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Important resolution properties of the high-resolution 3-axis neutron diffraction set-up were investigated in the frame of feasibility of its use for strain/stress measurements on bulk polycrystalline samples. The strain analysis was carried out by rocking the BPC-analyzer and the neutron signal registered by a point detector. The so-called rocking curve then provided a sample diffraction profile and could reflect the lattice or structural changes. In comparison with a conventional 2-axis set-up, this instrument alternative could be successfully applied, namely, in the strain/stress measurements in bulk samples exposed to an external load, e.g. in tension/compression rig, in aging machine etc. and provide average strain values over a large irradiated volume of the sample. [ABSTRACT FROM AUTHOR]

The study summarises the selection of dedicated techniques and procedures for measuring real stresses arising in shaft steelwork components due to car-shaft steelwork interactions as well as stresses at critical points of the car frame in the elevator installation in the Regis Shaft of the Wieliczka Salt Mine. The implemented solution and operational parameters of the hoisting installation in the Regis Shaft of the Wieliczka Salt Mine are summarised, the adopted measurement method and dedicated equipment are presented, focusing on the procedure for locating the critical points on the car frame and shaft steelwork. The purpose-built measurement set-up as well as the adopted stress measurement procedure and results are explained in detail. [ABSTRACT FROM AUTHOR]

This study investigated electrical strain gage technology, which is widely used in experimental stress measurement, on an application. Strain gages are used to precisely measure strain directly in a system. This method is carried out to verify the numerical and analytical calculations performed or to record the strain data generated during the active duty of a system and to investigate the fatigue damage. In particular, verifying numerical calculations in the strength-material recovery optimizations of mass-produced systems contributes to the development of the system. In this study, strain measurement using strain gage and strain measurement technology is presented on an application. Information was given about strain gages. A full bridge wheatstone bridge consisting of 4 linear gages was created on a prototype. The system was tested with a load cell validation. Structural finite element analysis of the prototype and analytical calculation of the fullbridge strain gage connection were performed. The results showed that the measurement with the strain gauge differed 1.20% and 1.40% from the analytical and numerical results, respectively. Thus, precision strain measurement technology was successfully presented in engineering systems. [ABSTRACT FROM AUTHOR]

One significant issue associated with in situ stress measurements is that the uncertainty of the results cannot be determined. In this study, we propose a novel analytical procedure for the anelastic strain recovery (ASR) method, an in situ stress measurement method, enabling us to conduct uncertainty quantification based on Bayesian statistical modeling (BSM). The new procedure consists of the following steps: i) measuring the ASR of a rock core with strain gauges, ii) applying a probability model based on BSM to the measured ASR data and simulating the probability densities of the elements of an in situ stress tensor and other parameters; and iii) regarding the probability densities as the results of in situ stress measurements with uncertainty. This paper presents the results obtained by applying the proposed procedure to simulated ASR data. The results show that the uncertainties of some parameters are reduced by giving the elastic moduli. Notably, the rates of uncertainty decrease vary for each parameter. To reveal the cause of these differences, we introduce the new evaluation tool, Sobol' indices, which comprise a global sensitivity analytic tool, to facilitate a quantitative discussion. [ABSTRACT FROM AUTHOR]

We propose a digital model for high quality superlattices by including fluctuations in the superlattice periods. The composition and strain profiles are assumed to be coherent and persist throughout the superlattice. Using this model, we have significantly improved the fit with experimental X-ray diffraction data recorded from the nominal InAs/GaSb superlattice. The lattice spacing of individual layers inside the superlattice and the extent of interfacial intermixing are refined by including both (002) and (004) and their satellite peaks in the fitting. For the InAs/GaSb strained layer superlattice, results show: (i) the GaSb-on-InAs interface is chemically sharper than the InAs-on-GaSb interface, (ii) the GaSb layers experience compressive strain with In incorporation, (iii) there are interfacial strain associated with InSb-like bonds in GaSb and GaAs-like bonds in InAs, (iv) Sb substitutes a significant amount of In inside InAs layer near the InAs-on-GaSb interface. For support, we show that the composition profiles determined by X-ray diffraction are in good agreement with those obtained from atom probe tomography measurement. Comparison with the kinetic growth model shows a good agreement in terms of the composition profiles of anions, while the kinetic model underestimates the intermixing of cations. [ABSTRACT FROM AUTHOR]

