Friction Shear Stress on the Surface of Iron-Based Coating/HSS during Sliding Wear of Pin Disk

With the increasing demand for lightweight and lower fuel consumption and safety of automobile industry, lightweight materials of high strength steel (HSS) are more and more widely used. The hot stamping technology, which is determined by the inherent mechanical properties of high strength steel, makes molds prone to wear failure in the harsh service environments. In this paper, a finite element model is proposed for analyzing the value and distributions law of friction shear stress of contact surface of the pin disk. Through the simulation process of sliding wear, two kinds of different cladding materials of the pin specimens including H13 and Fe65, were experimented under three different loads by using the software ABAQUS. And then the pin-on- disk wear test at elevated temperature was conducted to verify the effectiveness of the simula-tion results. The results showed that the friction shear stress of pin with iron-based cladding and H13 steel was different under different loads, but the distribution was basically the same;the normal friction shear stress increased gradually along the direction of the pin movement, and the tangential shear stress increased gradually from the center of the pin to the outside of the circle;the value of the friction shear stress of the normal joints on the contact surface was periodically fluctuating in the whole dynamic analysis step, while it was basically stable in the tangential direction.

Numerical simulation of two-dimensional granular shearing flows and the friction force of a moving slab on the granular media

This paper studies some interesting features of two-dimensional granular shearing flow by using molecular dynamic approach for a specific granular system. The obtained results show that the probability distribution function of velocities of particles is Gaussian at the central part, but diverts from Gaussian distribution nearby the wall. The macroscopic stress along the vertical direction has large fluctuation around a constant value, the non-zero average velocity occurs mainly near the moving wall, which forms a shearing zone.. In the shearing movement, the volume of the granular material behaves in a random manner. The equivalent fl＇iction coefficient between moving slab and granular material correlates with the moving speed at low velocity, and approaches constant as the velocity is large enough.

Jamming of packings of frictionless particles with and without shear

By minimizing the enthalpy of packings of frictionless particles, we obtain jammed solids at desired pressures and hence investigate the jamming transition with and without shear. Typical scaling relations of the jamming transition are recovered in both cases. In contrast to systems without shear, shear-driven jamming transition occurs at a higher packing fraction and the jammed solids are more rigid with an anisotropic force network. Furthermore, by introducing the macrofriction coefficient, we propose an explanation of the packing fraction gap between sheared and non-sheared systems at fixed pressure.

Mechanical Characterisation of Interface for Steel/Polymer Composite Using Pull-out Test: Shear-Lag and Frictional Analysis

Fibre-matrix interface is known to have contribution to the mechanical performance of fibre-reinforced composite by its potential for load transfer between the fibre and the matrix. Such load transfer is of great importance in dentistry when a post is used for fixing a ceramic crown on the tooth. In this study, a pull-out test was carried out to analyse the interfacial properties of a steel fibre embedded in a polyester and epoxy matrices. It was found that the fibre-matrix interface is debonded on the whole embedded length when the fibre stress reached the debonding stress. Then, the fibre stress fell down to the initial extraction stress required to pulling out the debonded fibre from the matrix. Both debonding stress and initial extraction stress initiated a linear increase with the implantation length after the debonding stress reached horizontal asymptotes. To analyse the fibre-matrix load transfer before debonding, an analytical shear-lag model was adopted to in this test conditions. Fitting the experimental results with the analytical model provided the interfacial shear strength. By considering the Coulomb friction at the fibre-matrix interface during the fibre extraction process, an analytical model which considers Poisson＇s effects on both fibre and matrix, was developed. In this model, knowledge of the initial extraction stress of the fibre provides the residual normal stress at the fibre-matrix interface.

