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This paper presents a three-dimensional fully hydro-mechanical coupled distinct element study on fault reactivation and induced seismicity due to hydraulic fracturing injection and subsequent backflow process, based on the geological data in Horn River Basin, Northeast British Columbia, Canada. The modeling results indicate that the maximum magnitude of seismic events appears at the fracturing stage. The increment of fluid volume in the fault determines the cumulative moment and maximum fault slippage, both of which are essentially proportional to the fluid volume. After backflow starts, the fluid near the joint intersection keeps flowing into the critically stressed fault, rather than backflows to the wellbore. Although fault slippage is affected by the changes of both pore pressure and ambient rock stress, their contributions are different at fracturing and backflow stages. At fracturing stage, pore pressure change shows a dominant effect on induced fault slippage. While at backflow stage, because the fault plane is under a critical stress state, any minor disturbance would trigger a fault slippage. The energy analysis indicates that aseismic deformation takes up a majority of the total deformation energy during hydraulic fracturing. A common regularity is found in both fracturing- and backflow-induced seismicity that the cumulative moment and maximum fault slippage are nearly proportional to the injected fluid volume. This study shows some novel insights into interpreting fracturing- and backflow-induced seismicity, and provides useful information for controlling and mitigating seismic hazards due to hydraulic fracturing.

Perfluoropolyether (PFPE) polymer lubricant performs an important role in protecting both the writing/reading elements in the recording head and the disk of magnetic storage devices from mechanical wear or damage, induced by direct contact. Under high-speed sliding, the nanometer thick lubricant shows complex behavior, such as shear thinning, slippage and bonding ratio, making it difficult to directly test or simulate its performance. Based on a numerical model, the present study obtains the mechanical response of the lubricant under normal and sliding contacts. The mechanical response is then entered into a finite element model (FEM) through definition of material behavior of the lubricant using a hyper-elastic constitutive model. By comparing the sliding contact simulations with lubricant and without lubricant, it is found that the presence of lubricant helps to reduce the contact stresses, mainly because the contact area is increased.

The seismic assessment of reinforced concrete (RC) structures before and after retrofitting is a challenging task, mainly because existing numerical tools cannot accurately model the evolution of concrete damage. This article proposes an innovative numerical method suitable to model and assess the ultimate carrying capacity of RC structures. The modelling approach proposes a steel constitutive material model with a damage factor that accounts for accumulated damage within the surrounding concrete domain, which effectively captures bar slippage. The proposed method is validated with experimental results from full-scale cyclic tests on deficient bare and CFRP-retrofitted RC joints tested previously by the authors. The results indicate that the proposed simulation method captures the extreme nonlinearities observed in the tested RC joints, with acceptable accuracy and computational robustness. The results of this study are expected to contribute towards the development of more reliable numerical tools and design guidelines for efficient seismic assessment of RC structures before and after earthquakes.

In this work, the effect of high temperature on the bond behavior between Recycled Asphalt Pavement (RAP) concrete and Fiber Reinforced Polymer (FRP) was studied. The use of RAP in concrete construction has been developed and utilized recently due to its various economic and environmental features. Nevertheless, very few studies have examined the bonding performance and failure mode between RAP concrete and FRP. A total of 46 asphalt pavement concrete specimens with three different concrete compressive strength were cast and tested under pullout test. The specimens were prepared using different RAP aggregate content and were subjected to elevated temperatures within a range from 23 °C to 600 °C. The heat damaged specimens were repaired using two Near-Surface Mounted Carbon Fiber Reinforced Polymer (NSM-CFRP) strips spaced at 50 mm with three different bonded lengths. According to the experimental results of the pullout test, RAP concrete specimens showed lower bonding strength and slippage than Natural Aggregate (NA) concrete specimens. Furthermore, specimens exposed to elevated temperatures showed a significant decrease in bonding strength and a significant increase in slippage. Results also indicated that as the temperature increased, specimens with high RAP aggregate content failed at higher slippage compared to specimens with low RAP aggregate content with the same compressive strength. Moreover, the relationships between bond load and strain of (CFRP) strips were established and discussed in the results. The failure mode in all specimens was concrete separation.