This study evaluated the effect of six screw-tightening sequences and two tightening methods on the screw preload in implant-supported superstructures. The preload was measured using strain gauges following the screw tightening of a metal framework connected to four implants. The experiment included six sequences ([1] 1-2-3-4, [2] 4-2-3-1, [3] 4-3-1-2, [4] 1-4-2-3, [5] 2-3-4-1, and [6] 3-2-4-1), two methods (one-step, three-step), and five replications. Significant differences were found between tightening sequences and methods. In the three-step method, a higher total preload was found in sequences 2 (312 ± 85 N), 3 (246 ± 54 N), and 4 (310 ± 96 N). In the one-step method, a higher total preload was found in sequences 1 (286 ± 94 N), 5 (764 ± 142 N), and 6 (350 ± 69 N). It is concluded that the highest total screw preload was achieved when anterior implants of the superstructure were first tightened in one step, followed by posterior implants. [ABSTRACT FROM AUTHOR]

The growth of single layer graphene by chemical vapor deposition on polycrystalline Cu substrates induces large internal biaxial compressive strain due to thermal expansion mismatch. Raman backscattering spectroscopy and atomic force microscopy were used to study the strain relaxation during and after the transfer process from Cu foil to SiO2. Interestingly, the growth of graphene results in a pronounced ripple structure on the Cu substrate that is indicative of strain relaxation of about 0.76% during the cooling from the growth temperature. Removing graphene from the Cu substrates and transferring it to SiO2 results in a shift of the 2D phonon line by 27 cm-1 to lower frequencies. This translates into additional strain relaxation. The influence of the processing steps, used etching solution and solvents on strain, is investigated. [ABSTRACT FROM AUTHOR]

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]

The article focuses on Optical fiber sensor based on Sagnac interferomter. Topics include that the sensor is designed by combination of photonic crystal fiber (PCF) and fiber Bragg grating (FBG) and the device is used for measuring various physical parameters including temperature and stress by the changes of physical characteristics such as interference, diffraction, and polarization caused by light propagation in the optical fiber.

Wall shear stress and wall streamline direction measurements were conducted on a generic delta wing model to demonstrate the potential of the white-light oil-film interferometry in three-dimensional flows. With the proposed algorithm, an automatic oil-film thickness calculation is possible and yields reproducible and plausible wall shear stress distributions on the leeward side of the delta wing for various angles of attack. [ABSTRACT FROM AUTHOR]

The recently developed theory for isotropic material failure is briefly outlined. Many steps and stages of the verification process for the theory are fully documented so that it can be used with assurance in a wide variety of directions. Then, the failure theory is used to develop a new measure or index for the degree of ductility of material failure in any state of stress. This new failure property is named the ductility number, Nd. It is rigorously derived, intuitively compatible, and very easy to use. Applications and interpretations of Nd are given. [ABSTRACT FROM AUTHOR]

