External Compressive Stress Research Articles

Effect of the parameters of the biaxial field of rock pressure on the shape of the fracture zone formed by an explosion of a cylindrical charge in a brittle medium

The effect of the biaxial field of external rock pressure on the deformation of the fracture zone formed by radial cracks in an elastic-brittle medium is studied. We consider cylindrical charges that are rather thin compared to the diameter of the explosive borehole. This allows one to exclude the grinding zone from consideration. At the initial moment of time, the system of emerging cracks originating at the boundary of the circular hole is assumed to be symmetric. To solve the problem, we use singular integral equations and the fracture criterion σϑ. The propagation trajectories of the system cracks are calculated in the quasistatic approximation in a step-by-step manner in relation to the parameters of the external compressive stress field. Two ideal variants of loading of the crack system are analyzed. In the first variant, gaseous detonation products penetrate into cracks, and the pressure in the explosion cavity and the cracks instantaneously equalizes. In the second variant, gases do not penetrate into the cracks of the system. The fracture zone is shown to become an ellipse whose long axis is oriented in the direction of the largest compressive stress in magnitude acting at infinity. The effect of the variants of loading of the crack system on the shape and dimensions of the deformed fracture zone is evaluated.

Influence of bending stresses on the magnetization process in Fe-rich amorphous wires (abstract)

We report a systematic investigation of the domain structure as well as the magnetization reversal in bent Fe-rich amorphous wires. The samples consisting of the composition Fe77.5Si7.5B15 were prepared by the water quenching technique leading to bistable magnetic behavior (square hysteresis loops) above a critical sample length of 60 mm. The outstanding magnetic properties of such wires are due to their intrinsic stress distribution frozen in during the fabrication process and their high magnetostriction constant λ>10−5.1 Bending these wires provides an elegant method of introducing additional external tensile and compressive stresses in the halves of the wire exerted to convex and concave curvature, respectively. Domain structures of accurately polished bent wires were recorded by means of magneto-optical Kerr microscopy. Due to the magnetostrictive coupling the stress distribution in the samples is clearly reflected by the domain structure: In zero applied field we observe a single domain in the convex part of the wire with the magnetization being aligned parallel to the wire axis. The concave half of the sample reveals a transversal multidomain structure. Observation of the evolution of the domain structure with external circular fields applied parallel to the bent wire axis reveal the process of the magnetization reversal. We obtain two processes corresponding to the nucleation of a reversed domain in the center of the wire where the stresses are minimum, or alternatively, at the surface of the wire, where the surface of the reversed domain exhibits a minimum. Both processes can qualitatively be explained within a simple micromagnetic consideration. This theory reveals the estimate ΔE≅2–3×10−8 J/m for the first nucleation of the reversed domain.

Effect of glass addition and quenching on the relation between inductance and external compressive stress in Ni-Cu-Zn ferrite-glass composites

The stress-inductance characteristic of ferrite-glass composites has been studied with special emphasis on the effect of heat treatment and glass chemistry. The stress-inductance relation of Ni-Cu-Zn ferrite has been greatly improved by incorporating glass and by quenching from high temperature. The effect of quenching temperature on the stress-inductance characteristic is discussed in terms of the bending strength and fracture mode of the composites, and creep and microcrack formation during quenching are proposed as responsible factors.

A Splittable CS Model Coil for ITER

The purpose of the Splittable CS Model Coil is twofold: to test the different conductors proposed for ITER in relevant conditions and to check the manufacturing processes foreseen for the ITER magnets. This model coil consists of a main coil in the shape of a circular solenoid and a single-layer removable insert. An inflatable steel jacket set between the main coil and the insert and a precompression system allows the insert to be put into compression at a stress level comparable to the one projected in the ITER Central Solenoid (CS) when it is used as a central bucking post for the toroidal magnet. The experimentation performed with this CS Model Coil will assess the dependence of the critical current on the imposed external compressive or tensile stress. >

Structural control of nonequilibrium WSi2.6 thin films by external stress

The influence of external stresses on a crystallization and a precipitation process for amorphous WSi2.6 films has been studied. An as-deposited amorphous WSi2.6 has crystallized as a hexagonal WSi2 by annealing at 400 °C for 1 h, and excess Si has precipitated to the WSi2/substrate interface. To verify whether the driving force of the precipitation to the interface is a stress relaxation, calculations of the volume change by a crystallization, precipitations (in the film and to the interface), and the stress measurement were performed. It was revealed that as-deposited film had a tensile stress, and it increased by precipitation of excess Si to the interface. That is, the driving force of the precipitation to the interface is not the stress relaxation. Then we tried to apply larger stress (compression and tension) to make clear an effect of stress on the structural change. By annealing at 350 °C under external tensile stress,the Si precipitated at the interface was not observed. On the other hand, by annealing under external compressive stress, a greater amount of Si has precipitated than that without external stress. These phenomena seem to be related to the stress-assisted diffusion similar to Nabarro–Herring creep.

