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Slow earthquakes, including low-frequency earthquakes and tremor, occur in the brittle-ductile (plastic) transition zone on plate boundary faults. To understand how transitions in deformation mechanisms can influence seismic behavior, we conducted stick-slip experiments on halite gouge at normal stresses (σn) of 8 to 113 MPa. In the brittle regime (σn ≤ 18 MPa), the halite gouge showed fast and regular stick-slip associated with velocity-weakening behavior. In contrast, increasing the normal stress within the semibrittle regime (σn ≥ 27 MPa) led to a significant decrease in slip velocity and stress drop, which was associated with a transition from velocity-weakening to velocity-strengthening behavior. Local stress measurements along the simulated faults, made using strain gauges, revealed that the critical nucleation length (Lc) increased with increasing normal stress. Macrostructural and microstructural observations showed that the transition from fast dynamic slip to slow quasi-static slip could be attributed to an increasing contribution from semibrittle/plastic deformation occurring within domains that are heterogeneously distributed within the gouge layer. Our findings suggest that brittle-plastic fault heterogeneity, which may be generated by spatial variations in pore fluid pressure and/or lithology, contributes to the emergence of slow earthquakes. [ABSTRACT FROM AUTHOR]

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: In this paper, an analytical study is carried out on the work‐hardening, elastic‐plastic stress distributions in a cracked body under antiplane shear deformation. A modified Ramberg‐Osgood law is introduced to describe the material behaviour, and stress and strain fields are derived in closed form. Compared with the conventional Ramberg‐Osgood formulation, the new law includes the effect of a new parameter, κ, which allows the transition from the ideally elastic behaviour (low stress regime) to the power law behaviour (large stress regime) to be controlled, thus providing 1 more degree of freedom to better fit the actual behaviour of engineering materials. A discussion is carried out on the features of stresses and strains close to and far away from the crack tip. [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]

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]

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 full automated NIR polariscope has been specially built for residual stress measurement in crystal silicon wafers for solar applications. The multiple configurations of the instrument allow measuring both the isoclinic and the isochromatic parameters on a full field. A new algorithm has also been developed to extract the maximal shear stress inside the silicon wafers without linking the isoclinic parameter to the isochromatic parameter. Hence, it is straightforward to use and the extraction errors are reduced. Coupling this improved data analysis with the comprehensive capabilities of the test rig, allowed to show that the effect of the cutting process on the residual stress inside the silicon wafers is predominant compared with the effect of the cast process, related to the thermal gradient and impurities. [ABSTRACT FROM AUTHOR]

Nickel aluminium bronze is the main material of the controllable pitch propeller in the dynamic positioning system of an ocean-going vessel. When using an X-ray stress measuring instrument to measure the residual stress in this material, measurement failure phenomena often appear since the X-ray diffraction profile of nickel aluminium bronze has a low signal-to-noise ratio. Therefore, the Bragg diffraction angle identified by the traditional method has a large uncertainty, which could cause a large random disturbance of the X-ray stress measurement. Considering the measurement noise and model error, a new approach based on the Bayesian model class framework is proposed to improve the performance of current X-ray stress measurement analysis. For model classes with different peak shape functions, the posterior distributions of the Bragg diffraction angle 2θB are identified first, the posterior probabilities of each model class are computed, a hyper-robust value of 2θB is obtained and finally the residual stress is calculated. Using the confidence intervals of 2θB, the uncertainty of the X-ray stress measuring instrument at each measurement can be determined. Several experiments show that the performance of the proposed method is better than that of the current instrumental method. Of course, the proposed method is also suitable for the residual stress measurement of other new materials and is not limited to nickel aluminium bronze. [ABSTRACT FROM AUTHOR]

Stress measurement methods using X-ray diffraction (XRD) methods are based on so-called fundamental equations. The fundamental equation is described in the coordinate system that best suits the measurement situation, and so making a comparison between different XRD methods is not straightforward. However, by using the diffraction vector representation, the fundamental equations of different methods become identical. Furthermore, the differences between the various XRD methods reside in the choice of diffraction vectors and the way of calculating the stress from the measured data. The stress calculation methods can also be unified using the general least-squares method, which is a common least-squares method of multivariate analysis. Thus, the only difference between these methods turns out to be in the choice of the set of diffraction vectors. In the light of these ideas, three commonly used XRD methods are compared: the sin2ψ method, the XRD2 method and the cosα method, using the estimation of the measurement errors. The XRD2 method with 33 frames (data acquisitions) shows the best accuracy. On the other hand, the accuracy of the cosα method with three frames is comparable to that of the XRD2 method. [ABSTRACT FROM AUTHOR]