Abstract Operational safety requires that container ships are designed to endure extreme wave loads. This paper studies extreme panel stresses simultaneously measured at two different deck locations of a container vessel sailing in the North Atlantic between Canada and Europe. Ship panel stresses contain whipping part (transient vibratory response of the hull girder due to wave impacts occurring mainly in the bow area), the latter whipping phenomenon is inherently present in on-board stress measurements. It must be noted that measured hydroelastic vessel panel stresses include other complex non-linear effects as well, for example springing. In many practical situations it would be useful to improve accuracy of some statistical predictions extracted from a certain stochastic random process, given another synchronous highly correlated stochastic process that has been measured for a longer time, than the process of interest. The latter situation may happen if one on-board sensor malfunctioned, and it yielded data record much shorter than the neighboring well-functioning sensor. In this paper the latter issue of improving extreme value prediction has been addressed. In other words, this paper studies an efficient transfer of information between two synchronous highly correlated stochastic on-board stress processes. Two correlated ship panel stress processes at mid and aft deck locations were studied in order to test efficiency of the proposed technique of improving one process extreme prediction, based on the other. This paper intends to stimulate further research and fill the gap that is currently visible in the literature on the latter important topic. Highlights • New statistical method is applied to on-board correlated measured ship panel stresses, bivariate case. • Introduced efficient transfer of information between two synchronous highly correlated stochastic stress measurements. [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 We discuss Bayesian inference for the identification of elastoplastic material parameters. In addition to errors in the stress measurements, which are commonly considered, we furthermore consider errors in the strain measurements. Since a difference between the model and the experimental data may still be present if the data is not contaminated by noise, we also incorporate the possible error of the model itself. The three formulations to describe model uncertainty in this contribution are: (1) a random variable which is taken from a normal distribution with constant parameters, (2) a random variable which is taken from a normal distribution with an input-dependent mean, and (3) a Gaussian random process with a stationary covariance function. Our results show that incorporating model uncertainty often, but not always, improves the results. If the error in the strain is considered as well, the results improve even more. [ABSTRACT FROM AUTHOR]

Abstract The implementation of the new type of ensemble, with constant tension force in the molecular dynamic simulations, is considered. In contrast to the isostress N t T ensemble, in which the stress components act on the surface and the volume elements, the new N f T ensemble is determined by the tension forces acting on each particle in the extended space. Correspondingly, instead of the stress–strain relation used in conventional theory, a new type of constitutive equation in terms of stretch and tension becomes an objective of the molecular dynamics simulations. Comparison with the Parrinello–Rahman method is made for the general external load and the temperature applied. Results for the aluminum lattice show that the suggested approach gives an unbiased sampling of the isostress–isothermal ensemble in the LAMMPS environment. Additionally, the problem of atomistic boundary condition was renovated, due to almost identical tension and traction forces. It was shown on several examples of strains that the tension forces properly represent the type and magnitude of the atomistic external load applied to the surface, despite the absence of any quantities related to the area in the constitutive equations. An analog of Cauchy’s stress theorem in the new setting is formulated and verified by numerical simulations. [ABSTRACT FROM AUTHOR]

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

Low-acyl gellan gum fluid gels were obtained using two different gel-promoting cations under the same processing conditions, and their rheological properties were investigated. For that reason, stress and frequency sweep measurements and flow curve tests were carried out. Small amplitude oscillatory shear assays demonstrated that these materials exhibit weak gel behavior despite the shape of their mechanical spectra being similar to those obtained from strong gels. However, the existence of a weak gel structure was confirmed by the fact that the difference between the elastic and viscous components was of only one order of magnitude. In addition, a reduction in the storage and lost modules and the viscosity as a function of the applied shear was observed with increasing cation concentration. Finally, in order to produce fluid gels, a higher concentration of the monovalent cation was required than when divalent cations were employed in the low-acyl gellan gum fluid gel formulation. [ABSTRACT FROM AUTHOR]

Cell elongation and differentiation has been shown to be modulated by topographical cues provided by grating substratum. However, little is known about the mechanisms and forces involved in the grating-induced cell elongation, due to the difficulty in fabricating soft elastic gels that allow 3-dimensional (3D) cell traction stress measurements. In this paper, we present a method to fabricate soft elastic polyacrylamide grating substrates, using an imprinted polyethylene terephthalate mould, for 3D cell traction stress measurements. Fibroblasts were observed to form protrusions in the grating grooves, and elongate and align parallel to the grating direction on the soft polyacrylamide grating substrates. Focal adhesions were also found to be aligned parallel to the grating direction as compared to cells on flat substrates, suggesting that grating grooves restrict focal adhesion growth perpendicular to the grating direction. The 3D traction stress measurements revealed that highly elongated fibroblasts on grating substrates exert anisotropic traction stresses, in the direction parallel to the grating direction. We propose that focal adhesion alignment along the grating direction may result in increased actin stress fibre formation in the direction parallel to the grating, leading to polarized traction stresses which drive cell elongation. [ABSTRACT FROM AUTHOR]

