Decrease In Compressive Stress Research Articles

Twyman effect mechanics in grinding and microgrinding

In the Twyman effect (1905), when one side of a thin plate with both sides polished is ground, the plate bends: The ground side becomes convex and is in a state of compressive residual stress, described in terms of force per unit length (Newtons per meter) induced by grinding, the stress (Newtons per square meter) induced by grinding, and the depth of the compressive layer (micrometers). We describe and correlate experiments on optical glasses from the literature in conditions of loose abrasive grinding (lapping at fixed nominal pressure, with abrasives 4-400 μm in size) and deterministic microgrinding experiments (at a fixed infeed rate) conducted at the Center for Optics Manufacturing with bound diamond abrasive tools (with a diamond size of 3-40 μm, embedded in metallic bond) and loose abrasive microgrinding (abrasives of less than 3 μm in size). In brittle grinding conditions, the grinding force and the depth of the compressive layer correlate well with glass mechanical properties describing the fracture process, such as indentation crack size. The maximum surface residual compressive stress decreases, and the depth of the compressive layer increases with increasing abrasive size. In lapping conditions the depth of the abrasive grain penetration into the glass surface scales with the surface roughness, and both are determined primarily by glass hardness and secondarily by Young's modulus for various abrasive sizes and coolants. In the limit of small abrasive size (ductile-mode grinding), the maximum surface compressive stress achieved is near the yield stress of the glass, in agreement with finite-element simulations of indentation in elastic-plastic solids.

Control of film properties during filtered arc deposition

Titanium nitride films may be deposited by filtered arc deposition (FAD) onto heated substrates or by ion assisted arc deposition (IAAD) onto unheated substrates. The stress and microhardness of the deposited films are strongly dependent upon the bias applied to the substrate in FAD. In the case of FAD onto substrates heated to 400 °C, an increasingly negative substrate bias results in a decrease in film compressive stress from 10 to 2 GPa. In the case of nitrogen IAAD onto ambient temperature substrates, the film properties are influenced by the nature of the assisting ion beam, specifically the energy and the relative arrival ratio. The stress ranges from 1 to 7 GPa and the hardness from 26 to 38 GPa. Pronounced effects are also observed in the development of preferred orientation. When the assisting N ion energy is increased from 500 to 1200 eV the orientation changes from (111) to (220). The stress evolution of the arc deposited films may be qualitatively understood in terms of the generalised model for momentum transfer, modified to account for the increased energy of the condensing particles generated by the arc process.

Draw pH and Storage Affect Rheological Properties of Mozzarella Cheese

ABSTRACTCheeses with whey pH at draw of 6.15 or 6.40 were stored at 4°for 50 days. Compression test at 10°(Instron) showed a decrease in compressive stress with storage. Failure points were near a true strain value of 0.5 for the cheeses at day 3. The failure region became less obvious by day 50. The hypothetical equilibrium stress (HES) in the stress‐relaxation test was higher with a draw pH of 6.40 than 6.15, possibly indicating that higher calcium led to a stronger network structure. The HES decreased with storage, suggesting cleavage of structural crosslinks caused by the coagulant.

Stress in Giant Magnetoresistive Ni66Fe16Co18/Ag Multilayer thin Films

AbstractThin film stress has been measured in (Ni66Fe16Co18 25 Å/Ag 50 Å) multilayer thin films that exhibit annealing-induced giant magnetoresistance (GMR) known as ‘discontinuous’ GMR1. This GMR results when NiFeCo layers are broken up into discontinuous ferromagnetic islands or platelets by immiscible Ag atom grain boundary diffusion normal to the film plane. As-deposited films display no GMR and are in compression. An MR value of 5 % with a relatively sharp profile can be induced in a ten bilayer sample annealed at 400°C for 15 min. Annealing generally results in a decrease in the as-deposited compressive stress and can result in tensile stress at high enough temperatures. Interestingly, at the annealing temperatures corresponding to the maximum induced GMR, there is a plateau in the otherwise monotonic decrease in compressive stress with increasing temperature.Stress-temperature plots reveal a plateau in the stress value during the heating of a ten bilayer sample due to plastic deformation in the film via densification. Isothermal stress-time plots done on a single sample show increasing compressive stress relief after each successively higher temperature anneal. The stress was also measured in a single bilayer film with the same volume of film as in a ten bilayer sample but far fewer interfaces. High and low angle x-ray diffraction (HXRD, LXRD) was used to reveal the structural evolution with annealing. Magnetic (M-H) hysteresis measurements revealed increasing coercivity and decreasing induced as-deposited in-plane magnetic uniaxial anisotropy with annealing temperature.

