Surface Tensile Stress Research Articles

S71 Residual Stresses in a Machined and Shrink Fitted Assemblies

A shrink-fit is a semi-permanent assembly system, widely used in industry, which is designed to resist the relative movement or transmit torque between two components. This done by creating high radial pressures at the interface of the constituent parts. Examples include fitting of gears to shafts to transmit torque and shrink fitted hard wearing sleeves to shafts for steel rolling mills. This paper presents measured and predicted residual stresses from a variety of shrink fitted assemblies, including aluminium alloys, stainless steel and cast irons. In a number of cases the sleeves shrink fitted to the shaft were subjected to prior machining or prior quenching to introduce initial residual stresses in the sleeve. Residual stresses were measured using a combination of deep-hole drilling (DHD) and incremental centre hole drilling (ICHD) techniques. The ICHD method provided near surface residual stress measurements to depths up to about 1mm. The DHD method measured through thickness residual stresses along radial lines through the outer sleeve and into the shaft up to depths of 400mm. Results are shown for a variety of assemblies and reveal residual stress that are significantly different from both simple analysis and finite element studies. For example, prior machining introduced near surface compressive residual stresses, that is then expected to be counteracted by the near surface tensile shrink fit residual stresses. However, measurements reveal that this is not the case.

Many-body effects on surface stress, surface energy and surface relaxation of fcc metals

The results of an investigation aimed at isolating the role played by pair-wise and many-body contributions in determining the surface stress, surface energy and surface relaxation for clean, low-index fcc metal surfaces are presented. General expressions for surface stress and surface energy are developed for generic embedded atom method (EAM) potentials and are contrasted with results derived from central-force pair potentials. Calculations are presented for specific forms. We find that these pair-wise and many-body contributions usually act in opposition to each other. Pair potentials tend to produce compressive surface stress contributions and favor outward surface relaxations, while the many-body component produces tensile surface stress contributions and favors inward relaxations. We also bring to light certain relationships between surface and bulk thermodynamic properties within the framework of these models. It is shown how surface stress can be expressed in an approximate form involving terms proportional to the product of an elastic modulus and the neighbor spacing characteristic of the material, and constants of proportionality that depend only on surface orientation. This form provides a good fit to a set of first-principles results as well. Finally, we demonstrate how various surface properties display a strong correlation with the ratio of bulk-to-shear moduli, B eq/ G eq.

In Situ Stress Measurements During Al UPD onto (111)-Textured Au from AlCl3-EtMeImCl Ionic Liquid

In situ stress measurements were made during Al underpotential deposition (upd) onto (111)-textured Au from Lewis acidic aluminum chloride - 1-ethyl-3-methylimidazolium chloride using the wafer curvature method. The surface stress response consists of three distinct features. In the potential range of 1.2 V to 0.6 V the surface stress moves in the tensile (positive) direction which we attribute to the desorption of AlCl4- from the Au surface. This is consistent with adsorbate-induced stress models that appear in the literature. At the start of Al upd, the surface stress moves in the compressive direction, in contrast to the tensile stress expected based on the positive lattice misfit. We attribute this compressive stress to the formation of Al-Au bonds which partially satisfy the bonding requirements of the Au surface atoms, thereby reducing the tensile surface stress inherent to the clean Au surface. In the latter stages of Al upd, the surface stress once again moves in the tensile direction which we attribute to Al-Au alloying.

Highly specific label-free protein detection from lysed cells using internally referenced microcantilever sensors

We report the investigation of label-free protein detection directly from lysed cells using microcantilever sensors. The integration of an internally referenced microcantilever sensor combined with peptide aptamer technology enables scalable and label-free detection of proteins from a complex biological environment (e.g. cell lysate). The internally referenced microcantilever sensor was found to be effective in minimizing both the effects of thermal drift and non-specific binding interactions with the backside of the cantilever, thereby allowing protein detection in a complex biological background. Highly specific peptide aptamers are used to modify the cantilever surface to specifically detect less than 80nM CDK2 protein from yeast cell lysate. This binding of CDK2 on the microcantilever generates a tensile surface stress of average magnitude equal to 70±22mN/m. Similar experiments conducted with quartz crystal microbalance (QCM) technology are consistent with the response observed using microcantilever sensors.

