Peak Shear Research Articles

A comparison of azimuthal and axial oscillation microfiltration using surface and matrix types of microfilters with a cake-slurry shear plane exhibiting non-Newtonian behaviour

The mode of application of oscillation, axial or azimuthal, did not influence filtration performance, when filtering a calcite mineral with a d32 value of 2.7µm. The equilibrium flux and deposit thickness correlated with shear stress, regardless of: filter type (metal slotted surface filter or homogeneous sintered filter); and mode of oscillation. Shear stress values up to 240Pa were used and the particle compact believed to be at, or near, the deposited solids showed non-Newtonian flow behaviour described by the Herschel-Bulkley equation. The shear was computed using Comsol® to model the shear at, and near, the oscillating surface. The peak shear (maximum value) was used in the correlation for flux, which appeared to fit the data well and provide a realistic prediction for sustainable flux using a force balance model.The existence of a yield stress in the compact appeared to limit the internal fouling of the matrix (homogeneous) type of filter, which had a membrane thickness of 8mm, but did not demonstrate significant internal fouling over time, nor between filtrations. Thus, the results were similar to those obtained for the surface filters, and the resistance to filtration was dominated by the deposit formed.

An overview of low back pain and occupational exposures to whole-body vibration and mechanical shocks.

This paper offers an overview of the relation of low back pain (LBP) to occupational exposures to whole-body vibration (WBV) and mechanical shocks. LBP is a condition of multifactorial origin and is a very common health problem in the general population. Among occupational risk factors, epidemiological studies of driving occupations have provided evidence for strong associations between LBP and occupational exposures to WBV and mechanical shocks. Since it is hard to separate the contribution of WBV exposure to disorders in the lower back from that of other individual, ergonomic or psychosocial risk factors, a quantitative exposure-response relationship for WBV cannot be outlined precisely. Experimental research has provided biodynamic support to the findings of epidemiological studies, showing that in controlled laboratory conditions exposure to WBV can cause mechanical overload to the human spine. The EU Directive on mechanical vibration has established daily exposure action and limit values to protect the workers against the risk from WBV. There is some evidence that the EU exposure limit values are excessive, so much so that an elevated risk of LBP has been found for WBV exposures beneath the EU limit values. In the Italian arm of the EU VIBRISKS prospective cohort study of professional drivers, measures of internal lumbar load (compressive and shear peak forces), calculated by means of anatomy-based finite-element models, were found better predictors of the occurrence over time of low back disorders than the metrics of external exposure suggested by the EU Directive on mechanical vibration. Further biodynamic and epidemiological studies are needed to validate the findings of the VIBRISKS study.

Dissimilar joining of AZ31B magnesium alloy and pure copper via thermo-compensated resistance spot welding

The feasibility of Mg/Cu dissimilar resistance spot welding (RSW) was investigated via a thermo-compensated process. Both physical factors and metallurgical properties of the welds affected the tensile shear properties of the joints. The mechanical properties of the Mg/Cu RSW joints were determined by the competitive relationship between these two factors. The increase in the nugget size with increasing Joule heat input improved the load-bearing ability of the joints. However, at the same time, the microstructure of the nugget transformed from an α-Mg solid solution fusion zone with a thin transition layer into an intermetallic compound (IMC)-enriching fusion zone with a thick transition layer. The mechanical properties of the joints deteriorated, owing to this transformation. All the Mg/Cu RSW samples fractured via interfacial failure (IF) mode and exhibited cleavage features. Although their ductility deteriorated owing to the IMCs, the Mg/Cu thermo-compensated RSW joints exhibited satisfactory tensile shear peak loads (maximum: 2626N), which are comparable to that (2745N) of Mg/Mg RSW joints. A reliable welding lobe suitable for industrial manufacture was obtained, when a welding time and a welding current of 100ms–400ms and 12kA–20kA, respectively, were recommended.

