Uniform Compressive Stress Research Articles

Influence of Compressive Stress to the Corrosion Rate of Magnesium

Magnesium has made an attention as implant material. Because it is decomposed and absorbed in the body, and its mechanical strength is stronger than that of polymers. It is, however, reported that the corrosion rate increases under the compressive elastic stress. In the other hand, it decreases in the specimen whose surface is applied to compressive residual stress by laser shot peening. This implies that compressive plastic deformation reduces the corrosion rate. In the present paper, the corrosion rate of magnesium that was plastically deformed by uniform high compressive stress was researched. As the result, the corrosion rate decreased as the compressive stress increased.

Finite element simulation of shot peening of an aluminum alloy considering hardening models

Shot peening is a surface engineering process acknowledged for its potential to develop fatigue strength and erosion-corrosion resistance of metallic materials. In the present study, a 3-D finite element model is employed to predict the effective parameters through a single shot impact and the accuracy of the simulation is validated using previous literatures. In order to induce uniform compressive residual stress patterns across the specimen, processing parameters such as shot velocity, impact angle and friction coefficient should be controlled. It is observed that by increasing the shot velocity and the friction coefficient, the depth of compressive residual stress increases. Moreover, a comparative study between isotropic and kinematic hardening models is performed to evaluate the significant role of the hardening models on the compressive residual stress. It is observed that the kinematic hardening model shows better compatibility with the experimental results compared to the isotropic hardening.

A comparison of split sleeve cold expansion in thick and thin plates

Split sleeve cold expansion is a widely used process in the aerospace industry to enhance the fatigue life of rivet holes in the aircraft structures. In the experimental investigation presented in this article, the full-field in-plane residual strains and the out-of-plane surface deformations around open cold-expanded holes were measured using stereoscopic digital image correlation in aluminium specimens of two different thicknesses giving thickness-to-diameter ratios of 0.25 and 1. The results demonstrate that the mechanics of hole deformation is significantly different for the thick and thin specimens. The specimens of 1.6 mm thickness underwent a combination of global bending and significant local warping during the cold expansion process. This localised warping caused a decrease in the minimum principal residual strains close to the edge of the hole, which cannot be predicted by the existing theoretical models as they do not account for the complex out-of-plane deformations that have a significant influence on the shape of the resulting residual strain profiles. In contrast, 6.35-mm-thick specimens did not bend globally mainly because of the higher second moment of area of their cross sections. The material close to the hole edge bulges out from both the faces of the specimen as a result of plastic deformation during the cold expansion process and the out-of-plane deformations are much more localised and lower in magnitude in comparison to the thin specimens. The plastic zone developed around the expanded hole is more axisymmetric and larger in size for the thick specimens. These results imply that the existing split sleeve cold expansion process is not as effective in creating a uniform compressive residual elastic stress field around the fastener holes in thin as it is in the thick specimens.

Upper-bound and lower-bound solutions for the axisymmetric compression of a concrete plug

Deep radioactive waste deposits require specific solutions to close underground galleries and avoid any radioactive migration in the environment. One investigated solution consists of a swelling clay plug that induces a swelling pressure of approximately 7MPa on the walls of the galleries. The clay plug is confined by a concrete plug to maintain and drive the swelling pressure towards the walls of the galleries. The concrete plug must therefore be designed to endure such a pressure. This paper addresses the mechanical strength of a cylindrical concrete plug with a ring-shaped tooth, a free face and a uniform compressive stress over the other face. Two experimental tests over 1/43 reduced samples are first performed and show two collapse mechanisms: dome collapse and tooth-shear collapse. Upper- and lower-bound solutions are investigated based on the Mohr–Coulomb criterion from nonlinear criteria of concrete. The choices of parameters for the friction angle (φ) and cohesion (C) are discussed in relation to the uniaxial compressive and tensile strength of the concrete and the magnitude of the stresses in the model. The results of the simplified analytical, numerical and experimental approaches are then compared, with good agreement found between the approaches.