Presentation of Empirical Equations for Estimating Internal Friction Angle of GW and GC Soils in Mashhad, Iran Using Standard Penetration and Direct Shear Tests and Comparison with Previous Equations

Presentation of empirical equations for estimating engineering properties of soils is a simple, low cost and widely-used method. One of the major concerns in using these equations is evaluating their accuracy in different conditions and regions which often lead to doubts about obtained results. Most of these equations were derived in special laboratories, different climate conditions and in soils with different geotechnical and geological engineering properties and were generalized to other conditions. The main question is that whether these methods are also applicable to other conditions. Using local equations and narrowing the usage range of various methods based on each region’s properties are appropriate methods to solve these problems. This leads to simplified and faster analysis and high reliability in the obtained results. In this paper, empirical equations were derived to estimate internal friction angle, based on SPT numbers of Mashhad City’s soils in Iran, using SPT and direct shear tests results from 50 samples (25 GW and 25 GC soil samples). The results showed similar values for predicted?φ?values by SPT test and?φ?values determined by direct shear tests.

Effect of pin rotating speed on lap shear strength of stationary shoulder friction stir lap welded 6005A-T6 aluminum alloy

Stationary shoulder friction stir lap welding （SSFSLW） was successfully used to weld 6005A-T6 aluminum alloy in this paper. Effect of pin rotating speed on cross section morphologies and lap shear strength of the SSFSLW joints were mainly discussed. Results show that joints without flash and shoulder marks can be obtained by the stationary shoulder. Cross section of the SSFSLW joint presents a basin-like morphology and little material loss. By increasing the rotating speed from 1 000 rpm to 1 600 rpm, both effective sheet thickness and lap width increase, while lap shear failure load firstly decreases and then increases. The maximum failure load of 14. 05 kN /s attained when 1 000 rpm is used. All SSFSLW joints present shear fracture mode.

Shear Resistance of Siltous Sands Improved with Bridelia Tannins

The ruin of several civil engineering works occurs due to shear rupture of the ground. When the stress is greater than the shear resistance, the internal friction angle and the cohesion of the soil loosen and rupture occurs. Cement and lime are often used to stabilize soils and improve soil strength. The costs and environmental problems of these technologies raise concerns and challenge researchers to innovate with clean, inexpensive materials, accessible to the most disadvantaged social classes. The question that this study seeks to answer is whether the binders derived from plant tannins, which also stabilize soils, improve the shear resistance of these soils. To do this, we determined for silty sand the shear parameters, notably the cohesion and the angle of internal friction in the non-stabilized state and when they are stabilized with the powder of the bark of the Bridelia under different water states. The results show that the addition of Bridelia powder to silty sand increases the cohesion of the soil by nearly 70.71% and the friction angle by 4.31%. But in unfavourable water conditions, the cohesion and internal friction angle of the silty sand material improved with Bridelia bark powder drops drastically by nearly 81.56%. but does not dissolve completely as for the same material. When it is not stabilized. This information is an invaluable contribution in the search for solutions to increase the durability of earthen constructions by improving the water-repellent properties of soils.

Shear strength criteria for rock,rock joints,rockfill and rock masses:Problems and some solutions

Although many intact rock types can be very strong,a critical confining pressure can eventually be reached in triaxial testing,such that the Mohr shear strength envelope becomes horizontal.This critical state has recently been better defined,and correct curvature or correct deviation from linear Mohr-Coulomb（MC） has finally been found.Standard shear testing procedures for rock joints,using multiple testing of the same sample,in case of insufficient samples,can be shown to exaggerate apparent cohesion.Even rough joints do not have any cohesion,but instead have very high friction angles at low stress,due to strong dilation.Rock masses,implying problems of large-scale interaction with engineering structures,may have both cohesive and frictional strength components.However,it is not correct to add these,following linear M-C or nonlinear Hoek-Brown（H-B） standard routines.Cohesion is broken at small strain,while friction is mobilized at larger strain and remains to the end of the shear deformation.The criterion ＇c then σn tan φ＇ should replace ＇c plus σn tan φ＇ for improved fit to reality.Transformation of principal stresses to a shear plane seems to ignore mobilized dilation,and caused great experimental difficulties until understood.There seems to be plenty of room for continued research,so that errors of judgement of the last 50 years can be corrected.

