Wire Stress Research Articles

848 SMA による CFRP 製圧力容器のタガ締め効果

In order to increase the burst strength of CFRP pressure vessel, their hoop stress should be reduced under an internal pressure. This paper presents a method how to increase to burst strength of CFRP pressure vessel. The shape memory alloy (SMA) wire memorized a compressive stress is wound around the surface of CFRP pressure vessel. When the CFRP pressure vessel is received the internal pressure, its hoop stress can be reduced by the compressive stress of SMA wire and then the experimental results of increasing burst strength are obtained. Furthermore, the experimental results are compared with numerical ones in this paper.

Experimental and Analytical Studies on Stress-Strain-Temperature Relationship of TiNi Shape Memory Alloy Subjected to Cyclic Loadings.

In order to investigate the effect of loading frequency on stress-strain-temperature relationship in pseudoelastic behavior of Shape Memory Alloys (SMA), tensile tests of TiNi-SMA wire at loading frequencies ranging from 0.001 Hz to 1 Hz were performed, and the stress, strain and temperature of wire were measured simultaneously. Using our proposed thermo-mechanical analytical model of SMA, those pseudoelastic behaviors were simulated numerically as well. Results showed that the loading frequency strongly affects temperature change of the wire and the stress-strain hysteresis loop. The analytical model could predict the time history of stress-strain-temperature relationship with accuracy, and thus the validity of the model has been confirmed. Moreover, by examining the variation of each term of the heat balance equation, the thermo-mechanical mechanism of the pseudoelastic behaviors was also clarified.

410 Residual Stress in a Drawn Pearlitic Steel Wire

410 Residual Stress in a Drawn Pearlitic Steel Wire

901 形状記憶合金補強による圧力容器の耐圧強度の向上

When pressure vessels are received internal pressure, the circumferential stress should be decreased in order to increase their burst strength. This paper presents a method how to increase the burst strength of pressure vessels. In order to increase the burst strength, shape memory alloy (SMA) wire memorized a compressive stress is wound around Aluminum and CFRP pipes which can be thought as a model of the cylindrical part of pressure vessel. When these pipes are received the internal pressure, their circumferential stress can be decreased by the compressive stress of SMA wire and the experimental results for increasing burst strength are shown. Furthermore, the experimental results are compared with numerical ones.

Time-Accurate, 3-D Computation of Wire Sweep During Plastic Encapsulation of Electronic Components

A computational technique is developed for accurate prediction of wire sweep during encapsulation of electronic components by transfer molding. The technique advances the current state-of-the-art by modeling the effects of the two-phase flow involved, the effects of the polymerization of the melt, and the effects of the time-dependence of the fluid and heat flows and of the wire stresses and deformations. The computational techniques used for separately computing the fluid and heat flows, for separately computing the structural-dynamic stresses and deformations, and for establishing two-way coupling between the separately computed “flow” and “structural” solutions are described. Validations comparing the computational predictions with the corresponding analytical solutions for reference cases with straight wires immersed in flowing liquids are presented and discussed. The validation results show close agreement with theory, and demonstrate the need for using large-deformation theory for computing wire deformations and stresses. Demonstrative results for the unsteady flowfield and wire sweep in a TO-220 package are also presented and discussed.

K-0401 抵抗溶接されたTi-50.9at%Ni合金線材の形状記憶特性(S08-1 機能特性・変態)(S08 形状記憶合金の製造・加工技術と機能発現)

Since the resistance welding technique is widely applied for joining in several metals and alloys, this may be also applicable for Ti-Ni alloys. It is also known in Ni-rich Ti-Ni alloys that the shape memory and mechanical properties depend on heat-treatment through microstructural change. In this study, the resistance-welding was applied for Ti-50.9at%Ni alloy wires with 1mm in diameter. In order to clarify the effect of heat treatment, various heat treatments were performed before and after the resistance welding. Mechanical characteristics such as fracture stress and strain were investigated by tensile tests. The fatigue life was evaluated using rotary-bending fatigue tests. Microstructural observation for welded zone and heat affected zone (HAZ) was also carried out by optical microscope and transmission electron microscope (TEM). It was found that the fracture stress of some resistance-welded wires exceeded 1GPa. Optical microscope and TEM observation revealed that microstructure near welded zone was affected by heat treatment, resulting in change of mechanical properties.

Estimation of Internal Stresses in Shape Memory Wires during Thermal Cycling under Constant Load: A Macromechanical Approach

Estimation of Internal Stresses in Shape Memory Wires during Thermal Cycling under Constant Load: A Macromechanical Approach

Estimation of Internal Stresses in Shape Memory Wires during Thermal Cycling under Constant Load: A Macromechanical Approach

Untrained shape memory alloys are very sensitive to the introduction of defects associated with the accumulation of plastic strain during thermomechanical cycling. These defects are responsible for the creation of an internal stress field that plays a fundamental role on the macroscopic memory properties (superelasticity and shape memory effects). In this paper a simple physical model based on a macroscopic analysis is developed for the evaluation of the global internal stress field created in Ti-Ni based shape memory wires during thermal cycling under constant load. The results obtained with this macromechanical approach are supported by calorimetric and electrical resistance (ER) measurements performed after failure of the material.