A technique to improve X-ray stress measurement using Debye-Scherrer rings is reported. In previous work, a Fourier-series-based generalization of the cosα method was proposed, which can measure the stress from a Debye-Scherrer ring. That technique and the cosα method have difficulties in determining the stress when the grain size of the specimen is relatively large and the Debye-Scherrer ring is grainy. To cope with this problem, in-plane averaging has been used to improve the cosα method when measuring coarse-grained specimens. In this study, Fourier series analysis is incorporated with in-plane averaging and it is explained how in-plane averaging improves the stress measurement. Furthermore, the validity of the new technique is demonstrated by measuring the stress of a carbon steel specimen. [ABSTRACT FROM AUTHOR]

ABSTRACT The layer-by-layer (LBL) assembly technique is an attractive method to make functional multilayer thin films and has been applied to fabricate a wide range of materials. LBL materials could improve optical transmittance and mechanical properties if the film components were covalently bonded. Covalently bonded nanocomposite multilayer films were prepared by employing hydrophilic aliphatic polyisocyanate (HAPI) as the reactive component, to react with Laponite and polyvinyl alcohol (PVA). FT-IR spectra suggested that HAPI reacted with Laponite and PVA at ambient temperature rapidly. Ellipsometry measurement showed that the film thickness was in linear growth. The influences of HAPI on the optical, mechanical and thermal properties of the films were investigated by UV-Vis spectroscopy, tensile stress measurement, DSC and TGA. The obtained results showed that the optical transmittance and mechanical strength were enhanced when the film components were covalently bonded by HAPI. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 545-551 [ABSTRACT FROM AUTHOR]

ABSTRACT This paper reviews some analyses of quantitative fractography measurements of the fatigue fracture surfaces of 7050 aluminium alloy specimens along with relevant fatigue crack information including crack initiating discontinuity size and type. These data were used to assess whether surface finish or applied stress level has any effect on the estimated effective crack initiating discontinuity size, namely the equivalent pre-crack size (EPS). The statistical distributions for the EPSs of the following initiating discontinuity types were examined: chemically etched pits, glass bead peening damage, mechanical damage, inclusions and porosity. The EPSs at various percentile levels for these types were determined on the basis of the samples considered. Finally, the correlation between measured initiating discontinuity depth and EPS was investigated, and good correlation was found in the case of mechanical damage. The purpose of conducting these analyses was to gain a better understanding of the parameters governing the fatigue crack-like effect of discontinuities to facilitate the better prediction of fatigue lives. [ABSTRACT FROM AUTHOR]

ABSTRACT Three-dimensional (3D) finite element analyses are carried out on single-edge bend [SE(B)] specimens for which the J-integral resistance curves ( J-R curves) have been experimentally determined to develop the constraint-corrected J-R curves for the X80 grade pipe steel. The constraint parameters considered in this study include QHRR, QSSY, Q SSY_ m, QLM, Q BM1, Q BM2, A2, h and Tz. The constraint-corrected J-R curves were developed on the basis of the constraint parameters obtained from finite element analysis and experimentally determined J-R curves associated with deeply cracked and medium-cracked SE(B) specimens and validated against shallow-cracked SE(B) specimens. The analysis results indicate that all the constraint parameters considered in this study except QHRR, QSSY, Q SSY_ m and QLM lead to reasonably accurate constraint-corrected J-R curves if the crack extensions are relatively small (≤0.7 mm). For larger crack extensions (≤1.5 mm), the Q BM1-based constraint-corrected J-R curve leads to the most accurate predictions of J among all the constraint parameters considered. [ABSTRACT FROM AUTHOR]

ABSTRACT Rotating bending fatigue test at very high cycle regimes was carried out on martensitic steel of 2Cr13 in air and 3.5% NaCl environment. The result showed that the S-N curve presents a stepwise tendency over the range of 106-108 cycles in both air and 3.5% NaCl environment. In air fatigue, cracks initiated from the sample surface and inclusions at subsurface and no typical fish eye feature in very high cycle fatigue were observed for all samples tested up to 6 × 108 cycles. In 3.5% NaCl solution, a fatigue limit over the range of 106-108 cycles exhibited with the corrosion fatigue strength reduced by 47% compared to the air fatigue. Multiple cracks initiated from surface and the number of crack origins increased with increasing stress level and surface proportion of fatigue propagation increased as number of cycles increased. [ABSTRACT FROM AUTHOR]