In Situ Stress Measurements During Al UPD onto (111)-Textured Au from AlCl3 – EMImCl Ionic Liquid

In situ stress measurements were made during Al underpotential deposition (upd) onto (111)-textured Au from Lewis acidic aluminum chloride, 1-ethyl-3-methylimidazolium chloride , using the wafer curvature method. The surface stress response consists of three distinct features. In the potential range of the surface stress moves in the tensile (positive) direction from a value arbitrarily chosen as zero. This likely involves the desorption of from the Au surface and is consistent with adsorbate-induced stress models that appear in the literature. At the start of Al upd, the surface stress moves in the compressive direction, in contrast to the tensile stress expected based on the positive lattice misfit. We attribute this compressive stress to the formation of Al–Au bonds which partially satisfy the bonding requirements of the Au surface atoms, thereby reducing the tensile surface stress inherent to the clean Au surface. In the latter stages of Al upd, the surface stress once again moves in the tensile direction, which we attribute to Al–Au alloying. The magnitude of the tensile stress change is close to that estimated from the elastic strain associated with the change in molar volume, using reaction kinetics reported for surface alloy formation in the upd region.

Hertzian fracture at finite friction: A parametric study

Friction has a profound influence on Hertzian fracture initiation when dissimilar materials are involved. Experimental studies show that the presence of friction results in higher fracture loads and fracture radii as compared to the frictionless case. It has also been shown recently that the experimental observations concerning Hertzian fracture initiation at unloading may be explained by the effect friction has on a surface tensile stress distribution. Presently a contact cycle between two dissimilar elastic bodies at finite Coulomb friction has been investigated numerically for a wide range of material parameters and contact geometries. Emphasis has been given to the surface tensile stress distribution which is assumed to be a governing parameter for Hertzian fracture initiation. In particular it was found that during loading the contact region divides into invariant stick and inward slip regions and the presence of outward frictional shear tractions reduces the maximum surface tensile stress and shifts it away from the contact contour as compared to the frictionless case. At unloading, the distributions of stick-slip zones were found to be severely history- and geometry-dependent and shear tractions reversed their direction over part of the contact area. Consequently, tensile stresses were found to grow at unloading. Results concerning the influence of the friction coefficient, Dundur's parameter and the specimen's Poisson's ratio on the absolute maximum surface tensile stress obtained at a frictional contact cycle are reported along with the magnitudes of the relative increase of maximum tensile stresses at unloading. Based on a critical stress fracture criterion it is discussed how the predicted increases will influence the critical loads required for crack initiation.

Effect of coating architecture on impact stress distribution in particulate erosion conditions

A computer simulation technique based on ABAQUS/Explicit was used to investigate stress and strain distribution at the surface and at the coating/substrate interface of multi-layer coatings under single particle impact. Eight different coating architectures and five material models were analyzed to determine possible stress reduction that could be obtained through a combination of layering patterns and material properties. Specifically, the elastic, elastic-plastic and brittle cracking coating models were used and coating response was analyzed using the surface tensile stress as a main evaluation criterion. It was found that stress reduction of up to 3.6 times was possible for the best configuration indicating that optimized coating architecture can significantly contribute to coating erosion performance.

Surface Stress, Thickness, and Mass of the First Few Layers of Polyelectrolyte

The effects of surface stress and mass loading upon the adsorption of polyelectrolytes onto flexible silicon micromechanical cantilever sensors (MCSs) were studied in situ. A self-assembled monolayer of 2-mercaptoethylamine chloride (2-MEA) on gold was used to achieve single-side adsorption on the MCS. Such a preparation gave a positive surface potential, whereas a bare SiOx surface gave a negative surface potential. Wide scan X-ray photoelectron spectroscopy confirmed that the adsorption of polystyrenesulfonate (PSS) and polyallylamine hydrochloride (PAH) followed the general rule expected from the electrostatic interaction between the substrate and the polyelectrolyte, whereas the adsorption polyethyleneimine (PEI) did not. The adsorption of PAH on SiO(x) from a 3 mM water solution containing 1 M NaCl was associated with a deflection of the MCS toward the polyelectrolyte monolayer (tensile surface stress) owing to the hydrogen bonding between neighboring amino groups. Here, a surface stress change of 1.4 +/- 0.1 N/m was estimated. The adsorption of PSS from a 3 mM water solution containing 1 M NaCl on a 2-MEA surface induced a deflection of the MCS away from the polyelectrolyte layer (compressive stress), toward the SiO(x) side. Here, a surface stress change of 3.1 +/- 0.3 N/m was determined. The formation of a PAH layer on top of the PSS layer resulted in a deflection of the MCS toward the PAH layer. This indicated that the adjacent PSS layer was deswelling, corresponding to a surface stress change of 0.5 +/- 0.1 N/m.