To model the elastoplastic behaviors of frozen soils, a binary-medium-based constitutive model is developed and validated by a series of cryotriaxial compressive tests. In the framework of the proposed model, frozen soils are conceptualized to consist of structural blocks and weakened bands. Herein, the structural blocks are idealized as bonded elements with elastic-brittle deformational behaviors. Moreover, the weakened bands are conceptualized as frictional elements whose deformational characteristics are described by a nonlinear Duncan–Chang hyperbolic model. The bonded elements are found to gradually break up and transfer into frictional elements, which collectively contribute to the resistance capability against external loading. From the micro perspective and in the representative volume element (RVE) of the soil specimen, nonuniform strain distributions and particle slippage mechanisms are considered in the strain concentration coefficient and breakage ratio to formulate a constitutive model. Predictions are calibrated with available laboratory results, demonstrating that the proposed model can reasonably account for a breakage mechanism and can quantitatively simulate the nonlinear elastoplastic behavior of frozen soils. Keywords: Frozen soils, Elastoplastic behaviors, Binary-medium constitutive model, Breakage ratio, Strain concentration coefficient

This study investigated the influence of special anchoring holes on the bond-slip behavior between CFRP composites and concrete. For this purpose, one hundred and forty-four concrete prisms (200 × 200 × 200 mm) were casted with different concrete compressive strength (20 MPa, 30 MPa, 40 MPa), holes direction (N: None, V: Vertical (Parallel to the fibers), H: Horizontal (Perpendicular to the fibers)), number of holes (0: None, 1, 2, 3, 4), CFRP sheet bonded length (100 mm, 150 mm) and CFRP sheet bonded width (100 mm, 150 mm). The bonding surface of each concrete blocks was prepared and then anchoring holes were drilled using rotary drill before bonding of CFRP sheet. The experimental results showed that the pattern of the anchoring holes has a significant effect on the bond-slip behavior. In general, both the bond strength and ultimate slippage increase as the number of holes increases and as the CFRP sheet width or length increase. However, for an equivalent CFRP sheet area, the influence of the length (parallel to the direction of loading) is more significant in improving the bond strength than the influence of the width of CFRP sheet. For similar number of anchoring holes, the horizontal (Perpendicular to the fibers) pattern was the most effective followed by vertical (Parallel to the fibers) pattern, and one-hole pattern respectively. The special characteristic of the present study is that the new proposed bond–slip model is based on anchored hole CFRP composite and concrete; instead, the existing bond–slip models are based on CFRP composite without anchorage and ordinary concrete. This proposed model is then assessed using experimental test results on anchored holes concrete bonded blocks subjected to double-shear pull-off test, existing bond–slip models in the literature, and database of pull tests published by several researchers. Finally, the proposed bond–slip model is provided an accurate prediction of the large test database of bond strength and corresponding slippage.

The performance of underground excavations is inevitably influenced by rock mass characteristics, presence of joints and their geometrical properties, depth below surface and state of in-situ stress field. The objective of this paper is to investigate the behaviour of deep underground tunnel opening existed between two bedding planes. Such planes weaken the strength of rock mass and may cause rock slippage/rotation along them. Therefore, the state of stress-displacement, after tunnel opening has been introduced, is examined using two-dimensional elasto-plastic finite-elements code, RS2D. The results indicate that, there is significant drop in the normal stress along joints over tunnel opening; slip occurs due to reversal in the direction of shear stress (e.g., inward shear displacement is produced) and there is discontinuity in the strength contours of rock surrounding tunnel after they have been intersected by bedding planes. Keywords: State of stress-displacement, Bedding planes, Tunnel performance, Depth of failure zones, Stability analysis

The effect of tack coat application on pavement interlayer shear strength attracts strong interest during asphalt paving. Given its extensive use, tack coat is known to behave as a bond material to reduce pavement distresses such as slippage crack. The effectiveness of tack coat in increasing shear strength may be affected by multiple factors, such as tack coat material, test condition, pavement surface condition, and moisture. This article is a literature review focus on how the interlayer shear strength varied when relevant influential factors are changing. Review results indicate that the interlayer shear strength increased with the decreased test temperature, increased traffic load (within design limit), and increased test confinement pressure. Additionally, the milled pavement surface always has higher shear strength then the non-milled pavement surface. It is also found that laboratory-prepared specimens resulted in higher interlayer shear strength than field pavement cores. The effect of other factors on tack coat application may follow different trends depending on mix type and existing pavement condition. For instance, optimum tack coat rate that corresponds to peak shear strength is widely reported, while it is also found that tack coat does not greatly affect shear strength on dry, clean and milled pavement surface. Furthermore, shear strength reduced when mixture is designed with high percentage of air voids or coarse aggregate structure, such as porous asphalt and stone mastic asphalt (SMA) mixtures. More findings and recommendations can be found in this paper. Keywords: Tack coat, Interlayer shear strength, Asphalt pavement, Temperature, Milling, Mixture type