ABSTRACT The crack growth retardation is studied theoretically by drilling two symmetric holes at appropriate locations along the crack flanks. A fatigue crack growth code for two-dimensional elastic problems is developed to approve the effectiveness of this method. The crack growth retardation was examined using a parametric study both on the arrangements of the flank holes and the diameters of holes. The numerical results reveal that for some cases, the presence of flank holes significantly decreases the stress concentration around the crack tip and its stress intensity factor. The best positions for crack flank holes to provide the highest crack growth retardation are shown to be where the line connecting the two centres of holes passes the crack tip. A larger hole diameter and a closer distance between the flank holes and the crack tip result in lower crack growth rate and higher fatigue life. [ABSTRACT FROM AUTHOR]

ABSTRACT Load-controlled three-point bending fatigue tests were conducted on API X80 pipeline steel to investigate the effects of stress ratio and specimen orientation on the fatigue crack growth behaviour. Because of the high strength and toughness of X80 steel, crack growth rate was measured and plotted versus Δ J with stress ratio. The fatigue crack length is longer in the transverse direction, whereas the fatigue crack growth rates are nearly the same in different orientations. Finally, a new fatigue crack growth model was proposed. The effective J-integral range was modified by Δ Jp in order to correlate crack closure effect due to large-scale yield of crack tip. The model was proved to fit well for fatigue crack growth rate of API X80 at various stress ratios of R > 0. [ABSTRACT FROM AUTHOR]

Britton criticizes the accuracy of the stress value obtained from electron backscatter diffraction (HR-EBSD) and surmises that the rotation field rather than rotation gradient field was used during geometrical necessary dislocations (GND) calculation process. It is our opinion, however, that the topic of the absolute values of the stresses based on cross correlation and the HR-EBSD technique is not discussed at all in our paper. Our paper is focused rather on relative values (the evolution of stress/strain partitioning at different tensile strains) but not on absolute values. It should, however, be mentioned that, due to the high orientation changes within grains, the error for stress measurements may be considerable, as pointed out by Britton. The stress measurements should, therefore, be regarded with care. We have checked the GND calculation code carefully and we confirm that the correct rotation gradient field data is adopted in the GND calculation process. [ABSTRACT FROM AUTHOR]

ABSTRACT The copper electroplating stress measurement method uses the grain growth in the copper on a machine element that has been subjected to repeated loads. Because this growth is also caused by thermal energy, the effect of the ambient temperature on grain growth density and grain orientation was investigated. Cyclic torsion tests were carried out at temperatures from 293 to 353 K. The relationship among the grain growth density, maximum shear stress, number of cycles, and ambient temperature was formulated to measure the maximum shear stress occurring on the machine element. Moreover, cyclic bending-torsion tests were also performed, and the orientations of grown grains were analysed by electron backscatter diffraction. The slip directions of grown grains corresponded closely with the direction of shear stress in spite of the ambient temperatures. This means that principal stresses can be measured by using the pole figure or the inverse pole figure of grown grains at temperatures up to 353 K. [ABSTRACT FROM AUTHOR]

Die Belastung bestehender Infrastruktur nimmt stetig zu. Bauwerke, insbesondere Brücken, müssen heute deutlich höheren Lasten standhalten als zum Zeitpunkt ihrer Planung und Erbauung. Insbesondere Ermüdung ist bei der Überprüfung und Nachrechnung der Bauwerke ein wesentlicher Aspekt, der in der Vergangenheit schon zu Schadensfällen geführt hat. Im Rahmen des DFG-Forschungsprojekts 'Genauigkeitsgrenzen von Lebensdauerprognosen - Experimentelle und numerische Untersuchung einer Spannbetonhochstraße unter Ermüdungsbeanspruchung' konnte an einer über 50 Jahre alten Spannbetonbrücke in Düsseldorf ein umfangreiches Bauwerksmonitoring (Komponenten: Dauermessung von Spannstahl- und Betondehnungen, Prüfung von Materialproben, Probebelastung, usw.) des Bauwerks durchgeführt werden. Es wird gezeigt, wie die generelle Unsicherheit, die mit Lebensdauerprognosen einhergeht, gezielt reduziert werden kann und sich dadurch die rechnerische Lebensdauer um ein Vielfaches verlängert. Unter 'bestmöglichen Bedingungen' - experimentell fundierter Kenntnis relevanter Eingangsgrößen - werden die Auswirkungen diverser Parameter (Material, Verkehrslasten, Strukturmodell, usw.) herausgearbeitet und ihre Beiträge auf die Prognosequalität quantifiziert. Dazu werden zunächst das Bestandsbauwerk, dann der Ersatzneubau sowie die Situation im Heerdter Dreieck in Düsseldorf, die eine spezielle Planung erforderte, erläutert. Increasing the accuracy of lifetime prediction by structural monitoring of a 50-year old pre-stressed concrete bridge Demands on the existent infrastructure are continuously rising. Today, structures, especially bridges, have to resist significantly increased loads compared to the ones scheduled during projection and erection. In course of inspections and reassessments fatigue turned out to be of high-relevance and even led to cases of severe damage in the past. In the DFG-funded research project 'Precision limits of lifetime prognoses - experimental and numerical investigation of an existent bridge structure subjected to fatigue' focus has been set on substantial structural monitoring of a 50-year old pre-stressed concrete bridge located in Düsseldorf. The measures comprise among others long-time recording of strains (concrete and tendons), material testing and trial loading. It is shown how to capture and systematically reduce inherent uncertainty of lifetime predictions. Thereby the computed structural lifetime considerably increases. In a 'best case scenario', where comprehensive experimental input data is at hand, single parameters (e.g.: material, traffic loads, and structural model) impact on the prognosis as well as on its belonging precision has been quantified. Therefore both, the existent as well as the newly erected structure in the context of Heerdter Dreieck in Düsseldorf which demands for specific projection measures are elucidated. [ABSTRACT FROM AUTHOR]

