Direction Of Shear Stress Research Articles

On the calibration-free two-component wall-shear-stress measurement technique using dual-layer hot-films.

The wall shear stress vector is an important quantity in fluid mechanics and is difficult to be measured. In this work, we first demonstrate that the directional sensitivity (sensitivity to yaw angle α) of a flush-mount hot-film sensor is cos1/3α using theoretical and experimental methods. Based on the directional sensitivity, a local two-component wall-shear-stress measurement technique is proposed using a pair of un-calibrated dual-layer hot-film sensors positioned perpendicular to each other. This technique use the heat fluxes transferred from the sensors to the fluid to determine both the magnitude and the direction of the wall shear stress so that a calibration is not required. Experimental results demonstrate that this technique is feasible when the angle between the stress and the centerline of the sensor is within ±15°. This valid angle range can be potentially increased if the two sensors are positioned with an angle larger than 90°.

Estimating reservoir geomechanical parameters for enhanced reservoir characterization: case study of “Tobi” field, Niger Delta

Reservoir geomechanical parameters in “Tobi” Field, Niger Delta were estimated using well log data with the intention of improving reservoir characterization and establishing stress regime of the field. A suite of well log data were interpreted, reservoirs were identified and correlated across three (3) wells and their geomechanical parameters computed from empirical relations. Three (3) reservoir units were delineated from these wells that falls within the hydrocarbon windows (Agbada Formation). We estimated several geomechanical parameters, which include, but is not limited to, Young’s modulus, Poisson’s ratio, bulk compressibility, unconfined compressive strength (UCS), shear modulus, heat production, vertical stress (overburden), minimum horizontal stress, maximum horizontal stress, shear stress normal to fault plane, shear stress in direction of dip, and shear stress in direction of strike. The bivariate crossplots of heat production and Young’s modulus indicated that the amount of heat produced by the shaly materials affects the elastic properties of the reservoir units and flow rate. The crossplots of Poisson’s ratio versus compressional velocity are expressly well-defined and exponentially decaying with the compressional velocity, indicating an inverse relationship between the two (2) parameters. For stress tensor analysis, the study confirmed the defining condition of Sv > SHmax > Shmin as normal fault, which is fault regime prevalent in the study area, in line with Andersen’s classification. Rotation of principal stresses on fault plane showed negative shear stress in strike direction. This research concluded that geomechanical parameters of hydrocarbon reservoirs in “Tobi” field are diagnostic in reservoir characterization and in establishing the type of faults in reservoirs.

Numerical modeling of ductile fracture of hot stamped 22MnB5 boron steel parts in three-point bending

With the increasing demand in car safety and energy consumption reduction, the driving force in developing components made of UHSS steels has risen during the last decade, increasing the use of hot stamping process. While several research studies have focused on the modeling of the fracture occurrence during hot stamping, very few analyze the ductility and failure behavior of hot stamped components during static loading as well as crashworthiness events. In this framework, the paper intends to study the failure behavior of hot-stamped boron steel 22MnB5 under different loading conditions. Three-point bending tests are conducted on hot stamped U-shaped beam assemblies to evaluate the effect of complex loading on the damage evolution. Through SEM-based microscopic analyses, the material failure mechanisms, such as the mode of void coalescence, are explored, as well as the relation between the direction of the maximum shear stress and fracture surface. A FE-based model of the three-point bending tests incorporating a ductile fracture criterion is calibrated and implemented in ABAQUS/Explicit software using VUMAT subroutines. It is proved that the numerical model is capable to properly reproduce the deformation sequence and predict two symmetric macro-cracks under a circular punch. The load-stroke curve of FE simulation is finally compared with that of simulation to show its reliability.