Influence of hydrogen fluence on surface blistering of H and He co-implanted Ge

The effect of hydrogen fluence on surface blistering of H and He co-implanted Ge is investigated using atom force microscope, X-ray diffraction and transmission electron microscopy. With a fixed He, we find that for 1×1016cm−2 H implantation fluence, only a few small dome-shaped blisters appear, for 3×1016cm−2 H implantation fluence, large blisters as well as craters are formed, while for 5×1016cm−2 H implantation fluence, no blisters can be observed. The strain evolution and platelet forming tendency are found to be relevant for the different blistering phenomenon. The weak blistering phenomenon for 1×1016cm−2 H implantation fluence may be attributed to less “free” H for the building up of internal pressure of platelets and the sustained growth of platelets. While the absence of blistering phenomenon for 5×1016cm−2 H implantation fluence is likely due to the retarded relief of the decreased uniform compressive stress throughout the damage region.

The effect of external stress on the electrical characteristics of AlGaN/GaN HEMTs

The electrical characteristics of AlGaN/GaN high electron mobility transistors under the application of uniform in-plane tensile and compressive stress were measured. The results demonstrate the change of the drain–source Ids–Vds characteristics as a function of the external stress. The output current at Vds=10V increases linearly with the stress with the slope about 3×10−6AMPa−1. It is associated with the piezoelectric effect and kink effect. Moreover, the magnitude of the kink effect is found to be affected by the stress. It displays a linear changing trend with the slope of 3.3×10−4mSMPa−1 within the stress level. The energy band structure is suggested to be responsible for the dependence of the kink effect on the stress.

The effect of external stress on the properties of AlGaAs/GaAs single quantum well laser diodes

The change of spectrum of the AlGaAs/GaAs single quantum well laser diode is measured under the application of uniform uniaxial in-plane tensile and compressive stress. In the range of the tensile stress we apply (up to 597MPa), the wavelength increases linearly at a rate of 5.3nmGPa−1. The energy band gap decreases with the tensile stress with the slope of −10meVGPa−1, which is close to the theoretical change of the heavy hole band edge with respect to the conduction band edge. There is a shorter wavelength peak existing on the spectrum as the tensile stress increases, suggesting a transition from the conduction band to a higher energy valence band. For the compressive stress (up to −516MPa), the wavelength decreases with the stress, but it shows an abrupt reduction from −162 to −200MPa. The threshold current also varies as a result of the change of the energy band structure.

The effect of saw kerf width on the value of the axial growth stress measured by slitting a log along its axis

The surface growth stress in logs can be determined by slitting the log axially and measuring the outward deflection of the two halves. The saw kerf removes stressed material which generates a compressive strain in the remaining material and thereby reduces the surface growth stress. The purpose of the work is to establish the magnitude of this error. The analysis assumes a uniform compressive stress in the core of the log and a logarithmic distribution in the outer region. The total axial force in the kerf before removal is calculated and, from this, the stress change in the material remaining after kerf removal is derived. Data are presented for a range of kerf widths and for three different growth stress distributions. Direct measurement of the kerf removal error was made by direct measurement of the contraction of the log and by strain gauges to measure the strain. The measured values were close to the calculated values for three growth stress distributions. The analysis yields acceptable values for the kerf removal error. The investigation concludes that for kerf widths not greater than one-tenth of the log diameter, the error in the measured tensile surface growth stress is less than 10%.

