual stress reached −404 MPa. The depth of residual stress affected layer was 750 μm. The peening area had a great influence on the fatigue property. Compared with the base metal (BM), the fatigue life of specimens peened on Area I was improved by 76%, while the fatigue life of specimens peened on Area II was improved by 125%. Finite element analysis revealed that the compressive residual stress induced by LSP in the whole edge of specimen peened on Area II was the main factor for further improving fatigue property. The relationship between compressive residual stress field and crack path was investigated to clarify the strengthening mechanism in different peening areas.

Material properties and membrane residual stresses of S690 high strength steel welded I-sections after exposure to elevated temperatures

This paper reports a thorough experimental investigation into the material properties and membrane residual stresses of S690 high strength steel welded I-sections after exposure to seven levels of elevated temperatures ranging from 30 °C (room temperature) to 950 °C. The experimental programme included heating, soaking and cooling of S690 high strength steel coupons and welded I-section specimens as well as post-fire material tensile coupon tests and membrane residual stress measurements, with the experimental rigs, procedures and results fully reported. The key post-fire material properties were then carefully analysed together with the test data collected from the existing literature, and a new set of retention factor curves of simple multi-linear shapes was proposed and shown to result in accurate predictions of post-fire yield and ultimate stresses for S690 high strength steel after exposed to elevated temperatures. Regarding post-fire membrane residual stresses, the measured distribution pattern and peak amplitudes in S690 high strength steel welded I-section after exposed to an elevated temperature of 300 °C generally remained unchanged in comparison with those in S690 high strength steel welded I-section at room temperature. However, for higher elevated temperatures ranging from 600 °C to 950 °C, the peak values of both compressive and tensile membrane residual stresses dramatically decreased, and moreover the discrepancy between the peak compressive and tensile membrane residual stress values became smaller and the transition regions (where the peak tensile residual stresses are changed to the peak compressive residual stresses) became narrower; this can be attributed to the fact that prominent elastic strain redistribution and residual stress relaxation of steel starts from around 500 °C–600 °C. A membrane residual stress predictive model was proposed for S690 high strength steel welded I-sections after exposed to elevated temperatures, and shown to well represent the measured membrane residual stress patterns and amplitudes over the full temperature range from 30 °C to 950 °C.

Development of beneficial residual stresses in glass fiber epoxy composites through fiber prestressing

The undesired residual stresses in fiber reinforced polymer composites are developed during their manufacturing processes due to the thermal and chemical shrinkage of the polymer matrix, which negatively affect the performance of the composites. Applying tensile stress to the reinforcement fibers during the curing of the matrix can reduce or eliminate the undesired residual stresses. Furthermore, the undesired tensile residual stress within the matrix can be replaced with beneficial compressive residual stress which can improve the mechanical properties of the composites. In this study, theoretical stress analysis was performed in order to determine the value of the optimum compressive residual stress that is associated with the highest tensile strength. This value was determined based on the tensile testing result of prestressed composites with a 40% fiber volume fraction. For the composites with different fiber volume fractions, a new approach was introduced to estimate the optimum fiber prestressing level which generates the optimum compressive residual stress within the matrix and consequently, the highest tensile strength can be achieved. In order to validate this approach experimentally, prestressed composites with 25 and 30% fiber volume fraction were prepared by applying the estimated optimum fiber prestressing levels during curing of matrix and tensile testing was performed. The result of the stress analysis showed that the value of the optimum compressive residual stress corresponding to the highest tensile strength is 2.5 MPa approximately. The tensile testing results confirmed the validity of the new approach in estimating the optimum fiber prestressing level for the composites with different fiber volume fractions. For both prestressed composites with 25 and 30% fiber volume fraction, the highest tensile strength was achieved when the theoretically estimated optimum fiber prestressing level was applied to the fibers during the curing of the matrix.

