Search

For CMOS technology, the increase of interconnects metal density is responsible for heterogeneous mechanical stress fields in active regions of silicon. Coupled mechanical–electrical measurements are performed to evaluate the impact of stress at circuit and device levels. This mismatch originated by interconnects metal lines stress is measured through the use of piezoresistive test structures. Local mechanical stress can thus be monitored in a simple process control compatible approach. [ABSTRACT FROM AUTHOR]

Copyright of Petroleum - Gas University of Ploiesti Bulletin, Technical Series is the property of Petroleum - Gas University of Ploiesti and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper shows the design of a fiber-based sensor for living activities in human body and the results of a laboratory evaluation carried out on it. The authors have developed a device that allows for monitoring the vibrations of human body evoked by living activities—breathing and cardiac rhythm. The device consists of a Bragg grating inscribed into a single mode optical fiber and operating on a wavelength of around 1550 nm. The fiber Bragg grating (FBG) is mounted inside a pneumatic cushion to be placed between the backrest of the seat and the back of the monitored person. Deformations of the cushion, involving deformations of the FBG, are proportional to the vibrations of the body leaning on the cushion. Laboratory studies have shown that the sensor allows for obtaining dynamic strains on the sensing FBG in the range of 50–124 μ strain caused by breathing and approximately 8.3 μstrain induced by heartbeat, which are fully measurable by today's FBG interrogation systems. The maximum relative measurement error of the presented sensor is 12%. The sensor's simple design enables it to be easily implemented in pilot's and driver's seats for monitoring the physiological condition of pilots and drivers. [ABSTRACT FROM PUBLISHER]

A typical compact pulsed magnet coil wound from copper and Zylon fiber was fabricated with optical fiber sensors embedded at different places in the Zylon layers. Measurements of deformation have been carried out during winding, cooling and with magnetic field pulses up to 10 T at room temperature and 41 T at 77 K. The results are in agreement with the calculated strain distribution by taking into account the anisotropy of fiber/epoxy composites. [ABSTRACT FROM PUBLISHER]

During dry friction the rheological behavior at the interface between a polymer surface and a rigid indenter is linked to the local pressure and the roughness of the surface of the indenter. This study on polycarbonate reports experimental results obtained at ambient temperature using rigid, spherical glass indenters of various radii. In a first step, a plot of the experimental friction coefficient μ versus the mean contact pressure pmean showed that below the yield stress ( pmean < 100 MPa) the intrinsic friction coefficient follows a master curve for smooth indenters. In a second step, roughened indenters were prepared by chemical etching, which allowed the monitoring of nanoscale roughness parameters. From 5.5 to 140 nm Rrms, the friction coefficient μ progressively fell to a plastic-like constant value, indicating that the nanoroughness mediates the friction. These results form the basis for a study of the rheology of confined polymer layers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 [ABSTRACT FROM AUTHOR]

Models for predicting the received time-domain waveform by a transducer as a result of an acoustic emission (AE) event are proposed. They aim at simulating AE examinations of large structures subjected to various stresses (e.g. mechanical loadings) in different domains (aerospace, pressure-vessel industries, etc.). The energy released by a crack under stress can propagate as guided waves in thin structures. In thick ones, the acoustic far field radiated by a crack under stress is dominated by the presence of Rayleigh wave. 2D models for guided waves in plate-like structures are proposed as well as 3D models for Rayleigh wave. A piston-like model is used to obtain the delivered voltage at the transducer output, whereas a formulation is proposed coupling models for the AE sources and for the propagation of guided or Rayleigh waves. Specifically, the coupling of the expression of the crack-opening displacement and Green's functions for Rayleigh wave is achieved through an integral formulation relying on the elastodynamic reciprocity principle. For the AE source model, a constant crack propagation velocity is considered. The exact analytical solution from a fracture-mechanics based model is used to obtain the crack opening displacement. Green's functions for Rayleigh wave are calculated using reciprocity considerations without the use of integral transform techniques. Predictions computed with this 3D model are compared to results from the literature for validation purpose on simple geometries and for a penny-shaped tensile crack. For thin structures, a similar coupling formulation based on the elastodynamic reciprocity principle has been derived, allowing the amplitudes of the possibly propagating guided modes at a given frequency to be predicted. [ABSTRACT FROM AUTHOR]

