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A new methodology for the estimation of tyre-contact forces is presented. The new procedure is an evolution of a previous method based on harmonic elimination techniques developed with the aim of producing low cost dynamometric wheels. While the original method required stress measurement in many rim radial lines and the fulfillment of some rigid conditions of symmetry, the new methodology described in this article significantly reduces the number of required measurement points and greatly relaxes symmetry constraints. This can be done without compromising the estimation error level. The reduction of the number of measuring radial lines increases the ripple of demodulated signals due to non-eliminated higher order harmonics. Therefore, it is necessary to adapt the calibration procedure to this new scenario. A new calibration procedure that takes into account angular position of the wheel is completely described. This new methodology is tested on a standard commercial five-spoke car wheel. Obtained results are qualitatively compared to those derived from the application of former methodology leading to the conclusion that the new method is both simpler and more robust due to the reduction in the number of measuring points, while contact forces’ estimation error remains at an acceptable level. [ABSTRACT FROM AUTHOR]

A comprehensive review is done of different NBTI mechanisms and models proposed in the literature over the past years. The Reaction-Diffusion (RD) model based comprehensive framework and the alternative Energy Well (EW) models are discussed. The model capabilities to simultaneously predict the temporal kinetics of stress and recovery are evaluated. Key experimental signatures that support or refute model assumptions are highlighted. [ABSTRACT FROM AUTHOR]

The prestress loss is one of the main factors affecting the safety of prestressed concrete structure. While the detecting signals like sound and light are difficult to spread in steel strands, there is no effective method for prestress detection of the bonded prestressed steel strands in existing structures yet. In this paper, taking into consideration that the electromagnetic oscillation characteristic can make the signal propagate effectively on the bonded prestressed steel strands, a nondestructive prestress detection method based on the electromagnetic effect to detect oscillation frequency is proposed. In a detection circuit, the steel strands are simulated as an inductance component, in which an induced electromagnetic signal passes through the steel strands to form resonance. And then, a frequency meter is used to detect the oscillation frequency of the resonant circuit. The oscillation frequency is supposed to have relationship with the prestress loading on the steel strands. A section of steel strands with a length of 1.2 m is adopted to test the correlation of stress and oscillation frequency. Both the theoretical and experimental results show that the resonant frequency of the circuit decreases with the increase of the stress of the strand and is linear in a certain range. [ABSTRACT FROM AUTHOR]

To face the increasing demand of residual stress measurement in many hi-tech industries, the integration of photoelasticity and advanced image acquisition equipment is a natural trend. With the integration of photoelasticity and spectrometry, the measurement capability of low-level stress and the stress in low birefringence materials can be enhanced. In fact, there is a significant correlation between the stress level and transmissivity spectrum. The key of the stress measurement method proposed in this paper is to find this scarcely explored correlation. By analyzing the periodic extinction phenomenon of isochromatic fringe pattern obtained from white light photoelasticity and the equation of transmissivity spectrum expressed in stress and wavelength, a three-dimensional (3D) systematic relationship of transmissivity with stress and wavelength can be established. By applying the 3D systematic transmissivity with stress and wavelength, the stress value can be determined directly from the transmissivity of the light transmitted through the polariscope. Moreover, when the proposed method is employed, the required parameters can be directly obtained from the database. There is no need to know the wavelength-dependent stress-optic coefficient beforehand. Glass, a very low birefringence material, was used to confirm the feasibility of the proposed method. Two regression approaches to search the transmissivity extremities were attempted to find the optimum systematic relationship. [ABSTRACT FROM AUTHOR]

Continuous, real-time and remote measurement of stress in underground coal mines plays a vital role in the safety of the mines. Vibrating wire-based geotechnical sensors are widely used for stress measurement of strata in underground coal mines. These types of sensors have several advantages over other geotechnical sensors. However, the measurements from these sensors are taken in-situ using conventional readout unit manually till date even in the case of deep underground coal mines where the depth of cover is more than 300 m. When sensor site moves to inaccessible places due to dynamic nature of mining, then the measurement is discontinued and instruments become abandoned. Also, sensors connected through wire get disconnected during movement of machinery, roof falls, and other associated hazards. Therefore, there is a need for wireless sensing platform for vibrating wire-based geotechnical sensors which can assess the stress on a real-time basis and obviate the impending mishap associated with the strata failure. Hence, in the present paper, authors have designed a prototype wireless real-time sensing platform for vibrating wire-based geotechnical sensors for continuous, real-time and remote monitoring of strata behavior. The laboratory trial and the field demonstration of the same have been carried out and compared with conventional readout. The results are in agreement. [ABSTRACT FROM AUTHOR]

In this work, a magnetoelastic sensor to detect the micrometer diameter variations of cylindrical elements is analyzed. A nearly zero magnetostrictive amorphous ribbon with nominal composition (Co 0.93 Fe 0.07 ) 75 Si 12.5 B 12.5 was selected as sensor nucleus. The sensor, based on Giant Stress-Impedance (GSI), is attached (glued) along the external perimeter of the cylindrical element. Changes in the cylindrical diameter, D M , induce effective tensile stresses, σ S , on the ribbon, giving rise to sensitive changes in the high frequency impedance, Z. The sensor response is analyzed in terms of the relationship between the induced strains and the diameter variations, where the effect of geometrical factors (cylinder diameter and sample length) is taken into account. The results indicate that although the maximum GSI ratio depends on the pre-induced bending stresses associated to the cylindrical configuration, the sample length plays the dominant role in the sensor sensitivity. The proposed device enables to monitor the micrometric diameter variation in cylindrical elements, with a maximum strain gauge factor (GF ≈ −80) for low induced strains. [ABSTRACT FROM AUTHOR]