A mobile instrumentation system was developed and mounted on an MF 285 tractor to measure the performance parameters of the tractor and attached implements. The system measures implement draft, fuel consumption, real forward velocity, tillage depth and engine speed. Other parameters such as wheel slippage, drawbar power and traction efficiency would be calculated by ASABE standard. Overall energy efficiency for the tractor-implement system was calculated, too. Three implements included of moldboard plow, disk plow and chisel plow at four forward velocities (1.5, 2.3, 3 and 4 km/h) in 23 cm depth and 1500 rpm engine speed was examined. Analysis of variance (ANOVA) of resulted data revealed that increase of forward velocity results in increase of implement draft, wheel slippage, drawbar power and overall energy efficiency but results in decrease of traction efficiency. Furthermore, fuel consumption decreased by increase of velocity from 1.5 km/h to 3 km/h but increased by increase of velocity from 3 km/h to 4 km/h. Moreover, it was observed that draft requirement for implements in tests ranged from 8.2 kN for the disk plow to 13 kN for the chisel plow and fuel consumption ranged from 10.72 L/ha for the chisel plow to 26.5 L/ha for the moldboard plow. The ranges in mentioned parameters indicate that energy saving can be readily done by selecting energy-efficient implements and by proper matching of the tractor size and operating parameters to the implements.

In this work a stable and reliable numerical model based on complementary variables is developed to study lubricated contacts characterised by slip at one or both surfaces and in the presence of cavitation. This model can be used to predict surface behaviour when cavitation induced by e.g. the presence of surface texture, slip, or a combination of the two is encountered, with varying surface parameters. For this purpose, two different algorithms are coupled to predict the formation of cavitation, through a mass-conserving formulation, and the presence of slip at the wall. The possible slippage is described by a limiting shear criterion formulated using a Tresca model. To show the flexibility of our model, several bearing geometries have been analysed, such as a twin parabolic slider, a cosine profile used to mimic a bearing, and a pocketed slider bearing employed to study the effect of surface texture. We observe that the lubrication performance (i.e. low friction coefficient) can be improved by using materials that promote slippage at the moving wall. The location of the slippage region can be optimised to find the lowest value of friction coefficient. Our theoretical developments and numerical implementation are shown to produce useful guidelines to improve and optimise the design of textured superoleophobic surfaces in the presence of lubricated contacts.

Designing contacts susceptible to fretting is a challenging task due to uncertainties related to friction. For example, coefficient of friction has shown to vary as a function of load cycles and so-called non-Coulomb friction can exist during individual load cycles. Concepts of stable and unstable friction are presented in this manuscript. Based on experiments, no fretting is to be expected if the utilization of friction is kept below unstable friction threshold. If contact is subjected to tangential load above this threshold, reciprocating slippage, fretting, is to be expected even if the contact was initially in stick. Experimental evidence for existence of such threshold is presented in form of friction data, slip data and fretting scars. publishedVersion

Modified cable bolts are commonly used in underground mines due to their superior performance in preventing bed separation when compared with plain strands. To better test the axial performance of a wide range of cable bolts, a new laboratory short encapsulation pull test (LSEPT) facility was developed. The facility simulates the interaction between cable bolts and surrounding rock mass, using artificial rock cylinders with a diameter of 300 mm in which the cable bolt is grouted. Furthermore, the joint where the load is applied is left unconstrained to allow shear slippage at the cable/grout or grout/rock interface. Based on this apparatus, a series of pull tests were undertaken using the MW9 modified bulb cable bolt. Various parameters including embedment length, test material strength and borehole size were evaluated. It was found that within a limited range of 360 mm, there is a linear relationship between the maximum bearing capacity of the cable bolt and embedment length. Beyond 360 mm, the peak capacity continues to rise but with a much lower slope. When the MW9 cable bolt was grouted in a weak test material, failure always took place along the grout/rock interface. Interestingly, increasing the borehole diameter from 42 to 52 m in weak test material altered the failure mode from grout/rock interface to cable/grout interface and improved the performance in terms of both peak and residual capacity. Keywords: Modified cable bolts, Load transfer performance, Shear slippage, Cable/grout interface, Embedment length

The objective was to assess the effect of velocity at three levels (i.e. 0.8, 1 and 1.2m/s), slippage at three levels (i.e. 10, 12 and 15%) and three levels of wheel load (i.e. 2, 3 and 4kN) on net traction utilizing a single-wheel tester in the soil bin facility of the Department of Agricultural Machinery of Urmia University. Analysis of variance (ANOVA) was developed to verify the effectiveness of the aforementioned parameters on the objective of the study at 1% significance level. It was found that the increment of wheel load and slippage results in the increment of net traction. However, it was deduced that velocity has no significant effect on net traction.