Shear strength properties of cable bolts using a new double shear instrument, experimental study, and numerical simulation

A newly developed double shear apparatus without contact between concrete blocks was developed to conduct a series of double shear tests. This new double shear apparatus is capable of determining the pure shear strength of pre-tensioned fully grouted cable bolt without friction between sheared concrete blocks. Five different types of cable bolt, with various pretension loads, were tested to investigate the influence of surface profile type and pretension load on the shear strength of cable bolt. Concrete blocks of 40MPa strength and the Stratabinder HS grout were used for consistency across the entire tests. The results showed that the plain cable bolts had higher peak shear load compared with the indented and spiral strand cable bolts. The shear displacement and peak shear load decreased by increasing the pretension load. A numerical analysis was carried out, based on the Fast Lagrangian Analysis of Continua (FLAC 2D) and the result was compared with the experimental data. It was observed that FLAC 2D is capable of simulating the performance of cable bolt satisfactorily.

Seismic vulnerability indices of ground for Değirmendere (Kocaeli Province, Turkey)

It is well known that the mechanical and physical properties of subsoil layers as well as poor construction practices play an important role in determining the level of structural damage sustained from earthquakes. Thus, sufficient knowledge of these properties is essential for estimating the weak points of a region. The ground vulnerability index (Kg), an indicator of the weak points of a region, also has a substantial importance role in mitigating earthquake hazards in multidisciplinary studies. In this context, we have used engineering basement shear wave velocity (vs30), fundamental frequencies and peak amplitude values of the horizontal-to-vertical ratio (H/V) to calculate Kg values for the study area (Kocaeli Province, Turkey). Structural damage was investigated after the August 17, 1999 Kocaeli (Mw = 7.4) Earthquake and compared with the calculated Kg values. The results indicate that the Kg values decrease towards the southern part of the study area, which is in good agreement with damage distribution from this earthquake. Kg values of >10 appear to be indicative of the most vulnerable areas in the study area. Structures built along the coastlines in Degirmendere area were the mostly severely damaged or collapsed entirely; we found that the subsoil beneath them have high Kg values of between 10 and 25 In contrast, Kg values in the southern districts, which sustained little or no damage, are relatively low (Kg < 10). In our study, the Kg values and soil types showed good agreement. Potential vulnerable areas also have poor subsoil conditions. Therefore, it could be important to consider these results for the future planning and designing of urban areas. These results could also be used as a rapid way to detect potential vulnerable areas before the occurrence of a destructive earthquake.

Effect of pressure with shear stress on gelatinization of starches with different amylose/amylopectin ratios

Effect of pressure with shear stress on the gelatinization of cornstarch with different amylose/amylopectin ratios (waxy 0/100; maze 23/77; G50 50/50; G80 80/20) was systematically investigated using a high-pressure rheometer. Onset and peak temperature of starch gelatinization as well as the peak viscosity were used to discuss the influence of pressure together with shear stress on the gelatinization of starch granules. The results showed that without shear stress, pressure could resist the gelatinization process due to weak swelling of starch granules and lower quantity of amylose released. However, the shear stress can simply counteract the influence of the pressure since its impact is much high on gelatinization. Under certain pressure and shear stress, both onset and peak temperatures of gelatinization were increased with increasing amylose content, which is in correspondence with the results from differential scanning calorimeter measurement, while the overall viscosity was lower when starches with a higher amylose content was used because part of its granular was not fully dissolved during the measurement. SAXS measurements were used to study the gel structure and stability of starch suspensions. It was found that the scattering intensity of starches in the measured range (0.1–1.0 nm−1) is G80 > waxy, indicating the amount of ordered semi-crystalline structures in amylose is higher. Peak values, q = 0.4 nm−1 and q = 0.2 nm−1, detected for waxy starch under different shear rates, indicates that higher shear stress which plays a dominant role compared with pressure, resulted in more degradation in amylopectin, inhibiting the formation of aggregate structure.

