Limiting Shear Strength Research Articles

3차원 효과를 고려한 암반사면의 안전율 변화에 관한 연구

In the slope stability analysis and design, Limit Equilibrium Method (LEM) and Shear Strength Reduction technique (SSR) are mainly used. Both methods are able to perform two and three dimensional analysis. SSR is considered to be more sensitive and more reasonable than LEM by many researchers. However, in practice LEM is still widely used because of the increase of analysis time and complexity of the model in SSR. In this study, three dimensional analysis of the protruding rock slope is performed by SSR in order to study the effects of protruding length using rock slope FLAC 3D. In this study, as results of analysis variations of the safety factor have been studied according to slope angle, slope height, the soil strength, protruding slope length projected variables. The results show that the factor of safety as more affected by the shapes of the protruding rock slope than the rock strength.

Determination of Physical and Mechanical Properties of Autumn Leaves of Maple, Bitter Orange, Oak, Boxwood, Yellow Poplar, and Brown Poplar Trees

Aims: The results will be used to design and construct a collecting device, specially the main sucking part. Study Design:In order to determine the physical properties of autumn leaves, twenty leaves from each tree of maple, bitter orange, oak, boxwood, yellow poplar, and brown poplar were collected with the same shape found on the ground (wrinkled or crumpled). Place and Duration of Study:Department of Agricultural Machinery, Faculty of Bio - System Engineering, University College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran ,July and august2012. Methodology: The maximum length, width, and thickness, as well as mass of each leaf were measured in varied moisture, static friction coefficient, true density, bulk density, and porosity. To determine the mechanical properties of friction coefficient and discharge and filling angles, the limit velocity and shear strength were also measured in the leaves. Results: Measurement of the leaves shear strength of maple, oak, bitter orange, OriginalResearch Article

Manufacturing of metal-based microparts: Fabrication strategies and surface engineering applications

A wide range of industrial applications, current and anticipated, drive the process of miniaturization of thermal and chemical devices. In certain cases, metal-based microsystems enjoy advantages of performance, cost, or both, over silicon-based counterparts. The critical bottleneck restricting the use of metal-based microsystems in actual applications has often been the lack of effective and economical manufacturing methods for metal-based microparts. In this paper, our recent efforts in fabrication of metal-based high aspect ratio microscale structures through various replication strategies, such as compression molding and roll molding, are summarized. The need for engineering surfaces of microscale replication tools through conformal coating deposition is illustrated. Two attempts to experimentally measure shear strength of coating/substrate interfaces are described. An estimate of the limiting shear strength of coating/substrate interfaces is achieved through examination of transverse coating cracks induced by substrate tensile loading. Experimental data obtained from two series of TiN/Cr/steel and TiN/Ti/steel specimens are presented. Issues associated with this approach are discussed. Direct failure of coating/substrate interfaces has been induced through compression loading of micro pillars containing inclined coating/substrate interfaces. Preliminary experimental results obtained from TiN/Ti/Si micro pillars are presented.

Adhesiefbruggen

A resin-bonded fixed partial denture is a prosthetic construction which can replace I or several teeth in an occlusal system and which comprises a pontic element which is adhesively attached to 1 or more abutment teeth. To compensate for the limited shear strength of the adhesive layer, the Jixed partial denture is occlusally supported by the abutment(s). A direct resin-bonded fixed partial denture is made of composite, reinforced or not by a frame of flexible metal or fiber material. For an indirect resin-bonded fixed partial denture, a metal, fibre-reinforced composite or ceramic substructure is fabricated in a dental laboratory. The basic principle of a resin-bonded fixed partial denture is minimal invasiveness. However, a restoration in an abutment tooth requires a certain occlusal space which is realized by tooth preparation. Resistance preparations may be performed to improve the longevity of resin-bonded fixed partial dentures. Both financially and biologically, a resin-bonded bridge is a cost-effective prosthetic construction. The longevity is limited, but when the construction fails the negative consequences for the abutments are generally limited, which leaves open several types of other treatments.

Biopolymer Stabilization of Mine Tailings

AbstractA feasibility study was performed on using xanthan gum and guar gum, two biopolymers that are naturally occurring and inexpensive, to stabilize mine tailings (MT). The simple fall cone method was adopted to evaluate the liquid limit and undrained shear strength of sun-dried MT mixed with xanthan gum or guar gum solutions at different concentrations. Environmental scanning electron microscopy (ESEM) imaging was also conducted to study the microstructure of the biopolymer-MT system. The results indicate that the inclusion of xanthan gum or guar gum increases both the liquid limit and the undrained shear strength of the MT, higher biopolymer concentrations leading to greater increases. The increase of the liquid limit and undrained shear strength of the MT mixed with a biopolymer solution is mainly attributable to the high viscosity of the biopolymer pore fluid and the bonding between the biopolymer and the MT particles. Guar gum is more effective than xanthan gum in increasing the liquid limit and u...

Tyramine‐Based Hyaluronan as a Tracheal Cartilage Substitute

Objective: To investigate and characterize a novel tyramine-based hyaluronan/gelatin (THA/G) composite material. First, we demonstrate the ability of THA/G to adhere and maintain respiratory epithelial cells in an in vitro model. Second, we assess the feasibility of THA/G as a biologic cartilage substitute in a rabbit model of tracheal reconstruction. Method: Immortalized human tracheal epithelial cells were grown on various concentrations of THA/G composites in vitro. Cricotracheal resection with replacement by THA/G was performed in 4 New Zealand white rabbits with auricular cartilage as control in 2 animals. Tracheal patency, graft retention, and mucosalization were evaluated via endoscopy, imaging, and histopathology. Results: Epithelial cell growth was demonstrated on THA/G composites in vitro. In the rabbit model, all composites remained intact within the tracheal resection. However, the limited shear strength of the THA/G posed difficulties in securing the construct. At 3 and 6 weeks postimplantation, composites revealed minimal histologic evidence of macrophage or lymphocyte infiltration and were without apparent degradation. Tracheal lumen diameter was preserved in all animals. No experimental animals had evidence of dynamic airway collapse or chondromalacia. On endoscopy, there was no evidence of tracheal inflammation or granulation. However, at 6 weeks there was limited respiratory mucosa present on histology. Conclusion: THA/G composites are a promising material for cartilage substitution. We demonstrate an ability to support epithelial cells and maintain tracheal structure. Improvements to increase the material’s shear strength are necessary so that it may have potential as an airway cartilage substitute.