First performed in 1993, laparoscopic adjustable gastric banding (AGB) became the most common bariatric surgical procedure throughout the world by 2008. More recently, AGB has grown less popular because of increased concerns over long-term complications and reoperation rates, with the most common major complication being band slippage. When this occurs, patients typically present with pain and obstructive symptoms of varying degrees. Radiologic studies play an important role in establishing the diagnosis of band slippage. Understanding the evolution of AGB surgical technique from its original “perigastric” placement method to the modern pars flaccida technique is important for radiologic interpretation. Once diagnosed, AGB slippage is generally treated by urgent band deflation, followed by surgical removal, revision, and/or conversion to an alternative bariatric procedure.

Asphalt pavements perform in a wide range of temperatures, especially in Eastern European countries, where the daily mean temperature of asphalt layers varies from −18 °C during winter to 47 °C during summer or even higher under more severe climatic conditions. Low temperatures preclude the use of high-stiffness binders because of their high susceptibility to thermal cracking. High temperatures during summer and a heavy static load contribution cause rutting, slippage, and high plastic deformation of heavy duty asphalt pavements. Many research programs on asphalt wearing layers affected by long-lasting high stress have been initiated to address this problem. Our theoretical analysis led to a plan and subsequent detailed laboratory research of modified AC 11 VS and SMA 11 S asphalt mixtures. We analyzed 11 different bitumens and the modification of the asphalt mixture aggregate distribution. The experimental results show extremely good rutting performance of the modified asphalt mixtures., This work was supported by the European Social Fund [Grant number VP1-3.1-ŠMM-10-V-02-022].

It is a common practice to apply a tack coat usually in the form of bituminous emulsion over an existing bituminous surface before laying another bituminous layer. The boundary between these two consecutive bituminous layers is the layer interface and the pavement stress distribution is highly influenced by the adhesion conditions at this interface. Poor adhesion causes adverse effects on the structural strength of the pavement system. A number of premature failures such as slippage failure and delamination failures result thus defeating the construction objectives. In the absence of a standard method and apparatus to address this field problem, an attempt has been made in this study to develop a simple testing arrangement to be used in a laboratory to determine the interlayer bond strength. Normal Marshall procedure has been used to prepare the specimens consisting of two different types of bituminous materials in lower and upper part of the same specimen. It is observed within the scope of study that Cationic rapid setting (CRS-1) emulsion applied at 0.25 Kg/m2 offers the best results of interlayer bond strength.

In this paper, the slippage velocity and displacement between particles and supercritical CO2 (SC-CO2) were studied to reveal the particle-SC-CO2 two-phase flow behavior. Visualization experiments were performed to directly measure the slippage velocity and displacement. Eight groups of experiments involving various pressures (7.89–10.96 MPa), temperatures (38.6–47.5 °C), particle diameters (0.3–0.85 mm), particle densities (2630 and 3120 kg/m3) and SC-CO2 flow rates (0.920–1.284 m/s) were conducted. The measured particle slippage velocities in the flowing direction were approximately 10.3% of the SC-CO2 flow rate. The measured particle slippage displacements were all at the centimeter level, which indicated that SC-CO2 had a superior particle transporting capability that was similar to those of liquids even if it had a low viscosity that was similar to those of gases. A numerical model was built, and analytic slippage calculations were performed for SC-CO2 for additional analyses. The density of SC-CO2 was found to have a greater influence on the slippage than the viscosity. Moreover, a comparison of the slippage between SC-CO2 and water showed that the particle slippage in water was constant, while the particle slippage in SC-CO2 continually accumulated at an extremely slow rate.\ud \ud

This chapter highlights the influence of the dynamic characteristic of yarn on the ballistic performance of fabric submitted to impact. A brief review of existing research works done on the dynamic tensile test known as the Hopkinson bar, and more recently the Split Flying Bar, is presented. A new dynamic tensile test, called the Split Flying Mass, has been proposed, ensuring improvement in the tension of yarn, accuracy of measurement, and avoiding any slippage of yarn inside the clamping jaws during high-strain velocity tests. Experimental results conducted on para-aramid multifilament yarn have confirmed the increase of stiffness, revealing the specific dynamic deformation mode of high-performance yarns used in ballistic applications.

Rutting is another major distresses found in asphalt pavements that can significantly affect the pavement performance and reduce its service life. Rutting is of concern for at least five reasons: (a) if the pavement drainage system is not perfect, rutting traps water causing hydroplaning, which is a potential threat to road vehicles at high speeds; (b) as the rutting depth deepens, steering becomes increasingly difficult and sometimes dangerous; (c) if the rutting is covered with snow in cold regions, the resistance of the pavement to slippage will decrease; (d) rutting has a negative effect on the pavement roughness, generally leading to the drop of riding comfort; and (e) rutting often results in the reduction of the structural layer thickness and therefore lowers the pavement strength, inducing some damages.