When multiple cracks approach one another, the stress intensity factor and J-integral value change due to the interaction of the stress field. Since the changes in these parameters are not always conservative in structural reliability evaluations, the interaction between multiple cracks should be taken into account. Section XI of the ASME Boiler and Pressure Vessel Code provides a flaw characterization rule for interacting multiple cracks. In Section XI, adjacent cracks are replaced with a coalesced single crack when the distance between the cracks is less than half of the crack depth. However, the criterion for the offset distance is given as an absolute value, although the magnitude of the interaction depends on the crack size. In the current study, an alternative criterion for the offset distance was examined. Linear-elastic and elastic-plastic analyses were performed for interacting semicircular and semi-elliptical surface cracks by the finite element method under a tensile or bending load. The change in the stress intensity factors and J-integral values due to the relative spacing of cracks was investigated. Based on the relationship between the magnitude of the interaction and the relative position of the cracks, the allowable ctriterion for the offset distance was discussed. [ABSTRACT FROM AUTHOR]

Earlier study shows that resistor thickness of the thick film strain gauge can affect its temperature characteristic, which is usually a roughly parabolic curve. Thicker resistors tend to exhibit a higher positive temperature coefficient of resistance (TCR) and a lower Tmin, the temperature at which the TCR changes to zero in the curve. This paper presents a possible explanation of this observation based on an analysis of strain profiles and resistivity behaviour difference in resistors with different thicknesses subjected to temperature variation. [ABSTRACT FROM AUTHOR]

We report on a thin-flim transistor (TFT) degradation encountered in short channel amorphous indium–gallium–zinc–oxide TFTs under high applied power condition leading to self-heating. Negative shift was observed in the initial stage of stress period followed by positive shift with severe degradation. To understand the causes of this phenomenon in depth, trap density-of-states were measured by photo-excited charge-collection spectroscopy and time-dependent recovery of stressed device samples was also studied. As a result, we found that the combination of hot carrier effect and self-heating in channel was responsible for the degradation. [ABSTRACT FROM AUTHOR]

We have studied a high field pulsed superconductor with high elastic modulus fiber reinforcement. We call the conductor Fiber Reinforced Superconductor (FRS). We have succeeded in making a sputtering target which consists of reacted Nb/sub 3/Sn single material by powder metallurgy. Nb/sub 3/Al superconductor is well known as a candidate for superconducting magnets for fusion reactors because of good properties of mechanical stress and irradiation toughness. To overcome the difficulty of fabricating into superconducting wire, we have made a single sputtering target of Nb-Al compound by powder metallurgy. Thin Nb/sub 3/Al films on MgO substrate were made using this target. Experimental results for these films are presented. [ABSTRACT FROM PUBLISHER]

We have fabricated by SNEP process Nb/Al/NbN/AlN/NbN Josephson junctions with the gap voltage V/sub g/=2/spl Delta//e/spl ap/4.0 mV, subgap leakage R/sub sg//R/sub n//spl ap/6.0, current density measured at the gap current rise J/sub g//spl ap/1.5 kA/cm/sup 2/. The (111)-textured NbN with transition temperature T/sub c//spl ap/16 K have been deposited at ambient substrate temperature. Phase composition and structure of the NbN films were investigated by X-ray diffraction analysis (XRD). It was found that the films have a structure close to the cubic /spl delta/-NbN (JCPDS card N38-11556) and the phase composition and intrinsic stress in NbN depend on Ar and N/sub 2/ partial pressure during DC magnetron sputtering. Cross-sectional TEM analysis showed that in-situ deposition of thin Al layer in the base Nb/Al/NbN electrode provides effective planarization of its surface and the result in improvement of tunnel junction parameters. [ABSTRACT FROM PUBLISHER]

The article discusses an investigation of the possibility of highlighting the processes associated with physical and chemical relaxation contributing to the general process of relaxation of the rubber face part of gas mask from the general spectrum of stress relaxation times. It suggests that the method of measuring the stress relaxation at indention allows to single out the processes of physical relaxation and estimate their proportion within the process.