X-Ray Temperatures, Luminosities, and Masses from XMM-Newton Follow-upof the First Shear-selected Galaxy Cluster Sample∗

Abstract We continue the study of the first sample of shear-selected clusters from the initial 8.6 square degrees of the Deep Lens Survey (DLS); a sample with well-defined selection criteria corresponding to the highest ranked shear peaks in the survey area. We aim to characterize the weak lensing selection by examining the sample’s X-ray properties. There are multiple X-ray clusters associated with nearly all the shear peaks: 14 X-ray clusters corresponding to seven DLS shear peaks. An additional three X-ray clusters cannot be definitively associated with shear peaks, mainly due to large positional offsets between the X-ray centroid and the shear peak. Here we report on the XMM-Newton properties of the 17 X-ray clusters. The X-ray clusters display a wide range of luminosities and temperatures; the L X −T X relation we determine for the shear-associated X-ray clusters is consistent with X-ray cluster samples selected without regard to dynamical state, while it is inconsistent with self-similarity. For a subset of the sample, we measure X-ray masses using temperature as a proxy, and compare to weak lensing masses determined by the DLS team. The resulting mass comparison is consistent with equality. The X-ray and weak lensing masses show considerable intrinsic scatter (∼48%), which is consistent with X-ray selected samples when their X-ray and weak lensing masses are independently determined.

Impaired Arterial Smooth Muscle Cell Vasodilatory Function In Methamphetamine Users

Objectives: Methamphetamine use is a strong risk factor for stroke. This study was designed to evaluate arterial function and structure in methamphetamine users ultrasonographically.Methods: In a cross-sectional study, 20 methamphetamine users and 21 controls, aged between 20 and 40years, were enrolled. Common carotid artery intima-media thickness (CCA-IMT) marker of early atherogenesis, flow-mediated dilatation (FMD) determinants of endothelium-dependent vasodilation, and nitroglycerine-mediated dilatation (NMD) independent marker of vasodilation were measured in two groups.Results: There were no significant differences between the two groups regarding demographic and metabolic characteristics. The mean (±SD) CCA-IMT in methamphetamine users was 0.58±0.09mm, versus 0.59±0.07mm in the controls (p=0.84). Likewise, FMD% was not significantly different between the two groups [7.6±6.1% in methamphetamine users vs. 8.2±5.1% in the controls; p=0.72], nor were peak flow and shear rate after hyperemia. However, NMD% was considerably decreased in the methamphetamine users [8.5±7.8% in methamphetamine users vs. 13.4±6.2% in controls; p=0.03].Conclusion: According to our results, NMD is reduced among otherwise healthy methamphetamine users, which represents smooth muscle dysfunction in this group. This may contribute to the high risk of stroke among methamphetamine users.

Feasibility of using rubber waste fibers as reinforcements for sandy soils

In this study, an alternative and environmentally friendly method for the reinforcement of dune sand is proposed. This technique consists of using randomly distributed rubber fibers to improve the engineering properties of sand. Rubber fibers are added to the sand with different percentages: 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75 and 2% of dry weight of sand. The experimental program carried out consists of investigating the effect of rubber fibers on the shear strength properties of sand. Reinforced and unreinforced samples are tested in the dense as well as loose state. The results obtained showed that the inclusion of rubber fibers in dune sand will improve the engineering properties of various civil engineering applications such as shallow foundations and slope. Therefore, incorporation of rubber fibers can enhance the shear strength characteristics, peak and residual strengths, and introduce more ductility to the mechanical behavior of sand. In addition to the technical effect, this paper emphasizes another environmentally attractive option, which is the use of rubber fibers as reinforcements for granular soils as this helps to remove some parts of these wastes and protect the environment.

Empirical Formula of Shear Strength of Rock Fractures Based on 3D Morphology Parameters

The prime objective of this work is to provide a reference to predict the peak shear strength of rock fractures. The paper studied some shear properties of rock fractures and proposed an empirical formula for the peak shear strength of rock fractures based on 3D morphology parameters. The rock fractures were induced in cylindrical sandstone and marble specimens by means of indirect tension. A rock direct shear apparatus (RDS-200) was adopted to conduct direct shear tests on five groups of rock fractures under different levels of normal load. Before the direct shear test, 3D morphology parameters of rock fracture surfaces were obtained using a 3D optical scanner. By analyses of direct shear test data, the relationships between peak shear strength, peak shear displacement, peak dilatancy angle, residual friction coefficient and peak normal stress were found. According to the evolution trends of peak shear strength and peak dilatancy angle along with the normal stress, an empirical formula was proposed to predict the peak shear strength of rock fractures in both sliding and cutting failure modes considering the 3D morphology parameters of rock fracture surfaces. The empirical formula could be commonly used for different types (sandstone and marble) and grain sizes (powder-grained, fine-grained, medium-grained and coarse-grained) of rock fractures.