Estimation of the heterogeneity of stress fields using misfit angles in focal mechanisms

The stress field of the Earth's crust is spatially heterogeneous on various scales. The focal mechanism of an earthquake provides important information associated with the stress state at the seismogenic depths. These focal mechanisms are affected by the pore fluid pressure and/or friction coefficient. In this study, we focused on misfit angles, particularly the difference in the angle between the slip direction in an observed focal mechanism and the resolved shear stress direction that can be obtained using the directions of the principal stress axes and the stress ratio of a reference stress field. Resolved shear stress does not depend on the fault friction or pore fluid pressure, allowing us to use misfit angles to evaluate the heterogeneity of stress fields if the effect of an error in a focal mechanism has been properly removed. By statistically evaluating the error in focal mechanisms using a Bayesian approach, we evaluated the misfit angles of the aftershocks of the 2000 Western Tottori Earthquake, in which numerous focal mechanisms could be precisely determined using dense seismic observation. The spatial distribution of the misfit angles of the aftershocks suggested that the stress field in the aftershock region, particularly in the southern portion of the region, was in a heterogeneous state. We also demonstrated that this spatial variability cannot be explained solely by errors in the focal mechanisms. If we assume a uniform stress field before the mainshock, the observed cumulative curve of misfit angles can be explained by coseismic stress changes and the background stress field's depth gradient of differential stress of 3.2 MPa/km.

Influence of joint location and connectivity on the shear properties of artificial rock samples with non-persistent planar joints

In this paper, direct shear tests of cement mortar samples with non-persistent planar joints are reported, to study the effects of joint connectivity ratio k (ratio of the length of the planar joint to the length of the specimen) and locations of a planar joint on the shear properties of artificial jointed rock samples. The test results indicate that (a) the shear stress-shear displacement curve of samples with non-persistent planar joint under direct shear stress consists of five stages. (b) For samples with a non-persistent planar joint, when the joint connectivity ratio k remains unchanged, the shear strength of the specimen increases as the distance s between the left end of the planar joint and the left edge of the specimen increases. When the distance s remains constant, the shear strength of the specimens increases with an increase in the joint connectivity ratio k. When both the joint connectivity ratio k and the distance s remain unchanged, the shear strength increases as higher normal stress is applied. (c) For samples with two non-persistent planar joints and constant joint connectivity ratio k, the shear strength increases as the two planar joints, respectively, are at the two ends of specimen, compared to the scenario where the two planar joints are at the middle of the specimen. The results also demonstrate that the proposed fitting model is suitable for characterizing the shear stress-shear displacement of artificial jointed rock specimens where a non-persistent planar joint is present.

Creep rupture mechanism and microstructure evolution around film-cooling holes in nickel-based single crystal superalloy specimen

The fracture mechanism and microstructure evolution around film-cooling holes in a nickel-based single crystal superalloy specimen under tensile creep at high temperatures were investigated using thin-walled plate specimens with close-packed film-cooling holes. The results demonstrated that the film-cooling hole structure has a weakening effect on the specimen for the creep life and creep ductility. In the specimen with the film-cooling holes, a large number of small cracks formed from initial cracks along the direction of the maximum resolved shear stress during the high-temperature creep process, and the cracks propagated along the direction perpendicular to the loading stress direction. Further, the microstructure evolution of the γ′ phase around the edge of the film-cooling holes was closely related to the local stress. While N-type rafting occurred in the high-stress zone, no significant change of microstructure was observed in the low-stress zone. Further, a modified damage model of the crystal plasticity theory was used to simulate the deformation of the specimen with cooling holes under multi-axial stress state, and the results of finite element analysis (FEA) agreed with both the test results and fracture morphology.

