Apparent Compressive Stress Research Articles

Relationship between crystal growth mode, preferred orientation and magnetostriction of (Tb 0.3Dy 0.7)Fe 1.95 alloys

The relationship between crystal growth mode, preferred orientation and magnetostrictive properties of (Tb 0.3Dy 0.7)Fe 1.95 alloys was investigated at different directional solidification rates. The results showed that preferred orientation had a strong influence on the characteristics of (Tb 0.3Dy 0.7)Fe 1.95 alloys. At lower solidification rates, the sample with <110> preferred orientation showed larger low-field magnetostriction and apparent compressive stress effect. The excessive solidification rate resulted in failure of preferred orientation and a poor magnetostrictive performance. With an increase in solidification rates, the crystal growth modes changed gradually from cellular and primary dendrite morphology to developed dendritic morphology. In addition, domain configurations were observed using magnetic force microscopy, and the change of magnetostrictive properties was interpreted in terms of revealing the domain configurations.

Apparent stress–strain relationships in experimental equipment where magnetorheological fluids operate under compression mode

This paper presents an experimental investigation of two different magnetorheological (MR) fluids, namely, water-based and hydrocarbon-based MR fluids in compression mode under various applied currents. Finite element method magnetics was used to predict the magnetic field distribution inside the MR fluids generated by a coil. A test rig was constructed where the MR fluid was sandwiched between two flat surfaces. During the compression, the upper surface was moved towards the lower surface in a vertical direction. Stress–strain relationships were obtained for arrangements of equipment where each type of fluid was involved, using compression test equipment. The apparent compressive stress was found to be increased with the increase in magnetic field strength. In addition, the apparent compressive stress of the water-based MR fluid showed a response to the compressive strain of greater magnitude. However, during the compression process, the hydrocarbon-based MR fluid appeared to show a unique behaviour where an abrupt pressure drop was discovered in a region where the apparent compressive stress would be expected to increase steadily. The conclusion is drawn that the apparent compressive stress of MR fluids is influenced strongly by the nature of the carrier fluid and by the magnitude of the applied current.

Effect of Directional Solidification Rate on Preferred Orientation, Microstructure and Magnetostriction of (Tb0.3Dy0.7)Fe1.95 Alloys

The effect of solidification rate on the preferred orientation, microstructure and magnetostriction of (Tb0.3Dy0.7)Fe1.95 alloys was investigated using a new “one-step” process. The functional relation between the crystal growth rate and the traction velocity was determined by the analysis of heat transfer. Results demonstrate that the crystal grows synchronously with the traction velocity as the traction velocity U≤360 mm/h. When the thermal gradient GL≈100°C/cm and the solidification rate V=70 mm/h, samples with a <110> preferred orientation can be obtained. Samples with the <110> preferred orientation show a large low-field magnetostriction and an apparent compressive stress effect. With an increase in solidification rate, the crystal growth mode will transform gradually from the cellular and primary dendrite morphology into the developed dendrite morphology. Crystals growing in the cellular morphology have a <110> preferred orientation. In the primary dendrite, the preferred orientation is <113>. However, a poor magnetostrictive performance and failed preferred orientation are observed in the developed dendrite.

Characterization of chick pea (Cicer arietum L) pastes using squeezing flow viscometry

Domestic type and commercial chickpea pastes ('humus'), as well as a commercial soy substitute, were squeezed at a constant displacement rate between 150 mm parallel Teflon plates, mounted on an Instron Universal Testing Machine, before and after stirring. At 1 mm height the crosshead was stopped and the stress relaxation followed. The apparent stress at 1 mm height and that after 1 and 2 min relaxation were considered consistency measures of the pastes. They were reproducible parameters, and sensitive enough to monitor differences between the products, batches of the same product and stirred and unstirred samples. A stronger consistency was reflected not only by a high apparent compressive stress before and after relaxation but also in a higher yield stress, as determined in shear with a parallel plates sensor, suggesting that the paste's texture is determined by a solid like matrix. Stirring invariably reduced the pastes consistency presumably by an irreversible disruption of their microstructure. The presence of suspended solid particles had little or no effect on the pastes ability to retain their consistency after stirring.

Rheological characterisation of almost intact and stirred yogurt by imperfect squeezing flow viscometry

Samples of plain yogurt of two national brands, almost intact and after stirring for 1 min by hand and with a domestic blender, were placed in a wide shallow TeflonR container. They were subsequently compressed with a wide TeflonR plate to induce imperfect lubricated ‘squeezing flow’. The recorded force versus height relationships were plotted on logarithmic co-ordinates. The resulting curves all had a clear linear part indicating the region where squeezing flow was dominant. Its slope was on the order of −1.2 to −1.3 in the almost intact specimens and −0.5 to −0.9 in the stirred samples. The test reproducibility, expressed in terms of the coefficient of variation (100σ/ x) was on the order of about 15% more than sufficient to detect textural differences between the two brands and to monitor textural changes caused by stirring. These were expressed in terms of the apparent compressive stress at two preselected heights (1 and 2 mm) and the residual stress after relaxation for two preselected times (60 and 120 s). The flowability of the stirred samples was also expressed in terms of apparent elongational viscosity versus biaxial elongational strain rate relationships. All these mechanical parameters had a modest dependence on the upper plate diameter but the latter had no effect on their sensitivity as measures of yogurt consistency. © 1999 Society of Chemical Industry

Rheological characterisation of almost intact and stirred yogurt by imperfect squeezing flow viscometry