Effect of Shot Blasting and Shot Peening Parameters on Residual Stresses Induced in Connecting Rod

This paper investigates the effect of shot blasting and shot peening parameters on residual stresses induced in connecting rod. Compressive residual stresses are induced using shot peening to increase fatigue life of connecting rod. Shot peening is also responsible for increase in surface roughness. Surface roughness is detrimental for fatigue life of the connecting rod. This necessitates shot blasting to reduce surface roughness. Shot peening and shot blasting processes are analysed to find optimum process parameters which will induce required value of compressive residual stress on the surface of connecting rod. Compressive residual stresses induced in the connecting rod specimen have been experimentally measured using X-ray stress analyser. The experimental results have been analysed using grey relational analysis to find optimum values of process parameters for target value of compressive residual stress and surface roughness. The experimental investigation and the analysis of it have resulted in achieving the desired value of compressive residual stress, which is 10.5% higher over the existing connecting rod. Surface roughness also decreases to 3.84 Ra which is 8.5% lesser than specified value to achieve better fatigue life.

Residual stress effect governing electromigration-based free-standing metallic micro/nanowire growth behavior

In this study, the effect of residual stress in a film on the growth behavior of a free-standing metallic micro/nanowire due to electromigration (EM) is examined. The growth of a wire is accompanied by atomic diffusion, accumulation of atoms, and release of compressive EM-induced localized hydrostatic stress due to the accumulation of atoms. Hence, the growth of the wire dominantly depends on the EM-induced localized stress caused by the accumulation of atoms. Because rigid passivation generates a strong localized stress field in the metallic interconnect, with greater accumulation of atoms, the EM-induced localized stress state for wire growth is influenced by passivation conditions, including the thickness and residual stress associated with passivation. Two samples with different passivation thicknesses, resulting in different levels of residual stress, were used to elucidate the influence of passivation conditions on the growth performance of Al microwires. The growth rate was experimentally measured. An x-ray diffraction system was used to obtain the value of residual stress in passivation, demonstrating that a higher absolute value of compressive residual stress results in a lower growth rate. In contrast, a lower absolute value increases the growth rate of the wire and can decrease the delamination risk of the topmost passivation, deposited by sputtering. Contrarily, a passivation that is too thin, resulting in a lower absolute value of compressive stress, increases the risk of passivation crack due to the accumulation of atoms by EM. A suitable passivation thickness for a desired wire growth must be determined based on this finding.

Effect of prebending curvature on bending strain and surface properties of stiffened plate during prestressed ultrasonic peening

Stiffened plates are widely used in components of airplane for its light weight and high stiffness and ultrasonic peening (UP) is the key forming technology. However, insufficient bending deformation and poor mechanical properties usually appear during free UP, and elastic prestressed UP is adopted. The effect of prebending curvature radii on bending deformation and surface properties is experimentally conducted. The results show that chordwise peening path contributes to enhancement of chordwise bending strain and smaller spherical deformation. Compared with free UP, more sufficient bending deformation, larger surface hardness with smaller surface roughness, and larger and deeper compressive residual stress are generated in prestressed UP. Spherical deformation coefficient is adopted to quantitatively describe the spherical deformation. With decrease of prebending curvature radius, bending deformation, surface hardness, and absolute value of maximum compressive residual stress are significantly increased; meanwhile, the spherical deformation coefficient is obviously decreased. More uniform surface morphology and larger total depth of compressive residual stress are acquired by applying a prebending moment before UP.

Investigation on residual stresses in milling of Ti-6Al-4V for both rake and flank application of different MWF strategies