While stress is a widely utilized concept, no direct methods facilitating its measurement are currently available. In our previous work we proposed stress entropic load (SEL) as a potential new marker of stress response in the human body. However, at that time no method for SEL measurement existed. In this pilot study we devised and then tested methodology for SEL measurement. Healthy male participants were monitored by indirect calorimetry and thermography while resting and subsequently while under prolonged mental effort. The acquired data was then used to calculate the temporal development of SEL for each participant. Our results show that SEL production increased significantly in participants subjected to prolonged mental effort. Furthermore, we observed that the calculated development of SEL over time may be used to accurately determine the time point at which participants started performing stressful tasks. [ABSTRACT FROM AUTHOR]

Block-and-hole polyhedra can be derived from a bar-joint triangulation of a polyhedron by a stepwise construction: select a set of non-overlapping disks defined by edge-cycles of the triangulation of length at least 4; then modify the interior of each disk by an addition or deletion operation on vertices and edges so that it becomes either a rigid block or a hole. The construction has a body-hinge analogue. Models of many classical objects such as the Sarrus linkage can be modelled by block-and-hole polyhedra. Symmetry extensions of counting rules for mobility (the balance of mechanisms and states of self-stress) are obtained for the bar-joint and body-hinge models. The extended rules detect mechanisms in many cases where pure counting would predict an isostatic framework. Relations between structures where blocks and holes are swapped have a simple form. Examples illustrate the finer classification of isostatic and near-isostatic block-and-hole polyhedra achievable by using symmetry. The present approach also explains a puzzle in standard models of mobility. In the bar-joint model, a fully triangulated polyhedron is isostatic, but in a body-hinge version it is heavily overconstrained. When the bodies are panels with hinge lines intersecting at vertices, the overconstraints can be explained in local mechanical terms, with a direct symmetry description. A generalisation of the symmetry formula explains the extra states of self-stress in panel-hinge models of block-and-hole polyhedra. [ABSTRACT FROM AUTHOR]

An improved ultrasonic method was developed theoretically and experimentally for plane stress measurement using critically refracted longitudinal (LCR) waves. Cruciform specimen method, combined with a digital image correlation (DIC) method, was applied to confirm the validity of this method. Based on the acoustoelastic theory, LCR waves with arbitrary detection directions were considered and relations between time-of-fight and biaxial principal stresses were described. To generate the LCR wave in cruciform specimen, a regular octagon polymethyl-methacrylate (PMMA) wedge was designed in accordance with Snell's law. Finally, validation experiments were performed under different step loads using cruciform specimens. In these experiments, the strain fields of cruciform specimens were extracted by DIC method and used to calculate the reference values of plane stress. By comparing the measured principal stresses with the reference values, the validation and precision of the improved ultrasonic method presented in this work were demonstrated. [ABSTRACT FROM AUTHOR]

This paper presents an evaluation method of residual stresses in large welded thin-walled structures based on eigenstrain analysis and small sample residual stress measurement. In this method, small samples containing weld and heat-affected zones are firstly cut from large thin-walled structures, then residual stress in the small samples are measured to determine the welding-induced eigenstrains using a finite element-aided inverse solution. Finally, residual stress in large thin-walled structures are evaluated based on the obtained eigenstrain distribution. The feasibility of the proposed method was validated by evaluating residual stresses in welded plates with different lengths or widths. The method was then applied to evaluating residual stress in a welded skin-stiffener panel. Good agreement between the evaluated residual stress and measurement by diffraction technique has demonstrated the practicability of the method. [ABSTRACT FROM AUTHOR]