There is a current research tendency towards the biodegradable thermoplastic materials from renewable re- sources since the environmental restraints play vital role in recent years. Starch is one of the renewable resources and abundantly available in the form of plant products. It is possible to blend starch with various thermoplastic materials to achieve such aims. In this study, an ethylene-vinyl acetate (EVA) copolymer resin (Luvax 40 W, DuPont) was blended with a modified starch (Maize Starch, Pendik Nisasta) in various amounts by means of a single screw extruder with different screw speeds. For this purpose, first starch was modified in a four neck spherical glass reactor. Modified starch was then blended with the EVA copolymer resin. Rheological analyses of these composites were performed by means of an AR G2 rheometer (TA Instruments) with parallel-plate geometry in a steady state condition. Rheological behavior and properties were recorded. The changes in viscosity with different temperatures, stress and strain dependence as well as general constitutive material behavior were determined in detail. As a result, the best formulation and process conditions were determined for the reasonable processability of starch/EVA blends from the obtained rheological data. [ABSTRACT FROM AUTHOR]

In present study, effect of quartz particle size on microstructure and stain resistance of porcelain tiles were examined. Milling time was utilized as a main parameter to control residual quartz particle size. 12, 16 and 20 min milling time were used in a laboratory condition. As milling time increases, the particle size of residual quartz decreases. This reduction in the residual quartz particle size results in enhancement of the microstructure. When the microstructure contains irregular pores with high aspect ratio which are generally formed around the residual quartz in the body, stain resistance of the porcelain tiles decreases. Therefore, microstructural changes versus quartz particle size were investigated considering stain resistance of the polished porcelain tiles. [ABSTRACT FROM AUTHOR]

Using molecular dynamics simulations with a Tersoff-type force field, we studied the deformation of cubic diamond film subjected to uniform strain rates at 30 K. The results show that at high strain rates, the diamond cubic phase transforms continuously to a multilayer graphene phase; and the graphitization begins from the (011) free surface and goes rapidly into the inner of the film. In this paper, we discuss the mechanism of graphitization and calculate the energy barrier of the graphitization. [ABSTRACT FROM AUTHOR]

The article presents a discussion on the paper "Determining Slipping Stress of Prestressing Strands in Confined Sections," by Mohamed K. ElBatanouny and Paul H. Ziehl. The discusser ask the authors as to how they obtained the transfer lengths when the data could not be found in the paper authored by Mohsen Shahawy and Moussa Issa. According to the discusser, environmental studies on development length and bond behavior after strand slippage have been conducted using the ECADA test method.

A new substrate material LSAT, a 30/70 mole % solid solution between LaA103 and Sr2AITaO6, has been prepared for the purposes of eliminating twinning, strain and non-isotropic microwave properties found in pure LaA103 substrates. At 300 K and 30/70 mole %, LSAT is cubic with lattice parameter of 7.737 Å. The dielectric properties of single crystal LSAT (30/70 mole %) substrates have been measured at 10 GHz and 300 K and determined to be: dielectric constant ε=22.5; and, loss tangent tan(δ) ⩽ 10-3. High quality c -axis oriented high critical temperature superconducting (HTSC), YBa2Cu307-δ (YBCO), thin films have been deposited on (001) single crystal LSAT substrates. The crystal quality of these films is excellent as evidenced by the full width half maximum (FWHM) rocking curve widths of typically 300 arc-seconds. Critical current densities (as measured using magnetization) are about 4 × 106 A/cm2 at 10 K. Microwave film properties include an onset transition temperature (Tc) higher than 91 K, transition width (ΔTc) less than 5 K, surface resistance RS lower than copper (30 mω) at 85 K and 35 GHz for a film of thickness 2500 Å. [ABSTRACT FROM PUBLISHER]