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Austenitic stainless steel (ASS) grade 304 is being extensively used in various high-temperature applications, which makes it important to study their properties at elevated temperatures, especially the flow stress behavior. The literature reveals flow stress of the material depends on influence of various input parameters, the important ones being the strain, strain rate and temperature. It is often noticed that these process parameters are determined by trial-and-error approach, which results in increased material failure and power losses. Constitutive models have also been developed to find the relationships between them, but these models have computational limitations and cannot capture the true stress behavior at elevated temperatures. Therefore, there is a need for formulation of a generalized explicit model/expression that can predict accurately the behavior ASS 304 at elevated temperatures. Therefore, this work proposed a new variant of genetic programming, gene expression programming (GEP), to formulate a model for true stress of ASS 304. True stress model formulated based on M-MGGP methodology has outperformed the GEP approach. Further investigation is carried out by sensitivity and parametric analyses to determine the relationships between process parameters, and it was found that the temperature has highest impact on the true stress of ASS 304 steel. [ABSTRACT FROM AUTHOR]

It is desirable to combine the stress measurement data produced by different methods to obtain a more reliable estimation of in situ stress. We present a regional case study of integrated in situ stress estimation by hydraulic fracturing, observations of borehole breakouts and drilling-induced fractures, and numerical modeling of a 1 km-deep borehole (EXP-1) in Pohang, South Korea. Prior to measuring the stress, World Stress Map (WSM) and modern field data in the Korean Peninsula are used to construct a best estimate stress model in this area. Then, new stress data from hydraulic fracturing and borehole observations is added to determine magnitude and orientation of horizontal stresses. Minimum horizontal principal stress is estimated from the shut-in pressure of the hydraulic fracturing measurement at a depth of about 700 m. The horizontal stress ratios ( S / S ) derived from hydraulic fracturing, borehole breakout, and drilling-induced fractures are 1.4, 1.2, and 1.1-1.4, respectively, and the average orientations of the maximum horizontal stresses derived by field methods are N138°E, N122°E, and N136°E, respectively. The results of hydraulic fracturing and borehole observations are integrated with a result of numerical modeling to produce a final rock stress model. The results of the integration give in situ stress ratios of 1.3/1.0/0.8 ( S / S / S ) with an average azimuth of S in the orientation range of N130°E-N136°E. It is found that the orientation of S is deviated by more than 40° clockwise compared to directions reported for the WSM in southeastern Korean peninsula. [ABSTRACT FROM AUTHOR]

Whilst crack growth retardation following the application of an overload during variable amplitude loading is a well-known spectrum effect, the order of smaller amplitude cycles can also affect crack growth. One method of accounting for such spectrum effects in crack growth prediction algorithms is by correcting the estimated effectiveness of each cycle or group of cycles. Such predictions are usually verified by comparison to demonstrated total fatigue lives. These corrections have been shown to be suitable for cracks that are at least several millimetres long. However, for physically small cracks: here defined as less than a few mm in depth, such predictions are often far less accurate. In the case of aluminium alloy aircraft structures, where cracks typically grow approximately exponentially from small discontinuities, these predictive algorithms should also be evaluated for their ability to predict small crack growth rates, rather than total life alone. To examine the more subtle crack growth acceleration and retardation effects from individual load cycles in typical aircraft structural 7XXX aluminium alloys, this paper presents the results of quantitative fractography measurements of very small fatigue crack growth increments produced under the application of specially engineered spectra. One such spectrum that contained short segments of constant amplitude loads of various mean stresses, was designed to examine the extent of crack growth retardation, such as from closure, at a range of small crack lengths. Other spectrum effects were also explored through use of test spectra with constant amplitude cycles that were either separate to or embedded within small segments of variable amplitude loading. The local growth produced in each case was then measured and compared to predictions produced by two closure/retardation correction methods; based on wake and plastic zone related phenomena. The results showed that the prediction methods, although they made allowances for the presence of subtle retardations and accelerations, did not accurately predict these effects over the increments of growth examined. [ABSTRACT FROM AUTHOR]

Predicting life times of structures, machines and their parts as well as very small electronic devices for medical purposes is especially difficult for very low stress amplitudes and very high numbers of cycles. The development of the ultrasonic-fatigue method resulted in a reliable testing technique for VHCF loading. Some of its properties are described in this paper. To offer an explanation for the somewhat controversial ultrasonic-fatigue properties reported in the literature, S - N tests were performed at ∼19 kHz and 20 Hz on polycrystalline copper – a nominally homogenous and ductile material. Moreover, plastic-strain measurements were performed. In addition, micro-structural features and their changes in the high and very-high cycle regimes are reported. [ABSTRACT FROM AUTHOR]

The cos α method and the 2D method are well known as X-ray stress measurements using an area detector. Although the X-ray exposure of the cos α method occurs once, the accuracy of the center of the detector is required due to usage of the oblique incident X-ray beam. In the 2D method, the X-ray beams have to be applied from multiple orientations, and multiple measurements are required. In this study, I propose a new method for X-ray stress measurement using an area detector. Its method is called the direct-method”. The diffraction angles are measured with the area detector and the normal incident X-ray beam, and then the stresses are optimized by a simplex method. To examine effectiveness of the direct-method, I measured the residual stresses caused by water-jet peening. The stresses obtained were close to those obtained by the other method. It is discussed that precision of a detector center is important in usage of the area detector. In the case of the normal incident X-ray beam, the shape of the diffraction ring is an ellipse and has point symmetry at the origin. Using this property, the center of the area detector can be corrected. Further, the direct-method was applied to measuring the residual stresses coming from the grinding process. After correcting the center of the diffraction ring, the stresses which were optimized by the simplex method corresponded to those measured by the sin 2 ψ method. In addition, the direct-method was extended to a cos α method. [ABSTRACT FROM AUTHOR]