An atomistic model to account for the impact of stress during solid phase epitaxial regrowth (SPER) is proposed. This model is based on the lattice kinetic Monte Carlo method. It has been compared with experimental data of regrowth velocity as a function of hydrostatic and non-hydrostatic stresses. In particular, it permits to provide a physical explanation of the observations upon in-plane uniaxial stress based on the assumption that {100} events occur through a dual-timescale atomistic mechanism. Our model also catches the fact that compressive normal uniaxial stress and hydrostatic pressure result in an enhancement of the regrowth velocity with a similar activation volume. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

In this article, an analytical model is developed for estimation of the maximum normal stress in a beam-column member subjected simultaneously to an axial load and bending moments. The analytical model is derived by defining the relationship between the maximum strain and average strains measured wirelessly from vibrating wire strain gages. On the basis of the experimental tests on a two-dimensional steel frame structure with beam-column members, the performance of the estimation model is evaluated by comparing the maximum strains directly obtained from electrical strain gages and the estimated maximum strains from the model. Using the model, a practical monitoring of the maximum stress in steel beam-columns is made possible by measuring three average strains at arbitrary locations. [ABSTRACT FROM AUTHOR]

ABSTRACT A simple method to analyse the notch sensitivity of specimens in fatigue tests is presented. The parameter m, which can be used to measure the notch sensitivity, the nominal stress and the stress concentration factor ( Kt) are used to establish the method. In order to verify the feasibility of the method, notch fatigue test results from our group and literatures were collected. The results reveal that an optimal value of parameter m does exist for each material. Life predictions indicated that the model is able to describe the life evolution for notched specimens under high cycle fatigue and low cycle fatigue tests. Because the geometry effect is accounted for Kt, the method is suitable for the conditions when the notch geometries and the absolute dimensions are similar to the tested specimens. [ABSTRACT FROM AUTHOR]

We report for the first time on the thorough experimental and theoretical assessment of the noise limit of mechanical stress and temperature measurements with micro-Raman spectroscopy. A comprehensive study has been performed in which, for different incident laser light intensities and acquisition times, 1000 Raman spectra of mono-crystalline silicon were acquired per setting. Curve fitting was employed to obtain the peak positions of all the spectra, from which the standard deviations of the measured peak positions were obtained versus the total accumulated amount of laser light incident on the sample during one measurement. It has been found that the noise in the obtained peak position decreases as 1/sqrt(n) over more than three decades of the incident amount of laser light. At very low light conditions, the noise decreases as 1/n. By comparing the experimental results obtained to recent theoretical work, we show that the acquisition is limited by photon shot noise over most of the range and is limited by electronic detector noise at very low light conditions only. Pixelation errors do not play a role. It is concluded that the low electronic noise of typical Raman spectroscope detectors is overkill for the investigation of mechanical stress and temperature in silicon and other materials with comparable peaks, as it has absolutely no influence on the noise level of such an experiment. Maximum Raman signal intensity on the detector and high quantum efficiency detection are more important. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We present a new full-field strain measurement method based on diffusing-wave spectroscopy. Our technique makes it possible to measure strains in the vicinity of the surface of highly light-scattering materials. Its main feature is an extreme sensitivity: the range of deformations measured is 10−5-10−3. To validate the measurements, experimental results from several plane stress configurations are compared with theoretical and numerical calculations. Furthermore, we propose an extension of the method for non-scattering materials. [ABSTRACT FROM AUTHOR]

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]