Microzonation Analysis of Cohesionless and Cohesive Soil

Urban seismic risk is a continuous worldwide issue, numerous researchers are putting great effort in dealing with how to minimise the level of the threat. The only way to minimise the social and economic consequences caused but the seismic risk is through comprehensive earthquake scenario analysis such as ground response analysis. This paper intends to examine the characteristic of shear wave velocity and peak ground acceleration on cohesionless and cohesiveness soil. In order to examine the characteristic of shear wave velocity and peak ground acceleration on cohesionless and cohesiveness soil, ground response analysis was performed using Nonlinear Earthquake Site Response Analysis (NERA) and Equivalent-linear Earthquake Site Response Analysis (EERA). The value of ground acceleration was initially high at bedrock and vanishes during the propagation process. It is thus, the measured acceleration at surface is therefore much lower as compare to at bedrock. Result shows that seismic waves can travel faster in harder soil as compared to softer soil. Cohesive soil contributes more to the shaking amplification than cohesionless soil such as sand and harder soil. This is known as local site effect. The typical example is the Mexico Earthquake that happened in 1985. As conclusion, peak ground acceleration for cohesive soil is higher than in cohesionless soil.

Increasing hip and knee flexion during a drop-jump task reduces tibiofemoral shear and compressive forces: implications for ACL injury prevention training

ABSTRACTAlthough most ACL injury prevention programmes encourage greater hip and knee flexion during landing, it remains unknown how this technique influences tibiofemoral joint forces. We examined whether a landing strategy utilising greater hip and knee flexion decreases tibiofemoral anterior shear and compression. Twelve healthy women (25.9 ± 3.5 years) performed a drop-jump task before and after a training session (10–15 min) that emphasised greater hip and knee flexion. Peak tibiofemoral anterior shear and compressive forces were calculated using an electromyography (EMG)-driven knee model that incorporated joint kinematics, EMG and participant-specific muscle volumes and patella tendon orientation measured using magnetic resonance imaging (MRI). Participants demonstrated a decrease in peak anterior tibial shear forces (11.1 ± 3.3 vs. 9.6 ± 2.7 N · kg−1; P = 0.008) and peak tibiofemoral compressive forces (68.4 ± 7.6 vs. 62.0 ± 5.5 N · kg−1; P = 0.015) post-training. The decreased peak anterior tibial shear was accompanied by a decrease in the quadriceps anterior shear force, while the decreased peak compressive force was accompanied by decreased ground reaction force and hamstring forces. Our data provide justification for injury prevention programmes that encourage greater hip and knee flexion during landing to reduce tibiofemoral joint loading.

Fracture mechanisms of Al/steel resistance spot welds in lap shear test

This study investigated failure modes, mechanical strength and fracture mechanism of Al/steel resistance spot welds in lap shear test. Three major fracture mechanisms and failure modes were identified: semi-brittle or brittle fracture in the intermetallic compound (IMC) layer which led to interfacial failure, ductile fracture in the aluminum fusion zone (FZ) which led to thickness failure, and ductile fracture in the aluminum heat affected zone (HAZ) which led to the engineering preferred button pullout failure. The failure mode and mechanical strength of the weld depended highly on the dimension and properties of the IMC layer, aluminum FZ, and aluminum HAZ. The IMC thickness was the dominant factor of the failure mode and mechanical properties. The button pullout failure or thickness failure was related to thin IMC thickness of no more than 3μm. Meanwhile, increasing the Al nugget size or steel bulge height helped to increase lap shear peak load and promote button pullout failure. Thick IMC layer with thickness more than 3μm tended to cause interfacial failure in the IMC layer, even with large Al nugget size and severe steel bulging.