The stress characteristics of metal nanowires: an atomistic simulation study

In this paper, we have used molecular statics calculations with the quantum corrected Sutten-Chen type many-body force field to study the stress distribution characteristic of nickel nanowires with ［100］, ［110］ and ［111］ crystallographic orientations in equilibrium state. The simulated results show that tensile stress on the surface of the nanowires causes them to contract along the length. It can be seen that the stress is tensile in surface region while compressive in core region. With the increasing of diameter, the average stress in core region is compressive and strongly decreased to approach to zero, while the surface tensile stress first increases, and then tends to a non-zero constant. The contraction ratio of length, and average stress in core and surface are always largest for ［100］ nanowire and smallest for ［111］ nanowire.

The steel superstrengthening phenomenon, part 2

The paper discusses a combined heat treatment that includes the potentialities of high-temperature thermal-mechanical treatment and intensive quenching. Due to high-temperature thermal-mechanical treatment and intensive quenching within the martensite range, the strength and plastic properties of materials are significantly improved and compressive residual stresses are formed at the surface and small tensile stresses in the core, which result in the increase of their service life. The suggested combined approach is also efficient in the case of the heat treatment of forgings with the use of forging heat. The suggested technology considerably saves energy resources and makes unnecessary intermediate operations such as repeated heating before quenching. Oil, as a quenchant, is replaced by plain water. The industrial quenching line can be placed directly in the forgery workshop and yield big economical benefits.

Three-dimensional thermal stress analysis on laser scribing of glass

In the laser scribing of glass a thermal stress is introduced into a glass plate by means of CO2 laser irradiation. The glass plate is rapidly cooled down by water jet immediately after the irradiation. For the purpose of theoretical clarification of the factors ruling the scribable condition and the crack depth, scribable conditions were acquired in laser irradiation experiments using a soda-lime glass plate having a thickness of 0.7 mm. Furthermore, the crack depth and the crack profile were observed for various values of the distance between the heating area and the cooling area. On the basis of the scribable conditions obtained from the experiments, a three-dimensional thermal stress analysis was conducted by a finite element method, allowing the following findings to be obtained. The scribable condition can be estimated from the maximum surface tensile stress in the cooling area and the maximum surface temperature. The crack depth in laser scribing depends on the surface tensile stress in the cooling area and the compressive stress field immediately under that area.

Surface stresses at an axisymmetric asperity in a rolling contact with traction

Rolling contact between a smooth cylinder and a cylinder with an axisymmetric surface asperity was modelled numerically. The influence of tangential slip and friction was investigated through relative contact movement between the cylinders. As the asperity entered the rolling contact it acted as a point type contact force, which gave a tensile surface stress in the forward rolling direction. The tensile stress maximum was greatly influenced by slip and coefficient of friction. Data for the simulations were captured from a gear example with surface initiated rolling contact fatigue or spalling. The cylindrical contact load and geometry corresponded to that at the roll-circle of the gear. The geometrical properties of the asperity were based on surface profiles of the gear flank. The combined isotropic and non-linear kinematic Chaboche material model was used with parameters determined from cyclic compression–tension tests on the gear material. The residual stress profile due to heat-treatment of the gear was included into the model. Two different frictional set-ups were investigated. One contained a non-zero coefficient of friction throughout the rolling contact. This was believed to compare to dry contacts. The other set-up was supposed to model lubricated rolling with asperity break-through to metal contact. Here friction was non-zero on the asperity and zero elsewhere in the contact. With traction throughout the cylindrical contact a sufficiently long start distance had to be travelled before the asperity interaction. Thus, the transient rolling distance was determined together with the slip limit for sliding in the cylindrical contact. Numerical predictions of residual stresses and surface distress angles suggested that the asperity friction model agreed with gear conditions. Evaluation of elastic–plastic asperity indentation suggested that the asperity deformation was approximately as severe as repeated macro-scale experiments with fatigue cracks. Since the stresses at the asperities were of the same size as those at the repeated indentations and since the Findley multi-axial fatigue criteria predicted fatigue damage, it was concluded that the stresses in front of the asperity could be sufficient to initiate rolling contact fatigue cracks in applications. The influences of some parameters on the stress maximum were also evaluated.