The equipment used in stress- and pressure-related non-destructive testing (NDT) experiments tends to have single functionality and a low degree of automation. There are also safety risks inherent in existing pressure testing methods. This paper develops a remote online NDT comprehensive experimental device. It uses a high degree of automation to remotely monitor changes in a pressure vessel’s prefabricated defects during pressure tests. Safety is guaranteed, as the operator is located remotely. The experimental pressure vessel employs a split structure connected by a quick-release system using flange-type U-slot bolt holes. Pressure vessel defects can be prefabricated in different forms, and the vessels can be disassembled and changed easily. This process reduces the experiment materials needed, lowers costs, and saves experimental time. The device can be used for various experiments, such as acoustic emission monitoring of the pressure-bearing and load-holding capacities of pressure vessels, measurement of pressurized vessel strain, and pressure vessel NDT (magnetic powder inspection, ultrasonic flaw detection, magnetic flux leakage testing, magnetic memory testing). Operators can obtain experimental data and conduct analyses simply by controlling the computer. The device can enrich the content of undergraduate experiments and solve the single-functionality problem of existing experimental equipment. With this device, the acoustic emission online monitoring experiment of pressure vessel and the stress measurement of pressure vessel are carried out. Which verify the diversity of function and reliability of the test. [ABSTRACT FROM AUTHOR]

Due to the weak interface in shape memory alloy wire–reinforced composites, the influence of interphase on the mechanical properties and stress distribution of hybrid composites is of considerable importance. In this article, a three-cylinder axisymmetric model using a pull-out test is developed to predict stress transfer and interfacial behavior between shape memory alloy wire, interphase, and matrix. In this article, only superelasticity behavior of the shape memory alloy wire is considered. Based on the stress function method and the principle of minimum complementary energy, stress distribution is derived for three different cases in terms of loading and boundary conditions (thermal loading model, intact model, and partially debonded model). Inhomogeneous interphase and different radial and hoop stress components in each phase are considered to achieve deeper physical understanding. Finite element analysis also performed to simulate stress transfer from the wire to the matrix through the interphase. To evaluate the accuracy of this model, the results of the work are compared with the results of the two-cylinder model proposed by Wang et al. and finite element results. [ABSTRACT FROM AUTHOR]

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

We need to predict the fatigue crack behavior for estimating the useful life of the components. Also, introducing the compressive residual stresses with some proper methods such as the cold expansion of holes can improve the fatigue life. Interaction of adjacent holes changes the values and distributions of created residual stresses and so their effects on the fatigue life. In this paper, we have studied the induced residual stress due to the cold expanding of two adjacent holes. Beneficial effects of the compressive residual stresses on the total fatigue lives and crack initiation cycles are investigated by using the numerical simulations and experimental tests. Some parameters as the hole geometries, expansion ratio and crack locations can affect the fatigue behavior. Results show that the expansion ratio has variable effects in comparison with other parameters. Reduction in distance between adjacent holes decreases the total and crack growth lives. 2D finite element model can precisely predict the fatigue growth of mixed mode through cracks in thin plates in the presence of the residual stress. [ABSTRACT FROM AUTHOR]

Experimental studies were conducted to investigate the uniaxial and biaxial ratcheting behaviors of Ultra-high molecular weight polyethylene (UHMWPE). The effects of stress amplitude, stress rate and hydroxyapatite content on uniaxial ratcheting behavior were studied firstly. It is found that the ratcheting strain and its rate increase as stress amplitude increases. However, the ratcheting strain and its rate decrease with rising of stress rate. Meanwhile, it is found that the ratcheting strain decreases with increase of hydroxyapatite content. The ratcheting strain rates with different hydroxyapatite contents are not obviously different. The modified ratcheting strain accumulative model was constructed to predict the uniaxial ratcheting behavior of UHMWPE with different stress amplitudes, stress rates and hydroxyapatite contents. It is seen that the predictions agree with the experimental results very well. The effects of different loading paths on biaxial ratcheting behavior of UHMWPE were studied. Both ratcheting strain and ratcheting strain rate are strongly influenced by the loading path. It is found that the uniaxial loading path gives the highest ratcheting strain and its rate while the proportional loading path gives the lowest ratcheting strain and its rate. [ABSTRACT FROM AUTHOR]