Strain and damage sensing in additively manufactured CB/ABS polymer composites

In this study, an experimental investigation is performed to observe the electromechanical response of CB (carbon black)/Acrylonitrile butadiene styrene (ABS) additive manufactured composite under quasi-static (tensile, shear, and mode-I fracture) and dynamic (mode-I fracture) loading conditions for the potential damage sensing applications. Dog bone tensile, double v-notch shear, and single edge notch bending (SENB) specimen printed with three different configurations (0°/90°, +45°/-45°, and 0°) are considered for the quasi-static condition. A modified split Hopkinson pressure bar along with high-speed video camera is used for dynamic fracture experiments. Four-point probe technique coupled with a high-resolution data acquisition system is employed to obtain the real-time electrical response. In the case of tensile loading, +45°/-45° printed specimens show a nonlinear change of electrical resistance due to unique failure mode. Under the shear loading, electrical resistance remains unchanged during the elastic deformation. After the damage evolution, +45°/-45° printed specimens exhibit a higher rate of change in electrical resistance due to alignment of the filaments along the maximum principle shear stress direction. For both static and dynamic fracture loading, a minimal change of electrical resistance is observed before crack initiation. However, after the crack initiation, a sharp change of electrical resistance for 0°/90° printed specimens indicates a faster crack propagation as compared to the +45°/-45° printed specimens.

Visualization and measurement of supersonic jet flow field evolution issuing from a rectangular nozzle with aft-deck

An experimental study is reported of supersonic jet surface flow structure visualization and wall shear stress field measurement issuing from a rectangular nozzle with aft-deck. The near-field surface flow structures evolution from over-expansion to under-expansion with the increase of nozzle pressure ratio (NPR) are successfully captured by surface oil flow visualization and shear sensitive liquid crystal coating (SSLCC) technique. The quantitative measurement result of shear stress vector field obtained by SSLCC shows that shear stress directions change significantly across the shock wave and expansion fans, while the magnitudes of shear stress have no obvious changes. Surface streamlines calculated by SSLCC image keep great consistency with the streamlines visualized using oil flow technique, which demonstrates the accuracy and potential application of SSLCC in supersonic jet surface flow visualization.

Constant Temperature Anemometer with Self-Calibration Closed Loop Circuit

In this paper, a Micro-Electro-Mechanical Systems (MEMS) calorimetric sensor with its measurement electronics is designed, fabricated, and tested. The idea is to apply a configurable voltage to the sensitive resistor and measure the current flowing through the heating resistor using a current mirror controlled by an analog feedback loop. In order to cancel the offset and errors of the amplifier, the constant temperature anemometer (CTA) circuit is periodically calibrated. This technique improves the accuracy of the measurement and allows high sensitivity and high bandwidth frequency. The CTA circuit is implemented in a CMOS FD-SOI 28 nm technology. The supply voltage is 1.2 V while the core area is 0.266 mm2. Experimental results demonstrate the feasibility of the MEMS calorimetric sensor for measuring airflow rate. The developed MEMS calorimetric sensor shows a maximum normalized sensitivity of 117 mV/(m/s)/mW with respect to the input heating power and a wide dynamic flow range of 0–26 m/s. The high sensitivity and wide dynamic range achieved by our MEMS flow sensor enable its deployment as a promising sensing node for direct wall shear stress measurement applications.

High cycle fatigue behavior and numerical evaluation of Alloy 690TT steam generator tube

High cycle fatigue behavior of Alloy 690TT steam generator (SG) tube under different maximum stresses was investigated at stress ratio R = 0.1 through experimental and numerical evaluation. The morphology of fatigue fracture surface was observed by SEM, and the crack initiation and propagation mechanism of Alloy 690TT SG tube was analyzed. The fatigue crack of Alloy 690TT SG tube initiated at the intrados surface edge, then propagated along the direction of maximum shear stress and penetrated through the side of the specimen, and finally transient fracture occurred in the direction perpendicular to the loading axis. With the increase of maximum stress, the number of fatigue crack initiation sources increased, but they were all distributed on the edge of the intrados surface, and a large number of persistent slip bands (PSBs) were formed on the intrados surface. The fracture mechanism of the tubular specimen was different from that of the bar specimen, and its fracture mode affected the life evaluation of the tubular specimen. The finite element analysis software ABAQUS and advanced fatigue durability analysis software FE-SAFE were first used to evaluate the fatigue life of Alloy 690TT SG tube. Compared with the experimental results, the error in predicting fatigue life by numerical method was acceptable.