Development of a classical force field for the oxidized Si surface: Application to hydrophilic wafer bonding

We have developed a classical two- and three-body interaction potential to simulate the hydroxylated, natively oxidized Si surface in contact with water solutions, based on the combination and extension of the Stillinger-Weber potential and of a potential originally developed to simulate SiO(2) polymorphs. The potential parameters are chosen to reproduce the structure, charge distribution, tensile surface stress, and interactions with single water molecules of a natively oxidized Si surface model previously obtained by means of accurate density functional theory simulations. We have applied the potential to the case of hydrophilic silicon wafer bonding at room temperature, revealing maximum room temperature work of adhesion values for natively oxidized and amorphous silica surfaces of 97 and 90 mJm(2), respectively, at a water adsorption coverage of approximately 1 ML. The difference arises from the stronger interaction of the natively oxidized surface with liquid water, resulting in a higher heat of immersion (203 vs 166 mJm(2)), and may be explained in terms of the more pronounced water structuring close to the surface in alternating layers of larger and smaller densities with respect to the liquid bulk. The computed force-displacement bonding curves may be a useful input for cohesive zone models where both the topographic details of the surfaces and the dependence of the attractive force on the initial surface separation and wetting can be taken into account.

Stress evolution of cold-drawn pearlitic steel wire subjected to uniaxial tension

The aim of this paper is to investigate the effect of uniaxial tension on the residual stress of cold-drawn pearlitic steel wire through X-ray diffraction in combination with layer removal technique. It is found that an extra 0.9% plastic strain is introduced to the steel wire due to the uniaxial tension using a universal electronic tensile machine. The XRD results indicate that uniaxial tension after drawing has dominate influence on the decrease of surface tensile residual stress and the corresponding stress gradient in the drawn wires.

In Situ Stress and Nanogravimetric Measurements During Underpotential Deposition of Pb on (111)-Textured Au

The surface stress associated with the underpotential deposition (upd) of lead on (111)-textured Au is examined, using the wafer curvature method, in acidic perchlorate supporting electrolyte. The surface stress is correlated to 0, the fractional Pb coverage, by independent nanogravimetric measurements using an electrochemical quartz crystal nanobalance (EQNB). The gravimetric results are similar to the data found in the literature, showing an electrosorption valency of 2 and the formation of a hexagonal close-packed monolayer of Pb. The complete Pb monolayer causes an overall compressive surface stress change of about -1.2 N m -1 . The stress-coverage curve can be divided into two linear regions separated by a plateau. The region at low to intermediate coverage is caused by the formation of Au-Pb bonds which decrease the charge density and reduce the tensile surface stress inherent to the clean Au surface. In the second linear region at high coverage, the Pb adlayer compresses and behaves as a free-standing elastic film with a biaxial modulus close to that for Pb (111) in the bulk. The plateau that separates these two linear regions corresponds to the stress relaxation hump that appears in the stress-potential curve. This stress relaxation is attributed to island coalescence.

Effects of Reduction Treatment on Fracture Properties of Cerium Oxide

The reduction treatment effects on the flexural strength and the fracture toughness of ceria were evaluated at room temperature. The results reveal that the flexural strength decreases significantly after reduction under very low oxygen partial pressures; however, in contrast, fracture toughness is increased by 30%–40% when the oxygen partial pressure was decreased to 10−20–10−22 atm range. The large microcracks and the surface tensile stresses developed upon reduction treatment and cooling process are responsible for the decreased strength. The enhancement in toughness is also discussed in terms of internal stresses, microcrack toughening, and crack deflection mechanisms.