Shot Peening Method for Aerofoil Treatment of Blisk Assemblies

Advanced compressor designs today often include blade integrated disc (blisk) rotors, with high demands on aerodynamic performance, resistance againsthigh load levels and foreign object damage (FOD).To increasethe highcycle fatigue (HCF) strength, compressive residual stresses are introduced into the surface and subsurface layer of aerofoil, fillet (transient area between aerofoil and disk) and annulus (intermediate area between aerofoils). For generatingcompressive residual stresses several different industrial production processes are used, beside ultrasonic shot peening, laser shock peening, deep rolling and shot peening wet and dry with glass or ceramic media is shot peening with steel media the mostly used technology. However, depending on the size of the componentaccessibility for tools might be limited and the set-up of economical production techniques challenging for blisk shot peening.This paper gives an introduction into blisk shot peening, a sophisticated mechanical surface technology for treating aerofoil surfaces of blisk rotors using special designed calliper nozzles assolution for introducing uniform residual compressive stress states, as well as consistentshot peening coverage levels.

ショットピーニング処理表面の微視的応力分布測定

Shot peening, which imparts compressive residual stress, is a very effective means for improving the fatigue strength and is widely used for springs. The relationship between fatigue strength and compressive residual stress by shot peening is well known and is a subject of many previous studies. Residual stress caused by shot peening is generally evaluated using X-ray stress measurement method, and it give rise to compressive residual stress macroscopically when the X-ray irradiation area is not small. On the other hand, in order to investigate the microscopic stress distribution of dents around the vicinity, there are research and experiments with big steel ball simulating a shot, and studies using FEM method confirms that tensile residual stress is generated locally, such as the center of a dent. However, identifying the residual stress generation mechanism by shot peening using calculation alone is a very difficult task because there are many factors involved. In this study, with the aim of clarifying experimentally the microscopic residual stress distribution of peening surface with CCW(conditioned cut wire), which is widely used for the production of spring, we have developed an X-ray diffractometer which makes it possible to measure the microscopic stress distribution. We prepared as specimen SUP9 (JIS G 4801: spring steels), shot peened at coverage of 10%, 60% and 300%. The microscopic residual stress distribution is measured in an area of 0.8mm x 0.8mm with 0.1mm step on each specimen surface. Obtained results are summarized as follows: Shot peened surface has average compressive residual stress present in large irradiation areas, but the tensile stress and compressive stress of the yield stress order has been distributed in local areas of 100μm or less. It became clear that, even if the coverage of the shot peening is increased, there is not much difference of macroscopic residual stress, and an overall uniform compressive stress distribution is not obtained; but there is a large residual tensile stress in the local area. There is no correlation between surface shape and residual stress distribution due to shot peening. In the stress distribution around the dent by single shot, unlike previous research results using shot peening of the sphere, it clearly indicates a residual stress distribution with no regularity.

Practical moment–rotation relations of steel shear tab connections

An analytical model for shear tab connections in modern steel buildings is proposed. This connection model includes the concrete slab effects and has unsymmetrical behaviors under positive and negative moments. Under positive moment, the flexural strengths are determined by two stress patterns: linear triangular tensile stress along shear tab combined with uniform compressive stress of 0.30fc′ on slab at yielding state; uniform yielding stress along shear tab combined with uniform compressive stress of 0.85fc′ on slab at ultimate state. Under negative moment, shear tab plate is the contributor to the flexural strength and the concrete slabs are neglected. Comparisons between experimental and analytical results indicate that the proposed steel shear tab models are able to capture major behaviors with a compatible effort often made in a typical structural design office. Seismic studies of one three-story non-ductile braced frame including proposed models demonstrate the capabilities and simplicities for practical structural engineering application.

Elastic Buckling of Rectangular Hollow Section Tapered Columns Subjected to Uniform Compressive Stresses

Elastic Buckling of Rectangular Hollow Section Tapered Columns Subjected to Uniform Compressive Stresses

Analysis and Computer Modeling of Magnetoelastic Characteristics of FeNi-based Amorphous Ring-shaped Core under Uniform Compressive and Tensile Stresses

Paper presents methodology of generation of the uniform, compressive or tensile stresses in ring-shaped amorphous alloys core. In this study we use the set of special nonmagnetic, cylindrical backings. These backings enabled the core to be wound as well as create the possibility of generation of uniform compressive and tensile stresses. Using presented methodology the magnetoelastic characteristics were experimentally determined for Fe40Ni38Mo4B18 Metglas 2826 MB amorphous alloy. Knowledge about these properties is important for users of inductive components with amorphous alloys cores due to the fact, that changes of fl ux density due to magnetoelastic effect exceed 40%.