Effects of External Stresses on the Low Temperature Thermal Oxidation of Silicon

Thermal oxidation of silicon was conducted under the application of external compressive or tensile stress at relatively low oxidation temperature. The effect of external stress appeared in different ways depending on the oxidation temperature. While the stress effect of oxidation at 800°C was well interpreted with the linear-parabolic oxidation model (L-P model), that at a temperature lower than 700°C contradicted the L-P model and strongly suggested the existence of an oxidation reaction of interstitial silicon atoms in the oxide.

External and/or Internal Stress Effects on the Optical Properties of Semiconductor Microstructures

This paper reviews the influence of homogeneous strains, external and/or internal, on the electronic and optical properties of semiconductor microstructures such as epilayers, quantum wells and super-lattices. The effects of large external compressive stress (\\vecS) on the interband (intersubband) transitions of two systems are discussed in detail: (a) \\vecS|| [100] on biaxially strained bulk GaAs and two GaAs/Ga0.79Al0.29As single quantum wells (SQWs) grown on (001) Si and (b) \\vecS|| [100] and \\vecS|| [110] (piezoelectric effect) on a (001) GaAs/Ga0.73Al0.27As SQW structure.

Effect of external compressive stress on the domain configuration of barium titanate ceramics

Abstract When the sintered BaTiO3 specimens were treated at 200°C and cooled under compressive stress, notable change in domain configuration occurred. As a result of external compressive stress applied during transformation from cubic to tetragonal, the banded domain structure has changed to a simple lamellar one and the 90° domains have aligned. The observed change in domain configuration under external stress has been explained in terms of elastic strain energy minimization.

Deformation by the Stress‐Induced Transport of Helium Bubbles in Silicon Carbide

Silicon carbide (SiC) containing He atoms expands by annealing above ∼ 1300°C, owing to the formation and growth of He bubbles. An external compressive stress applied during annealing retards expansion in the stress direction, while promoting it in the lateral directions. It is proposed that He atoms in the bubbles on grain boundaries perpendicular to the compression axis are transported to the bubbles on boundaries parallel to the stress axis. The transport of He accompanies changes in the volumes of the bubbles to maintain equal pressure in all the bubbles. The volume changes of the bubbles are caused by the flow of SiC‐constituting atoms from or to the boundaries where the volume‐changing bubbles exist. This process results in a jacking action which alters the thickness of boundary atom layers. It produces macroscopic strains. The plausibility of the proposed process is examined on the basis of energetics.

HVEMin situobservation of effects of an external compressive stress on the climb rate of interstitial loops

Abstract The rate of climb of Frank loops of the interstitial type formed in silver during electron irradiation at 130°C in the presence of an external compressive stress has been studied using a combined in situ irradiation/deformation experiment in a high-voltage electron microscope. In the presence of the external compressive stress Frank loops are elongated in the direction nearly perpendicular to the external compressive stress. The results have been compared with those obtained previously but in the presence of an external tensile stress.

Influence of transverse compressive and axial tensile stress on the superconductivity of PbMo 6S 8 and SnMo 6S 8 wires

The behaviour of the critical current density, J c, of PbMo 6S 8 and SnMo 6S 8 monofilamentary wires with external transverse compressive stress, σ t, and axial tensile stress, σ a, was investigated. Varying the reinforcing steel content in the wire matrix, different axial prestress states, e.g. the compressive, tensile and unstressed state were realized. The observed variation of J c, versus σ a was significantly smaller compared with that of Nb 3Sn wires, which is explained by the higher upper critical magnetic field, B c2, of the Chevrel phase. The elastic strain range of 0.6–0.8% (with 0.2% compressive prestrain of the filament) fulfils the requirements for future technical applications of this type of wire material. The effect of transverse applied compressive stress, σ t, on I c and B c2 ∗ of the Chevrel phase wires was investigated in magnetic fields up to B = 22 T and T = 4.2 K. Analogous to Nb 3Sn wires, a strong degradation of the critical current density with σ t was observed. As for the axial tensile stress, the influence of σ t on J c is found to increase with the applied magnetic field. At 20 T the transverse compressive stress effects reduce J c about twice as much as the axial tensile stress. At present externally steel reinforced PbMo 6S 8 wires can be compared with Nb 3Sn wires, the effect of transverse stress appears to be considerably smaller in the Chevrel phase wire, possibly as a consequence of the higher upper critical field with respect to Nb 3Sn.