Calculation of residual stresses in amorphous wires

The residual internal stresses in a cylindrical wire produced in the rotating-water melt spinning process and a coated wire obtained by drawing from a melt have been calculated within the thermal viscoelasticity and structural relaxation theories. The coated wire consists of the core and the sheath with different thermal properties. The problem is considered with allowance made for the generation and the relaxation of stresses in the core and the sheath in the temperature range from initial (corresponding to the liquid state of a two-layer wire) to room temperature. The distributions of the residual stresses have been calculated for the free amorphous metallic wire and the amorphous wire with the sheath having a different elastic modulus and thermal expansion coefficient. The influence of preparation conditions and thermal properties of materials on the calculated parameters is analyzed.

Topographic measurement of electromigration-induced stress gradients in aluminum conductor lines

We report a set of data on the evolution of stress in thin-film metallization wires during the transient region of electromigration. The excellent strain sensitivity of the x-ray microbeam topography technique allows real-time, spatially resolved measurements at the lowest currents reported to date (1.0×104–1.4×105 A/cm2). While the steady-state results agree qualitatively with the Blech’s stress gradient model [I. A. Blech, J. Appl. Phys. 47, 1203 (1976)], the threshold-length product calculated from our data is about 2–3 times smaller than previously reported values. Stress evolution during the transient state displays local fluctuations which cannot be attributed to experimental errors, indicating possible microstructural effects on local flux divergence even in the case of wide, nonbamboo wires.

Recovery stress generation in shape memory Ti 50Ni 45Cu 5 thin wires

The recovery stresses evolving in constrained Ti 50Ni 45Cu 5 (at.%) shape memory wires were investigated in thermomechanical experiments performed in combination with electric resistance measurements. The hysteretic stress–temperature responses of the wires in constrained thermal cycles were analyzed by comparing the experimental results with simulated responses using a phenomenological algorithm developed for prediction of uniaxial thermomechanical SMA behaviors. The effects of individual SMA material parameters, constraint parameters, test boundary conditions and thermomechanical history on the evolution of recovery stresses in SMA wires are predicted.

Investigation of Stress of Contact Wire Clamped with Steady Arms Under a Moving Constant Force Passing by.

Presently, the maximum speed of Shinkansen trains reaches 300km/h. In this high-speed operation, one of the factors in estimating the quality of current collecting behavior is the stress of contact wire. There are various fittings clamped to the contact wire of overhead catenary equipment. These fittings dynamically become hard spots for pantograph collecting current. Above all, large magnitudes of contact wire stress have been marked at steady arm points. Though being under statics, in order to reveal the fundamental properties in the relation between constrain conditions of steady arms and a moving constant force, analytic calculations are carried out.

New Carquinez Bridge, Northeast of San Francisco, California: Technological Design Advancements

The new Carquinez Strait Bridge, northeast of San Francisco, California, will be the first major suspension bridge to be constructed in the United States since the second Chesapeake Bay Bridge in Maryland in 1973. It will replace an existing steel cantilever truss bridge, built in 1927, that was found to be seismically inadequate. The new bridge consists of an orthotropic closed steel box girder superstructure, two main cables 512 mm (20 1/8 in.) in diameter, reinforced concrete towers, and gravity anchorages. The design has set a new standard in modern suspension bridge design in the United States, particularly with respect to seismic safety. Some of the key elements of the design that are discussed are the global design loading criteria for long-span suspension bridges, the design of allowable stresses in main cable wire, the state-of-the-art design detailing of critical welded connections, the finite-element analysis approach for the box girder to determine the actual plate stresses and stress concentrations, and the design of the reinforced concrete tower leg sections for enhanced ductile seismic performance.

Interfacial mechanical properties and fracture morphology of a TiN-coated steel wire upon tensile loading

The state of stress in a TiN-coated stainless steel wire upon tensile loading was analyzed theoretically using a classical model of continuum elasticity, from which the interfacial mechanical properties of the coating system were deduced. Specimens for the tensile test were prepared by deposition of TiN films on stainless steel wires using a hollow cathode discharge ion plating (HCD-IP) coater. Cross-section SEM shows that the TiN produced by the ion plating technique has good coverage on the steel wires and that the thickness ratio between the thickest and the thinnest coatings is 3.57. The failure mechanism of the TiN films upon tensile loading is found to depend on the coating thickness. Opening mode prevails in the thick coatings where periodic cracks perpendicular to the tensile axis developed; on the other hand, shearing mode takes place in the thin coatings where cracks inclined to the tensile axis by 45° occurred. On the basis of the experimental observations and the theoretical calculation, the shear strength of the TiN, the ultimate shear strength and the bonding strength of the TiN/steel interfaces were estimated to be 15.36, 9.87 and 1.06 GPa, respectively.