Relation between viscosity and flow characteristics in uni-directional CF/PA6 laminates near the melting point

In this study, the viscosity of unidirectional carbon fiber reinforced thermoplastic (CFRTP) laminates near their melting point was evaluated to discuss the relationship between the thermal fusion conditions and the flow of the fibers and matrix. The laminates were regarded as a fluid flowing in the direction perpendicular to the fibers. The microscopic flow of the fibers and matrix was observed during a parallel plate compression test conducted near the melting point. On the basis of this observation, the viscosity and flow properties were evaluated by the finite element method (FEM). The results of the parallel plate compression test showed that the test conditions and the decrease in the thickness of the laminates are related to the apparent viscosity of the unidirectional plate. In addition, cracks in the direction of the maximum shear stress were detected via in situ observation near the melting point of the matrix. The occurrence of this phenomenon depended on the apparent viscosity of the unidirectional laminates, and it was found that no cracks occurred when the apparent maximum viscosity of the unidirectional laminates was lower than a threshold.

RETRACTED ARTICLE: Numerical simulation of temperature field and temperature stress of thermal jet for water measurement

ABSTRACT Thermal-jet for water Measurement spallation is a rock removal process that utilizes induced thermal stress to fracture the rock into small fragments before melting of the rock occurs. Because of the low conductivity, thermal stress will be created on the rock surface. When the thermal stress exceeds the strength of the rock, cracks will form and expand. Eventually, rocks disintegrating into small fragments. The simulation result obtained by the Crank–Nicolson method of the temperature field and the distribution of thermal stress has been analyzed. The result indicates that during thermal spallation drilling, the temperature of the surface exposed to the thermal-jet for water Measurement rises rapidly and create temperature gradients in both radial and axial directions. Because of volume expansion, the heated part is subjected to compressive stress in radial direction and shear stress in axial direction, respectively. The result is very helpful to the field application.

Wall shear stress measurements by white-light oil-film interferometry

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.Graphic abstract

Experimental study of stress anisotropy and noncoaxiality of dense sand subjected to monotonic and cyclic loading

Abstract The noncoaxiality of the principal stress direction and plastic principal strain increment has been broadly recognized as an influencing parameter for design of soil structures. Here we performed a series of systematic hollow cylinder experiments to study the effects of stress anisotropy on the noncoaxiality of dense Babolsar and Toyoura sands. A total of 25 undrained torsional shear tests were carried out under constant mean confining pressure, and fixed principal stress directions, α. We investigated the stress-strain behavior of dense sands for different α-directions, and cyclic stress ratio, CSR, under monotonic and cyclic loading conditions. The results show that the noncoaxiality value depends on the CSR, the level of plastic strain, and α-direction. Independent of the principal stress direction, maximum noncoaxiality value was observed at peak shear strength when there is most interlock between sand particles. Minimum noncoaxiality was recorded in α = 45° tests, in which the direction of maximum shear stress coincided with the horizontal bedding plane direction (weakest plane).

Fabrication of a Shear Stress Sensor Matrix Using Standard Printed Circuit Board and Overmolding Technologies

In contrast to pressure distributions that can, nowadays, easily be measured using commercial sensor sheets, this is not yet the case for frictional or shear stresses. Those stresses act parallel to a surface, which makes it more challenging to develop suitable sensors. A number of shear sensor prototypes have been reported until now, but realizing a matrix of shear sensors remains a big challenge because of cost and complexity issues. Therefore, this article presents a fabrication approach for realizing a matrix of shear sensors using standard PCB and molding technologies. The presented sensor is based on changing the coupling of optical power between a light-emitting diode and a set of photodiodes in combination with an overmolding step, as realizing a mechanical transducer. To demonstrate the fabrication flow, a first demonstrator incorporating a five-taxel sensor matrix has been realized, which is able to record the in-plane shear stress magnitude and direction.