Experiments were conducted to measure the extent of slippage occurring when thin disks are processed by high-pressure torsion. Separate tests were conducted on aluminum, copper and iron. The results show the extent of slippage varies between these three materials such that there is very little slippage in aluminum, slightly more slippage in copper and significant slippage when using iron. For all materials, the extent of slippage increases at both faster rotational speeds and lower imposed pressures.

This paper presents the behaviour of microbraid reinforced polymer composites (mBRPC) subjected to impact loading conditions. Ballistic impact tests were performed by firing 7.94 mm steel balls onto composites reinforced with microbraids having different architectures, braid angles and of different materials (Kevlar® and Dyneema®). Two high speed cameras were employed to record the impact events. Experimental results revealed an improvement in the ballistic limit, of up to 19.5% for certain types of mBPRC, with respect to composites made with unidirectional fibres. Visual inspection of the impacted laminates revealed similar deformation mechanisms for composites reinforced with microbraids having different architectures and of different material. The slippage of the impactor through the layers of the laminates could have had detrimentally affected the ballistic properties of the manufactured composites. Modifications in the arrangement of the reinforcing phase are needed to fully exploit the potential of the microbraids in polymeric structures.

© 2015 COSPAR. The dual-reciprocating drill (DRD) is a biologically-inspired concept which has shown promise in planetary environments, requiring a lower overhead force than traditional rotary drilling techniques. By using two reciprocating backwards-facing teethed halves to grip the surrounding substrate, it generates a traction force that reduces the required overhead penetration force. Research into DRD has focused on the effects of operational and substrate parameters on performance compared to static penetration, with minimal study of the geometrical parameters which define the drill head. This paper presents the exploration of the effects of drill head design on drilling depth and power consumption. Sixteen variations of the original design were tested in planetary regolith simulants up to depths of 800. mm. The experiments showed relationships between final depth, total drill radius and cone shape, though the teeth design had a negligible effect on performance. These results can be used alongside the previous research to optimise the future design and operation of the DRD. Drill stem bending was seen to cause an increase in drilling speed and depth, leading to the exploration of the mechanics of diagonal drilling. This resulted in the proposal of a fully-integrated system prototype that incorporates both reciprocating and lateral motion mechanisms.

Textile reinforcements for composites comprise, in decreasing order of importance, 2D and 3D woven, braided, knitted, and nonwoven fabrics. The chapter describes the mechanical properties of the fabrics in the following sequence: fibre properties → yarn structure → fabric structure. Properties of glass, aramid, HMPE, carbon, ceramic, and natural plant fibres are described. Properties of continuous filament yarns are close to those of the fibres. The modulus and strength of staple fibre yarns are affected by yarn twist, with losses due to obliquity and slippage. A digital representation of 2D woven fabric structure is based on the forms of crossover in different repeat units. Six modes of deformation are considered: in-plane, two tensile, and shear; out-of-plane, two bending, and twist. Energy minimisation is used to model these properties. The basic properties determine the response of forms in composites: planar and uniaxial curvature; double curvature in draped forms. Braids are structurally similar to weaves. Simple knits have properties determined by the loops of yarn. Warp knits can be used to trap straight reinforcing yarns in various directions. Spacer fabrics join two knit layers. A method of press forming nonwoven webs with drawable fibres is mentioned. Despite the developments of the last 100 years, more research is needed to match computer-aided design and performance prediction to the level at which it is used in other branches of engineering. There may be potential for the use of carbon nanotubes and grapheme in textile forms. Sources of information are described.

Fracking does cause earthquakes of a size that can be felt, but extremely rarely. Of the thousands of fracking operations that are carried out every year, only a handful have ever caused earthquakes large enough to have been felt. The key to the earthquakes are faults that are very common below the surface. These are natural fractures whose sides slip against each other when enough force is put on them. This slippage is very rare in most parts of the world where the faults are held tight by friction, but if tectonic and mountain building forces build up they may be too big to be resisted. The connection with fracking is that faults slip slightly more easily when there’s frack fluid around so the engineers and geologists have to avoid faults – or if that’s unavoidable – monitor activity so that they can shut the frack fluid pressure off if earthquakes are building up.

Strand bond is the unique interaction between prestressing strand and adjacent concrete, and directly affects the performance of the strand in the anchor region. However, strand bond depends upon numerous factors, such as concrete properties and strand surface condition. The Standard Test for Strand Bond (STSB) has been developed to assess the bonding capacity of prestressing strands. Test data are used to propose a bond stress–slip model and investigate the bond stress distribution. The study outcomes are verified by STSB of 0.6 in. (15.2 mm) and 0.7 in. (17.8 mm) strand conducted at the University of Arkansas and collected in the literature. Experimental and analytical results show that the proposed model can predict bond stress versus slippage of prestressing strand within a 2% error. The results also show that the bond stress distribution along the embedment length is not linear or uniform as was assumed by previous researchers.