The absolute stress in the in-service steel members is a critical indicator employed for the evaluation of structural performance. In the field of structural health monitoring, the stress is usually monitored by the stress monitoring system. However, the monitored stress is the relative value, rather than the absolute value. The longitudinal critically refracted wave has shown potential for use in absolute stress measurement. The accurate measurement of the longitudinal critically refracted wave time-of-flight is the core issue with this method. In this study, a cross-correlation-based algorithm is presented for stress evaluation using the longitudinal critically refracted wave. Specifically, a cross-correlation theoretical formula is derived and a five-step framework is proposed for the longitudinal critically refracted wave time-of-flight measurement. Four steel members are employed to investigate the parametric calibration using the longitudinal critically refracted wave to measure the stress. On this basis, the proposed cross-correlation-based algorithm is used to evaluate the stress of a steel member. The results indicate that the cross-correlation-based algorithm can measure the longitudinal critically refracted wave time-of-flight without filtering the noise signal, and the stress measurement results are better than those of the traditional peak value method. The proposed method provides a potential way to measure the absolute stress in practical engineering applications. [ABSTRACT FROM AUTHOR]

In this paper, we present the viscoelastic solutions for rockmass supported with discretely mechanically or frictionally coupled (DMFC) rockbolts to reveal the coupling rheological mechanisms. The analytical solutions are first acquired by applying the Laplace inverse transforms. The effect of different viscosity coefficients and supporting parameters on the coupling model rheological behavior are then investigated. It is concluded that the variation of the rockbolt axial force or rock mass stress and displacement have a close relationship with rheological parameters and support parameters. In addition, the variations of mechanical states of rockbolts and rock mass are closely related to the rheological model. [ABSTRACT FROM AUTHOR]

A device for in situ use with a micro-Raman microscope to determine stress from the Raman peak position was designed and validated. The device is a four-point bend machine with a micro-stepping motor and load cell, allowing for fine movement and accurate readings of the applied force. The machine has a small footprint and easily fits on most optical microscope stages. The results obtained from silicon are in good agreement with published literature values for the linear relationship between stress and peak position for the 520.8 cm−1 Raman peak. The device was used to examine 4H–SiC and a good linear relationship was found between the 798 cm−1 Raman peak position and stress, with the proportionality coefficient being close to the theoretical value of 0.0025. The 777 cm−1 Raman peak also showed a linear dependence on stress, but the dependence was not as strong. The device examines both the tensile and compressive sides of the beam in bending, granting the potential for many materials and crystal orientations to be examined. [ABSTRACT FROM AUTHOR]

Large residual stress induced during the electroforming process cannot be ignored to fabricate reliable metal microdevices. Accurate measurement is the basis for studying the residual stress. Influenced by the topological feature size of micron scale in the metal microdevice, residual stress in it can hardly be measured by common methods. In this manuscript, a methodology is proposed to measure the residual stress in the metal microdevice using micro Raman spectroscopy (MRS). To estimate the residual stress in metal materials, micron sized β-SiC particles were mixed in the electroforming solution for codeposition. First, the calculated expression relating the Raman shifts to the induced biaxial stress for β-SiC was derived based on the theory of phonon deformation potentials and Hooke’s law. Corresponding micro electroforming experiments were performed and the residual stress in Ni–SiC composite layer was both measured by x-ray diffraction (XRD) and MRS methods. Then, the validity of the MRS measurements was verified by comparing with the residual stress measured by XRD method. The reliability of the MRS method was further validated by the statistical student’s t-test. The MRS measurements were found to have no systematic error in comparison with the XRD measurements, which confirm that the residual stresses measured by the MRS method are reliable. Besides that, the MRS method, by which the residual stress in a micro inertial switch was measured, has been confirmed to be a convincing experiment tool for estimating the residual stress in metal microdevice with micron order topological feature size. [ABSTRACT FROM AUTHOR]

The article responds to comments on a paper about the transfer length in prestressed self-consolidating concrete (SCC) box and I-girders. It notes the elimination of conventional concrete (CC) load-slip curves mainly because of paper length's constraints. It agrees on the increase in time strain due to concrete shrinkage and creep.