Changes in State of Stress on the Southern San Andreas Fault Resulting from the California Earthquake Sequence of April to June 1992

The April to June 1992 Landers earthquake sequence in southern California modified the state of stress along nearby segments of the San Andreas fault, causing a 50-kilometer segment of the fault to move significantly closer to failure where it passes through a compressional bend near San Gorgonio Pass. The decrease in compressive normal stress may also have reduced fluid pressures along that fault segment. As pressures are reequilibrated by diffusion, that fault segment should move closer to failure with time. That fault segment and another to the southeast probably have not ruptured in a great earthquake in about 300 years.

The influence of surface finish and strain hardening on near-surface residual stress and the friction and wear behavior of A2, D2 and CPM-10V tool steels

The effect of surface finishing method on near-surface residual stress, relative cold work and sliding friction and wear behavior of commercially available air hardening A2, D2, and CPM-10V tool steels was investigated. Microstructural characterization was accomplished using X-ray diffraction and scanning electron and optical microscopy combined with macrohardness measurements. The wear tests were performed using low load-slow speed reciprocating sliding conditions with tool steel flats in unlubricated contact with a 52100 steel spherical slider. The coefficient of friction and mass loss were measured during the course of wear testing and residual stress measurements were made before and after wear testing. Surface grinding and polishing conditions had a significant effect on surface residual stress but had little effect on tool flat sliding wear rates. Residual stress measurements performed after wear testing showed a decrease in compressive residual stresses as wear rate increased. Tool steel wear rates were a linear function of sliding distance except for the initial run-in period. The low wear rates, the run-in friction behavior, and the constancy of near-surface mechanical properties indicate that during run-in surface finish was wear rate controlling and that sample microstructure and composition controlled long-term sliding friction and wear behavior. The low wear rates and the post wear residual stress measurements also indicate that oxidative wear was the primary mechanism responsible for tool flat material attrition. CPM-10V steel flats exhibited the lowest coefficient of friction and the highest resistance to wear which can be attributed to the high volume fraction and homogeneity of V-Cr-C carbides.

A quantitative interpretation on possible correlations between intraplate seismic activity and interplate great earthquakes along the Nankai trough

The Tonankai earthquake occurred in 1944 along the Nankai trough between the continental Eurasian plate and the subducting Philippine Sea plate. We investigated spatial and temporal correlations between the occurrence of this event and intraplate seismic activities in the inland region of southwest Japan. In order to elucidate the possible relationship and dynamic coupling between the 1944 Tonankai and the 1946 Nankaido earthquakes, we calculated stress changes due to the Tonankai earthquake by applying a three-dimensional finite element method and compared them with post-seismic activity. Agreement between them appears quite well at a depth of ∼ 10 km, indicating that stress release in an E-W direction associated with the Tonankai earthquake may have reduced the seismic activity in the inland region. Particularly, the observed drastic decrease of seismicity in the Wakayama region just after this event can be explained by significant decrease of compressive stresses in the E-W direction. Extensive seismicity quiescence preceding the 1946 Nankaido earthquake, which occurred adjacent to the source region of the Tonankai event, may be related to the enhancement of N-S oriented compressive stress due to accelerating northward movement of the Philippine Sea plate. Therefore, in addition to the decrease of stresses in the E-W direction, the increase of the N-S oriented compressive stresses might play an important role to yield low seismic activity just after the Tonankai event. The calculated results show that the post-seismic shear stress increased and the normal stress decreased near the hypocentral area of the 1946 Nankaido earthquakes, while the shear stress decreased and normal stress increased in its surrounding area on the fault. This indicates that the Tonankai earthquake made it easier for the rupture of the Nankaido earthquake to originate at the observed hypocenter. This triggering mechanism may explain the synchronous pattern of historical great interplate earthquakes along the Nankai trough; a great earthquake occurs in the western region within a few years after the first breakage in the eastern block.