Direct stress field estimation through waveform matching

SUMMARYConventionally, the routine workflow of stress field estimation from seismic data consists of two steps: focal mechanism inversion and stress inversion. This two-step workflow suffers from the cumulative uncertainties of both the focal mechanism inversion process and the stress inversion process. To mitigate the cumulative errors, a few previous studies have put efforts to directly estimate the stress field using P-wave polarities. In this study, we develop a new approach to directly estimate tectonic stress fields with better accuracy through waveform matching. This new approach combines the two steps into a one-step workflow to mitigate the cumulative uncertainties through the physical relationship between a stress field and the recorded waveforms. This method assumes a homogeneous stress field in space in the local source region and that the fault slip occurs in the direction of the resolved shear stress acting on the fault plane. Under these assumptions, the stress pattern that generates the theoretical waveforms that best fit the waveforms observed is directly retrieved as the true stress field. The merits of the new approach include that this approach can mitigate the cumulative uncertainties suffered from the conventional two-step workflow and does not require determination of the focal mechanisms of each event; thus, this method is applicable to data sets with few stations. Synthetic tests with and without noise are conducted to demonstrate the performance and merits of this method. Then, the new approach is applied to a real data set from central Oklahoma between March 2013 and March 2016. The resulting stress pattern is consistent with that estimated from previous studies examining the same region. These applications show the benefits and validity of the new approach.

Shear deformation behavior of Zircaloy-4 alloy plate

Zircaloy-4 alloy is widely used in light water reactors. During cold rolling, this alloy is prone to cracking under shear stress. The microstructural characteristics after shear deformation have been investigated in this study in order to provide technical support for avoiding failure of this alloy. Shear tests for recrystallized Zircaloy-4 alloy plate were performed at room temperature using a designed shear testing device. Shear fracture surface and microstructure were carefully characterized by scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) techniques, respectively. Results showed that grains in the initial plate are strongly oriented with their c-axis close to the transverse direction (TD). Shear fracture surface can be simply divided into two typical zones based on the morphology features: (I) smooth zone and (II) rough zone. The plate exhibited anisotropy of shear yield strength in the order given as: Normal direction (ND)<Rolling direction (RD)<TD < 45° away from TD (TD45°), which was associated to the initial texture based on the Schmid factor theory. The fracture shear strain increased with the increase area of zone (I). Prismatic <a> slip and {101‾2}<1‾011> tensile twinning were the predominant deformation modes during the shear deformation. In addition, {101‾2}<1‾011> tensile twinning activity was high in grains oriented with their c-axis perpendicular to the shear stress direction (SSD). Furthermore, work hardening occurred due to slip and twinning in the shear deformation region (SDR), which substantially increased the microhardness of the SDR (198 HV) as compared to that of matrix (157 HV). Shear failure tended to occur on the RD-TD45° plane with external load.

Effect of scan strategy and heat input on the shear strength of laser cladded Stellite 21 layers on AISI H13 tool steel in as-deposited and heat treated conditions

Coating of hard-facing, wear and corrosion resistant materials on working surfaces of engineering parts made of relatively lower grade materials plays an important role in their service life as this is dictated by the coating material rather than the substrate material. However, the quality of coating in terms of pores- and crack- free deposition, low dilution and good bond strength is vital for the working life of coatings. In this work, bond strength of laser cladded Stellite 21 layers deposited on AISI H13 tool steel with different scanning strategies and line energy is investigated by subjecting the clad-substrate interface to shear force. As Stellite 21 is deposited to improve surface property of high-temperature dies and also for refurbishing worn out dies, bond strength of cladded specimens subjected to a high thermal cycle was also measured. Three sets of shear test specimens of rectangular clad build-up were made with different deposition strategies. First two sets have same laser line energy, but interfacial layers have overlapped clad tracks deposited in two orthogonal directions to study the effect of track orientation on the bond strength. In the third set line energy was doubled by reducing the scan speed. Bond strength was more for shear force applied along the direction of clad tracks. Higher interfacial bond strength of clad tracks parallel to shear stress direction compared to transverse tracks could be resulting by the similar effect that the orientation of fibers in a composite have on its strength. Deposition with higher line energy also had higher bond strength because of more uniform overlapped clad interface. However, specimens subjected to heating up to 1000 °C followed by furnace cooling had much reduced bond strength due to grain coarsening. Results are supported by the micro-structure, micro-hardness, dilution and elemental analyses of cladding and fractured surfaces.

