Bent Strip Research Articles

Elastic Bending of Steel-Polymer-Steel (SPS) Laminates to a Constant Curvature

The shear strain of the interlayer in the elastic regime for a Steel-Polymer-Steel (SPS) laminate material has been studied during bending to a constant curvature. An analytical model is developed and the influence of process parameters are analyzed. The tension in the cover sheets is also determined and, finally, a moment diagram is calculated. The results show that the moment in the SPS laminate is nonuniform along the bent strip even though the curvature is constant because of the tension and compression forces introduced in the cover sheets by the shear reaction force of the interlayer material.

A Reconfigurable Spiral Antenna for Adaptive MIMO Systems

We present a reconfigurable spiral antenna for use in adaptive MIMO systems. The antenna is capable of changing the sense of polarization of the radiated field. It is fabricated by using an RF-MEMS technology compatible with microwave laminate substrates developed within the author's group. The proposed antenna structure is built on a number of rectangular-shaped bent metallic strips interconnected to each other with RF-MEMS actuators. Two senses of polarization, RHCP and LHCP, are achieved by configuring the physical structure of the antenna, that is, by changing the winding sense of the spiral, through judicious activation of MEM actuators. The fabrication process for the monolithic integration of MEM actuators with bent microstrip pixels on RO4003-FR4 microwave laminate substrate is described. The measured and calculated radiation and impedance characteristics of the antenna are given. The operating frequency of the presented antenna design can easily be adjusted to be compatible with popular IEEE networking standards such as 802.11a.

On a Testing of Mechanical Properties of Material Surfaces

Hardness testing is a method frequently used for evaluating the resistance of body surfaces to the influence of contact loading. The Vickers hardness test is applied for this purpose in a case when the material is sufficiently ductile and no cracks occur in the corners of the indents. Testing of the surface hardness of such materials as glass and ceramics on the basis of the Vickers testing method must take into account the energy that is spent on crack spreading. This paper describes a more exact and accurate method for evaluating resistance to microcrack formation on the surface of a material. To evaluate the conditions for crack spreading, it is necessary to test a specimen under loading in bulk. The suggested procedure involves a bent strip. As bending stresses are known, from them and from the differences in crack length along and across the strip, the resistance of the material surface to crack propagation is determined.

Photomechanical effect in films of polyvinylidene fluoride

Photothermal bending of strips of polyvinylidene fluoride was initiated by a laser beam with a power of a few milliwatts. A bending strip generated a force of 10−4N that propelled a 1 g oscillating wheel of a mechanical clock. The frequency of photomechanical resonance at pulsed illumination was inversely proportional to the length of the strip. The proposed model explained bending as a result of uneven thermal expansion on opposite sides of the strip. The model predicted, in agreement with experiment, that the force is proportional to beam power and does not depend on the shape or position of the beam in the strip.

On the estimation of the toughness of surface microcracks

Hardness testing is a method frequently used for evaluating the resistance of body surfaces to the influence of contact loading. The Vickers hardness test is applied for this purpose in a case when the material is sufficiently ductile and no cracks occur in the corners of the indents. Testing of the surface hardness of such materials as glass and ceramics on the basis of the Vickers testing method must take into account the energy that is spent on crack spreading. This paper describes a more exact and accurate method for evaluating resistance to microcrack formation on the surface of a material. To evaluate the conditions for crack spreading, it is necessary to test a specimen under loading in bulk. The suggested procedure involves a bent strip. As bending stresses are known, from the differences in crack length along and across the strip, the resistance of the material surface to crack propagation is determined.

A silicon spectrometer for transition radiation detection for space applications

A novel design of a Transition Radiation Detector, based on Silicon Microstrip Detectors, is presented. Owing to the relatively high ionization energy release in semiconductor material (a few hundred keV), a magnetic field should be used to separate the radiating particle from TR X-ray photons. We have developed a full Monte-Carlo code to study in detail the performance of this detector such as bending power, strip pitch, charge sharing, and detection efficiency. We also present the results obtained with a small prototype exposed to an electron/pion beam at CERN PS. The particle identification capability allows the distinction of hadron from electrons up to 40GeV/c and the spectrometer rigidity is almost 40GV.

Experimental Study of the Microstructure and Stress of Electroplated Gold for Microsystem Applications

Gold, used as an X-ray absorber for lithography and as a structural or conducting material in microsystems, was deposited from a commercially available sulfite electrolyte. The effects of current type and an arsenic additive on the gold microstructure and residual stress were studied. Using a simple bent strip method, good agreement with literature stress values determined via other methods was obtained. Without arsenic, residual stresses are tensile regardless of current type. With 25 ppm arsenic, the stress is compressive for direct current (ca. with pulsed current reducing the stress to compressive; this has been noted previously with thallium as an additive. The addition of arsenic does not appreciably change the film grain size but does lower the twin density and modify texture. Pores were observed in all the gold films, but were larger and less concentrated for films produced with arsenic; for the case of direct current with arsenic, the pores were concentrated at the grain boundaries. Consistencies in the microstructural observations and thin film stress theories are discussed. © 2003 The Electrochemical Society. All rights reserved.