Mechanical stresses in low pressure chemically vapour deposited silicon films

Stresses vs. deposition temperature and annealing time have been studied in silicon films 0.15 and 0.30 μm thick. The films were deposited onto oxidized silicon wafers by low pressure chemical vapour deposition from a gas mixture containing 5% SiH 4 and 95% Ar in a horizontal-type reactor at temperatures of 793–853 K. The films were annealed during 0.25–1.0 h flowing argon at 1223 K. Stresses have been found to increase from about 300 to about 500 MPa as the deposition temperature increases from 833 to 853 K. This is due to oxidation of film crystallites during deposition and a change in the condensation mechanism with temperature. The validity of a model allowing for crystallization of the amorphous phase during deposition has been confirmed by X-ray diffraction, reflection high energy electron diffraction and scanning electron microscopy. It is shown that a decrease in compressive stresses in the films containing a considerable fraction of amorphous phase is caused by crystallization and dynamic recrystallization of the films owing to annealing. A general equation has been derived which describes changes in the film elastic energy during crystallization taking into account plastic deformation. By using the deformation mechanism map it is shown that the stress reduction during annealing of polycrystalline films is caused by low temperature dislocation (power law) creep.

Stress control in reactively sputtered AlN and TiN films

Al and Ti planar magnetron targets have been sputtered in Ar/N2 mixtures to deposit AlN and TiN films on unheated substrates; rf and dc discharges were used for the AlN and TiN deposition, respectively. The N2 flow was always sufficient to produce a nitrided target layer and x-ray diffraction showed single-phase films of AlN and TiN1.2. In N2 discharges, the AlN film stress varied from −19 GPa (compressive) to +2.5 GPa (tensile) as the pressure increased from 0.2 to 5 Pa. Intrinsic tensile stress in reactively sputtered compound films has not previously been reported. A similar change was observed in the stress of TiN films. Zero-stress AlN and TiN films were obtained at ∼1 Pa for the sputtering conditions used. The rapid decrease in compressive stress with increasing pressure is associated with a rapid decrease in both target voltage (for constant applied power) and deposition rate. Calorimetry measurements of the power flux at the substrates show an increase with pressure. With increasing Ar content, at a constant pressure, the compressive stress decreases although the target voltage and deposition rate increase; the substrate power flux decreases. The surface coverage of N on the targets increases with increasing N2 pressure because the N+2 flux increases. The compressive stress is probably due to bombardment of the film by neutral N atoms reflected with high energy from the targets. The decrease in deposition rates and increase in substrate power density may result from increased sputtering rates of N atoms from the target with a consequent decrease in metal atom sputtering.

Stress-strain state of the Sayano-Shushenskoe dam during filling of the reservoir

1. The results of monitoring by means of long-term on-site observations and inspections indicate the satisfactory state of the gravity-arch dam during its construction and simultaneous staged filling of the reservoir. The change in the main parameters (deformations, stresses, seepage heads and discharges) characterizing the static behavior of the structure is occurring in conformity with the changes in the hydrostatic load, temperature effects, and concreting, and grouting the joints of the dam. 2. Staged construction and loading of the dam substantially affect its stress-strain state. Construction of the dam in an incomplete profile (the long absence of the fourth columns, toothing on the downstream face, zones of unsealed concrete) under conditions of a constantly increasing hydrostatic load leads to a redistribution of arch and cantilever stresses, to a decrease of compressive stresses in the fourth columns, and to an increase in the third. The actual values of the arch stresses in the first column of the dam at an elevation of the upper pool level close to 500 m are commensurate with the calculated at the normal pool level. This is explained by the fact that owing to the toothings existing on the downstream face the arch on the second columns is not closed. A considerable role in the construction and construction-operating periods is played by the temperature and moisture factors, increasing the compressive stresses on the upstream face compared with the design. As a result, the upstream face of the dam in past stages of filling was compressed practically over the entire height [4]. 3. The “curtain-drainage” cutoff system provides an effective reduction of head on the upstream face of the foundation. Zones of an excess head were not found within the main part of the underground contour of the dam. The discharges of the drain devices do not exceed the design assumptions.

有向性加工層の残留応力に関する研究 フライス加工層における切れ刃作用密度の効果

The feed per tooth fz for slab-milling was varied to observe effects of the density dz (=1/fz) of cutting edges acting on machined surface in unit length. As the dz is increased, macroscopic residual stresses σxv and σyv translate into a compressive stress and microscopic residual shear stress τzxw decreases. Decreasing dz results in growing fiber texture in a machined layer and the principal slip planes α·Fe {110} in medium carbon steel concentrate along a direction inclined to the machined surface. The microscopic τzxw is generated by the slip on the planes. The effects of dz, on τzxw for up-milling are stronger than for down-milling. The effects of dz appears also in a carbide phase in high speed steel.