The experimental research shows that ceramic top coat (TC) exhibits obvious strength difference (SD) in tension and compression, called SD property. This property significantly affect stress evolution, however, there are few attentions to it. In this paper, the stress evolution in TC layer is investigated by considering SD property. To reflect its property, a return mapping algorithm model for unified strength theory (UST), proposed by us, is applied. The results reveal that SD property leads to the movement of maximum tensile stress from interface to the position above it. It suggests that the crack might not be directly initiated at interface but above it, which has been reported in experimental studies too. The results also reveal that the possibility of above-interface cracking could be increased by varying the material properties, such as elevating compressive-tensile strength ratio and reducing yield strength of TC, and by changing the coating geometries, such as thickening thermally grown oxide (TGO) layer and increasing TC interfacial amplitude-wavelength ratio. [ABSTRACT FROM AUTHOR]

The direct stress measurement is critical for the constitutive law investigation of concrete materials and dynamic behavior study of concrete structures under strong dynamic loadings where the strain-rate effect and the plastic behavior should be considered. In this article, an embedded dynamic internal normal stress sensor for concrete by employing piezoelectric lead-zirconate-titanate (PZT) patch as a sensing element is developed. After being calibrated under sinusoidal loadings with different frequencies, periodical square loadings, and random loadings, the developed dynamic internal normal stress sensor is further calibrated with a unique self-developed free-falling drop hammer with different impact velocities. The sensitivity of the developed normal stress sensor is determined accordingly. Finally, the developed sensors are employed to monitor the dynamic normal stress time history at different locations of concrete cylinder specimens under impacts with different velocities using a large-scale drop hammer test facility. The dynamic increase factors of concrete strength under impact are determined and compared with the values determined by the ComitéEuro-International du Béton code. The experimental results indicate that the PZT-based embedded dynamic internal normal stress sensor provides a novel way for the direct dynamic normal stress measurement of concrete specimens under impact loadings. [ABSTRACT FROM AUTHOR]

The objective of the present paper is to propose a methodology to numerically simulate (i.e., initialize) the pre-mining stress field in complex but rather frequent situations in which the classical overburden-weight assumption and existing stress measurements are in disagreement and where the stresses strongly vary from one zone to another, even at constant depth. This methodology is illustrated by the case of a deep mine in France that exploits a 10°-dipping coal seam, in which numerous stress measurements were carried out. Virgin principal stresses in this mine have been shown to be highly heterogeneous and anisotropic. To correctly reproduce such a challenging initial stress state in a numerical model and to be able to later calculate mining-induced stresses, five distinct methods (M#1 to M#5) are successively presented and compared, along with their advantages and drawbacks. All of them are based on “fixed” boundary conditions, with null normal displacements on all lateral boundaries except on the top one, which is considered as a free surface of the Earth coinciding with the natural flat topography. The initial conditions of the model assume that the pre-mining stress components linearly depend on the Cartesian coordinates x , y and z (depth), and the Simplex Method is used to calculate the linear coefficients by minimizing the squared difference between the measured stresses and their simulated values. We show that the use of 3D stress gradients produces more realistic results than a 1D vertical stress gradient. [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]

This paper investigates the ability of the USAF characteristic K approach to represent the growth of cracks from small naturally occurring material discontinuities. The examples discussed in this paper are associated with two different load spectra. The first case studied involves crack growth in AA7050-T7451 under a combat aircraft load spectrum. The second case studied the crack growth in AA7050-T7451 under a civil aircraft load spectrum. It is shown that using the root mean square value of ΔK in a load block to characterize the stress intensity factor together with the NASGRO equation, with the constants determined from constant amplitude tests on long cracks, enables the growth of small cracks under these two different complex load spectra to be reasonably accurately represented. [ABSTRACT FROM AUTHOR]

Erdaoya tunnel in the highway connecting Shiyan (Hubei province) and Manchuan, (Shanxi province) was studied in the study. Various problems occurred in the construction of the tunnel, including large deformation of surrounding rocks, cracks of preliminary supports and secondary linings as well as creeping down and collapse of surrounding rock masses along schistosity planes. In which, the most serious problem was large deformation of surrounding rocks, which not only dramatically delayed the normal construction progress of the tunnel, but also brought a huge challenge for the safety of builders. In order to solve this problem, detailed investigations were made on site in the study to reveal the regional geological, engineering geological and hydrogeological conditions of the tunnel. By conducting geo-stress measurement on site, the characteristics of geo-stress field of Erdaoya tunnel were analyzed from four aspects, including magnitudes of stress, coefficient of lateral pressure, orientation of stress and the relationship between magnitudes of geo-stresses and depths. By applying the DIPS software for interactively analyzing geological locator data, structure characteristics of rock masses were analyzed for preferred structural planes and schistosity planes in the tunnel site. Furthermore, the authors tested the physical and hydrological properties of the rock specimens collected on-site. So various physical properties (density, void fraction, and wave velocity) and water absorption hydrological property of schist were obtained, which provide underlying parameters support for the deformation and support of surrounding rocks of the tunnel. [ABSTRACT FROM AUTHOR]

In this study, in situ white X-ray microbeam diffraction experiments were conducted to investigate the microscopic deformation behavior of a Cu-Al-Mn superelastic alloy during tensile testing. Local deformation both at a grain scale and an intragranular scale was revealed by analyzing Laue spot streaking that occurred within a grain and in some grains with different orientations. The streaking measured within a grain under tensile load showed inhomogeneous behavior because of an inhomogeneous martensitic transformation. Moreover, the effect was dependent on grain orientation. In a grain with a high Schmid factor, a large dispersion in the 2θ diffraction angle of Laue spots was observed due to significant Laue spot streaking, which can be attributed to that grain's favored martensitic transformation. [ABSTRACT FROM AUTHOR]

