Bimetallic Strip Research Articles

A magnetostrictive acceleration sensor for registration of chest wall displacements

The present study concerns a novel acceleration sensor built up using a bimetallic strip with one freely oscillating end. The strip consists of a magnetostrictive amorphous ribbon glued on a nonmagnetic metal ribbon. The sensor’s effectiveness is demonstrated for the case of chest wall displacements as resulting from cardiorespiratory activity. The cheap and easy-to-handle novel sensor offers multiple information on the so-called sleep apnea syndrome.

Residual Stresses in Galvanizing

Zinc coating is formed by heterogeneous assembly of phases in which mechanical properties greatly differ. In the galvanizing process the great difference between the linear thermal expansion of the iron substrate and the Zn has proven to be the source of important residual stresses. The primary objective of this paper is to determine the residual stresses which promote crack formation and deterioration of corrosion resistance. Because direct determination by x-ray diffraction has been difficult, three other methods are proposed. The first one led us to calculate an average stress by measuring the variation of crack length with applied load resulting from a Vickers small indentation. The second is an application of the Timoshenko's bimetallic strip method based on the difference in thermal expansion coefficients. The third is deduced from the variation of the curvature of one-face galvanized specimens. These results are compared and the homogeneous value of residual stresses are shown.

Micromechanics: A toolbox for femtoscale science: “Towards a laboratory on a tip”

Micromechanics and microscopy at the atomic scale became inseparably linked in 1986 with the invention of scanning force microscopy (SFM). The extreme sensitivity of these nanoscale science methods extends their use well beyond force detection. In principle, every signal domain such as magnetic, electrical, thermal, chemical, stress, and flow can be detected at ultimate limits of sensitivity, speed, and size through transduction into mechanical motion. We first pioneered the use of such SFM sensors as calorimeters enabling the detection of chemical reactions involving heat changes at the femtojoule level. These devices, which utilize the well-known “bimetallic strip” principle, have since been extended to a novel form of optical absorption spectrometer also capable of outperforming conventional techniques. Detection of stress induced in thin films on micromechanical devices is also being actively pursued for electrochemical processes. Volume changes and heat having evolved during phase transitions have been separated successfully using a variation of the bimetallic method analogous to standard thermal analysis. The attachment of picoliter amounts of material at the apex of the cantilever device, the attachment of tiny zeolite crystals, and the fabrication of miniature shovels or thermocouples at the tip region will lead to the creation of laboratory on a tip. The use of arrays extends the capabilities of these devices to applications such as artificial noses or for process control and has significant potential for sensor applications of all kinds. Progress so far indicates that a complete laboratory can be shrunk to the dimensions of the tip of a needle.

Slit-pore mechanism to control flow through a filter membrane

Since Malpighi's time (1) anatomical observations of the kidney have been related to their possible function. Recent observations note that many angiotensin II (Ang II) receptors are found inside the glomerulus (2). What could their function be? Ang II is a potent vasoconstrictor. No obvious shrinkage of the glomerular capsule due to Ang II action has been observed. This constricting effect has to be found in the glomerular tuft, where its vessels accomplish two functions: they serve as a flow bed for perfusion and as an optimally enlarged filtration membrane. Filtration takes place through pores, minute openings: in our case 'slit pores'. Why slit pores and not minute round pores? How could pores of any kind be made to allow an enhanced throughflow by a constricting control mechanism? A comparison with the mechanism involved in the function of a bi-metallic strip might provide the answer. A metal rod of a certain length will expand when heated and contract when cooled. Its change in length depends on the inherent qualities of that particular metal: its thermal expansion coefficient. This wellknown phenomenon has been put to practical use by bonding two different metals together. The greater expansion or contraction of one metal with respect to the other will bend the bi-metallic strip to one side or the other. This is the 'working mechanism' of the ubiquitous mechanical thermometer. If we replace the strips of metal with a biological substance that can be made to contract and place this contractile strip in close bonding next to an inert strip of tissue, an analog to the bi-metallic strip can be seen

