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Stress measurements are required to prevent collapse accidents of structures. Surface SH‐wave acoustoelasticity can measure principal stress difference nondestructively and easily. Currently, surface SH‐wave acoustoelasticity can measure with high precision using a T‐type surface SH‐wave sensor in ideal environments such as in the laboratory. However, in actual environments, it cannot be measured with high precision due to change in the temperature of the specimen. In this paper, temperature dependence of surface SH‐wave acoustoelastic constants was verified to investigate the influence of specimen temperature on surface SH‐wave acoustoelasticity. In addition, the measuring system of surface SH‐wave acoustoelasticity using a cross T‐type surface SH‐wave sensor to reduce the influence of specimen temperature was developed. [ABSTRACT FROM AUTHOR]

Abstract Generally, material stress measurement using ultrasonic longitudinal critically refracted (LCR) wave is inevitably influenced by ambient temperature and coupling condition, which limits its industrial application. In this article, the sensitivity of stress measurement accuracy to temperature variation and coupling condition is discussed analytically and numerically. Based on this, the ultrasonic signal-detecting mode is improved by one-transmitter-two-receiver signal-detecting configuration. Meanwhile, a novel coupling condition is also created by directly filling with couplant between the ultrasonic probe and the measured surface. The testing results showed that the temperature sensitivity could be reduced to 0.81 ns/°C compared with −16.82 ns/°C of the traditional one-transmitter-one-receiver signal detecting configuration, and less distortion and attenuation of the detecting LCR wave signals could also be obtained. Further, a pre-stretched aluminum alloy with uniaxial stress was employed to verify the feasibility of the developed method and probe. The stress measurement accuracy could achieve 20 MPa compared with the simulation results. [ABSTRACT FROM AUTHOR]

A method for stress measurement of steel strands by using electromagnetic oscillation (EMO) circuit only at its both ends, on the basis of magnetic-elastic effect, is proposed in this paper. The basic principle of EMO measurement method is presented, the circuit of EMO is designed, and the experimental system is set up. By stretching the seven-wire steel strand, the stress measurement experiments are carried out. The experimental results indicate that EMO method is an effective approach to measure the stress of steel strands, and it is expected to be used in the stress detection of the existing structures. [ABSTRACT FROM AUTHOR]

To accurately measure in situ stresses using overcore techniques, the key is to find the relationship between the stresses and measured strains on the wellbore wall and on the core at two stages, i.e. before and after overcoring. For gas shales, where there exist large pressure and temperature changes, we developed an analytical model for the stage before overcoring to study the evolution of all field variables, i.e. temperature, pressure, stress, strain and displacement (TPSSD), when an inclined wellbore is drilled in an infinite and homogenous thermo-poro-elastic media (THM) subjected to three far-field principal stresses, whose axes may not coincide with the horizontal and vertical planes. In that paper we investigated the thermal and poro-elastic effects on the strain changes around and especially at the wellbore wall. As an extension of the previous work. In this paper, we describe an analytical model to give the mechanical responses of the wellbore and core for the stage after overcoring. Strain changes at the wellbore wall are examined in detail because these are measured by the overcore method. By using the analytical solutions presented at a specific time and the strains before overcoring as an initial state, the transient solutions for the evolution of temperature, pressure, stress, strain and displacement (TPSSD) are obtained so that for the two critical stages before and after overcoring a reasonable estimate of the in situ stresses can be obtained. As well as the strain changes, the temperature and pressure at the wellbore wall, which vary with time, are also required to find in situ stresses in the inverse model. Fortunately, their effects become progressively less important with time due to the small size of overcored sample. The critical time is calculated when the thermal and porous effects can be ignored. Two cases, i.e. constant and exponentially time-varying temperature boundary conditions, are investigated. [ABSTRACT FROM AUTHOR]