Based on 232 sets of well-test results measured at depths from 135.9 to 1407.19 m in 15 coalbed methane (CBM) development blocks in China, correlations between parameters including reservoir pressure (P o ), shut-in pressure (P c ), breakdown pressure (P f ), in-situ stress, coal permeability, and depth ( D ) were determined. The distribution of in-situ stress in the eastern margin of the Ordos Basin (EMOB), southern Qinshui Basin (SQB), and western Guizhou province (WGP) were analyzed systematically, and its control on the coal reservoir permeability was also addressed. The minimum and maximum envelope curves of the stress ratio (including k (( σ H + σ h )/2 σ v )), K H ( σ H / σ v ) and K h ( σ h /σ v )) variability with depth was obtained using the Brown and Hoek (1978) method, and the average envelope curves were established by mathematical derivation on the condition that horizontal principal stresses increase linearly with depth. The results show that the maximum principal stress ( σ H ), minimum principal stress (σ h ) and vertical stress (σ v ) vary with depth and location. Generally, there are two main stress regimes in major coalfields in China: σ H > σ h > σ v (59.48%) and σ v > σ H > σ h (34.52%). The σ H > σ h > σ v stress regime has the smallest proportion (6%), which appears mainly in relatively shallower coal seams (< 742.84 m). Stress ratios, including k , K H and K h , were plotted between two envelopes, which can be used to estimate the range of σ H and σ h at a certain depth. With increasing depths, three ratios decrease toward a fixed value, e.g., K H → 0.86, k → 0.74, and K h → 0.6. For coal seams with a depth > 1000 m, k is generally < 1, indicating that the σ v gradually becomes the dominant stress. Coal reservoir permeability decreases exponentially with the increase in effective in-situ stress (EIS, ( σ H + σ h + σ v )/3 − P o ). Vertically, four distinct vertical bands of coal permeability can be found in the EMOB, SQB and WGP, defined by the compression and deformation of the coal-matrix under certain stress regimes: in shallow coal seams (EMOB, < 800 m; SQB, < 650 m; WGP, < 500 m), coal reservoirs are within a strike-slip faulting stress regime ( σ H > σ h > σ v ) where σ H and σ h tend to increase, and coal permeability decreases exponentially with an increasing depth; in intermediate coal seams (EMOB, 800–1000 m; SQB, 650–825 m; WGP, 500–750 m), the σ v > σ H > σ h stress regime plays a major role, with relatively high coal permeability. For deep coal seams (EMOB, > 950 m; SQB, > 825 m; WGP, > 750 m), CBM development conditions deteriorate due to a state of “extremely low permeability and extremely high in-situ stress”. [ABSTRACT FROM AUTHOR]

We use a relatively simple analytic model incorporating two primary geomechanical factors-in situ stress and frictional coefficient of discontinuity-to assess the critical pore pressure increase associated with CO geological storage that initiates shear activation of pre-existing fractures and faults. Shear activation of fractures/faults can break the sealing integrity along the discontinuities, providing possible CO leakage channels. With an example of Gyeongsang Basin, Korea, which is considered a potential onshore geological storage site, the available in situ stress measurement data are analyzed to infer the stress states at an assumed storage depth of 1 km. The stress magnitudes in the basin are characterized by their spatial heterogeneity, implying that the critical pore pressure may vary depending on locations. As another primary factor for the analysis, frictional coefficient is shown to be possibly correlated with clay content in the host rocks encompassing the discontinuities, and in the infillings within the discontinuities, which demonstrates the possibility of estimating the frictional property from the clay content measurable using borehole geophysical logs. Based on the in situ stress conditions coupled with pore pressure change and assumed frictional coefficient of 0.6, the critical pore pressure is estimated, which would induce shear activation along well-orientated discontinuities for slip under the given stress states and consequently provide potential CO leakage pathways. The estimated critical pore pressure as an upper bound of allowable pore pressure is 4-8 MPa above the hydrostatic pore pressure in most of the basin, whereas the same is 0-4 MPa in the southern part of the basin. These results may be useful in the site selection stage for CO geological storage project. [ABSTRACT FROM AUTHOR]

Coated cemented carbide inserts with diverse compressive residual stresses in the film structure were manufactured applying different substrate bias voltages. Moreover, a portion of the coated specimens was annealed for eliminating compressive residual stresses. Residual stress measurements, nanoindentations, nano- and inclined-impact tests, as well as FEM-supported calculations were performed for assessing the coating's mechanical properties, cohesion, brittleness and adhesion. Furthermore, the cutting performance of the coated inserts was investigated in turning AISI 1045. According to the attained results, coating residual stresses affect significantly the film properties and wear behavior. Hereupon, a certain residual stress level can be considered as optimum. [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]

Numerical and experimental studies of the transit of a mode-2 internal solitary wave over an isolated ridge are presented. All studies used a quasi-two-layer fluid with a pycnocline centred at the middepth. The wave amplitude and total fluid depth were both varied, while the topography remained fixed. The strength of the interaction between the internal solitary waves and the hill was found to be characterized by three regimes: weak, moderate, and strong interactions. The weak interaction exhibited negligible wave modulation and bottom surface stress. The moderate interaction generated weak and persistent vorticity in the lower layer, in addition to negligible wave modulation. The strong interaction clearly showed material from the trapped core of the mode-2 wave extracted in the form of a thin filament while generating a strong vortex at the hill. A criterion for the strength of the interaction was found by non-dimensionalizing the wave amplitude by the lower layer depth, a/ℓ. A passive tracer was used to measure the conditions for resuspension of boundary material due to the interaction. The speed and prevalence of cross boundary layer transport increased with a/ℓ. [ABSTRACT FROM AUTHOR]