Anisotropic shear behavior of rock joint replicas

In this study, an anisotropic shear behavior of joint replicas is investigated under constant normal load condition (CNL). A new anisotropic peak shear strength model is proposed incorporating actual peak dilation angle and shear component of asperities. In this model, peak dilation angle is modified with mean plane to find out actual dilation angle and shear component is back calculated from experimental results. The results show that as the ratio of normal stress to compressive strength increases, peak dilation angle decreases exponentially whereas shear component increases in power function form. Further, an empirical model for estimation of peak shear displacement is proposed based on maximum asperity angle and friction angle. Afterwords, shear stiffness is calculated as a ratio of predicted shear strength and peak shear displacement. To conduct this study, three different natural joint roughness is transferred to silicon rubber molds and these molds are used to make joint replicas of mated joint of 90mm diameter and 50mm height by mixture of cement, sand, and water in the ratio of 1:1.5:0.45 by weight. The surface cloud of joint surface are generated using 3D non-contact type profiler. In this study, total 144 direct shear tests are conducted on prepared joint replicas using four normal stresses (0.25, 0.5, 1, and 1.5MPa).

ANALYSIS ON EFFECT OF PLATE SPACING ON SHEAR STIFFNESS OF PERFOBOND CONNECTORS

In order to discuss the reasonable plate spacing of perfobond connector, the influence of plate spacing on the shear stiffness of perfobond connector is analyzed through the push-out model test and based on the theory of elastic foundation beam. The calculation formula for perfobond shear stiffness is proposed, which accounts for the influence of plate spacing. Research results indicate that the plate spacing has little effect on shear capacity and peak slip of perfobond connector but changes the shear stiffness. Shear stiffness approximately linearly increases as the plate spacing increases, gradually approaching the single plate shear stiffness. The main influence factor for the shear stiffness of perfobond connector is the spacing-diameter ratio, which is suggested to be no less than 3.3 when multi perfobonds are arranged in parallel.

Cosmology constraints from shear peak statistics in Dark Energy Survey Science Verification data

Shear peak statistics has gained a lot of attention recently as a practical alternative to the two point statistics for constraining cosmological parameters. We perform a shear peak statistics analysis of the Dark Energy Survey (DES) Science Verification (SV) data, using weak gravitational lensing measurements from a 139 deg$^2$ field. We measure the abundance of peaks identified in aperture mass maps, as a function of their signal-to-noise ratio, in the signal-to-noise range $0<\mathcal S / \mathcal N<4$. To predict the peak counts as a function of cosmological parameters we use a suite of $N$-body simulations spanning 158 models with varying $\Omega_{\rm m}$ and $\sigma_8$, fixing $w = -1$, $\Omega_{\rm b} = 0.04$, $h = 0.7$ and $n_s=1$, to which we have applied the DES SV mask and redshift distribution. In our fiducial analysis we measure $\sigma_{8}(\Omega_{\rm m}/0.3)^{0.6}=0.77 \pm 0.07$, after marginalising over the shear multiplicative bias and the error on the mean redshift of the galaxy sample. We introduce models of intrinsic alignments, blending, and source contamination by cluster members. These models indicate that peaks with $\mathcal S / \mathcal N>4$ would require significant corrections, which is why we do not include them in our analysis. We compare our results to the cosmological constraints from the two point analysis on the SV field and find them to be in good agreement in both the central value and its uncertainty. We discuss prospects for future peak statistics analysis with upcoming DES data.

Feasibility study of dissimilar joining of aluminum alloy 5052 to pure copper via thermo-compensated resistance spot welding

A parametric study was used to investigate the feasibility of dissimilar Al/Cu joining by a thermo-compensated resistance spot welding process. The tensile shear properties of the joints were found to be affected by both the weld's physical properties and metallurgical factors: (1) With increasing heat input, the nugget size and indentation increased, which led to the failure mode of the joint to change from interfacial failure to pull-out mode. (2) There was a critical heat input at which the microstructure changed in the fusion zone. At normal heat input, the fusion zone consisted of a significant amount of α-Al solid solution and a thin transition layer (α-Al/θ-CuAl2 eutectic to θ-CuAl2) at the Al/Cu interface, producing a high nugget's shear strength. At high heat input, the fusion zone mainly consisted of Al–Cu intermetallic compounds (IMCs), producing a low nugget's shear strength. The fractograph revealed cleavage features in the interfacial failure mode and dimples in the pull-out mode, which implied that the crack propagated respectively in the IMC zone and the periphery of the nugget. The Al/Cu thermo-compensated resistance spot weld joints presented a tensile shear peak load comparable to that of Al/Al joints, though their ductility was deteriorated by the IMCs.