Electro-optical effects of externally applied 〈100〉 uniaxial stress on InGaAsP 1.3 and 1.5 μm injection lasers

The changes in the polarization of the emission, spectrum, and light-current (L-I) behavior of a 1.3 and 1.5 μm InGaAsP channeled substrate buried heterostructure laser and double-channel planar buried heterostructure laser under an external uniaxial compressive stress perpendicular to the junction were studied at room temperature. It was found that the TM emission (electric vector perpendicular to the junction) reached threshold even at a stress level of ∼1×108 dyn cm−2. For stress ≤4×108 dyn cm−2, the TM emission, although reaching threshold first, was found to exist only over a limited range of currents. At high currents only TE emission (electric vector parallel to the junction) was observed. The appearance of the TE emission gave rise to nonlinear L-I characteristics. When both TM and TE emissions were seen, the former occurred at a higher energy. The limited stability of TM emission with current at low stresses is explained by invoking spectral hole burning effects which reduce the gain saturation power for TM mode than the TE mode. At high stresses ≥4×108 dyn cm−2, the increased gain for TM-polarized light ensures its stability at all currents. From our results it can be concluded that to avoid TM emission, and the associated spectral changes and nonlinear L-I characteristics, the tensile stress in the plane of the active layer should be less than 108 dyn cm−2.

The isotype Al 0.05Ga 0.95As/Al 0.35Ga 0.65As interface of the LPE-grown double heterostructure at elevated temperature

The isotype interface of a double heterostructure is studied by measuring the capacitance-voltage characteristic ( C/ V technique). For the LPE-grown Al 0.05Ga 0.95As/Al 0.35Ga 0.65As system it is shown that the effective barrier height of the p-type heteroboundary can be estimated even in the range below 25 meV by recording the C/ V characteristic at lower than room temperature. Experimental evidence is given for the first time that the effective barrier height at the isotope p/ P interface of the NpP-type heterostructure may be raised after treatment at elevated temperature. This reaction at the heteroboundary depends on the mechanical stress additionally introduced by the solder. The gradual increase in light output often observed in AlGaAs double heterostructure diodes during operation at elevated temperature can be well approximated by a step-like function of the operation time and a characteristic delay time. The process is mainly thermally controlled with an activation energy of about 0.53 eV. A correspondence is found between the microscopic process at the p/ P interface and the gradual increase in light output. Therefore, it is suggested that the reaction at the isotype interface of LPE-grown AlGaAs heterojunctions is at least partly the origin of the increase in light output during operation at elevated temperature. Both phenomena are not dependent on the operation current and are more effective at low external compressive stress.

Raman study on the variation of the silicon network of a-Si:H

The silicon network of the ‘‘device-quality’’ hydrogenated amorphous silicon (a-Si:H) fabricated by a glow-discharge method has been studied by means of Raman spectroscopy, infrared spectroscopy, and mechanical stress measurements. Attention has been focused on the variation of the network structure induced by the change in fabrication conditions. An increase in the substrate temperature results in a shift of the TO peak in the Raman spectra toward a high wave number, an increase in the compressive mechanical stress, and a decrease in the hydrogen content in a-Si:H. It is found that the hydrogen content of the monohydride configuration (CHm) has a positive correlation with the compressive stress in a-Si:H, and the hydrogen content of the dihydride configuration (CHd) has the opposite correlation. It is also found that the position of the TO peak (ωTO) shifts toward a low wave number as the CHm increases, and that the ωTO shifts toward a high wave number when an external compressive stress is applied to a-Si:H. The experimental results suggest that the shift of the TO peak in the Raman spectra originates from the change in the force constant of Si–Si bonds induced by hydrogen atoms of a monohydride configuration in the silicon network. Variations of the silicon network caused by the change in substrate materials are also discussed.

Theoretical analysis of dry friction in brittle and ductile materials

An analysis is proposed to study the mechanical fracture of the microscopic junctions which cause friction and wear in materials. The analysis applies the Griffith energy balance concept and the Rice line integral J to a junction model which is fractured when two opposite cracks advance under an external compressive and shear stress (mode I and mode II fracture). It is found from the model that the friction coefficient is proportional to γ p / Hd, where γ p is the fracture surface energy, H is the hardness of the material and d is the average junction size. For highly brittle materials the predicted junction size is about 10 −9m, suggesting that the heat generated during friction must be due to the direct stimulation of surface atoms into random thermal vibration by the sudden release of elastic energy stored in a junction of molecular dimensions. In the case of ductile materials the predicted junction sizes are of the order of 10 −4–10 −5m, in good agreement with the wear particle diameters determined experimentally.