Investigating the Contact Responses of the Roller Cavity Surfaces in the Compressor Blade Rolling Process

The investigation of the contact responses is the key for evaluating the local wear of dies in the plastic forming process. This paper investigated the contact load distributions and evolutions of the roller cavities in the compressor blade rolling process by the FEM. It was the first study to quantify the distributions and evolutions of the contact responses for rolling irregular components. The results indicated that the maximum contact pressure is generally present at the center of the contact interfaces, and the magnitudes of contact pressure decreased with evolution of the blade rolling process. The rolling contact interfaces can be divided into the backward slip zone, the stick zone, and the forward slip zone based on the shear stress distributions. The stick zone was a narrow belt which separated the forward and the backward slip zone, and the shear stress in the stick zone was nearly zero. The shear stress magnitudes in the forward slip zone were smaller than those in the backward slip zone, and the directions of shear stress in forward and backward slip zones were adverse. The magnitudes of shear stress over the forward and backward slip zones decreased with evolution of the blade rolling process. The distributions of local sliding were in a V‐shape, the local sliding in the stick zone was nearly zero, and the bigger sliding in backward and forward slip zones was present at the boundaries of rolling entrance and exit sections. The local sliding velocity magnitudes in the backward slip zones were always bigger than those in the forward slip zones, and the magnitudes of local sliding at the rolling entrance sections were bigger than those at the rolling exit sections. In general, the local sliding velocity magnitudes increased firstly and decreased sharply at 2T/3. The current paper develops the distributions and evolutions of contact responses in the blade rolling process. The contact responses can be used for studying the wear of roller cavities to avoid the accuracy inconsistency of the shaped blade.

Theoretical studies on bidirectional interfacial shear stress transfer of graphene/flexible substrate composite structure

Interfacial mechanical properties have a great influence on the overall mechanical performance of graphene/flexible substrate composite structure. Therefore, it is necessary to study interfacial shear stress transfer between graphene and flexible substrate. In this paper, a two-dimensional nonlinear shear-lag model (2D model) is presented. Taking the effects of Poisson’s ratio of the graphene and substrate into consideration, the bidirectional interfacial shear stress transfer between graphene and flexible substrate subjected to uniaxial tension is investigated by the 2D model when the Poisson’s ratio of substrate is larger than that of graphene. In the elastic bonding stage, the semi-analytical solutions of the bidirectional normal strains of the graphene and bidirectional interfacial shear stresses are derived, respectively, and their distributions at different positions are illustrated. The critical strain for interfacial sliding is derived by the 2D model, and the results show that the critical strain has a micron-scaled characteristic width. The width size of graphene has a significant influence on the critical strain when it is less than the characteristic width, but the size effect can be ignored when the width of graphene is larger than the characteristic width. In addition, the Poisson’s ratio of substrate can also affect the critical strain. Based on the 2D model, the finite element simulations are made to investigate the distribution of graphene's normal strains and interfacial shear stresses in the interfacial sliding stage. Furthermore, compared with the results obtained via one-dimensional nonlinear shear-lag model (1D model), the distributions of graphene’s normal strains and interfacial shear stresses calculated by 2D model show obvious bidimensional effects both in the elastic bonding stage and in the interfacial sliding stage when the width of graphene is large. There exists a compression strain in the graphene and a transverse (perpendicular to the tensile direction) shear stress in the interface, which are neglected in the 1D model. And the distributions of graphene’s tensile strain and longitudinal (along the tensile direction) interfacial shear stress are not uniform along the width, which are also significantly different from the results of 1D model. Moreover, the critical strain for interfacial sliding derived by the 2D model is lower than that obtained by the 1D model. However, when the width of graphene is small enough, the 2D model can be approximately replaced by the 1D model. Finally, by fitting the Raman experimental results, the reliability of the 2D model is verified, and the interfacial stiffness (100 TPa/m) and shear strength (0.295 MPa) between graphene and polyethylene terephthalate (PET) substrate are calculated.