Multistage mini hydraulic fracturing tests were performed in a borehole located in central Hungary in order to determine in-situ stress. At depth of about 500 to 560 meters, observed pressure versus time curve in metamorphic rock (mica schist) show a typical results. After each pressurization cycle, the fracture breakdown pressure in the first fracturing cycle is lower than the reopening pressures in the subsequent reopening and step-rate phases. It is assumed that the composition of the drilling mud and observed foliation of the mica schist have a significant influence on the pressure values. In order to investigate this problem, numerical modeling was performed using the discrete element code (ITASCA Particle Flow Code, PFC), which has been proven as an effective tool to investigate rock engineering problems associated with hydraulic fracturing. The code presented in this study enables simulating hydro-mechanically coupled fluid flow in crystalline rock with low porosity and pre-existing fractures (represented by the smooth joint contact model in PFC) in two dimensions. In this study, the sensitivity of the effect of foliation angle and fluid viscosity on the peak pressure is tested. The anomalous characteristics of the pressure behavior are interpreted in that way that the drilling mud penetrates the sub-horizontal foliation plane, it clogs the plane of weakness and makes the opened fracture tight. Eventually, the process prevents leak-off from the opened fracture that might explain the increased fracture reopening pressure in subsequent cycles. [ABSTRACT FROM AUTHOR]

State of charge (SOC) estimation is one of the important tasks of battery management system (BMS). Being different from other researches, a novel method of SOC estimation for pouch lithium-ion battery cells based on stress measurement is proposed. With a comprehensive experimental study, we find that, the stress of the battery during charge/discharge is composed of the static stress and the dynamic stress. The static stress, which is the measured stress in equilibrium state, corresponds to SOC, this phenomenon facilitates the design of our stress-based SOC estimation. The dynamic stress, on the other hand, is influenced by multiple factors including charge accumulation or depletion, current and historical operation, thus a multiple regression model of the dynamic stress is established. Based on the relationship between static stress and SOC, as well as the dynamic stress modeling, the SOC estimation method is founded. Experimental results show that the stress-based method performs well with a good accuracy, and this method offers a novel perspective for SOC estimation. [ABSTRACT FROM AUTHOR]

Robot-assisted therapy can provide effective rehabilitation training for stroke patients. The interfacial stress between the manipulator and the grasped patient's body is very important for a rehabilitation therapy robot. This paper presents a measurement method, which is able to decouple the measurement of the three-dimensional (3-D) interfacial stress components. To implement the method, interfacial stress sensors were fabricated based on plate capacitance and a superelastic material, while a high-resolution microcapacitance measurement circuit was developed based on a minimal system microprocessor and a programmable controller, and experiments are carried out by using a 3-D stress simulation equipment. The results show that the measurement circuit is capable of measuring a range of 1 fF–30 pF capacitance with a resolution better than 1 fF, and the sensor is capable of measuring Z-direction normal compressive stress at a range of \text0-3.0 \textkgf/\textcm^2 with a sensitivity of \text101 \textfF/\textkgf/\textcm^2 and X - and Y-direction shear stress at a range of 0-1.0 \textkgf/\textcm^2 with a sensitivity of \text118 \textfF/\textkgf/\textcm^2. This method can be applied to rehabilitation therapy robots to decouple the measurement of the 3-D interfacial stress components. [ABSTRACT FROM PUBLISHER]

The photoelastic technique has seen some renewed interest in past few years with digital images and image processing new methods becoming readily available. However, further research is needed to improve the precision, the accuracy and the automation of photoelastic technique. The aim of this research work is to get new numerical equations for the phase-shifting method in digital photoelasticity using a plane polariscope. The model was developed to plane polariscope because of the simplicity and low cost of this equipment. To develop the phase shift and respective intensity equations only the analyzer is rotated. A ring under diametral compression is used for the experimental validation. From these intensity equations, the equations for isoclinic and isochromatic parameters are deduced by applying a new numerical technique. This approach can be used to calculate the isoclinic and isochromatic parameters using any number of images. Several analysis are performed with different number of photographic images. The results showed errors reduce when more phase-stepped images are utilized. Hence, one concludes that the uncertainties in results due to effects of errors on photoelastic images can be reduced with a larger amount of phase-stepped images. [ABSTRACT FROM AUTHOR]