The liquid jet impact onto a clamped elastic plate is investigated. The two-dimensional jet of constant thickness and with flat vertical front is initially advancing towards the elastic plate along a flat, rigid, and horizontal plane at a constant uniform speed. The elastic plate of variable thickness is mounted perpendicular to the rigid plane. The maximum stress during the early impact stage is estimated for a given retardation time and a given relaxation time of the plate material. The stresses during the initial impact stage are compared with the static stresses in the plate placed in an equivalent uniform flow. It is shown that the static stresses are always smaller than the bending stresses during the early stage of impact for a given speed and thickness of the jet. This implies that if the stresses in the plate are smaller than the yield stress of the plate material with no plastic deformations in the plate occurring during the unsteady impact stage, then the plate behaves elastically after the impact and plastic deformations are not achieved. Approaching the plastic deformations is treated here as a damage to the plate. The maximum stress increases with an increase in jet thickness. A critical value of the jet velocity, below which the plate is not damaged by the jet impact, is obtained for given characteristics of the plate. [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]

Stress measurement that provides early indication of stress status has become increasingly demanding in the field of Non-destructive testing and evaluation (NDT&E). Bridging the correlation between micro magnetic properties and the applied tensile stress is the first conceptual step to come up with a new method of non-destructive testing. This study investigates the characterization of applied tensile stress with in-situ magnetic domain imaging and their dynamic behaviors by using magneto-optical Kerr effect (MOKE) microscopy assisted with magneto-optical indicator film (MOIF). Threshold magnetic field (TMF) feature to reflect 180 ° domain wall (DW) characteristics behaviors in different grains is proposed for stress detection. It is verified that TMF is a threshold feature with better sensitivity and brings linear correlation for stress characterization in comparison to classical coercive field, remanent magnetization, hysteresis loss and permeability parameters. The results indicate that 180 ° DWs dynamic in the inner grain is highly correlated with stress. The DW dynamics of turn over (TO) tests for different grains is studied to illustrate the repeatability of TMF. Experimental tests of high permeability grain oriented (HGO) electrical steels under stress loading have been conducted to verify this study. [ABSTRACT FROM AUTHOR]

A computationally efficient surrogate model was developed based on artificial neural networks (ANN) to investigate the effect of the new generation of wide-base tires on pavement responses. Non-uniform tire contact stress measurements were obtained using a stress-in-motion instrument. The measured 3-D contact stresses were applied on two extreme 3-D flexible pavement finite element models representing low-volume (thin) and high-volume (thick) roads. Eleven critical pavement responses were modeled at two different material properties input levels-detailed and simplified-depending on data availability. The results rendered by the ANN surrogate models were highly accurate with average prediction error less than 5 % and R-square values higher than 0.95. In addition, two sensitivity analyses were performed to investigate the variables effect on pavement responses. It was found that the type of tire (wide-base vs. dual tire assembly) is more influential than the inflation pressure on pavement responses. However, the tire inflation pressure seemed to have a significant effect on near-surface responses. The developed models were incorporated into a tool to assist designers and engineers in investigating the effect of the pavement responses of wide-base versus dual tire assembly under typical loading conditions and pavement structures. [ABSTRACT FROM AUTHOR]

This is a brief comment to highlight and discuss issues with regards to the high resolution, cross correlation-based, electron backscatter diffraction (HR-EBSD) results presented within the work of He et al. (2016) Advanced Engineering Materials. In this comment, two specific concerns are raised: one, the stress measurements, reported to be as high as 20 GPa, are unreasonable and due to a known artefact in the form of HR-EBSD analysis, which has been corrected in state-of-the-art measurements by patterning remapping; and two, the GND field measurements are incorrectly calculated and show the variations in lattice rotation and are no derived from the gradient of the lattice rotation field, as required when following Nye's analysis. An example of reasonable data is presented to highlight how these artefacts can be avoided in practice using more appropriate analysis techniques. [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]

A series of triaxial creep tests were conducted on warm frozen silts extracted from Qinghai-Tibet Plateau at temperature of −1.5 °C under confining pressures of 0.5, 1.0, and 2.0 MPa, respectively. The applied test stress levels were 30, 50, 60, and 70% of triaxial shear strength, respectively. The test results indicate that the creep strain increases with the increase in applied stress level and there is a stress threshold, based on which the test results can be classified into two types of creep strain curves. The creep strain curve only includes primary and secondary creep stages when the stress level is less than the threshold value. When the stress level exceeds the threshold value, the creep strain velocity gradually increases and the specimen quickly fails in tertiary creep stage. Based on the creep test results, a fractional order rheological element model is established for warm frozen silt, which is also generalized from uniaxial stress state to the three-dimensional stress state. From the analysis on the features of the stress threshold, a creep strength criterion is also proposed simultaneously. Comparing the calculated results of the warm frozen silt with the tested ones, it is found that the predicted results of the proposed model are in good agreement with the test results. In the proposed fractional order model, the relationship between the damage factor and time is established to describe the damage degree of the specimen. Compared with the existing creep constitutive model of frozen soil, the proposed fractional order model has advantages of fewer model parameters, higher simulation precision and wider applicability in analyzing the mechanical properties of warm frozen silt. [ABSTRACT FROM AUTHOR]

This paper reports a novel process to fabricate low cost dummy wafers with stress and temperature sensors for wafer level packaging. The polysilicon piezoresistors and Pt resistors are fabricated in 4-in. wafers with the same pad layout as the actual wafers used in wafer level packaging. Further, the sensors are diced and attached in a face-to-face manner at the test points of the large-size dummy wafers by using benzocyclobutene films. After etching away the substrate material, the sensors are transferred to the dummy wafers, and these wafers are then ready for residual stress measurement in wafer level packaging. The polysilicon stress sensors and Pt resistors are fabricated and transferred, and the longitudinal gauge factors before and after the transfer are measured to be 34.2 and 33.0, respectively. The deviation of the longitudinal gauge factors between pre and post transfer is less than −3.5 %, indicating a sufficient level of accuracy of the transferred sensors for stress measurement. The transverse gauge factors are measured to be much lower than the longitudinal gauge factors and can be neglected. The temperature coefficient of the Pt sensor is measured to be 1.73 × 10/°C. [ABSTRACT FROM AUTHOR]