Effect of mechanical degradation of laminated elastomeric bearings and shear keys upon seismic behaviors of small-to-medium-span highway bridges in transverse direction

Laminated elastomeric bearings have been widely used for small-to-medium-span highway bridges in China, in which concrete shear keys are set transversely to prohibit large girder displacement. To evaluate bridge seismic responses more accurately, proper analytical models of bearings and shear keys should be developed. Based on a series of cyclic loading experiments and analyses, rational analytical models of laminated elastomeric bearings and shear keys, which can consider mechanical degradation, were developed. The effect of the mechanical degradation was investigated by examining the seismic response of a small-to-medium-span bridge in the transverse direction under a wide range of peak ground accelerations（PGA）. The damage mechanism for small-to-medium-span highway bridges was determined, which can explain the seismic damage investigation during earthquakes in recent years. The experimental results show that the mechanical properties of laminated elastomeric bearings will degrade due to friction sliding, but the degree of decrease is dependent upon the influencing parameters. It can be concluded that the mechanical degradation of laminated elastomeric bearings and shear keys play an important role in the seismic response of bridges. The degradation of mechanical properties of laminated elastomeric bearings and shear keys should be included to evaluate more precise bridge seismic performance.

Shear strength behavior of geotextile/geomembrane interfaces

This paper aims to study the shear interaction mechanism of one of the critical geosynthetic interfaces,the geotextile/geomembrane, typically used for lined containment facilities such as landfills. A largedirect shear machine is used to carry out 90 geosynthetic interface tests. The test results show a strainsoftening behavior with a very small dilatancy （〈0.5 mm） and nonlinear failure envelopes at a normalstress range of 25e450 kPa. The influences of the micro-level structure of these geosynthetics on themacro-level interface shear behavior are discussed in detail. This study has generated several practicalrecommendations to help professionals to choose what materials are more adequate. From the threegeotextiles tested, the thermally bonded monofilament exhibits the best interface shear strength underhigh normal stress. For low normal stress, however, needle-punched monofilaments are recommended.For the regular textured geomembranes tested, the space between the asperities is an important factor.The closer these asperities are, the better the result achieves. For the irregular textured geomembranestested, the nonwoven geotextiles made of monofilaments produce the largest interface shear strength.

An improved wall shear stress measurement technique using sandwiched hot-film sensors

In this letter we present a novel wall shear stress measurement technique for a turbulent boundary layer using sandwiched hot-film sensors. Under certain conditions, satisfactory results can be obtained using only the heat generated by one of the hot-film and a calibration of the sensors is not required. Two thin Nickel films with the same size were used in this study, separated by an electrical insulating layer. The upper film served as a sensor and the bottom one served as a guard heater. The two Nickel films were operated at a same temperature, so that the Joule heat flux generated by the sensor film transferred to the air with a minimum loss or gain depending on the uncertainties in the film temperature measurements. Analytical solution of the shear stress based on the aforementioned heat flux was obtained. The preliminary results were promising and the estimated wall shear stresses agreed reasonablywell with the directly measured values （with errors less than 20%） in a fully developed turbulent pipe flow. The proposed technique can be improved to further increase precisions.

Shear properties of cemented rockfills

Application of cemented rockfilling to underground mining could not be separated from the corresponding backfill’s shear strength properties. The shear of cemented rockfill(CRF)-rock wall and the shear interaction occurring within CRFs both have some disadvantageous failure chances. In this study,we tried to investigate the complete shear properties of CRFs using direct shear and triaxial tests of cemented granite rockfill. Large-scale triaxial testing was held to accommodate the large CRF sample.Direct shear testing on the prepared flat and smooth surfaces was assessed with brief conversions and their corrections were used to approximate the shear strength envelopes of CRF joint interfaces. Two types of CRFs with the same aggregate size and distribution but different unconfined compressive strengths(UCSs) due to different mixture designs indicated insignificant differences between their basic friction angles, and also their asperity inclination angles. Nevertheless, investigation between direct shear test and triaxial test showed that the specimen with higher UCS tended to have a slightly lower friction angle but a higher cohesion than the other one.