Abstract This study investigates the effects of both rake and flank applications of different Metal Working Fluid (MWF) strategies on residual stresses in the machining of Ti-6Al-4V alloy. Cryogenic (Liquid CO2), Minimum Quantity Lubrication (MQL) and emulsion strategies were studied with modified CoroMill600 milling cutter via internal channels delivering media to insert rake face and flank face. The cutting force, minimum chip thickness and chip morphology were analyzed to understand more about this novel approach of rake and flank delivery of different MWFs in milling. The results reveal the formation of compressive residual stresses until 55-60µm beneath the machined surface irrespective of the type of MWF strategies. The highest value of compressive residual stress was observed at the machined surface of liquid CO2. The magnitude of the traced compressive residual stress profile shows a trend of positive slope gradient beneath the surface for both parallel and perpendicular to feed directional residual stress components. In contrast, residuals stresses in emulsion and MQL strategies were observed with a different trend in generation of compressive residual stress components, where the parallel to feed directional component shows an inflection point with a an initial negative slope gradient followed by a positive one to beneath the machined surface. An increase in the cutting forces and minimum chip thickness values were also observed for liquid CO2, due to the high shear resistance of Ti-6Al-4V alloy at machining zone, which was confirmed from the chip morphology analysis. Overall results show that cryogenic CO2 leads to higher compressive residual stresses at the surface and positive slope gradient beneath the material. The higher cutting forces in Z-axis and minimum chip thickness value in liquid CO2 are also attribute to the higher compressive stresses in Ti-6Al-4V workpiece at cryogenic CO2 environment.

THE ESTIMATION OF ROLLER STRENGTHENING INFLUENCE ON THE ENDURANCE LIMIT OF SHAFTS WITH PRESSURIZED HUB

The influence of roller strengthening on endurance limit under bending of the 25 mm and 50 mm diameter shafts made of steel 20 and 25 mm diameter shafts made of steel 40X with a pressurized hub has been examined. Its been stated that the endurance limit of roller strengthened shafts with a pressurized hub depends not only on a value of compressive residual stresses in their dangerous section but on the character of its distribution. The valuation of a surface hardening influence on the endurance limit of shafts by the surface residual stresses criterion and the average integral residual stresses criterion has been shown that the average integral residual stresses criterion calculated through the parts dangerous section surface layer thickness equal the critical depth of the non-propagating fatigue crack can be recommended for the hardened shafts with a pressurized hub endurance limit increase prediction. Its been shown that on a diameter of a shaft with a pressurized hub raising it is necessary to increase a thickness of a hardened surface layer with compressive residual stresses.

Effects of tool vibration on surface integrity in rotary ultrasonic elliptical end milling of Ti–6Al–4V

Titanium alloys have been applied in aerospace, biomedical, and chemical industries due to their superior mechanical properties. As a novel machining method, rotary ultrasonic elliptical machining has been successfully introduced into high-speed side milling of Ti–6Al–4V recently. However, the surface integrity in end milling of titanium alloy using this method is still unclear. In this study, a comprehensive experiment on surface integrity in rotary ultrasonic elliptical end milling of Ti–6Al–4V was conducted at various vibration amplitudes and cutting speeds. Results show that regular substantial micro-vibration textures in the form of separated ridges are obtained on the machined surfaces in RUEEM. Surface roughness values rise from Ra 0.160 μm to Ra 0.758 μm with the increasing cutting speed and vibration amplitude. Both the thickness of subsurface deformed layer and the value of surface micro-hardness increase with rising amplitude at low cutting speeds, while the hardening effect gradually weakens as the cutting speed increases to 160 m/min. Besides, the values of surface compressive residual stress gradually decrease with vibration amplitudes at low cutting speeds, while opposite trends show at the high cutting speed (160 m/min). This study can provide a new method for the effective control of the surface integrity for high-speed end milling of titanium alloy.

Effect of ultrasonic impact treatment on redistribution of residual stresses in dissimilar thickness girth welds

Effect of repeated ultrasonic impact treatment on redistribution of residual stresses in a dissimilar thickness girth butt weld of pipes with a diameter of 530 mm of low alloyed (0.9%C-2%Mn-1%Si) steel was studied. Residual stresses were measured by the X-ray method based on measurement of microdeformation of a crystal lattice of a material under its influence. The research results showed that tensile residual stresses in the girth weld were formed at the inner side of the pipe after welding. Ultrasonic impact treatment of the weld at the inner side caused complete transformation of residual stresses from tensile to compressive ones when speed was in the range from 0.06 to 0.12 m/min. However, reduce in speed of treatment down to 0.04 m/min gave a negative effect. The values of compressive residual stresses in heat affected zone on the side of the thinner pipe were decreased.