Porous anodic oxide formation results from a morphological instability of uniform barrier oxide growth leading to the establishment of pores. To gain insight into this process, evidence for microstructural changes in the oxide accompanying pore initiation in anodic alumina was sought through two types of experiments: potentiodynamic anodizing and stress measurements during dissolution of the anodic films. Cyclic voltammetry during anodizing in sulfuric acid shows that pore formation coincides with the appearance of localized ohmic- conducting regions close to the oxide-solution interface of individual pores. These defects induce large current increases which are apparently responsible for growth of concave scalloped features on the metal-oxide interface at the pore base. It is argued that interface defects are generated by surface forces in the oxide that accompany flow contributing to pore initiation. Stress measurements reveal that pore initiation introduces tensile residual stress into the oxide at the pore base, suggesting the formation of vacancy-type defects in the film. Such defects are explained by increases of local conduction current density due to the concentration of anodizing current in pores. Both sets of experiments reveal that pore formation generates locally defective oxide, which may help explain the phenomenon of burning during high-rate anodizing. [ABSTRACT FROM AUTHOR]

Fusion welding is a joining process widely used in the industry. However, undesired residual stresses are produced once the welding process is completed. Post-weld heat-treatment (PWHT) is extensively employed in order to relieve the welding residual stresses. In this study, effect of PWHT time and temperature on the residual stresses of a ferritic stainless steel is investigated. Residual stress distributions in eight welded specimens were measured by using an ultrasonic method. Ultrasonic stress measurement is a nondestructive method based on acoustoelasticity law, which correlates mechanical stresses with velocity of an ultrasonic wave propagating within the subject material. The ultrasonic wave employed could be longitudinal or shear wave produced by the longitudinal (normal) or transverse (shear) transducers, respectively. Ultrasonic stress measurements based on longitudinal waves use longitudinal critically refracted (LCR) waves in this direction, while shear wave methods use an ultrasonic birefringence phenomenon. The results show that the effect of PWHT can be successfully inferred by both longitudinal and shear wave methods, but the former is found to be more sensitive to stress variation. Furthermore, the distribution of subsurface residual stresses is found to be more distinguishable when theLCRmethod is employed. [ABSTRACT FROM PUBLISHER]

This paper presents a back analysis procedure for identification of the elastic parameters of transversely isotropic rock cores, containing an overcoring triaxial strain probe, from the strains measured during a biaxial test. A three-dimensional finite element model was developed to simulate the biaxial test on the overcored rock specimen and to compute the strains at the location of the strain gauges. Different optimisation algorithms were tested and the most suitable one was selected. The back analysis procedure was tested for identification of the five elastic parameters and the two orientation angles that characterise a transversely isotropic rock core. Despite that, with the developed methodology, convergence was reached and all those parameters could be identified, sensitivity analyses demonstrated that the results obtained were not stable, and therefore, they were not reliable. By introducing constrains based on common practice and previous experience, a stable and robust methodology was achieved: the three elastic parameters, E , E and ν , are reliably identified using the value of G calculated with Saint-Venant expression and a fixed value of ν , while the orientation parameters are obtained from observation of overcored rock. Analysis of the results shows that application of this methodology represents an enormous step forward when compared with the traditional use of isotropy. Besides, the methodology is general and can also be used with other types of overcoring equipment. The five elastic parameters and the two orientation angles obtained can then be used, together with the overcoring strains, to compute the complete in situ state of stress. [ABSTRACT FROM AUTHOR]

The constitutive models based on grain size effect are crucial for analyzing the deformation of metal foils. Previous investigations on the constitutive models concentrate on the foils whose thickness/average grain diameter ( T/ D) ratios are more than 3. In this study, the commercial pure titanium foils with thickness of 0.1 and 0.2 mm were employed as the experimental materials. The mechanical properties of foils with dimensions of nine different T/ D ratios categorized into three ranges ( T/ D < 1, 1 ≤ T/ D < 3, T/ D ≥ 3)were tested. Meanwhile, the fracture behaviors and fracture mechanisms of the samples with different T/ D ratios were compared and analyzed. Besides, three constitutive models incorporating the surface layer effect and grain boundary strengthening effect were established for the three T/ D ratio ranges correspondingly. In these models, the thickness of the surface layers is set T for T/ D < 1 foils, D for T/ D > 3, and increases with D linearly in 1 ≤ T/ D < 3. The results calculated by the three models were compared. The experiments indicate that those models are all in good agreement. [ABSTRACT FROM AUTHOR]

Neutron diffraction was used to describe the residual stress distributions in self-piercing riveted (SPR) joints. The sheet material displayed a compressive residual stress near the joint, and the stress gradually became tensile in the sheet material far away from the joint. The stress in the rivet leg was lower in the thick joint of the softer steel sheet than in the thin joint of the harder steel sheet. This lower magnitude was attributed to the lower force gradient during the rivet flaring stage of the SPR process curve. This study shows how the residual stress results may be related to the physical occurrences that happened during joining, using the characteristics curve. The study also shows that neutron diffraction technique enabled a crack in the rivet tip to be detected which was not apparent from a cross-section. [ABSTRACT FROM AUTHOR]

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]