Nonlinear shear behavior of rock joints using a linearized implementation of the Barton-Bandis model

Experiments on rock joint behaviors have shown that joint surface roughness is mobilized under shearing,inducing dilation and resulting in nonlinear joint shear strength and shear stress vs.shear displacement behaviors.The Barton-Bandis(B-B) joint model provides the most realistic prediction for the nonlinear shear behavior of rock joints.The B-B model accounts for asperity roughness and strength through the joint roughness coefficient(JRC) and joint wall compressive strength(JCS) parameters.Nevertheless,many computer codes for rock engineering analysis still use the constant shear strength parameters from the linear Mohr-Coulomb(M-C) model,which is only appropriate for smooth and non-dilatant joints.This limitation prevents fractured rock models from capturing the nonlinearity of joint shear behavior.To bridge the B-B and the M C models,this paper aims to provide a linearized implementation of the B-B model using a tangential technique to obtain the equivalent M-C parameters that can satisfy the nonlinear shear behavior of rock joints.These equivalent parameters,namely the equivalent peak cohesion,friction angle,and dilation angle,are then converted into their mobilized forms to account for the mobilization and degradation of JRC under shearing.The conversion is done by expressing JRC in the equivalent peak parameters as functions of joint shear displacement using proposed hyperbolic and logarithmic functions at the pre-and post-peak regions of shear displacement,respectively.Likewise,the pre-and post-peak joint shear stiffnesses are derived so that a complete shear stress-shear displacement relationship can be established.Verifications of the linearized implementation of the B-B model show that the shear stress-shear displacement curves,the dilation behavior,and the shear strength envelopes of rock joints are consistent with available experimental and numerical results.

Studies on the Coefficient of Friction During the Oblique Impact of a Hard Sphere Against a Ductile Solid Target

Following the original approach of Bowden and Tabor and introducing state variables, an effective friction coefficient μ_e for solid particle erosion is defined as a combination of shearing term and ploughing term. In the case of continuous sliding, based on considering the interaction between asperities under certain condition, it is indicated that during the oblique impact of a hardened steel sphere against a mild steel target, a possible value of μ_e is 0.05, which was chosen in all of the calculations by Hutchings for consistency with both experiments and calculations. In the case of continuous ploughing, it is shown that the value of μ_e is a function of the impact process and the initial impact angle and is greater than 0.05 on an average for Hutchings' experiments. It is suggested that the variation of sliding, rolling and ploughing state at each instant in the impact process makes “the coefficient of friction” equal to 0.05 for Hutchings' experiments, and in general, makes the effective friction coefficient during particle impact on metal far less than the friction coefficient during simple continuous sliding on an average.

Effects of Polypropylene Fibers on the Shear Strength of Sandy Soil

This paper presents the effect of two types of polypropylene fibers on shear strength parameters of sandy soil. To achieve the goals of this research, a sandy soil was obtained from a depth of 40 cm from the natural ground surface around American University of Sharjah. Two types of polypropylene fibers;one highly flexible with flat profile and the other with relatively high stiffness and crimpled profile were used in this study with four different aspect ratios (L/D) for each type. The initial physical properties of the sand such as specific gravity, angle of internal friction and shear strength were obtained in accordance with American Standard for Testing and Materials (ASTM). The sandy soils were mixed with the two types of fibers at different percentages by dry weight of the sand and four different aspect ratios. The test results of the study showed that the shear strength of the sand increased with increasing the flexible flat profile fibers content. Also it was noticed that by increasing the aspect ratio of the flexible flat profile the angle of internal friction and the shear strength increased. The crimpled profile fiber increased the shear strength of the sand under high normal load and has small or no effect on shear strength of the sand at low aspect ratio under low normal load.

DYNAMIC EFFECTIVE SHEAR STRENGTH OF SATURATED SAND

The dynamic effective shear strength of saturated sand under cyclic loading is discussed in this paper.The discussion includes the transient time depen- dency behaviors based on the analysis of the results obtained in conventional cyclic triaxial tests and cyclic torsional shear triaxial tests.It has been found that the dy- namic effective shear strength is composed of effective frictional resistance and viscous resistance,which are characterized by the strain rate dependent feature of strength magnitude,the coupling of consolidation stress with cyclic stress and the dependency of time needed to make the soil strength sufficiently mobilized,and can also be ex- pressed by the extended Mohr-Coulomb's law.The two strength parameters of the dynamic effective internal frictional angle φd and the dynamic viscosity coefficient η are determined.The former is unvaried for different number of cyclic loading,dy- namic stress form and consolidation stress ratio.And the later is unvaried for the different dynamic shear strain rate γt developed during the sand liquefaction,but increases with the increase of initial density of sand.The generalization of dynamic effective stress strength criterion in the 3-dimensional effective stress space is studied in detail for the purpose of its practical use.