A site characterization program was carried out for a proposed Deep Geological Repository (DGR) project for Ontario Power Generation’s (OPG) low- and intermediate-level nuclear waste repository near Kincardine, Ontario. The repository is proposed to be constructed at approximately 680 m below ground surface within the competent argillaceous limestone of the Cobourg Formation. The in situ stress state at the project site will have significant impact on both the short- and long-term performance of repository openings, such as emplacement caverns and access shafts. As part of the site characterization program, an evaluation of the in situ stress state of the project site was conducted which consisted, primarily, of a review and synthesis of existing stress measurements conducted at various locations throughout Ontario and the midwestern U.S. Based on geomechanics data from deep boreholes and stress measurement data, a simplified FLAC3D model of the full stratigraphic profile was developed and used to simulate the influence of regional tectonic strain in the project area. In particular, this method takes into account the rock properties, such as stiffness, for discrete units at the DGR site. The model was calibrated on the basis of in situ stresses measured at Norton Mine, in a similar geological environment as the DGR site, and with site-specific borehole televiewer observations (i.e., breakouts). The model-predicted horizontal in situ stress profile showed general agreement with the observations and also showed the significant influence of discrete rock unit stiffness. [ABSTRACT FROM AUTHOR]

Stress-birefringence measurement is critical in optical glass materials. A laser self-mixing interference (SMI) stress measurement system with a measuring range of 1 deg to 179 deg is presented. The light source of the system is a He-Ne laser with a variable frequency difference. Birefringent external cavity SMI experiments are conducted with the laser with different frequency differences. Experimental results show that a large frequency difference decreases the cross-saturation effect between the two laser eigenstates, and alternate oscillations are more likely to occur, which directly improves the sensitivity and expands the measuring range of the system. A piece of neodymium glass is tested with the system and the results are given, proving that the large frequency difference laser SMI system provides a simple, low-cost, and high-sensitivity stress measurement method. [ABSTRACT FROM AUTHOR]

Steel and composite steel-concrete bridges are subjected to random traffic loads along their life cycle which generate significant dynamic impacts. The road-roughness of asphalt pavements is one of the most important aspects that contributes to the significant increase of the stress amplitudes and hence to serious load-induced fatigue concerns. In this context, welded joints are well known as the weakest points in bridges, since they are prone to stress concentrations leading to initiation of fatigue cracks being in current design codes evaluated using primarily the nominal stress method (NSM). However, a more accurate stress definition, which considers the complexity of the stress field at the welds, becomes necessary mainly in old roadway steel bridges that are often subjected to out-of-plane stresses. In this paper, the hot-spot stress method (HSM) is used to evaluate the fatigue life of a welded joint subjected to distortion induced-fatigue, considering the vehicle speeds and a progressive deterioration model for the road pavement. The welded joint was modelled by solid elements and was integrated with a 3D dynamic bridge model using the sub modelling technique. Besides the importance of considering the bridge-vehicle dynamic interactions with the pavement road-roughness, the dynamic amplification effects on local stresses and the relatively high scatter found in the fatigue lives considering global and local approaches show that a detailed local stress definition is fundamental to evaluate the fatigue performance of existing roadway bridges. The effects of the annual traffic increase rate on the fatigue life are also discussed. [ABSTRACT FROM AUTHOR]

As a part of the DECID2 French National Project (2008–2012), construction of a large platform entirely made of smart composites was carried out and two demonstrators were installed. During a previous study, an ABAQUS model of smart composite platform was set up to perform numerical simulations that predict the mechanical behaviour of bolt-fastened platform under static three-point bending load, and a stress concentration is observed around the bolt holes. Unidirectional composites are subjected to delamination at very low stress, and this cannot be tolerated because most of the applications of pultruded structures are in civil engineering, which involves human safety. Therefore, it is essential to study the correlation of delamination onset and find a technology to enhance delamination strength. In this study, a numerical analysis was carried out to enhance the delamination strength around the bolt holes. Bidirectional fiberglass cloths were wrapped around unidirectional pultruded beams to reinforce the structure and to prevent delamination. Due to the high cost of these cloths, a study was also carried out to select an appropriate cloth material by taking into account two aspects: density and number of layers of cloths. The selected cloth was compared with conventional continuous fibreglass mat, and it was found that bidirectional fibreglass cloth material performs well in preventing delamination, even though it is expensive. [ABSTRACT FROM AUTHOR]

