Considerable Compressive Stress Research Articles

Structure and stripe domain of melt-spun HoMn6Sn6-xGax ribbons

Topological magnetic skyrmions are expected to become a new generation of information carrier units, and exploring new magnetic skyrmion host materials and their magnetic domain structures is critical. This paper prepared HoMn6Sn6-xGax ribbons by melt-spinning and annealing and studied the effects of the second phase and doping Ga on the structure and magnetic domain of the ribbons. The results show that doped Ga only replaces the Sn sites in the HoMn6Sn6 phase, and the maximum substitution rate of Ga in the HoMn6Sn6 phase is close to 1/6. The unequal substitution of crystal positions causes the lattice to bear considerable compressive stress and negative strain. With an increase in doped Ga content, the lattice constant and cell volume of the HoMn6Sn6-xGax phase gradually decrease, and the substitution positions also change from mainly occupying Sn(2c) sites to occupying Sn(2e) and Sn(2d) sites simultaneously. Doping Ga enhances the preferential orientation in the grains, Ga occupying Sn(2d) sites enhances 〈009〉 orientation, and occupying Sn(2e) sites contributes to the enhancement in 〈204〉 orientation. Whether doped with Ga or not, the ribbons have stable stripe domains with HoMn6Sn6 structure. Increasing Ga content from x = 0.3 to x = 1.6 decreases the spin reorientation temperature, Curie temperatures, and the difference between the two temperatures.

A Fully Coupled Mechano-Electrochemical Model for All-Solid-State Thin-Film Li-Ion Batteries with Non-Porous Electrodes: Effects of Chemo-Mechanical Expansions on Battery Performance and Optimization Strategies for Stress Evolution

A comprehensive and novel mechano-electrochemical coupling model for all-solid-state Li-ion batteries (ASSLBs) is developed, in particular, focusing on the influence of the volume changes caused by ions redistribution in the electrodes on the electrical and mechanical properties of the battery. The mathematical relationship between the partial molar volume and Poisson’s ratio is determined for the condition of zero stress. The roles of the partial molar volumes of cathode and anode, the thickness and Young’s modulus of the spacer are investigated. The results show that the electrode volume changes significantly during the charging and discharging process. Due to the mechanical imbalance, the confined cell generates considerable compressive stress (approximately 0.6 MPa). Reducing the partial molar volume of the anode can not only eliminate the compression stress but augment the capacity. Note that for the ASSLBs containing inorganic (oxide or sulfide) solid electrolytes (SEs), adjusting the material parameters to obtain proper compressive stress instead of a bulky cell holder may be another useful method to overcome the poor interface contact. Finally, by introducing polyurethane foam or other soft blocks with a suitable thickness and Young’s modulus as spacers, the stress of the cell can be reduced by 79.33%.

A comprehensive study on surface integrity of nickel-based superalloy Inconel 718 under robotic belt grinding

ABSTRACTSurface integrity of materials should be considered under robotic belt grinding in order to achieve desired finishing quality. In this work, the surface integrity of nickel-based superalloy Inconel 718, involving morphological structure, surface roughness, residual stress and structural domain size, was characterized systematically. A novel predicted model of grinding parameters optimization was proposed based on linear weighting function. The result shows that considerable compressive stress (about−355 MPa) and minimum roughness on material surface are achieved simultaneously at the grinding force of 178 kPa and belt speed of 31 m/s. The morphological structures and microhardness for the specimen under the optimized condition were further analyzed and discussed. Surface hardness is increased by 15%. Grain refinement and a large number of dislocations occur in the subsurface, which are attributed to continuous partial dynamic recrystallization associated with combined effects of plastic deformation and thermal treatment, which results from grinding force and belt speed. The new findings are of significance for ensuring surface integrity with optimal process parameters.