The multi-dimensional ultrasonic-assisted pulsed-laser surface irradiation method was introduced to relieve the residual stress in the AISI 1045 steel specimen based on the Nd:YAG pulsed-laser machine. In this stress relief process, the acoustic energy was imposed into the AISI 1045 steel specimen accompanied by the pulsed-laser surface irradiation, which could be called as the multi-dimensional ultrasonic-assisted stress relief (MDUASR). The mechanism of the MDUASR was discussed based on the thermal activation theory. In addition, the experiments for the MDUASR and the multi-dimensional ultrasonic stress relief (MDUSR) were carried out to validate the residual stress relieving effect and the energy-saving effect of the MDUASR. The results show that the MDUASR has good effect on relieving residual stress and the MDUASR can reduce the energy consumption compared with the MDUSR. Furthermore, the mechanism of the MDUASR can be attributed to the metal softening effect and the dynamic stress effect. The findings confirm that the thermal energy induced by pulsed-laser surface irradiation can be adequately utilized to enhance the metal plasticity, which results in that the residual stress relieving effect of the MDUASR can be improved compared with the MDUSR. It can be concluded that the MDUASR belongs to an energy-saving and green environmental protection technology during the manufacturing process. [ABSTRACT FROM AUTHOR]

The presented study introduces the development of the multi-reflection grazing-incidence X-ray diffraction method (MGIXD) for residual stress determination. The proposed new methodology is aimed at obtaining more reliable experimental data and increasing the depth of non-destructive stress determination below the sample surface. To verify proposed method measurements were performed on a classical X-ray diffractometer (Cu Kα radiation) and using synchrotron radiation (three different wavelengths: λ = 1.2527 Å, λ = 1.5419 Å and λ = 1.7512 Å). The Al2017 alloy subjected to three different surface treatments was investigated in this study. The obtained results showed that the proposed development of MGIXD method, in which not only different incident angles but also different wavelengths of X-ray are used, can be successfully applied for residual stress determination, especially when stress gradients are present in the sample. [ABSTRACT FROM AUTHOR]

The results of residual stress measurements on autofrettage monoblock pressure vessels before and after 100+ pressure and temperature cycles; and, for the first time, in-situ stress measurements on a vessel under high working pressures as measured by neutron diffraction is presented here. High-pressure vessel design depends heavily on finite element analysis (FEA) which, though useful, requires more data to execute a comparison of the stresses encountered in a working pressure vessel. In-situ pressure stress measurements by neutron diffraction may provide useful data for refinements in FEA calculations and determine vessel pressure/temperature cycling behavior. [ABSTRACT FROM AUTHOR]

The present work studied the ultrasonic fatigue fracture of the partially pre-alloyed Fe-Cu-Mn-C powder metallurgy steel fabricated by die-wall lubricated warm compaction. The microstructure and ultrasonic fatigue fracture behaviour were analyzed. A mathematical model was established to solve the fatigue crack growth process. Results indicate that the Fe-2Cu-0.5Mn-1C sintered material has good mechanial properties. The fatigue crack initiates at large pore cluster near the surface of sample, and the ultrasonic fatigue striations have been observed near crack source area. The crack source area is divided into several small regions: the micro fatigue source area, crack growth area and fast fracture area. In addition, if the material breaks at 107 times of cycles loading in fatigue tests, the crack \stabe growth stage accounts for about 8.3×105 cycles, which is only a small part of the whole ultrasonic fatigue fracture process. The cycle times of crack stabe growth stage is inverse proportion to the square of the stress. [ABSTRACT FROM AUTHOR]

A two-step finite element framework is presented that examines the effect of microscale thermal residual stress on the nanoindentation properties of fibre-reinforced composites. Firstly, micromechanical modelling is used to determine the residual stress state following thermal cooldown of a carbon-fibre composite material from cure temperature. A three-dimensional finite element nanoindentation model is then used to characterise the effects of residual stress on material properties determined by nanoindentation theory. The results show that the hardness of the matrix pockets decreases following thermal cooldown due to the existence of equibiaxial tensile residual stresses. The hardness property is also found to decrease for the majority of interfacial region stress states, while the microstructural areas where the effects of the residual stress are nullified are determined. The indentation modulus property is relatively insensitive to the microstructural residual stress, and thus is the recommended indentation property to be determined when carrying out a comparative parametric analysis between microstructural regions. The property changes are shown to be insensitive to any errors associated with contact area estimation using the Oliver and Pharr method. [ABSTRACT FROM AUTHOR]

Severe blade vibrations may reduce the useful life of the high-speed blade. Nowadays, non-contact measurement using blade tip-timing (BTT) technology is becoming promising in blade vibration monitoring. However, blade tip-timing signals are typically under-sampled. How to extract characteristic features of unknown multi-mode blade vibrations by analyzing these under-sampled signals becomes a big challenge. In this paper, a novel BTT analysis method for reconstructing unknown multi-mode blade vibration signals is proposed. The method consists of two key steps. First, a sparse representation (SR) mathematical model for sparse blade tip-timing signals is built. Second, a multi-mode blade vibration reconstruction algorithm is proposed to solve this SR problem. Experiments are carried out to validate the feasibility of the proposed method. The main advantage of this method is its ability to reconstruct unknown multi-mode blade vibration signals with high accuracy. The minimal requirements of probe number are also presented to provide guidelines for BTT system design. [ABSTRACT FROM AUTHOR]

X-ray diffraction techniques have been developed to measure flow stresses of polycrystalline sheet metal specimens subjected to large plastic deformation. The uncertainty in the measured stress based on this technique has not been quantified previously owing to the lack of an appropriate method. In this article, the propagation of four selected elements of experimental error is studied on the basis of the elasto-viscoplastic self-consistent modeling framework: (1) the counting statistics error; (2) the range of tilting angles in use; (3) the use of a finite number of tilting angles; and (4) the incomplete measurement of diffraction elastic constants. Uncertainties propagated to the diffraction stress are estimated by conducting virtual experiments based on the Monte Carlo method demonstrated for a rolled interstitial-free steel sheet. A systematic report on the quantitative uncertainty is provided. It is also demonstrated that the results of the Monte Carlo virtual experiments can be used to find an optimal number of tilting angles and diffraction elastic constant measurements to use without loss of quality. [ABSTRACT FROM AUTHOR]