In-service shear check of heated cased insulated flowlines

Starting friction would be induced and preserved somewhere along the seabed route of cased insulated flowlines（CIF） when the pipe carries service loads.The axial pipe-soil interaction can be divided into three pipe sections：the sliding section,the fixed section and the starting friction section.Although limited to a relatively small length of the pipe,the pipe coats of the starting friction section would suffer much higher shear force caused by thermal expansion than those of the sliding section or the fixed section.Based on the axial equilibrium equation of this kind of insulated pipeline,we developed a method for checking the shear force on CIF coats and their interfaces.The typical example shows that starting friction effect should be taken into account when checking the lap shear strength of heatshrinkable sleeves on CIF field joints.

Effect of refilling time on microstructure and mechanical properties of friction spot welded LY12 aluminum alloy

Friction spot welding （FSpW） was successfully used to produce joints of LY12 aluminum alloy. The effects of refilling time on microstructure and mechanical properties of FSpW joints were systematically studied. Results show that the cross-section of FSpW joint presents a basin-like morphology. A white bonding ligament exists in the center of the joint. The stir zone can be clarified into sleeve affected zone and pin affected zone based on different grain sizes. With increasing the refilling time from 2. 0 s to 3.5 s, grains in the stir zone become coarser, microhardness of the joint decreases and tensile shear failure load of the joint firstly increases and then decreases. The maximum tensile shear failure load of 8 130 N is attained when the refilling time is 3.0 s. Shear-plug fracture mode and shear fracture mode can be observed in the tensile shear tests. The maximum hardness of 169. 7 HV is attained in the joint center when the refilling time is 2. 0 s.

Soil shear properties as infl uenced by straw content:An evaluation of field-collected and laboratory-remolded soils

Following a rice or wheat harvest, a large amount of crop residue （straw） is retained in fields. The straw is often incorporated into the soil in order to increase the soil organic carbon storage and to reduce soil erosion. However, it has become apparent that the incorporated straw can significantly alter soil shear properties, which can dramatically affect energy inputs for tilling and other soil management practices. In this study, laboratory-remolded wheat straw-soil samples were compared with field-collected straw-soil samples; we found high correlations for the cohesion （R2=0.9084） and internal friction angle （R2=0.9548） properties of the samples. Shear tests on rice and wheat straw with different moisture content levels clearly demonstrated the relatively higher shear strength of wheat straw compared to rice straw. The cohesion of remolded rice and wheat straw-soil samples exhibited an increasing linear trend with an increase in densities, whereas the internal friction angle data for these samples exhibited a quadratic trend. Overlapping the cohesion curves revealed that the wheat straw-soil and rice straw-soil samples had the same cohesion at a straw density of 0.63%. Similar results were obtained when the internal fraction angle curves overlapped; the resultant point of intersection was observed at a straw density of 0.46%. As a whole, the remolded sample methodology was found suitable to simulate the shear properties of soils sampled directly from fields.

A Novel Shear Mode MR Damper and Its Mechanical Performance

This paper presents a linear shear mod magneto-rheological(MR) damper which can be applied to vibration control system.The proposed MR damper featured by a small amount of MR fluid,absence of a gas chamber or diaphragm and piston with helix slotted.Because of the absence of a gas chamber or diaphragm,unnecessary damping force caused by gas compression is not generated.Magnitude and damping coefficient of damping force are two important indexes to evaluate performance of MR damper.The piston with helix slotted is developed based on mechanical analysis on rheological characteristics of MR damper,and the damping performance of MR damper with helix slotted piston is investigated through performance experiments and comparison with analytical simulation.The results indicate that helix slot may increase friction coefficient on surface of the piston,and improve the maximum damping force without reducing damping coefficient of the damper.The reflux of MR fluid may be increased by adjusting helix angle suitably,which avoids the settlement of MR fluid.