Iron-based shape memory alloy for the fatigue strengthening of cracked steel plates: Effects of re-activations and loading frequencies

The paper discusses the application of an iron-based shape memory alloy (Fe-SMA) for the fatigue strengthening of steel plates. The shape memory effect (SME), which is the characteristic behavior of the Fe-SMAs, was used for the prestressed strengthening of steel plates. One steel plate without any pre-cracks and two steel plates with pre-cracks were retrofitted with Fe-SMA strips. The SMA-strengthened specimens along with a reference unstrengthened specimen were then subjected to high cycle fatigue (HCF) loading. The effect of multiple re-activations and different loading frequencies (e.g., fr = 0.005, 5, 10, and 15 Hz) on the HCF behavior of the Fe-SMA was investigated. The test results showed that the achieved prestressing level (i.e., recovery stress) in the Fe-SMAs for an activation temperature of 260 °C was in the range of 330–410 MPa, resulting in compressive stresses in the range of 35–72 MPa in the steel plates. Furthermore, it was observed that the recovery stress decreases slightly during cyclic loading, which should be considered in the design. The loss in the prestressing level was approximately 17–20% of the original prestressing; however, the re-activation (i.e., a second activation) process could retrieve a significant portion of the loss. The test results showed that the activated Fe-SMA strips could apply considerable compressive stresses to the cracked steel plate, which reduce the tensile stresses and stress intensity factors (SIFs) at the vicinity of the crack tip, resulting in a significant increase in the fatigue life of the specimens and a complete fatigue crack arrest in some cases.

Extending sleeve life in a borehole pipe by thermocyclic treatment

The wear resistance of cylindrical bushes in borehole pumps may be improved by thermocyclic treatment of the cast Kh12 steel blanks, including 3–4 cycles over the range 25–950°C, with 30-min holding at the elevated temperature. In that case, a relatively hard martensite layer (HRC 65) is formed at the bush’s working surface. The martensite layer is also characterized by elevated impact strength. The wear resistance of the bush may also be increased by the formation of considerable compressive stress (500 MPa) in a (5–6)-mm layer at the bush’s working surface under the influence of martensitic transformation at the end of heat treatment.

X-ray determination of the stress state of rolling-stock components

For the example of steel rolling-stock components, the X-ray determination of the surface stress is considered, with special preparation of the surface at the point of measurement. The effectiveness of this method when using a prototype portable X-ray diffraction system is demonstrated. The operating principle of that system is as follows. In the presence of mechanical stress, the diffraction angle changes, and the diffraction peak is shifted in the recorded diffraction spectrum. The diffracted X-rays recorded by the detector are converted to digital information regarding their intensity distribution, by means of an analog–digital converter, and sent to a PC. STRESSCONTROLL software is developed for computer analysis of the diffraction spectra. That software displays the diffraction spectra in graphical form, controls the operation of the diffraction system, and calculates the stress by means of a database on metals and phases. The computer analysis includes determination of the spectrum’s center of gravity. The software separates out the background, approximates the data set as a curve, and permits precise calculation of the center of gravity of the smoothed profile. The surface stress is determined for fragments of a 20GL steel solebar cut from the edge of a bearing aperture of radius R55, Before testing, the fragments are subjected to normalization or to bulk–surface quenching. The surface stress is found to be close to zero for the normalized fragment, while considerable compressive stress is observed for the quenched sample. Thus, the shape of the diffraction peak and the level of surface stress are directly related to the microstructure of the steel. In that case, the X-ray determination of the surface stress may provide information regarding the state of the surface.

Single-Crystal PMN-PT MEMS Deformable Mirrors

This paper describes microelectromechanical systems deformable mirrors (DMs) fabricated from Pb(Mg <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/3</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sub> )O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -PbTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> single crystal (PMN-PT) for use in ocular adaptive optics. The DM is a piezoelectric unimorph with 35 actuators on a 13-mm circular membrane. Each actuator inside the 8-mm pupil achieves a static stroke of over 5 μm at 10 V. Dynamic measurements prove that the DM can be operated up to a 2.27-kHz bandwidth. The large stroke with low driving voltage and high operating bandwidth confirm that the DM is a promising candidate for use as a wavefront corrector in vision science applications. The measured piezoelectric properties of the PMN-PT are in close agreement with factory specifications, demonstrating that the piezoelectric properties of single-crystal PMN-PT are not degraded by the bonding and lapping process used here. The large 13-mm-diameter 30-μm-thick membrane is produced by constructing silicon rings to protect the membrane from the considerable compressive stress present in the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer of a silicon-on-insulator wafer. In the prototype mirror, residual stress in the electrode metal results in an initial peak-to-valley surface flatness of 3.3 μm which is reduced to 0.7 μm by iterative computation of the control voltages applied to the electrodes.