This chapter shows how water permeability may be calculated from measurements of drying under a vacuum. The results obtained are for water vapour transport at low pressures, and gas slippage theory is then used to compare them with liquid water permeability measurements on samples of the same mixes. The experimental work includes the drying procedure and also the ISAT and the high pressure test for direct permeability measurements. The results from all of these tests are compared and additional gas and liquid permeability data from Chapter 5 are included for comparison. It is concluded that, with appropriate analysis, all of the procedures give comparable values for intrinsic permeability.

This chapter reviews the importance of quality in textile materials and details some of the key requirements desired by consumers. The chapter then discusses the physical characteristics of fabrics, such as material construction, mass, finished width, design and other characteristics. The following sections deal with the specific performance characteristics of fabrics, such as: colour fastness, breaking strength, seam slippage, resistance to abrasion and pilling, and dimensional stability. The importance of care labelling for clothing and the Eco-Tex 100 standard are discussed. The chapter concludes by considering the impact of material testing on quality assurance.

This chapter describes fabric properties required for the smooth working of the apparel manufacturing process. The low stress fabric mechanical properties relevant in this context are explained, together with the parameters that affect sewability. The mechanisms determining seam pucker and seam slippage are discussed.

Publisher Summary Foams have several applications in oil field operations. They are used as a circulation medium for drilling wells, for well cleanouts, and as fracturing fluids. These applications differ slightly from the application of foam as a means of removing liquid from producing gas wells. The former applications involve generating the foam at the surface with controlled mixing and using only water. In gas well liquid removal applications, the liquid-gas-surfactant mixing must be accomplished down hole and often in the presence of both water and liquid hydrocarbons. The principal benefit of foam as a gas well dewatering method is that liquid is held in the bubble film and exposed to more surface area resulting in less gas slippage and a low-density mixture. In addition, foam is a particular type of gas and liquid emulsion. Gas bubbles are separated from each other in foam by a liquid film. Surface-active agents (surfactants) generally are employed to reduce the surface tension of the liquid to enable more gas-liquid dispersion. The liquid film between bubbles has two surfactant layers back to back with liquid contained between them. This method of tying the liquid and gas together can be effective in removing liquid from low volume gas wells. The application of foam to unloading low rate gas wells generally is governed by two operating limitations, which are economics and the success of foam surfactants in reducing bottom hole pressure. Both limits are defined by comparison to other methods of unloading wells.

Publisher Summary Chain drives are an important part of a conveyor system. They are used to transmit needed power from the drive unit to a portion of the conveyor system. This chapter explains the various types of chains that are used to transmit power in a conveyor system and the advantages and disadvantages of using chain drives. It also explains the correct installation procedure for chain drives, how to maintain chain drives, and how to calculate speeds and ratios that will enable one to make corrections or adjustments to conveyor speeds. It shows how to determine chain length and sprocket sizes when making speed adjustments. Chain drives are used to transmit power between a drive unit and a driven unit. Chain drives can consist of one or multiple strand chains, depending on the load that the unit must transmit. The chains need to be matched with the sprocket type, and they must be tight enough to prevent slippage. This chapter describes chain selection, that is, selecting a plain or detachable-link chain, a roller chain, or sprockets. It also explains chain installation, chain length, multiple sprockets, and chain speed and provides preventive maintenance procedures.

Publisher Summary The increasing availability of high-frequency data has made possible a detailed study of intraday statistics. The positive correlation between price volatility and volume is both well known and well documented. Slippage gives an indication of relative liquidity. On the open outcry futures exchange, customer orders may be broken into smaller increments at the discretion of the floor broker. Slippage is by construction an increasing function of the number of contracts being traded. There are, however, sharp differences first between the times of the day at which the order is executed and second between the varied sub periods. The variance of returns may not systematically translate into additional costs to liquidity traders. Transaction costs could stay quite small despite a high variance of returns. Very large volumes might in fact “absorb” any market shock. This phenomenon seems to occur in other markets. It must also be recognized that liquidity is only one of the determinants of the cost of executing an order.

PVC-based exercise mats are the de facto standard practice surface for the millions of regular American hatha yoga practitioners. The ‘sticky mat’ provides a lightweight slip- resistant surface in dry conditions. However, this mat has inherent performance drawbacks and longstanding biocompatibility concerns. ‘Postures’ or asana-styles demand different properties from the standard exercise mat. The amount of perspiration generated by practitioners varies by style and athletic ability. In both cases the individual requires a slip-resistant practice surface. Standard foamed closed-cell PVC mats and cotton rugs provide insufficient properties in wet and dry conditions. This study investigates changes in the ability of a mat to resist slippage upon absorption of water for the PVC mat, cotton rug and a novel slip-resistant and absorbent fibrous material. Dynamic coefficients of friction as a function of absorbed water are examined. The efficacy of each mat to resist slippage with absorbed water is correlated to expected sweat generation during practice. A prior predictive sweat loss response model to metabolic rate, environment and clothing is used.