Degradation in planar high-k metal gate p- and n-channel MOSFETs, respectively, under negative bias temperature instability (NBTI) and positive bias temperature instability (PBTI) stress is studied using different characterization methods. Ultrafast measure stress measure (UF-MSM) method with a measurement delay of a few microseconds is used to characterize the threshold voltage shift ( \Delta VT ). Gated-diode or direct current IV is used to directly estimate the trap generation (TG) during BTI, after correcting for the measurement inconsistencies. BTI experiments are performed under DC stress at different stress bias ( V\mathrm {G-STR} ) and temperature ( T ) values also under AC stress at different pulse duty cycle (PDC) and frequency ( f ) values. Measured \Delta VT as well as TG show remarkable similarities between NBTI and PBTI stress, under both DC and AC stress. It is shown that TG dominates NBTI and PBTI degradation under both DC and AC stress. [ABSTRACT FROM PUBLISHER]

This paper presents the Self-excited Acoustical System (SAS) in elastic construction stress change measurement. The system is based on the acoustical autoresonance phenomena and enables an indirect measurement of the construction effort level. The essence of the SAS system is to use a piezoelectric vibration emitter and a piezoelectric vibration receiver placed at a distance, which are coupled with a proper power amplifier, and which are operating in a closed loop with a positive feedback. This causes the excitation of the system. The change of the velocity of wave propagation, which is associated with the change of the resonance frequency in the system is caused by the stress change in the examined material. A variable, which determines the change of the acoustic wave velocity, is called an acoustoelastic coefficient β . Such a coefficient allows to determine the absolute stress value in the tested material. [ABSTRACT FROM AUTHOR]

A reliable and noninvasive measurement method for the inspection of naturally birefringent transparent media is presented in this paper. It allows us to achieve a spatially resolved analysis of the stress state of birefringent materials. The developed system is based on photoelasticity and exploits a controlled laser conoscopy technique and a scanning system to perform local measurements in the volume dimensions of the media, which can be displaced over a grid of points. The configuration of the proposed laser conoscopic system is presented, and a dedicated algorithm, designed to perform digital analysis of the fringe patterns, is also described. The design and the realization of the system are discussed, as well as the advantages of the proposed system over the classic diffuse light polariscope technique. The method has been experimentally validated through laboratory tests on birefringent samples with known induced stress. The system has demonstrated its sensitivity to stress and its capability to achieve a spatial resolution on the order of 0.1 mm to resolve stress gradients (uncertainty on the stress amplitude of ±0.1 MPa). [ABSTRACT FROM AUTHOR]

Connecting rods often fail when subjected to stresses greater than their yield limits. They are designed to support both compressive (usually more intense) and tractive forces. Engineers have used finite element simulations to create new conrod shapes, but the original design still follows the one developed several decades ago. The validation of the results is usually performed through experimental destructive tests or through field evaluations. Thus, a cheaper, non-destructive tool that could expedite the validation process would benefit test engineers and designers. The stress field of a part might be obtained from several methods, the most common of which is through the use of strain gages. In this work, we evaluate the application of electronic speckle pattern interferometry (ESPI) to measure stresses in conrods. The measurements were performed on the flat surface in the conrod web and the results were compared with those from finite element simulations. The region examined corresponds to the inner portion of the rod body, excluding only its slightly thicker edges. To eliminate or at least reduce the influence of the uncontrollable factors (noise) on the results, an experimental design was developed, based mainly on the concepts of the design of experiments (DOE). The tests were performed with a conventional forged connecting rod submitted to compressive stresses. The measurements of the stress and strain fields obtained by the ESPI technique were in accordance with the simulations, showing that this technique is a useful tool for design engineers, improving the safety of engine applications. [ABSTRACT FROM AUTHOR]