Steady shear measurements on three yield-stress fluids, a foam and two types of emulsions, were carried out using a smooth torsional parallel-plate geometry, with different gap spacings to assess the effect of wall slip on the normal stress differences. The classical Mooney analysis gave slip-corrected flow curves that agreed with data from a roughened cone-and-plate for all three materials, despite the fact that the compatibility requirement between the flow curve and slip velocity functionalities was not satisfied, indicating that the method is robust for this geometry. All three materials exhibited finite normal stresses following yielding, with power-law exponents of approximately 0.4, as well as shear stresses that can be represented by the Herschel–Bulkley model. The systems showed complete slip for shear stresses below the yield stress, with the stress transmitted to the unyielded material through a thin liquid layer causing an elastic deformation that was measurable for the unyielded foam, which can be represented by the Mooney–Rivlin elastic constitutive equation. The unyielded foam exhibited large sample-to-sample variations in the apparent modulus for identical loading conditions. [ABSTRACT FROM AUTHOR]

Accurate measurements of in situ stress in deep soft rocks are needed to design the tunnel support system and to evaluate the stress redistribution process. Due to the difficulty and weakness of current methods in deep soft rock stress measurement, a new one, rheological stress recovery method to determine the three-dimensional stress tensor is proposed. It is supposed that rock stresses will recover gradually with time and can be measured by embedding transducers into the borehole. According to this method, an original three-dimensional pressure transducer to measure rock stresses is designed and manufactured. In order to investigate the accuracy of the measurement, calibration test and model test have been performed. Both uniaxial and tri-axial calibration tests are conducted to evaluate the transducer performance. For model test, the cement mortar was used to simulate the effect of the surrounding materials. This test considered different rock strengths as well as different types of loading. The results indicate that this transducer is good for stress measurement. [ABSTRACT FROM AUTHOR]

Tectonic activities are frequent in the Lhasa terrane because of the ongoing collision between the India and Eurasia plates. Knowledge of the stress state is critical to evaluate the crustal stability and the design of underground excavations. Because of the limitations imposed by natural conditions, little research has been performed on the present crustal in situ stress in the Tibetan Plateau, and further study is imperative. In this study, hydraulic fracturing measurements were conducted in Nyching County (LZX) and Lang County (LX), Lhasa terrane to characterize the shallow crustal stress state. The results indicate that the stress state in the LZX borehole is markedly different from that in the LX borehole, in both magnitude and orientation. At the same measurement depths, the magnitudes of horizontal principal stresses in the LX borehole are 1.5-3.0 times larger than those in the LZX borehole. The stress regime in the LX borehole favors reverse faulting characterized by SH> Sh> Sv, where SH, Sh, and Sv are maximum horizontal, minimum horizontal, and vertical principal stresses, respectively. The SH and Sh values are approximately three and two times greater than Sv. Fracture impression results reveal that SH in the LX borehole are predominantly N-S, while in the LZX borehole the maximum horizontal principal stress is mainly in the NNE-direction. The heterogeneity of the regional stress state might be a result of the population and distribution of local structures and seismic activities. The stress state in the LX borehole has exceeded the critical state of failure equilibrium, and there is an optimally orientated pre-existing fault near the borehole. It can be concluded that the optimally orientated fault is likely to be active when the stress has built up sufficiently to destroy the frictional equilibrium; it is suggested that research focus should be placed on this in future. The stress states in boreholes LZX and LX indicate uniformity of the regional stress field and diversity of the local stress fields resulting from the interactions among regional dynamic forces, tectonic stress field, and geological structures. [ABSTRACT FROM AUTHOR]

A theoretical generalized plane-strain thermo-poro-elastic (THM) wellbore model is developed for application to the conventional overcore stress measurement method, under the situations when the thermal effect cannot be decoupled from the measured strains on the borehole walls. The THM theory developed by Coussy is used to describe the effects of both the pore pressure and the temperature on the stress and strain distributions around an inclined wellbore, which is assumed to be drilled instantly and subjected to initial stresses with arbitrary directions. The Laplace transformation is used to obtain the temperature, pressure, displacement, strain and stresses in the three-dimensional state around the wellbore. As special cases, the solutions of the above field variables are also provided for the poro-elastic (HM), thermo-elastic (TM) and pure elastic (CM) cases. Based on the THM solutions obtained, the stresses at the borehole wall, which vary with time, provide a bridge to find the in situ stresses from the measured strains at the wellbore surface. In this THM overcore stress measurement method, the temperature and the pressure (if a fluid is present) at the wellbore wall are another two parameters that need to be measured for stress inversion. [ABSTRACT FROM AUTHOR]

Modeling and experiments are used to investigate Lamb wave propagation in the direction perpendicular to an applied stress. Sensitivity, in terms of changes in velocity, for both symmetrical and anti-symmetrical modes was determined. Codes were developed based on analytical expressions for waves in loaded plates and they were used to give wave dispersion curves. The experimental system used a pair of compression wave transducers on variable angle wedges, with set separation, and variable frequency tone burst excitation, on an aluminum plate 0.16 cm thick with uniaxial applied loads. The loads, which were up to 600 le, were measured using strain gages. Model results and experimental data are in good agreement. It was found that the change in Lamb wave velocity, due to the acoustoelastic effect, for the S1 mode exhibits about ten times more sensitive, in terms of velocity change, than the traditional bulk wave measurements, and those performed using the fundamental Lamb modes. The data presented demonstrate the potential for the use of higher order Lamb modes for online industrial stress measurement in plate, and that the higher sensitivity seen offers potential for improved measurement systems. [ABSTRACT FROM AUTHOR]