The sliding surfaces are present in most machine components and it is desirable to minimize the friction in order to reduce energy loss and wear. In contrast, clutches and brakes depend on friction in order to function. The function of a clutch is to permit smooth, gradual connection, and disconnection of two elements having a common axis of rotation. A brake acts similarly except that one of the elements is fixed. In pivot bearings, clutch plates, and disk brakes there is friction among circular surfaces under distributed normal pressure. In the design of belt drives and band brakes the impending slippage of flexible cables, belts, and ropes over sheaves and drums is important. This chapter presents a drum subjected to the two-belt tensions T 1 and T 2 , the moment M necessary to prevent rotation, and a bearing reaction R . The forces acting on the differential element are calculated using the equilibrium of the element. The tension increases from T at the angle θ to T + dT at the angle θ + dθ .

Publisher Summary This chapter provides an overview of engineering analysis. Fibrous Reinforced Plastics (RPs) differs from most other engineering materials because they combine two essentially different materials, fibers and plastic (resin), into a single material. In designing the RPs, certain important assumptions are made. The first and the most fundamental is that the two materials act together, and that the stretching, compression, as well as twisting of fibers and of resin under load is the same, that is, the strains in fiber and resin are equal. This assumption implies that a good bond exists between fiber and resin to prevent slippage between them and to prevent wrinkling of the fiber. The second major assumption is that the material is elastic, that is, strains are directly proportional to the stresses applied, and when a load is removed, the deformation disappears. More or less implicit in the theory of materials of this type is the assumption that all of the fibers are straight and unstressed or that the initial stresses in the individual fibers are essentially equal.

This research aims to establish an optimal design method of filament wound structures. Filament winding is one of the most reliable and affordable production techniques for high performance composite structures such as pressure tanks, pipes and motor cases of rockets which are widely used in the aerospace application. However, the problem with filament winding is that the trajectory of the fiber path and the corresponding fiber angles cannot be chosen freely because of the stability requirement of fiber path. Most design and manufacturing of filament wound structures are based on manufacturing experiences, and there is no established design rule. In this research, possible winding patterns considering the windability and the slippage between fiber and mandrel surface were calculated using the semi-geodesic path algorithm. In additiori, finite element analyses using commercial code, ABAQUS, were performed to predict the behavior of filament wound structures. On the basis of the semi-geodesic path algorithm and the verified finite element analysis method, an optimal design algorithm for filament wound structures was suggested using the genetic algorithm.

This chapter discusses that when the mean free path of the measuring gas is greater than the diameter of the capillary through which it is traveling, the random kinetic energy of the gas is transferred to movement of the gas molecule through the capillary or slippage of the molecules occurs at the pore walls. This slippage causes the molecules of the gas to travel at a higher velocity in the direction of transfer. This phenomenon is known as the Klinkenberg effect. Measurements of absolute permeability are generally made more conveniently with a gas than with a liquid; therefore, this method is in common use.

Ultra-high Molecular Weight Polyethylene (UHMWPE) fiber is a kind of high-tech fiber proved to be the best bulletproof fiber by far. Because of a good ability of deformation Biaxial Weft Knitted (BWK) fabrics is a possible candidate for some molded bulletproof products such as helmets. The ballistic impact Behavior of Biaxial Weft Knitted UHMWPE composites has been investigated in this paper. It was found that ballistic performances were influenced by the pressing pressure strongly. The composites were manufactured under pressure of 1Mpa, 2Mpa, 5Mpa, respectively, which results in different matrix contents and ballistic performance. Those samples with higher matrix contents were penetrated by the ‘51’ lead-core bullet fired by the ‘54’ handgun, whereas a sample with lower matrix content arrested the bullet effectively. The ballistic impact responses of penetrated and non-penetrated composites were analyzed comparatively. Both in penetrated and non-penetrated composites, the main failure mode of fiber is cut-out by shear, especially for the penetrated samples, in which there seem to exist a change of failure modes from shear fracture to tensile rupture along the thickness of the target. But for the non-penetrated composites, tensile rupture can be observed only in those layers where the bullets were stopped. Most fibers in the following layers behave in an elastic manner although a ‘back bulge’ would come into being under ballistic impact. The difference of the delamination in the tow kinds of samples were studied also. Because of the peculiar fabric construction, some special phenomena were observed in the research such as yarn slippage and the fragments of the bonding coils.