Samples of plain yogurt of two national brands, almost intact and after stirring for 1 min by hand and with a domestic blender, were placed in a wide shallow TeflonR container. They were subsequently compressed with a wide TeflonR plate to induce imperfect lubricated ‘squeezing flow’. The recorded force versus height relationships were plotted on logarithmic co-ordinates. The resulting curves all had a clear linear part indicating the region where squeezing flow was dominant. Its slope was on the order of −1.2 to −1.3 in the almost intact specimens and −0.5 to −0.9 in the stirred samples. The test reproducibility, expressed in terms of the coefficient of variation (100σ/ x) was on the order of about 15% more than sufficient to detect textural differences between the two brands and to monitor textural changes caused by stirring. These were expressed in terms of the apparent compressive stress at two preselected heights (1 and 2 mm) and the residual stress after relaxation for two preselected times (60 and 120 s). The flowability of the stirred samples was also expressed in terms of apparent elongational viscosity versus biaxial elongational strain rate relationships. All these mechanical parameters had a modest dependence on the upper plate diameter but the latter had no effect on their sensitivity as measures of yogurt consistency. © 1999 Society of Chemical Industry

Imperfect squeezing flow viscometry of mustards with suspended particulates

Samples of commercial mustard and a mustard spread all with suspended particulates were placed in a wide Teflon R container and were compressed with a wide Teflon R plate to induce imperfect ‘squeezing flow’. The recorded force vs. height relationships were plotted on logarithmic coordinates. The resulting curves had a clear linear part marking the region where squeezing flow was dominant. The slope of this linear region was on the order of −0.8 to −1.0. When the upper plate was stopped at a preset height the force decayed to a level well above that which is produced by buoyancy, indicating a yield stress of a considerable magnitude. The tests reproducibility was on the order of about 10%, more than sufficient to detect textural differences between the products and to monitor the effect of the compression rate and the upper plate diameter (or gap). The textural differences between the products were expressed in terms of apparent compressive stress at 0.5, 1 and 2 mm height and the residual apparent compressive stress after 60 and 120 s relaxation. The magnitude of all the mechanical parameters had a modest dependence on the upper plate diameter but which had no effect on their sensitivity as measures of product consistency. Increasing the compression rate from 0.1 to 0.2 mm s −1 had relatively small effect on the magnitude of the apparent stress which was probably due, atleast in part, to the considerable yield stress of these products. It was concluded that the imperfect squeezing flow viscometry is a convenient and sensitive method to evaluate the texture of mustard and mustard products whether or not they contain seed parts.

Structure and hardness enhancement of Fe/TiC multilayered films

Multilayered films composed of iron metal and TiC ceramics, have been synthesized by ion beam sputtering at room temperature. Hardness testing revealed that a maximum value of HK = 4200 kg/mm 2 was obtained for individual layer thicknesses of t Fe = 6 nm, t TiC = 8 nm. Structural investigation by X-ray diffraction showed that these multilayers were formed with sharp interfaces. Individual layer structures were found to depend on layer thickness. Apparent compressive stress in the plane of the film and (111) texture in the TiC layers are considered as an explanation for the hardness enhancement. Annealing at 400°C for 2 h under vacuum led to the decrease of HK to 1300 kg/mm 2.

In-Situ Observation of Stress in Cu/Pd Multilayers

ABSTRACTStress evolution was studied during growth of Cu/Pd multilayers using an in-situ, laserbased wafer curvature technique which allowed measurement of stress changes associated with sub-monolayer thickness increases. The apparent stress in the Cu layers changes during growth, from compressive, for thickness less than about 0.5 nm, to tensile for thicknesses above this. The stress behavior in the Pd layers depends on the thickness of the underlying Cu layer. Pd deposited on thick (2 nm) Cu layers is under an apparent compressive stress, while Pd deposited on thin (&lt; 1 nm) Cu layers is initially under a tensile stress but changes to a compressive stress at about 0.5 nm. The overall compressive stress maxima observed in multilayers at a bilayer period of 2 nm is explained by this in-situ behavior. The stress behavior in this system is consistent with either island growth of Cu, or thickness dependent alloying behavior, or both.

Microscopy investigation on fracture mechanisms in hot-isostatically pressed Si3N4/SiC-platelet composites

Fracture mechanisms in hot-isostatically pressed (HIP) Si3N4/SiC-platelet composites have been investigated by transmission electron (TEM) and scanning electron (SEM) microscopy followed by profilometric analyses. Two composites containing 25 vol% platelets were compared. They were fabricated from the same raw materials and by the same procedure except for the cooling rate from the sintering temperature. The study consists of experimental observations as well as measurements of fractographic parameters which dictates the level of toughening, such as the percentage of intergranular fracture, lengths and angles associated with the debonding process at the matrix/platelet interface. The presence of microcracking in the neighbourhood of the main crack, a higher fraction of intergranular fracture, as well as substantial debonding at the nitride/carbide interface up to high orientation angles were found in the composite cooled at low rates (∼ 100°Ch−1) which, despite the unchanged microstructure, was substantially tougher than that cooled at ∼ 650°Ch−1. These trends were not observed in the composite subjected to fast cooling. The stronger interfacial bonding found after fast cooling under high pressure was attributed to an apparent compressive stress remaining stored at the grain boundary, rather than to a weakening of the platelets or the matrix grains. Calculations based on the mechanics analysis of crack/interface interactions and on quantitative profilometric data, indicated a difference of about one order of magnitude in the apparent interface fracture energy of the two composites.