Pulsed tandem gas metal arc welding (PT-GMAW) is being developed to increase productivity and minimise weld-induced distortion in ship-building. The PT-GMAW process was used in pulse–pulse mode to butt-weld two different strength and thickness steels; the residual stress and hardness profiles of the welds are reported and correlated. [ABSTRACT FROM AUTHOR]

By analyzing the field data from nine metro-station pits with aspect ratios (AR) of pit length to width of 6.6-19.4 in Shanghai soft clay, this paper investigates the potential corner effects (i.e., the retaining walls near pit corners have stronger capabilities to resist deformation than those distant away as a product of spatial arching effects across the pit corners) of long and narrow multipropped metro station excavations. Contrary to the two-dimensional (2D) plane-strain assumption widely adopted in practice for analysis of a metro station excavation (i.e., deformations of the pit in which the displacements of all points along the longitudinal sides are assumed to be parallel to a given plane in the transverse direction and the values of these displacements do not depend on the distance perpendicular to the plane), seven out of the nine metro station pits exhibited apparent corner effects and only two showed plane-strain conditions. Because of the stiffening effects from the pit corners, the minimum wall deflections occurred near the pit corners and the maximum occurred near the middle span of the pits. The development of the maximum wall deflections along the longitudinal sides of the pits, which were normalized by the final excavation depths, can be bounded by two liner curves. Because of their narrow widths, the observed corner effects of the metro stations were less pronounced than that of a rectangular excavation with an AR of about 2.0. Distinctly different from the findings in literature for regular rectangular excavations with AR of 1.0-2.0, the variation of either the pit length-to-depth ratio or the pit length-to-width ratio hardly affected the corner effects of metro station pits. The derived graphical solutions accounting for the influence of pit lengths on corner stiffening effects can be used as references for future design and construction of a long and narrow multipropped pit in soft clays. The monitoring data regarding the adjacent building settlements demonstrate that the mobilized corner stiffening effects during excavation were helpful in constraining the ground deformation and protecting the structures or facilities in the proximity. [ABSTRACT FROM AUTHOR]

The article presents miscellaneous topics including the stress analysis software March 2013.1 from MSC Software Corp. and publication of topics from the 2013 Proceedings of International Conference on Airworthiness and Fatigue in the journal "Science China Physics, Mechanics & Astronomy."

This paper presents an experimental study on the aggregate contact behavior in asphalt mixture. As a three-phase material composed of aggregates, asphalt binder, and air voids, asphalt mixture is considered as a viscoelastic material at a low stress level. The behavior of the mixture depends largely on the interaction among different components. A contact model between two aggregates is very important for understanding the deformation mechanism of the mixture. In this study, a contact model between two aggregates was reviewed in details. A closed-form time-dependent relationship between the contact forces and the relative particle/binder movements was derived. An experimental test was designed to evaluate the model which contains two elastic particles bonded by a thin layer of asphalt binder. The displacement and resistant force of the aggregate-binder system under uniaxial compression loading were documented using a cabinet X-ray tomography system. The effectiveness of the model was evaluated by comparing the experimental results with the theoretical model predictions. It was found that the model performs better when the thickness of binder is thinner. Polynomial regression equations are more suitable to fit the model-predicted results with experimental results. Selection of the model parameters is also critical to the performance of the model. The effect of the binder film thickness on the aggregate-aggregate contact was also discussed with different binder layer thicknesses. It was found that the stiffness of the aggregate-binder-aggregate system increases as the bonding layer gets thinner, which indicates that optimum asphalt content is very important to the mix design of asphalt concrete. [ABSTRACT FROM AUTHOR]

Shear deformation of -Sn along five different lattice orientations is studied at the atomic level. Simulated models are perfect -Sn lattice without defects. To study the atomic behavior and constitutive relationship of -Sn in shear, the -Sn models are simulated by a molecular dynamics simulation package, LAMMPS, and the shear stress is computed by using virial stress. A modified embedded-atom method is employed for the -Sn potential. The constant shear strain rate, 17.5 (%/ns), is applied. Simulation is conducted by using a canonical ensemble. To investigate thermal effects, the models are simulated at three different temperatures, 27, 127, and 227°C, and the results were compared with experimental data. [ABSTRACT FROM AUTHOR]

We show suppressed relaxation behavior and an apparent hardening effect under repeated loading in metallic glasses through cyclically tensile stress relaxation experiments. The effects are attributed to the gradual exhaustion of deformation units via activation energy spectra analysis. We find the suppression is partly alleviated and rapidly saturates with increasing the time interval between the cyclic loadings, reflecting the observed phenomena are associated with the un-recovered activated deformation units. These results may shine light on the long-standing issues such as the fatigue damage, cyclic hardening, and the deformation mechanism of metallic glasses. [ABSTRACT FROM AUTHOR]