Cold rolling of multi-layer explosively cladded strips

The fabrication of multi-layer (bimetallic and trimetallic) composites for electrical and electronic switches is reported. A thin layer of solder metal (AgCuZn) is explosively cladded onto a copper plate; the resulting bimetallic strip is rolled to a thickness of 2 mm and subsequently explosively cladded onto a 2 mm thickness silver-cadmium oxide plate. Rolling is then employed to form the trimetallic composite at its final thickness. The effect of the cladding-rolling variables on the soundness and micro- and macrostructural properties of the multilayer strips is evaluated in terms of “surface integrity”; emphasis is also directed towards the influence of rolling on the integrity of the bi- and trimetallic strips. A theoretical approach for calculating force and torque during the rolling of the multi-layer strips is proposed and experimentally validated; experimental and theoretical results are in good agreement.

Two-mode elliptical core optical fiber sensors for strain and temperature measurement

We propose two sensing methods for strain and temperature measurement based on conventional elliptical core (e core), two-mode fiber strain sensors, that combine the properties of a two-mode, e core fiber sensor and (i) a bimetallic strip or (ii) refractive index changes in a liquid filled hollow core fiber. The output from a conventional two-mode, e core fiber sensor is (i) projected upon a multimode fiber attached to a bimetallic strip or (ii) projected from an angular endface onto the endface of a multimode fiber. The multimode fiber acts as a spatial filter and picks up part of the two-lobe pattern incident upon its core. A measurement of the differential phase variation gives an indication of the strain. The modulation depth of the output signal is shown to be a faithful indication of the temperature in both cases. Strain sensitivities typical of two-mode fiber sensors (0.033 degrees phase shift mu strain-1 cm-1, minimum detectable strains of 0.17 mu m m-1 for 1 m sensing length) have been obtained with a temperature compensation accuracy of +or-1 degrees C over a 75 degrees C range. A theoretical model has been developed and experimental results are shown to match closely with theoretical predictions.

Fabrication of trimetallic strips by explosive cladding and rolling

The fabrication of trimetallic composite contacts for electrical and electronic switches is reported. A thin layer of solder metal is explosively cladded onto a copper plate, the resulted bimetallic strip is rolled to a thickness of 2 mm and the cladded/rolled bimetallic is explosively cladded onto a 5 mm thick silver plate. Rolling is subsequenty used for forming the trimetallic composite to its final thickness. The effect of the cladding/rolling variables on the integrity, the soudness and micro- and macrostructural properties of the fabricated composite plates is evaluated in terms of “surface integrity” by using standard metallographic methods, microhardness testing and microprobe analysis. Interest is also directed towards the detailed characterization of the interface zones since defects at these zones could affect the electrical properties of the fabricated trimetallic components.

A role for regulated secretion of apical extracellular matrix during epithelial invagination in the sea urchin.

Epithelial invagination, a basic morphogenetic process reiterated throughout embryonic development, generates tubular structures such as the neural tube, or pit-like structures such as the optic cup. The 'purse-string' hypothesis, which proposes that circumferential bands of actin microfilaments at the apical end of epithelial cells constrict to yield a curved epithelial sheet, has been widely invoked to explain invaginations during embryogenesis. We have reevaluated this hypothesis in two species of sea urchin by examining both natural invagination of the vegetal plate at the beginning of gastrulation and invagination induced precociously by Ca2+ ionophore. Neither type of invagination is prevented by cytochalasin D. In one species, treatment with A23187 three hours before the initiation of invagination resulted in the deposition of apical extracellular matrix at the vegetal plate, rather than invagination. This apical matrix contains chondroitin sulfate, as does the lumen of the archenteron in normal gastrulae. When the expansion of this secreted matrix was resisted by an agarose gel, the vegetal plate buckled inward, creating an archenteron that appeared 3-4 hours prematurely. Pretreatment with monensin, which blocks secretion, inhibits both Ca2+ ionophore-stimulated folding and natural invagination, demonstrating that secretion is probably required for this morphogenetic event. These results indicate that alternatives to the purse-string hypothesis must be considered, and that the directed deposition of extracellular matrix may be a key Ca(2+)-regulated event in some embryonic invaginations. A bending bilayer model for matrix-driven epithelial invagination is proposed in which the deposition of hygroscopic material into a complex, stratified extra-cellular matrix results in the folding of an epithelial sheet in a manner analagous to thermal bending in a bimetallic strip.