This article examines the structural behaviour of six structural units composed of single, simply paired and paired-interconnected bending-active members, coupled with a single cable element. The form-found curvilinear shape of the members is achieved through fastening by contracting auxiliary elements, as well as through further deformation by decreasing the cable’s length. The overall structural behaviour of the units is investigated based on a step-by-step finite-element analysis. All units are evaluated with regard to the components’ stresses and deformations developed during the form-finding process and subsequent external vertical loading, for different possible section thickness values of the elastic members. [ABSTRACT FROM AUTHOR]

Based on critical refraction longitudinal wave (Lcr wave) acoustoelastic theory, correction method for grain size effect on surface stress measurement was discussed in this paper. Two fixed distance Lcr wave transducers were used to collect Lcr wave, and difference in time of flight between Lcr waves was calculated with cross-correlation coefficient function, at last relationship of Lcr wave acoustoelastic coefficient and grain size was obtained. Results show that as grain size increases, propagation velocity of Lcr wave decreases, one cycle is optimal step length for calculating difference in time of flight between Lcr wave. When stress value is within stress turning point, relationship of difference in time of flight between Lcr wave and stress is basically consistent with Lcr wave acoustoelastic theory, while there is a deviation and it is higher gradually as stress increasing. Inhomogeneous elastic plastic deformation because of inhomogeneous microstructure and average value of surface stress in a fixed distance measured with Lcr wave were considered as the two main reasons for above results. As grain size increasing, Lcr wave acoustoelastic coefficient decreases in the form of power function, then correction method for grain size effect on surface stress measurement was proposed. Finally, theoretical discussion was verified by fracture morphology observation. [ABSTRACT FROM AUTHOR]

Seven points were selected to measure in situ stress, and the simulation software ANSYS was used to introduce a 3D geological model of Licun colliery, which has a thick coal seam and large mining height. A BP neural network was applied to the inversion of in situ stress, and distributions of σ1, σ2, and σ3 were achieved. This proved that a BP neural network can be applied to the inversion analysis of the colliery’s in situ stress. Furthermore, different angles α between the maximum principal stress and roadway axial were simulated. The results showed that as α increases, the shallow maximum principal stress varies from symmetric distribution to asymmetrical distribution. Finally, this becomes a symmetric distribution as the concentrated contours vary from the roof to two sides at the same time. The maximum tensile stress of the roof and α were positively correlated, and the depth of the maximum tensile stress and α were negatively correlated. The tensile stress of the roof surrounding shallow rock increases as α increases, and the roof tends to cause tensile failure. Thus, the roadway axial and the maximum principal stress should be laid out in parallel as much as possible, and angle α should be less than 30º in the Licun colliery. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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

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

Dry-stacked masonry walls gives rise to geometric imperfections: the height variation of different masonry blocks ΔH and the roughness of the support area Δh. This paper studies the effect of ΔH on the structural response and the load bearing capacity of masonry walls by highlighting the load percolation. Furthermore, an algorithm was developed to define a stress multiplier coefficient respecting the imperfections ΔH. The algorithm allowed predicting 77% of the amplified stress compared to the FE analysis and showed that the geometric imperfections govern the load percolation in a wall as well as the cracking mode and the bearing capacity. [ABSTRACT FROM AUTHOR]