The impact of different aperture distribution models and critical stress criteria on equivalent permeability in fractured rocks

AbstractPredicting equivalent permeability in fractured reservoirs requires an understanding of the fracture network geometry and apertures. There are different methods for defining aperture, based on outcrop observations (power law scaling), fundamental mechanics (sublinear length‐aperture scaling), and experiments (Barton‐Bandis conductive shearing). Each method predicts heterogeneous apertures, even along single fractures (i.e., intrafracture variations), but most fractured reservoir models imply constant apertures for single fractures. We compare the relative differences in aperture and permeability predicted by three aperture methods, where permeability is modeled in explicit fracture networks with coupled fracture‐matrix flow. Aperture varies along single fractures, and geomechanical relations are used to identify which fractures are critically stressed. The aperture models are applied to real‐world large‐scale fracture networks. (Sub)linear length scaling predicts the largest average aperture and equivalent permeability. Barton‐Bandis aperture is smaller, predicting on average a sixfold increase compared to matrix permeability. Application of critical stress criteria results in a decrease in the fraction of open fractures. For the applied stress conditions, Coulomb predicts that 50% of the network is critically stressed, compared to 80% for Barton‐Bandis peak shear. The impact of the fracture network on equivalent permeability depends on the matrix hydraulic properties, as in a low‐permeable matrix, intrafracture connectivity, i.e., the opening along a single fracture, controls equivalent permeability, whereas for a more permeable matrix, absolute apertures have a larger impact. Quantification of fracture flow regimes using only the ratio of fracture versus matrix permeability is insufficient, as these regimes also depend on aperture variations within fractures.

A pressure and shear sensor system for stress measurement at lower limb residuum/socket interface

A sensor system for measurement of pressure and shear at the lower limb residuum/socket interface is described. The system comprises of a flexible sensor unit and a data acquisition unit with wireless data transmission capability. Static and dynamic performance of the sensor system was characterised using a mechanical test machine. The static calibration results suggest that the developed sensor system presents high linearity (linearity error ≤ 3.8%) and resolution (0.9 kPa for pressure and 0.2 kPa for shear). Dynamic characterisation of the sensor system shows hysteresis error of approximately 15% for pressure and 8% for shear. Subsequently, a pilot amputee walking test was conducted. Three sensors were placed at the residuum/socket interface of a knee disarticulation amputee and simultaneous measurements were obtained during pilot amputee walking test. The pressure and shear peak values as well as their temporal profiles are presented and discussed. In particular, peak pressure and shear of approximately 58 kPa and 27 kPa, respectively, were recorded. Their temporal profiles also provide dynamic coupling information at this critical residuum/socket interface. These preliminary amputee test results suggest strong potential of the developed sensor system for exploitation as an assistive technology to facilitate socket design, socket fit and effective monitoring of lower limb residuum health.

Shear behavior and analytical model of perfobond connectors

In steel and concrete composite girders, the load transfer between the steel beam and the concrete slab is commonly ensured by installing shear connectors. In this paper, to investigate the nonlinear behavior of perfobond connectors, a total of 60 push-out specimens were fabricated and tested with the variables for the hole diameter, the concrete strength, the thickness of concrete slab, the diameter, strength and existence of perforating rebar, the thickness, height and distance of perfobond ribs. The failure mode and the load-slip behavior of perfobond connectors were obtained. A theoretical model was put forward to express the load-slip relationship. Analytical formulas of shear capacity and peak slip were also proposed considering the interaction between the concrete dowel and the perforating rebar. The calculation results of the proposals agreed well with the experimental values.