Preparation and properties of iron-nickel bi-metallic strip made by a PM route

Preparation and properties of iron-nickel bi-metallic strip made by a PM route

A simple sagittal focusing crystal which utilizes a bimetallic strip

A sagittal focusing monochromator which utilizes a bimetallic strip as its active focusing member has been designed and has undergone preliminary testing. The crystal bender is very easy to use as only setting the temperature of the bimetallic strip is necessary to adjust the focus. The mechanism utilizes bending rods mounted on live centers which prevent twisting of the crystal. A finite element analysis has been done on a new ribbed crystal which, based on the analysis, would have very small aberrations.

The Various Approximations of the Bimetallic Thermostatic Strip

A thin strip, formed by bonding two dissimilar materials, constitutes a simple thermostatic element. If edge effects are neglected, then the strip is reduced to a uniform beam, or plate, with two degrees-of-freedom. The flexure occurs only because of the bond and interfacial shear which is also accompanied by transverse normal stress. These latter stresses are very localized at the end and edges. Here, the elementary approximations, and refinements via finite elements, are presented and compared. Deflections are given with reasonable accuracy by the simple approximations, but the severe interfacial stresses are revealed only by the refinements.

Stress in thick diamond films deposited on silicon

20-μm-thick diamond films deposited on Si single-crystal substrates by microwave plasma-enhanced chemical vapor deposition showed significant curvature. The internal stress distribution was estimated using the model of an elastic bimetallic strip. The results indicate that the films are under a mean tensile stress of 1.1 GPa, and are discussed using information from x-ray diffraction and Raman spectra.

NEW CERAMIC DEVELOPMENTS AT ELMWOOD

In the early 1980s Elmwood Sensors, part of Hawker Siddeley's Instruments and Controls Division, was totally reliant on a single 15‐year‐old product range of electro‐mechanical thermostats using a bimetallic strip. Dissatisfied with this insecure situation and uncertain about the long‐term sales life for electromechanical sensors, the company decided that it should start looking for advanced technology substitutes.

On a model for the temperature distribution in moving bimetallic strips

We propose a mathematical model for the study of the temperature distribution in each component of a bimetallic strip, moving along a horizontal line, at a prescribed steady speed. A simplified model for the temperature averaged over a transversal cross section in bronze and steel respectively is considered. We prove that conduction in the direction of the strip motion can be neglected if the speed V exceeds some computable value.

Thermal Stresses at the Edge of a Bimetallic Thermostat

The plane stress problem of a semi-infinite, bimetallic thermostat subjected to uniform heating or cooling is treated with the theory of elasticity. Solutions to this problem are expressed as the sum of a basic solution for a bimetallic strip of infinite length and a series of complementary solutions. Interlayer peeling stresses at the free edge of the bimetallic thermostat are shown to be singular or nonsingular (but still higher than the nominal values) depending upon whether the combination of the two Dundurs’ bimaterial constants, α (α−2β), are greater or less than zero. In an example problem, current solutions agree well with finite element results while results predicted by a modified beam theory show a large deviation from the other two solutions near the free edge. Boundary layer effects near the free edges of a bimetallic thermostat are also discussed.