Bent strips in external magnetic fields and with applied currents

Current and magnetic field profiles of bent strips in external magnetic fields and with applied currents are numerically calculated. The flat strip is correctly obtained as the limiting case of bent strips when the bend angle is zero. The Meissner response and the flux penetration are studied, the latter under the consideration of high critical currents and small bends. The dependence of these profiles on the creep exponent (by a material relation E alpha (j / jc)n) is also studied. In the presence of an external magnetic field the flux penetration is delayed in bent strips compared with at strips. In the case of an applied current the flux penetration from the strip edge is also delayed, but a flux front starting from the corner is also observed.

Influence of the molecular structure on slow crack growth resistance and impact fracture toughness in Cr‐catalyzed ethylene‐hexene copolymers for pipe applications

AbstractIn this study we correlate parameters describing molecular structure (molar mass distribution, short chain branching content, intermolecular heterogeneity) of different ethylene‐hexene Cr‐catalyzed copolymers, with slow crack growth and rapid crack propagation resistances, respectively measured with Bent Strip and Charpy tests. The PTREF technique, coupled with classical techniques, was used. Two new indices were proposed to correlate mechanical properties and molecular structure. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 916–928, 2001

Flux field profiles and magnetization curves for bent thin strips in transverse field

The flux penetration in superconducting bent strips is calculated and compared to those calculated for flat strips. Using a modified Bean critical state model, the current and flux field profiles are calculated as a function of the coordinate parallel to the strip surface. It is shown that the flux penetration is delayed in bent strips compared to flat strips.

Elastoplastic equilibrium of an isotropic strip with a circular hole under pure bending

The range of variation of external forces over which the plastic region in a bent strip develops from initiation to complete envelopment of a circular aperture is determined. A perturbation method is used to construct a solution for these interactions.

Data base of field incidents used to establish HDPE geomembrane stress crack resistance specifications

Geomembranes made from high-density polyethylene (HDPE) have a relatively high percent crystallinity, and are therefore of concern with regard to stress cracking. The stress crack resistance (SCR) of HDPE geomembranes must be properly evaluated and specified accordingly. A research project was initiated in 1990 to investigate the stress cracking behavior of HDPE geomembranes in the field. A total of 16 field sites were located, in which HDPE geomembranes showed some degree of stress cracking. The SCR of retrieved field samples was evaluated by both the bent strip and notched constant tensile load (NCTL) tests. The test data indicates that the bent strip test could not adequately predict the stress cracking field performance of HDPE geomembranes. In contrast, the NCTL test could distinguish the SCR of the retrieved field geomembranes. Based on the NCTL test data obtained from the field geomembranes, a 100 hour transition time is recommended to be the minimum value for an acceptable HDPE geomembrane specification. In addition, a single point notched constant tensile load (SP-NCTL) test was also established for quality control and quality assurance purposes. The recommendation for the SP-NCTL test is set at 200 hours failure time under an applied load of 30% room temperature yield stress.

Effects of Thickness and Hardness on Springback of Cold Rolled Stainless Steel Strip for Spring

Stainless steel strip is widely used for flat spring which requires corrosion resistance. SUS301 steel is especially used for the material of a spring as it is given high strength by cold rolling. However, scattering of the angle of bent product due to the large springback of the material appears to be a problem in a certain production. In this study, the effect of slight differences in thickness and hardness on the amount of springback in two lots of SUS301 is investigated. The material specification of each is within the tolerance of JIS G 4313, however, the lots are from different steel makers. L-shape bending test which is similar to a multiforming mechanism is adopted in this investigation. Results obtained show that the springback angle decreases with the increment of thickness and the decrement of hardness, but the change itself is very small within the same material lot. In addition, the relationship between the springback angle and the hardness does not apply through the different material lots, and it even appears to have a reversed tendency. Therefore, hardness is not appropreate to estimate the springback. Within the present experiment, the springback angle correlates with the stress corresponding to the strain at the surface of bent strip regardless of the difference in not only material lots but also bending direction against rolling direction.