Ｓ３５Ｃ鋼はめあい軸の疲労強度に及ぼすロール加工圧力の影響

By using the specimens of press-fitted part of axles which were cold surface-rolled under various rolling pressures, the relations among its mechanical properties, surface residual stress and fatigue strength, and the change in surface residual stress during the process of fatigue have been studied.The results obtained are as follows.(1) The fatigue strength increased linearly with the increase in rolling pressure. For the specimen of mean Hertz pressure 2.83×103MPa, the fatigue strength was 277MPa and its increasing rate relative to that of the normalized specimen was 216%.(2) The fatigue strength increased as the work-hardening volume and surface compressive residual stress increased, and linear correlations existed between the fatigue strength and these quantities.(3) The surface compressive residual stress decreased with stress cycle. It decreased linearly to the logarithm of number of stress cycles at the outside of the fitted part, and decreased curvilinearly at the inside of the fitted part. The decreasing rate at the inside of the fitted part was over two times faster than that at the outside. As cyclic stress increased, the decrease of surface compressive residual stress became more notable.

Compressibility and constitutive equation of arterial wall in radial compression experiments

A large number of papers treat the tensile properties of arterial wall, but few treat compressive properties. Almost everybody assumes incompressibility; few have measured the vessel wall fluid extrusion due to compressive loading. In this work, uniaxial compressive force is applied directly on rabbit thoracic artery in the radial direction to study its constitutive equation under compressive stresses. The resulting stress-strain curves show that the wall material becomes increasingly stiffer at larger compressive strain, quite similar to the behavior in tension. A pseudo-strain energy function of the exponential type which has been applied successfully on the tension side is used to identify the material constants on the compression side. The material constants are identified in two ways: with and without the assumption of incompressibility. To determine the compressibility of the wall, the fluid extrusion accompanying this type of loading is measured. and is found to be in the range of 0.50–1.26% of the undeformed tissue volume per 10 kPa compressive stress loading in the radial direction. At compressive stresses higher than 30 kPa, the percentage of fluid extrusion per unit compressive stress decreases. At this degree of fluid extrusion the tissue is only slightly compressible (or nearly incompressible). However, the use of incompressibility assumption in the stress-strain relationship results in a set of material constants which is very different from that derived without that assumption.

すみ肉溶接継手の止端の研削及びワイヤピーニングによる疲れ強さ向上(第2報)

Various mechanical methods of improving the fatigue strength were investigated by testing the base plate and cruciform fillet welded joint specimens of 40 kg/mm2-80 kg/mm2 class steels. The results obtained are summarized as follows:1) If a peening condition is suitable to a material, the compressive residual stress induced by peening increases as a yield strength increases. As the ratio of applied cyclic stress range to absolute value of the compressive residual stress decreases, the waste of compressive residual stress by applied cyclic stress decreases and the effect of improving a fatigue life (strength) increases. Therefore, the peening effect can increase with incresaing the yield strength of material.2) It is possible to consider that a suitable condition of peening is to add the compressive residual stress as large as a yield strength of the material used, and that ari over peening ravages a surface, and may rather result in a reverse effect.3) As a result of increasing the yield strength of a weld toe and inducing. the compressive residual stress to a weld toe, by peening., a root failure occurs sometimes in the case of non-load-carrying type cruciform, fillet welded joint similarly in thee case of load-carrying type fillet welded double tee joint. Therefore, it is necessary to consider the critical leg length according to a treating condition of a weld toe, in a joint design.

Microstructural study of hot-deformed cemented carbides

Abstract The microstructure of cemented transition-metal carbides has been characterized in both the as-sintered condition and after uniaxial plastic compression at temperatures of 1100 and 1400°C. Both the dislocation structure and the dislocation density were non-uniform within the same sample for all compositions and conditions investigated. These findings are attributed to the large but localized internal stresses developed during liquid-phase sintering and to localized differential thermal contraction on cooling from liquid-phase sintering. Later evidence suggested the presence of a thin film of Go at two-grain interfaces, although it could not be detected by X-ray microchemical analysis because of limited spatial resolution. The likely mechanism of high-temperature deformation is grain-boundary sliding. WC grain shapes were significantly less sharp and angular for samples compressed at 1400°C then for those compressed at 1100°C. It is suggested that this rounding of WC grains occurred as a consequence of a solution and reprecipitation process, which also may have resulted in a larger effective load-supporting cross-sectional area between adjacent WC networks, leading to the previously reported levelling (rather than sharp decrease) of compressive yield stress with respect to temperature as the temperature exceeds the binder liquidus.