FABRIC MECHANICAL AND PHYSICAL PROPERTIES RELEVANT TO CLOTHING MANUFACTURE —

In Part 1 of this series of papers, we investigated the importance of fabric overfeed in the sewing operations during tailoring. It was also shown how fabric bending rigidity, formability, shear and hygral expansion are important in clothing manufacture. The present paper is concerned with the measurement and experimental study of seam balance, breaking elongation and bending properties of seams. The aim is to evaluate quantitatively the consumption of sewing thread and the relationship between the degree of fabric overfeed during sewing and the curvature of the seam in the garment. Balanced seams have much higher breaking elongation and more symmetrical bending properties than unbalanced seam structures. A natural curvature and curling couple result from fabric overfeed during sewing. The value of the curvature is time‐dependent because of fabric viscoelastic effect and also depends on the level of fabric overfeed, the tensile and longitudinal compressive module of the component fabrics and the structure of the seamed composite. The natural curvature of the seam may be derived quantitatively from the relative lengths of overfeed fabrics using a modified theory for a bimetallic themostatic strip.

Thermal stresses in the bulk and epitaxial growth of III-V materials

Reviews dislocation generation by thermal stresses in the bulk growth of compound semiconductors. Wafer bowing by thermal stresses is analyzed in the GaAs/Si heteroepitaxial system. The quasi-steady-state (QSS) heat-transfer/thermal-stress model for glide dislocation formation during crystal growth is outlined. Next, the key predictions of the model are presented and related to crystal-growth practice. Finally, by a suitable extension of Timoshenko's treatment for the bimetallic strip, the authors determine the reduction in bowing in GaAs/Si wafers for two alternative multilayer structures.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Anomalous twin boundaries in epitaxial zinc selenide grown on (100)oriented GaAs substrates by molecular beam epitaxy

Abstract Anomalous ‘bent’ microtwins lying in a 〈111〉 direction and containing high concentrations of Ga and As have been observed in ZnSe epitaxial layers grown on (100)-oriented GaAs substrates by molecular beam epitaxy at 410°C. The bend radius R meas of 0·928 × 10−5 m compares favourably with a theoretical value based on the use of expressions applicable to a bimetallic strip comprised of GaAs and ZnSe.

Forces, Moments, and Displacements During Thermal Chamber Cycling of Leadless Ceramic Chip Carriers Soldered to Printed Boards

Solder joints between ceramic chip carriers (CCC's) and printed wiring boards (PWB's) are likely to experience large thermal strains during operation in the field. Strains applied during accelerated temperature cycling have been shown to cause cracks in the solder and electrical failures (opens). The forces and moments exerted on the solder (and the resulting displacements) arc inferred from strain gage measurements of the in-plane deformation and bending of the PWB and the CCC. It is found that below room temperature, most of the expansion mismatch is accommodated by "bi-metallic strip" type bending of the PWB and the CCC. The change in bending during a temperature change from - 25°C to +35°C is consistent with the classical bi-metallic strip equation, given material properties from the literature. Above room temperature most of the mismatch is accommodated by shear in the solder. Upon repeated temperature cycling, there is a repeatable stress-strain hysteresis, which is attributed to plastic deformation in the solder. This deformation is lower for staggered tin pillar joints than for in-line 60/40 solder post joints. It is lower still when the PWB in-plane expansivity is constrained by copperclad invar (CCI) layers included in the stack-up. Using mechanical equilibrium conditions, we can calculate the force per joint and solder shear displacement. The force represents up to 35 percent of the ultimate force calculated from the ultimate shear strength.

Thermal Buckling of a Bimetallic Strip

A theoretical foundation is provided for the difficulties encountered in manufacturing a snap acting bimetallic strip thermostatic which will snap within ±10 degrees of a prescribed temperature. It is obtained by modifying Timoshenko’s pioneering analysis to allow for a realistic support frame whose coefficient of thermal expansion differs from the composite coefficient for the bimetallic strip. Results are compared with those of Timoshenko and with predicted behavior when the support frame is rigid and thermally inert.