Publisher Summary A shaft is a structural member that is used to transmit power as well as rotational motion. This chapter focuses on the analysis of a determinate shaft of simple geometry that is subjected only to torque. The stress and deformation in a shaft are primarily because of the applied torque because temperature and support settling have little effect. Temperature does not change the response because no shear strain is induced in a shaft made of an isotropic material. Settling of the support of a shaft, which represents a slippage at the boundary, induces a uniform rigid body rotation throughout its length. Because of the circular symmetry, this rotation is inconsequential, except that it changes the reference to measure the angle of twist without any change to the angle itself. The analysis is for the applied torque load, and it is introduced in stages that included the analysis of internal torque, torsion formula, and deformation analysis. Deformation analysis establishes the relationship between the angle of twist and the shear strain.

Publisher Summary This chapter proposes a general numerical scheme aimed at stimulating the evolution of a soil subject to a liquefaction phenomenon, the constitutive behavior of which is described by means of a regularized Bingham model. This procedure is based on the combination of a variational principle for the velocity field and a step-by-step time integration algorithm making it possible to follow the geometry changes. A first illustration of the method implemented in a finite element code is also presented in the chapter. The adoption of a Bingham model instead of a Newton model for describing the behavior of the liquefied soil results in increasing the soil resistance and thus limiting the amplitude of geometry change of liquefied soil spreading. Some hypotheses, such as the prefect bonding assumption between the liquefied soil and the substratum can be investigated and replaced by a more realistic boundary condition allowing for possible slippage beyond a certain shear stress level.

Foams have several applications in oil field operations. They are used as a circulation medium for drilling wells, for well cleanouts, and as fracturing fluids. These applications differ slightly from the application of foam as a means of removing liquid from producing gas wells. The former applications involve generating the foam at the surface with controlled mixing and using only water. In gas well liquid removal applications, the liquid-gas-surfactant mixing must be accomplished down hole and often in the presence of both water and liquid hydrocarbons. The principal benefit of foam as a gas well dewatering method is that liquid is held in the bubble film and exposed to more surface area resulting in less gas slippage and a low-density mixture. In addition, foam is a particular type of gas and liquid emulsion. Gas bubbles are separated from each other in foam by a liquid film. Surface-active agents (surfactants) generally are employed to reduce the surface tension of the liquid to enable more gas-liquid dispersion. The liquid film between bubbles has two surfactant layers back to back with liquid contained between them. This method of tying the liquid and gas together can be effective in removing liquid from low volume gas wells. The application of foam to unloading low rate gas wells generally is governed by two operating limitations, which are economics and the success of foam surfactants in reducing bottom hole pressure. Both limits are defined by comparison to other methods of unloading wells.

In this paper, the pre-slip transient behaviour was investigated using three types of rubber material subjected to tangential loading prior to gross slippage or sliding. A special-purpose rig was constructed which has a friction-surface cradle support structure with vertical leaf springs and a normal loading support structure with horizontal leaf springs. A somewhat non-linear increase of tangential shear force with displacement in the transient pre-slip region and distinctive characteristics were obtained for each rubber type. Thickening and thinning of the rubber specimen during sliding depend primarily on rubber hardness.

To investigate the question of how faults affect the migration of fluids in petroleum reservoirs, we evaluated the state of stress and pore pressure acting on the major faults in four oil and gas fields in the northern North Sea. Many of the faults bound hydrocarbon reservoirs. Our goal was to test the hypothesis that faults that are being reactivated in the current stress field are permeable and thus tend to leak, whereas those that are not (i.e. faults that are inactive in the current stress field) are likely to seal. To address this question, we utilize a detailed analysis of the magnitude and orientation of all three principal stresses in a number of wells in each field. These data, along with information on pore pressure, allowed us to resolve the shear and effective normal stress acting on distinct 100 m × 100 m elements of individual fault planes. By comparing the stress state resolved on each fault element to expected stress at failure (using a Coulomb failure criterion) we created color-shaded maps showing the proximity to fault slip (and hence leakage) along each fault. Fault reactivation and hydrocarbon leakage in this area appears to be caused by three factors: (1) locally elevated pore pressure due to buoyant hydrocarbons in reservoirs abutting the faults, (2) fault orientations that are nearly optimally oriented for frictional slip in the present-day stress field, and (3) a relatively recent perturbation of the compressional stress caused by postglacial rebound. We demonstrate that the combination of these three factors may have recently induced fault slippage and gas leakage along sections of previously sealing reservoir-bounding faults in some fields, whereas in others, the stress and pore pressure are not sufficient to cause fault reactivation. We show that only in cases where reservoir-bounding faults are not potentially active, the pore-pressure difference across faults can become quite high. Hence, the leakage potential of reservoir-bounding faults appears to exert an important influence on potential hydrocarbon column heights.