Preferentially oriented (0 0 2) ZnO thin films withc-axis-oriented wurtzite structure have been grown on Si (1 0 0) and glass substrates using radio frequency magnetron sputtering. The residual stresses have been determined and calculated via the Stoney formalism. The ZnO thin films have been also characterised by X-ray diffraction and scanning electron microscope, and their stoichiometry was verified by Rutherford backscattering spectroscopy. The evolution of the residual stress was studied as a function of film thickness in the 10–1200 nm range. A growth scenario is proposed and a possible correlation between the residual stress, film’s texture and crystallographic orientation is highlighted. The crystalline quality was found to improve, while the stress values decreased with increasing thickness, and as a ramification the thicker films developed better sensing response to gases. The mechanical (stress) and electrical properties of the films were also investigated as a function of the film thickness, which tended to manifestly improve in dependence on thickness as well. We attribute this to the fact that the thinner films are under vehement misfit stress that declines with increasing the film thickness further. [ABSTRACT FROM AUTHOR]

A measurement methodology involving high-voltage capacitance–voltage ( $C$ – $V$ ) was proposed to determine the trapping profile of a stressed AlGaN/GaN heterostructure field-effect transistor (HFET). Comparing the curves between initial (device without stress) and stressed (device with stress) $C$ – $V$ measurements revealed that the transient behavior was dominated by ionized acceptor-like traps, and the trapping profile within the high drain-to-source OFF-state stressed AlGaN/GaN HFET could be deduced. [ABSTRACT FROM AUTHOR]

One of the most important characteristics of the material allowing us to predict its applicability for specific tasks as a single object or as an integral part of the whole structure is the presence of stresses. There are many methods to measure stress. Among them, increasingly important and recognised as the most accurate non-destructive method is the X-ray measurement technique. The aim of this study was validation of the results obtained by the X-ray stress measurement method. Stress measurements were performed on samples of the three materials subjected during measurement to the effect of tensile forces. Studies revealed close relationship between the stress values measured by X-ray technique and actual values present in the examined material. The summation of residual stresses present in the material and stresses caused by the effect of external forces was observed. [ABSTRACT FROM AUTHOR]

Abstract: The modified Doorstopper stress measurement technique consists in recording the recovered strains caused by stress relief at the bottom of a borehole drilled in a rock mass and converting the relieved strains into stresses by using the deformability parameters at the measuring point. This conversion is usually based on the assumption of a linear elastic behaviour. Hence, when plastic strains are induced at or near the borehole bottom prior to or during stress relief, the stress tensor calculated by assuming an elastic behaviour can be wrong. Plastic strains develop at the borehole bottom or in its vicinity, causing local damage. Core discing is probably the most visible manifestation of core failure, however, even if no visible signs of damage are present, plastic strains can be induced at or near the borehole bottom, affecting the recovered strains and the calculated stresses. Using Flac3D, the stress relief process for different 3D in situ stress states in an elasto-plastic cohesion softening friction hardening model is simulated in order to determine if the non-elastic behaviour can be detected from the strain recovery curves. Errors on the far-field stress state obtained by assuming an elastic behaviour are calculated. Finally, means of minimizing core damage in the presence of high in situ stresses are briefly explored and discussed. [Copyright &y& Elsevier]

Model validation remains a serious problem within the field of computational granular materials research. In all cases the rigor of the validation process is entirely dependent on the quality and depth of the experimental data that forms the point of comparison. Neutron and X-ray diffraction methods offer the only quantitative non-contact method for determining the spatially resolved triaxial stress field within granular materials under load. Measurements such as this can provide an unprecedented level of detail that will be invaluable in validating many models. In this paper the theoretical foundation underpinning diffraction-based strain measurements, their conversion to local stress in the particles and ultimately into the bulk stress field is developed. Effects such as elastic anisotropy within the particles of the granular material, particle plasticity and locally inhomogeneous stress distribution are shown to not offer any obstacles to the method and a detailed treatment of the calculation of the bulk stresses from the particle stresses is given. [ABSTRACT FROM AUTHOR]

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]

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]

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]