Silicide formation process in ultra-thin Ni-silicide film for advanced semiconductor devices: mechanism of NiSi2 formation at low temperature

Atomic-resolution high-angle annular dark-field scanning-transmission electron microscopy and ab-initio calculations were used to reveal the reaction involved in the formation of ultra-thin Ni silicide film at 300°C. We found that a Ni-adamantane structure, in which Ni atoms occupy the tetrahedral interstitial voids of Si, forms at the initial stage of the reaction. We also found that the adamantane structure is under considerable compressive stress due to lattice-mismatch at the adamantane structure-Si interface (5.6%). Then, NiSi2 forms just beneath the Ni-adamantane structure at a much lower temperature than the NiSi2 formation temperature reported for the reaction between a Ni layer and Si substrate (800°C). Our analyses strongly suggest that the Ni-adamantane structure acts as a precursor in the formation of NiSi2.

Effects of Forming Conditions on Wrinkling in Necking of Tube End

The effects of forming conditions on wrinkling in the neck of stainless-steel tubes were investigated using experiments and three-dimensional finite element simulations. The materials used for this study were tubes designed for automotive exhaust parts. When the axial or radial forming pitch of the rollers is large, the outside of the tube is subjected to considerable compressive stress in the circumferential direction by contact with the rollers. Simultaneously, the inside of the tube is subjected to considerable tensile stress in the circumferential direction. Consequently, the tube is subjected to excessive localized forming, which causes the curvature to become uneven in the circumferential direction, thereby resulting in wrinkling. The number of contact points with the rollers was determined. Results show that the optimum forming conditions were easily determined to achieve short forming times and high dimensional accuracy.

Evaluation of isotropy in wet-mix sprayed concrete

It is well known that there are differences between the fresh mix concrete and the placed concrete sprayed using dry or wet-mix process. Because of that, the characterization of such material is carried out in cores extracted parallel to the spray direction from sample panels. However, in many applications (e.g. tunnel lining), considerable compressive stresses appear along the transversal direction. In this paper different spayed concretes are evaluated. It was observed that the values of compressive strength and modulus of elasticity were different depending on the direction of measurement. These differences are related to a preferential orientation of the coarse aggregate due to the characteristics of the casting process. Rather than applying classic empirical methods, the concrete mixes used in this study were designed according to a new proportioning method based on the difference between the composition of the fresh mix concrete and the placed concrete.

Characterization of Nano-crystalline Diamond Films Grown Under Continuous DC Bias During Plasma Enhanced Chemical Vapor Deposition

AbstractNanocrystalline diamond films have generated much interested due to their diamond-like properties and low surface roughness. Several techniques have been used to obtain a high re-nucleation rate, such as hydrogen poor or high methane concentration plasmas. In this work, the properties of nano-diamond films grown on silicon substrates using a continuous DC bias voltage during the complete duration of growth are studied. Subsequently, the layers were characterised by several morphological, structural and optical techniques. Besides a thorough investigation of the surface structure, using SEM and AFM, special attention was paid to the bulk structure of the films. The application of FTIR, XRD, multi wavelength Raman spectroscopy, TEM and EELS yielded a detailed insight in important properties such as the amount of crystallinity, the hydrogen content and grain size. Although these films are smooth, they are under a considerable compressive stress. FTIR spectroscopy points to a high hydrogen content in the films, while Raman and EELS indicate a high concentration of sp2 carbon. TEM and EELS show that these films consist of diamond nano-grains mixed with an amorphous sp2 bonded carbon, these results are consistent with the XRD and UV Raman spectroscopy data.

Study of the structure of hard graphite-like amorphous carbon films by electron diffraction

The structure of thin hard carbon films was investigated by transmission electron diffraction using a filter of inelastically scattered electrons. It was shown for the first time that in the amorphous graphite-like carbon films under considerable compressive stress the interplane distance d 002 could be shortened down to approximately 0.300 nm. Also, substantiation was given for a simple procedure for the estimation of the first coordination sphere radius in amorphous carbon films. This radius was determined from the maximum of the corresponding diffraction halo. It was shown that this procedure gave the radius of the first coordination sphere very close to its real value for graphite-like structure but did not work so well for a diamond-like structure.

Deformation-induced nonequilibrium grain-boundary phase in submicrocrystalline iron

The shapes of Mössbauer spectra of coarse-grained annealed armco iron and submicrocrystalline (SMC) iron with a grain size of 0.22 μm were compared. The SMC was made from the armco iron by pressure shear and subsequent annealing at 420 °C. We intended to separate an additional subspectrum, which appears as a result of the grain refinement. That subspectrum was attributed to grain-boundary atoms or the “grain-boundary phase” (GBP). The volume fraction of that phase was determined. On the average, the GBP interatomic spacing was suggested to be 1% larger than that of the grain phase (GP) and the presence of considerable compressive stresses in the GBP were deduced. A possible reason for the satellite subspectrum appearing after the grain refinement was that it was attributed to a sudden change in the fundamental characteristics of the solid at a certain critical value of the lattice parameter, which varies continuously in going from the geometrical boundary to the grain center.