Residual quenching stresses in amorphous ferromagnetic wires produced by an in-rotating-water spinning process

The residual stress-tensor components in amorphous ferromagnetic wire produced by an 'in-rotating-water' spinning process are calculated on the basis of the theory of viscoelasticity. The viscoelastic behaviour of the solidifying wire near the point of vitrification is studied and the effect of the relaxation process on the residual quenching stresses is clearly elucidated. The radial dependence of the residual stress-tensor components obtained is consistent with the magnetic behaviour of amorphous wire with small negative saturation magnetostriction. The residual stress amplitude is investigated as the function of wire radius and the parameters of the cooling process.

A Study of Mechanical Stability Issues in Multilevel Air-Dielectric Interconnect Schemes for ULSIs

Air-dielectric interconnect schemes are under active consideration for use in high performance LSIs because they can improve speed significantly. However, mechanical stability is the biggest engineering issue in these schemes. In this paper, an investigation of mechanical stability issues is presented. It is found that the deflection of the wires due to their own weight is unlikely to be a problem. For a typical long wire cross-section of 2 µm×2 µm, wires of length slightly more than 1mm can be allowed without appreciable sag. On the other hand, it is found that the initial tensile stress in the metal wires produces significant bending stresses at the bottom of the via plugs. The dependence of the bending stress on various geometrical parameters is studied in detail. It is found that bending stresses of more than 1 GPa can result even for a very low initial tensile stress in the wire of 20 MPa.

In-situ stress state measurements during chip-on-board assembly

In this work, die stresses in wire bonded chip-on-board (COB) packages have been measured using special [111] silicon stress test chips. The test die incorporate an array of optimized eight-element dual polarity piezoresistive sensor rosettes, which are uniquely capable of evaluating the complete stress state (six stress components) at points on the surface of the die. Sensor resistance measurements were recorded before packaging, after die attachment, and throughout the encapsulant cure process. Using the appropriate theoretical equations, the stresses at sites on the die surface have been calculated from the raw sensor resistance data. Also, three-dimensional (3-D) nonlinear finite element simulations of the chip-on-board packages were performed, and the stress predictions were correlated with the experimental test chip data.

Stress state of a matrix and an inclusion consisting of a twisted multifilament superconductor with a normally-conducting core in the presence of an interaction of the longitudinal current with a transverse magnetic field

A study is made of the stress state arising in an infinite matrix into which is “potted” a long cylindrical inclusion consisting of a twisted multifilament composite superconductor with a core of normal metal as a result of the interaction of the longitudinal component of the transport current with a uniform external magnetic field. It is shown that the approximation of a homogeneous conductor with average elastic properties can be used to calculate the macroscopic stresses in a NbTi-Cu wire embedded in an epoxy matrix.

Work Hardening of Hypereutectoid and Eutectoid Steels during Drawing.

Work hardening of pearlite and bainite during drawing of high-carbon steel wires was studied by using stress-strain curves of drawn wires and making a detailed observation of their microstructure. The study revealed the following relationship between flow stress and strain in high-carbon steel wires. Flow stress σ is represented by a weighted average of the strengths of ferrite and cementite. The amount of work hardening Δσ is represented by an equation corresponding to exp(Be) where B is a constant that depends on the initial microstructure of the steel wire and e is the strain. When the initial microstructure of steel wire is made up entirely of a pearlite lamellar structure, the value of B is 0.5. When the initial microstructure contains some bainite, the value of B is lower than 0.5. Finally the flow stress was formulated as a function of carbon content, supercooling degree, and e. The calculated maximum flow stress showed good correlation with the measured flow stress of 0.8 % C and 0.2%Cr-0.92%C steel wires during drawing.

Microstructural evolution upon thermomechanical processing of non-sag tungsten

The thermally activated detachment of dislocations from bubbles may explain the variable stress sensitivity of the stationary creep in a broad stress region. The models of this kind of creep predict that, on the one hand, there should be an optimum bubble size that depends markedly on the applied stress while, on the other hand, the length of the bubble rows should play a secondary role, as the creep rate is primarily governed by the size of the individual bubbles. Although the kinetics of the detachment of the grain boundaries from bubbles should govern the final microstructure of non-sag tungsten both in the stress relieved and in the recrystallized conditions, a recent model on the thermally activated detachment will be really effective, only if the size of the dispersoid is in the nanosized region. A simple method is also described for monitoring the relaxation of the long-range residual stresses in thin non-sag wires.