Elastic behaviour of shrink-fitted forming die assemblies. Part II: Numerical application and results

A study is presented on the elastic behaviour of a set of assemblies consisting of a cylinder prestressed by a shrink-fitted ring of different length as is customary in extrusion toolsets. An accurate analysis is carried out of the individual and interactive effects pertaining both to the bulk support provided by the relatively unstressed parts of the die, and the external compressive stresses induced by radial support of the shrinking ring.

Deformation mechanism for a steel matrix close to inclusions under compression

1. Nonmetallic inclusions promote strain localization under compression, and their effect depends on temperature which governs matrix and inclusion ductility. Near rigid inclusions marked strain microinhomogeneity develops (at a maximum near the 0° pole, and a minimum near the 90° pole in relation to the external compressive stress), promoting formation of microfailure in inclusions. 2. Ductile inclusions control development of strain for the matrix of low-carbon steels, which due to high ductility is adapted to inclusion deformation. The level of inhomogeneity for strain development near ductile inclusions is less than that near rigid inclusions. Cavities forming during melting of sulfide inclusions promote development of significant strains, however, their distribution is different from near rigid inclusions.

The effect of stress on the temperature dependence of ultrasonic velocity

The effects of applied elastic stress on the temperature dependence of ultrasonic velocity has been investigated in commercial aluminum and copper. Velocities of 10-MHz longitudinal and shear waves as a function of temperature were measured when specimens of these metals were subjected to external compressive stresses applied in a plane perpendicular to the direction of propagation. In all measurements, the velocity increased linearly as the temperature was lowered in the range between 280 and 200 K. The slopes of the linear relationships of the longitudinal velocities were found to decrease linearly as the amount of stress was increased within the elastic limit of the specimen. The maximum decrease in the temperature dependences of the longitudinal velocities of aluminum and copper were, respectively, 23 and 6%. These occurred at applied stresses of 96 and 180 MPa. The temperature dependence of the shear velocity in aluminum, however, remained unchanged with the application of stress.

アルミニウム切削面の残留応力に及ばす切削条件の影響について

It is important to measure the value and distribution of residual stress for clarify its actual condition in the vicinity of the cutting surface, because the residual stress produced in the vicinity of a cutting surface is detrimental to precision manufacturing as it causes strain in the material to be cut and promotes corrosion. In this paper, the authors have conducted orthogonal dry cutting of commercial pure aluminium plates and examined the effects of cutting conditions on the distribution of the residual stress in the vicinity of a cutting surface. Residual stress is measured mainly by a mechanical method. However, as for the measurement of stress in the external surface by X-ray diffraction is also conducted in order to obtain a higher degree of accuracy. The results can be summarized as follows:The residual stress distribution, in most cases shows tensile stress in the external surface and compressive stress in the interior. A similar tendency can be found in the case of cutting iron and steel materials. The effects of cutting conditions on the residual stress distribution are comparatively simple and systematic, the residual stress being proportional to the cutting speed and the rake angle. On the other hand, the effects of depth of cut are rather complex. Stress in the external surface is rather independant of depth of cut, while the maximum tensile stress in the interior is conversely proportional to it.

Analytical method of evaluating deformational properties of rock

1. The deformation modulus of joint-zone portions is several hundred times less than the deformation modulus of the monolithic rock, and rises as a consequence of the increase in the actual contact area with increase in the compressive stresses; tending, in the limit, to reach the deformation modulus of the monolithic rock. 2. The deformation modulus of a jointed rock massif is a variable characteristic which depends on the natural and external compressive stresses acting. The magnitude of the deformation modulus of the massif depends on the jointing characteristics, expressed by joint frequency and gap opening, and the microtopography of the walls, and also on the deformational properties of the monolithic rock in its fresh and weathered conditions. 3. Analytical computations of deformation moduli for specific conditions in the foundations of hydraulic structures have demonstrated their satisfactory agreement with the results of field determinations of deformation moduli by methods which employ static-load plate tests. 4. The analytical method of assessing deformational properties of rock massifs can be used to obtain deformation-modulus values for computations in the preliminary stages of design, for distribution of the field-investigation results obtained from experiment areas, to regions of the rock massif, for adjusting deformation-modulus values, according to recorded data on joints, in constructional foundation pits, with the aid of nomograms, and also in the preparation of geomechanical mock-ups, in connection with model investigations of rock foundations and abutment slopes of dams.