Determination of stress in coatings by the bending strip method in the case of large displacements

The classical formulae derived through the simple plate theory for determining stress in coatings by the bending strip method have been widely used to date. However, their application is limited to bending displacements, which are small compared to the thickness of the strip. Since the actual measured displacements are often greater, the question for the applicability of this theory arises. To the best of our knowledge, a satisfactory answer to this question has not yet been presented. There are publications stressing only the danger of bifurcation of experimental specimens at high curvature values when this theory becomes inapplicable. The present work provides an answer by solving the geometrically non-linear problem of the theory of elasticity involving large deflections of coated strips by the finite element method. Data on the errors of classical formulae and two practically applicable conditions for reaching a minimal admissible error are given.

Stress intensity factors for side-by-side edge cracks under bending

This note concerns the Mode I and II stress intensity factors occurring at twin cracks on the tension side of a strip in bending. Both cracks penetrate the strip normal to its edge and to a depth that is halfway through its width. By applying an appropriately-tested finite element procedure, the effects on the stress intensity factors of interaction between the cracks can be tracked as a function of crack separation.

Autohesion of crosslinked polyethylene

Thin strips of crosslinked linear high-density polyethylene were melted and then crystallized in contact by cooling to room temperature. The work required to peel the strips apart by pulling one strip away from the other at 90° was found to be remarkably high, 5 to 30 kJ/m 2 , and in some cases the strips could not be separated in this way. However, adhesion measured in T-peeling was much lower, about one-tenth as large. Adhesion was also fairly small, 200 to 600 J/m 2 , using other test methods designed to minimize bending strains. Thus, most of the work of separation is normally expended in bending, probably in plastic yielding of the outer layers of bent strips. However, even when bending energy losses were minimized, the residual adhesion was much greater than expected for Van der Waals bonding ( about 0.05 J/m 2 ). Apparently, cocrystallization of molecular strands lying on either side of the interface greatly enhances the intrinsically low level of autohesion of amorphous polyethylene, probably by local yielding processes around the line of separation. Some effects of test temperature were also examined in T-peeling. Adhesion passed through a pronounced maximum at temperatures of 75-100°C before reducing to very low values in the melted state. This maximum was absent in tests with reduced bending. It is, therefore, attributed to extra work expended in plastic bending over a narrow range of temperature, probably due to a lower yield stress at these temperatures and not to an increase in the actual adhesion.

An assessment of geometry effects on plane stress fatigue crack closure using a modified strip-yield model

Using a modified strip-yield model, plane stress constant-amplitude fatigue crack growth simulations under conditions of small-scale yielding were performed for the edge-cracked strip in tension, the edge-cracked strip in bending, and the compact tension specimen with load ratios R = 0.5, 0.0, −1.0and−2.0. From these simulations, fatigue crack opening loads were predicted as a function of crack length. Geometry, loading type and crack length were observed to affect crack opening loads. The geometry-loading dependence was particularly evident for extended fatigue crack growth. Geometry-loading dependence was observed to increase for R < 0. Reductions in the crack opening loads following extended crack growth were also observed. These reductions were demonstrated to occur in the absence of large-scale plasticity in the remaining ligament. A normalized maximum applied stress intensity factor K max/σ o√W, where σ o and W represent the flow stress and specimen width respectively, was demonstrated to represent an approximate measure of small-scale yielding crack closure response similitude under plane stress conditions with R ⩾ 0. When crack opening loads were correlated in terms of this parameter, little geometry-loading dependence was observed.

Determination of the Neutron Angular Response Using a Single Etched Track Detector

A method for the determination of the neutron angular response as a function of incident angle is described using only one exposure of a single bent plastic detector strip in a half cylindrical geometry. After etching, the detector surface is scanned along the centre line in parallel narrow fields. On the basis of the equation derived from the irradiation geometry the distance of each field can be correlated to the angle of neutron incidence a. Thus, the track density values correspond to all angles from O o to 90 o. The application of the least square fit method provides: (a) correction in case of an inaccurate irradiation geometry, (b) the proper 'source-detector' distance correction of the neutron fluence, and (c) a method for estimating the angular response as a function of angle a of neutron incidence using the simple empirical equation p (a)=a+b X cos (2a+p).

Vectorial analysis of bends in optical strip waveguides by the method of lines

The vectorial analysis by the method of lines is extended to investigate optical waveguides consisting of several circularly bent strips. Bessel functions of very large and complex order are employed to calculate radiation loss and intensity distribution, for example, for a rib waveguide.

The Internal Stress in Ni, NiFe , CoFe , and CoNi Layers Measured by the Bent Strip Method

The physical meaning and formulas for the calculation of the different, but interrelated, types of the internal stress (IS) in thin films (instantaneous, residual, and average) are reviewed. These formulas are then applied to the cases of plated Ni and , , and alloys. The IS profiles (the IS distribution through the film thickness) are given for all cases. The relationship between the IS and the structure parameter (phase composite, crystallite size, and microstain) changes with alloy composition is discussed.