Wall stress and strain analysis using a three-dimensional thick-wall model with fluid–structure interactions for blood flow in carotid arteries with stenoses

Wall mechanics and fluid–structure interactions play important roles in artery collapse and plaque cap rupture, which leads directly to heart attack and stroke. A three-dimensional thick-wall model with fluid–structure interactions was introduced and solved using ADINA to investigate the wall stress and strain distributions and flow properties of blood flow in carotid arteries with symmetric and asymmetric stenoses. The Navier–Stokes equations were used as the governing equations for the fluid. The tube wall was assumed to be hyperelastic, homogeneous, isotropic and incompressible. The Ogden material model was used for the tube wall. Experimental data for a silicone tube with a 78% stenosis by diameter was used to derive the stress–strain relationship for the material. Results obtained indicate that severe stenosis causes considerable compressive stress in the tube wall which may be related to plaque cap rupture. Stenosis severity and asymmetry have considerable influence on wall stress and strain distributions. Three-dimensional wall deformation, flow pressure, velocity and shear stress fields were investigated.

On the measurement of residual stress in plastic pipes

AbstractRecent work on the determination of residual stress in drawn pipes has revealed an error in previous methods used. Such pipes have residual stresses very different from those induced by melt extrusin during conventional pipe processing. In particular, it appears that there are considerable compressive stresses at the bore, and the hoop and axial values are not equal. In an attempt to measure these values, tests were performed on slit rings of varying length, and a pronounced dependence of ring overlap on length was observed. This was contrary to previous assumptions, and a corrected version of the analysis has been developed, which enables the true hoop and axial stresses to be determined by testing rings of various lengths. For isotropic pipes, it has been shown that hoop and axial stresses are roughly equal. Previous results obtained on thin pipe rings can now be corrected by multiplying by the factor 1/(1‐v). For anisotropic drawn pipes, a combination of rings and thin axial strips is used to determine the residual stresses. These pipes can show remarkably low stresses at the bore, which may play a significant part in determining their performance.

Preparation and characterization of cubic boron nitride and metal boron nitride films*

AbstractBoron nitride has generated much scientific interest due to the outstanding material properties of its cubic modification (c‐BN) which can be compared with those of diamond, and to its metal (M) boron nitride compounds (MBN) which have extraordinary mechanical properties such as high hardness and high elasticity. This paper compares and discusses both of these thin film materials, concentrating in particular on their preparation and their mechanical properties in view of future applications as wear‐resistant coatings.There is a strong indication that the mechanism of c‐BN film formation by commonly used physical vapour deposition (PVD) methods is based on recoil implantation of surface atoms into deeper layers. This process creates considerable compressive stress compromising the production of technologically valuable coatings of c‐BN composition. On the other hand BN‐based transition metal films can be made as hard as or even harder than c‐BN films if suitable preparation methods are applied which promote nanometric grain sizes and a mixed phase composition. This paper discusses: (1) Ti implantation into hexagonal BN layers; and (2) co‐sputter deposition from a Ti and Hf target, respectively, and from a BN target; and (3) Ti/BN multilayer interdiffusion. MBN films show good adhesion to metallic substrates such as HSS steels, and preliminary wear tests with a pin‐on‐disk tribometer indicate promising characteristics.Bonding and chemical composition of the films were investigated by electron spectroscopy for chemical analysis (ESCA)‐Auger spectroscopy, the structure and crystallite size by glancing angle x‐ray diffractometry, and the hardness and elasticity by the nanoindentation technique.

Three-dimensional finite element stress analysis of a cantilever fixed partial denture

A three-dimensional mathematical model was generated, representing a three-unit cantilever fixed partial denture and its supporting mandibular structures. First and second premolars were used as abutments with one posterior cantilever pontic. A 5 lb vertical load was applied to the pontic. Vertical and horizontal stresses were analyzed by means of a three-dimensional finite element stress analysis technique. The results showed that a cantilever pontic creates considerable compressive stress on the abutment nearest to the pontic and produces tensile stress on the abutment farthest from the pontic.