Effects of Erbium alloying on the structural and piezoelectric properties of Aluminum Nitride thin films annealed under extreme thermal conditions

ABSTRACTEffects of adding Erbium(Er) to Aluminum Nitride thin films on their structural and piezoelectric are reported along with stability of the films after annealing them at temperatures up to 600° C. The thin films samples were deposited on the (001) p-type silicon substrates by reactive magnetron sputtering, using the Er alloyed Aluminum targets with Er atomic concentrations of 0, 1, 3 and 4% and the magnetron sputtering power of 200 W. The samples were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). XPS analysis was used to confirm the stoichiometry of AlN phase, Er atomic content and its possible chemical state in the films. Results show that alloying with Er results in higher piezoelectric coefficient d33 as compared to that in Er-free AlN thin films. Structural analysis of the films by XRD shows the shift of (0002) AlN peak to lower 2θ values upon Er doping, indicating the presence of uniform internal compressive stress.

Finite Element Analysis (FEA) for Wrinkling Initiation in ASTM A36 Steel Sheet Metals

Thin metal sheets are increasingly used for different purposes in automotive and aerospace industry. These sheets are prone to wrinkling during forming which is a major defect. Wrinkles are formed due to non uniform compressive stresses resulting from multi axial stretching of materials. Its initiation may be due to material properties, geometric constraints and stress applied. This research is focused on FEA of steel ASTM A36 sheets to predict their wrinkling initiation and growth.

Investigation of Surface Integrity on TC17 Titanium Alloy Treated by Square-spot Laser Shock Peening

Laser shock peening (LSP) is an innovative surface treatment method, which has been shown to greatly improve the fatigue life of many metallic components. This work investigates surface integrity of TC17 titanium alloy treated by LSP with innovative square laser spot. Nd: glass laser with duration of 30 ns and spot size of 4 mm×4 mm is applied. The surface morphology and surface residual stress of the TC17 titanium alloy, treated with varying peening parameters such as laser power density and overlapping ratio, have been studied in detail. The results show that laser pulse energy greatly influences surface morphology and surface residual stress around single-spot treated areas, and compressive residual stresses are saturated as laser pulse energy is over 55 J. There are significantly different surface morphologies and residual stress distributions at the overlapped areas with different overlapping ratios. A relative smooth surface is produced with uniform compressive residual stress distribution at an overlapping ratio of 8%. The experiment of residual stress relaxation is implemented by measuring residual stress at the center of four overlapped spots and by four point bending fatigue test at the frequency of 105 Hz. The compressive residual stresses induced by LSP are found to relax quite slowly under cyclic fatigue loading.

Based on Bearing Centerless Strengthening and Polishing Processing Multiple Collision Finite Element Simulation Analysis

To further understand the bearing performance’s influence of the plastic deformation after balls and bearing rings surface multiple collision in ball bearing’s strengthening and polishing processing by the strengthening and polishing machine. ABAQUES software is used for finite element analysis in the three-dimensional modeling of multiple collision, and the plastic strengthen the performance of bearings is researched mainly. The results shows that the raceway surface is significant plastic strengthen in multiple collisions, Yield ability is enhanced largely, and surface residual stress state present for the compressive stress. Raceway surface strengthening process requires a particular number of times to ensure the processing, with strengthening processing times increasing, bearing raceway surface strength is saturated, then, the number continued to increase to strengthen, the surface strength is no significant increase. But after the collision of ball, uniform residual compressive stress is forming in the bearing surface, good for improving the fatigue strength and bearing life.