In some alloys such as 9%Cr heat resistant steels and magnesium alloys, the creep constitutive equation of the power-law requires a term of threshold stress due to the presence of second phase particles. It is necessary to establish an estimation method of C ∗ for such alloys to predict the life of their components. In this paper, the General Electric/Electric Power Research Institute (GE/EPRI) method and the reference stress method were modified to estimate C ∗ for power-law creep materials with threshold stress. The finite element method was used to verify the accuracy of the modified methods. The accuracy of the calculation equation of C ∗ in the American Society for Testing Materials (ASTM) E 1457 was also assessed. The results indicated that the modified GE/EPRI method was sufficiently exact as an engineering method. h 1 was slightly affected by the applied load and significantly affected by the threshold stress. The accuracy of the modified reference stress method increased with increased applied load and was within ±40%. The accuracy of the calculation equation of C ∗ in ASTM E 1457 was not affected by the threshold stress and the equation could be directly used for power-law creep materials with threshold stress. [ABSTRACT FROM AUTHOR]

Rock Joint Rate (RJR) is a novel method for predicting the penetration rate (PR) of tunnel boring machines (TBMs) in hard rock environments. This model is devised based on a combination of geological and operational data obtained from a number of tunnels excavated in igneous and sedimentary rocks. The Geological condition, TBM excavation parameters and the tunnel diameter are regarded as the main input parameters in the RJR method. The rock mass uniaxial compressive strength (UCS) and the discontinuities' characteristics along the tunnel excavation axis including the number, frequency, orientation, spacing and aperture of the joints are the principle geological parameters. In addition, the machine thrust force and the cutterhead rotation speed (RPM) have been introduced as the main involved operational parameters of the machine. Easy to use input parameters, the simple investigation procedure, not requiring complicated laboratory tests and the capability to control the overall costs of a project as well as precise estimations of the operation time by dint of accurate determination of penetration rate (PR) are the main advantages of the proposed RJR model. In this method, a number of indices including the machine stress index (M S ), strength ratio (S R ), raw penetration rate (PR w ) and basic penetration rate (PR b ), which are derived from the integration of the main input parameters in RJR model are defined for evaluating the penetration rate of the machine. Overall, in this research, around 140,000 performance databases corresponding to 22,300 boring strokes of three different tunnels with a total excavated length of about 19 km were utilized to validate the proposed RJR model. According to the acquired results in this study, the estimated value of PR by the suggested method of RJR (PR RJR ) shows a good agreement with the field penetration rates (PR Field ). Therefore, this model can be employed as a new method for predicting the penetration rate of TBMs in hard rocks. [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]

The discrete element method (DEM) in use today generally considers the bonds that bind discrete elements into a continuum to be elasto-perfectly-brittle. Such brittle bonds only give accurate failure loads for large size structures where LEFM applies. But for small to medium size structures of quasi-brittle materials such as rocks and concretes, the presence of the fracture process zone (FPZ) has significant impacts and needs to be considered. To properly model size effects, an exponential softening contact bonds model was implemented which is tied to input fracture energy and also addresses particle size issue. This was followed by a successful study of the classical size effect problems of similar edge notched beams subjected to direct tension and three-point bending. The overestimation of failure loads by brittle bonds are then addressed. The discrete nature of DEM also facilitates the use of different particle packing for structure construction, and provided insights on how FPZ evolves under sustained loading. [ABSTRACT FROM AUTHOR]

Improving room temperature ductility and formability is a bottleneck for a wide industrial application of Mg alloys, but even the mechanism for the effect of alloying elements on the deformation behavior of Mg is not clearly known. Here, using a molecular dynamics simulation, we clarify the role of alloying elements in improving the room temperature ductility of Mg alloys: Solute atoms have stronger dislocation binding tendency and solid solution strengthening effect on basal slip planes than on non-basal slip planes, reduce the anisotropy in the critical resolved shear stress between slip systems, and eventually improves the room temperature ductility. We predict that any solute elements with a size difference from Mg can improve the room temperature ductility, once the alloying amount is carefully controlled. By proving the validity of the prediction experimentally, we provide a new guide for designing Mg alloys with improved room temperature ductility and formability. [ABSTRACT FROM AUTHOR]