Ultrahard coatings from Ti-BN multilayers and by co-sputtering

Two new techniques for the preparation of very hard Ti-B-N coatings are presented. The first method is accomplished in two steps: (i) the deposition of a multilayer coating of the sequence Ti-BN by reactive or non-reactive sputtering from a titanium and a hexagonal BN target respectively; (ii) a subsequent thermal treatment of the multilayer to induce a diffusion-activated mixing process between the titanium and BN layers with consequent phase transformations. The coatings were characterized with respect to stoichiometry by X-ray photoelectron spectroscopy with respect to structure by glancing angle X-ray diffractometry and with respect to hardness and residual stress by micro-indentation and the substrate-bending method respectively. Hardness values up to 6000 HV were observed at a concentration ratio [ Ti]:[ B]:[ N] = 1:0.5:0.4. The coting with this compositional ratio is assumed to comprise a mixture of two solid solutions of the type Ti(B x ,N x ) and TiN 1-x (B y . Thsi new technique has the advantage that almost stress-free coatings with good adhesion to metallic and non-metallic substrates are obtained. The second method is a co-sputtering process from a titanium and BN target. With this method coatings of considerable compressive stress are obtained.

Effect of Overburden Pressure and Water Saturation on Gas Permeability of Tight Sandstone Cores

Research conducted to determine the potential of nuclear explosions to stimulate gas production verifies that the gas permeability of tight sandstone cores is markedly decreased with increasing overburden pressure. Water saturation also reduces the gas permeability by a pressure. Water saturation also reduces the gas permeability by a large amount. The relative permeability, however, does not change significantly with overburden pressure. Introduction Research on the potential of nuclear explosions to stimulate gas production from low-permeability (tight) sandstone reservoirs is being conducted by the U. S. Bureau of Mines in cooperation with the Atomic Energy Commission. This report describes the part of that research that was conducted to establish part of that research that was conducted to establish correlation between permeability measured on dry cores at low external pressure (routine analysis) and permeability at reservoir conditions. Cores used in this research were obtained from two Plowshare gas-stimulation projects. Project Gasbuggy Plowshare gas-stimulation projects. Project Gasbuggy cores from the Pictured Cliffs formation, Choza Mesa field, Rio Arriba County, N. M., can be described as very fine grained, slightly calcareous, well indurated sandstone. Project Wagon Wheel cores from the Fort Union formation, Pinedale field, Sublette County, Wyo., can be described as very fine grained, slightly calcareous, very well indurated sandstone. Underground reservoirs are under considerable compressive stress as a result of the weight of overlying rocks (offset somewhat by internal-fluid pressure). The resultant net confining pressure or pressure). The resultant net confining pressure or effective overburden pressure is referred to in this report simply as overburden pressure. The resulting effects on the physical properties of the reservoir rock have been studied. Overburden pressure causes only a small decrease in porosity, which can usually be ignored. This was confirmed for Project Gasbuggy and Project Wagon Wheel cores. A commercial laboratory found that the porosity of these cores is reduced by about 5 percent of the original porosity. The effect of overburden pressure on permeability, however, is appreciable and varies considerably for different reservoir rocks, causing greater reductions in permeability for low-permeability rocks. The effect permeability for low-permeability rocks. The effect of overburden pressure on relative permeability has been found to be small or nonexistent. This report presents material that confirms and extends previous research findings on the effect that overburden pressure has upon the permeability of dry cores. Also presented are the results of research on the relative gas permeability of low-permeability cores under overburden pressure. Apparatus and Procedure Cylindrical cores 2.0 to 7.5 cm long and 2.5 cm in diameter were cut parallel to the bedding plane. After the cores were dried overnight in a vacuum oven (4.5 psia, 70C), the gas (N2) permeability of each core psia, 70C), the gas (N2) permeability of each core was measured in a Hassler cell. An external pressure of 100 psi over the inlet pressure was used to maintain a good seal between the rubber sleeve and the core. Permeability was measured at inlet pressures of 45, Permeability was measured at inlet pressures of 45, 60, and 100 psia, with atmospheric pressure at the outlet. A bubble tube and timer were used to measure gas flow rate. Initial permeability (ki) then was calculated by the Klinkenberg technique to correct for the effect of gas slippage. All other permeabilities reported here were calculated by this permeabilities reported here were calculated by this method.