Crack-contact problem for an elastic layer with rigid stamps

The plane crack-contact problem for an infinite elastic layer with two symmetric rectangular rigid stamps on its upper and lower surfaces is considered. The elastic layer having an internal crack parallel to its surfaces is subjected to two concentrated loads p on its upper and lower surfaces trough the rigid rectangular stamps and a pair of uniform compressive stress <TEX>$p_0$</TEX> along the crack surface. It is assumed that the contact between the elastic layer and the rigid stamps is frictionless and the effect of the gravity force is neglected. The problem is reduced to a system of singular integral equations in which the derivative of the crack surface displacement and the contact pressures are unknown functions. The system of singular integral equations is solved numerically by making use of an appropriate Gauss-Chebyshev integration formula. Numerical results for stress-intensity factor, critical load factor, <TEX>$\mathcal{Q}_c$</TEX>, causing initial closure of the crack tip, the crack surface displacements and the contact stress distribution are presented and shown graphically for various dimensionless quantities.

Buckling of Thin Cylindrical Shells Under Locally Elevated Compressive Stresses

Thin cylindrical shells used in engineering applications are often susceptible to failure by elastic buckling. Most experimental and theoretical research on shell buckling relates only to simple and relatively uniform stress states, but many practical load cases involve stresses that vary significantly throughout the structure. The buckling strength of an imperfect shell under relatively uniform compressive stresses is often much lower than that under locally high stresses, so the lack of information and the need for conservatism have led standards and guides to indicate that the designer should use the buckling stress for a uniform stress state even when the peak stress is rather local. However, this concept leads to the use of much thicker walls than is necessary to resist buckling, so many knowledgeable designers use very simple ideas to produce safe but unverified designs. Unfortunately, very few scientific studies of shell buckling under locally elevated compressive stresses have ever been undertaken. The most critical case is that of the cylinder in which locally high axial compressive stresses develop extending over an area that may be comparable with the characteristic size of a buckle. This paper explores the buckling strength of an elastic cylinder in which a locally high axial membrane stress state is produced far from the boundaries (which can elevate the buckling strength further) and adjacent to a serious geometric imperfection. Care is taken to ensure that the stress state is as simple as possible, with local bending and the effects of internal pressurization eliminated. The study includes explorations of different geometries, different localizations of the loading, and different imperfection amplitudes. The results show an interesting distinction between narrower and wider zones of elevated stresses. The study is a necessary precursor to the development of a complete design rule for shell buckling strength under conditions of locally varying axial compressive stress.

Transmission electron microscopy observations on the phase composition and microstructure of the oxidation scale grown on as-polished and yttrium-implanted β-NiAl

Phase transformations and microstructural evolution of thermally grown oxide scale on polycrystalline β-NiAl at 1100 °C up to 6 h, with and without (e.g., as-polished) yttrium implantation, were examined by glancing angle X-ray diffraction, photostimulated luminescence, scanning and transmission electron microscopy. Site-specific TEM specimens were prepared by using focused ion beam in-situ lift-out technique. The oxide scale developed on as-polished β-NiAl consisted of the islands of 390 nm-thick flat regions (e.g., patches) in 916 nm-thick scales. Regardless of microstructure, the oxide scale consisted of α-Al 2O 3 with very little trace of θ-Al 2O 3, and had uniform compressive residual stress. The oxide scale on Y-implanted β-NiAl had a two-layer microstructure: the outer layer was mainly α-Al 2O 3 and the inner layer was made up of α-, δ-, and θ-Al 2O 3 phases. Clearly, the Y addition retarded the θ-to- α Al 2O 3 phase transformation. The oxide scale on Y-implanted β-NiAl, in general, consisted of a 722 nm-thick layer with islands of 470 nm-thick patched regions, some of which contained Y-rich nodules that protruded with thickness up to 1200 nm. Except for islands of patch-regions, the oxide scale developed on Y-implanted β-NiAl was thinner (722 nm) than that on as-polished β-NiAl (916 nm).