Residual stress influence on fatigue lifetimes of electroplated AISI 4340 high strength steel

ABSTRACTResidual stresses play an important role in the fatigue lives of structural engineering components. In the case of near surface tensile residual stresses, the initiation and propagation phases of fatigue process are accelerated; on the other hand, compressive residual stresses close to the surface may increase fatigue life. In both decorative and functional applications, chromium electroplating results in excellent wear and corrosion resistance. However, it is well known that it reduces the fatigue strength of a component. This is due to high tensile internal stresses and microcrack density. Efforts to improve hard chromium properties have increased in recent years. In this study, the effect of a nickel layer sulphamate process, as simple layer and interlayer, on fatigue strength of hard chromium electroplated AISI 4340 steel hardness – HRc 53, was analysed. The analysis was performed by rotating bending fatigue tests on AISI 4340 steel specimens with the following experimental groups: base material, hard chromium electroplated, sulphamate nickel electroplated, sulphamate nickel interlayer on hard chromium electroplated and electroless nickel interlayer on hard chromium electroplated. Results showed a decrease in fatigue strength in coated specimens and that both nickel plating interlayers were responsible for the increase in fatigue life of AISI 4340 chromium electroplated steel. The shot peening pre‐treatment was efficient in reducing fatigue loss in the alternatives studied.

Finite element analysis on stresses field of normalized layer thickness within ceramic coating on aluminized steel

Multilayer ceramic coatings were fabricated on steel substrate using a combined technique of hot dipping aluminum(HDA) and plasma electrolytic oxidation(PEO). A triangle of normalized layer thickness was created for describing thickness ratios of HDA/PEO coatings. Then, the effect of thickness ratio on stresses field of HDA/PEO coatings subjected to uniform normal contact load was investigated by finite element method. Results show that the surface tensile stress is mainly affected by the thickness ratio of Al layer when the total thickness of coating is unchanged. With the increase of Al layer thickness, the surface tensile stress rises quickly. When Al 2O 3 layer thickness increases, surface tensile stress is diminished. Meanwhile, the maximum shear stress moves rapidly towards internal part of HDA/PEO coatings. Shear stress at the Al 2O 3/Al interface is minimal when Al 2O 3 layer and Al layer have the same thickness.

Size-dependent effects on equilibrium stress and strain in nickel nanowires

Using molecular static calculations with the quantum corrected Sutten-Chen-type many-body potential, we have studied the stress and strain characteristics in nickel nanowires along [100], [110], and [111] crystallographic orientations under the equilibrium state. The main focus of this work is the size-dependent effects on these characteristics above. We deduce from the common neighbor analysis that surface region approximately consists of two layer atoms. Further, we extract the equilibrium characteristics in both surface and core regions of nanowires. The results show that with increasing diameter, the equilibrium stress and strain which are compressive decrease sharply in the core region, while the surface tensile stress starts to increase, and gradually trends to a nonzero constant. Due to much larger compressive stress and smaller modulus, the core of [100] nanowire endures larger compressive strain than that of [110] and [111] nanowires.

Prevention of Stress Corrosion Cracking in Welded Joint of Type 304 Stainless Steel by Laser Peening

In order to prevent stress corrosion cracking (SCC) of austenitic stainless steel weldment, a novel technique -laser peening- has been introduced which is able to convert surface tensile stresses in the weldment to surface compressive stresses. In this paper, water-immersed welded specimens of type 304 stainless steel are peened by Q-switched Nd: glass laser with a wavelength of 1.06μm. A residual compressive layer is produced on the specimen surface by scanning laser pulse to cover the heat affected zone (HAZ) along the weld line. The residual compressive stress value based on X-ray measure is significant enough to prevent the initiation of stress corrosion cracking that is also validated by the finite element analysis. The SCC accelerated tests for comparing the potential against SCC of the specimens, which are unpeened and peened by laser pulse with different laser spot coverage, are carried on. The results show that stress corrosion cracks on the surface of unpeened specimen occur after immersion for 25 hours in boiling 42% MgCl2 solutions at 143°C. In contrast, the specimen with 45% laser spot coverage cracks after immersion for 300 hours, while, cracks are observed on the surface of laser-peened specimen with 80% laser spot coverage after 985 hours of testing. The results show that laser peening is an effective technique for improving the residual stress distribution and the SCC resistance of 304 stainless steel weldment.