Direct expressions for linearization of shear strength envelopes given by the Generalized Hoek–Brown criterion using genetic programming

The non-linear Generalized Hoek–Brown (GHB) criterion is one of the most broadly adopted failure criteria used to estimate the strength of a rock mass. However, when limit equilibrium and shear strength reduction methods are used to analyze rock slope stability, the strength of the rock mass is generally expressed by the linear Mohr–Coulomb (MC) criterion. If the GHB criterion is used in conjunction with existing methods for analyzing the rock slope, methods are required to determine the equivalent MC shear strength from the GHB criterion. Deriving precise analytical solutions for the equivalent MC shear strength from the GHB criterion has not proven to be straightforward due to the complexities associated with mathematical derivation. In this paper, an approximate analytical solution for estimating the rock mass shear strength from the GHB criterion is proposed. The proposed approach is based on a symbolic regression (SR) analysis performed by genetic programming (GP). The reliability of the proposed GP solution is tested against numerical solutions. The results show that shear stress estimated from the proposed solution exhibits only 0.97% average discrepancy from numerical solutions using 2451 random sets of data. The proposed solution offers great flexibility for the application of the GHB criterion with existing methods based on the MC criterion for rock slope stability analysis.

Experiment on Ultimate Shear Strength Parameters of Bolt Anchored Section

The bolt support is one of the effective support means to stable the surrounding rocks in underground projects. To determine the ultimate shear strength parameter between the surrounding rocks and bolting mass interface would have important project value to the bolt support design. In order to easy and accurately determine the shear strength of the bolting layer in the bolt design, based on elastic-plastic theory, a theoretical model under the bolt pulling function was established. The load transmission function during the bolt function process was derived. The theoretical relationship between the limit shear strength parameter of the bolting layer interface and the bolt pulling test curve was obtain. The shear strength parameter between the resin anchoring agent of the bolt support in mine roadway and the coal rock mass was determined. The results show that with the bolt pulling test curves, the cohesive strength of the bolting layer and the shearing rigidity coefficient of the bolting layer interface could be easily obtained and could provide the references to the bolt support design.

Chemo-mechanical effects in kaolinite. Part 1: prepared samples

The results of laboratory tests on chemo-mechanical interactions in kaolinite samples prepared with inorganic, salt, acid and base solutions are presented. In particular, the effects of the different solutions on the liquid limit, one-dimensional compressibility, permeability and residual shear strength are considered. Kaolinite proves relatively insensitive to salt solutions, whereas variations in pore fluid pH cause large strength changes, associated with non-negligible changes in one-dimensional compressibility. The partly inconsistent effects induced by acids and bases on the residual shear strength and on the one-dimensional compressibility do not permit any easy interpretation of the experimental evidence. Mineral dissolution and the associated formation of new compounds are probably involved in the behaviour observed. These aspects will be investigated in part 2 of this paper.

The Influence of the Dielectric Constant and Electrolyte Concentration of the Pore Fluids on the Undrained Shear Strength of Smectite

ABSTRACT It is common knowledge that the engineering properties of clays are greatly influenced by the type of pore fluids. However, the impact of the pore fluids on the geotechnical properties of the samples is even more dependent on the type of mineral and interlayer ions. Completely different behaviours could be observed with identical pore fluids but different clay minerals and vice versa. The liquid limit, plastic limit and undrained shear strength were determined for two types of smectites with different interlayer cations, namely Ca and Na-smectite. The pore fluids were varied by using different dielectric constants (e) and electrolyte concentrations (n0). The results show that the two kinds of soils respond in a similar way but with a different magnitude depending on the ion occupation.

Probability modelling of shear strength parameters of RCC gravity dams for reliability analysis of structural safety

ABSTRACT Modelling concrete shear strength is the main difficulty in probabilistic reliability analysis of gravity dam structural safety. The main reason arises from the lack of test data on the parameters. This paper proposes a procedure for probability modelling of Roller Compacted Concrete (RCC) gravity dam shear strength based on all tests performed during dam construction and all available data. The procedure embraces several methods: statistical analysis of RCC density, analysis of scatter at different spatial scales, data unification, and a physical formulation of the RCC intrinsic curve. A case study demonstrates the applicability of the procedure on an existing RCC gravity dam. The probability distributions obtained are incorporated into the formulation of the shear strength limit state using a first order reliability method and Monte Carlo simulations.

French recommendations for limit-state analytical review of gravity dam stability

ABSTRACT This article presents the recent French recommendations drawn up by FRCOLD for the design of gravity dams. Recognising the disparities in the approaches of the various dam engineering bodies, the recommendations aim at harmonising practices to arrive at a standard approach. They adopt the same limit state design method as already used in the Eurocodes, with particular emphasis on cracking and shear strength limit states. They define a series of new parameters which were not introduced in earlier methods such as characteristic strength of materials, partial factors of safety and inclusion of new design situations. The background to the new format is the probabilistic concept of the acceptable design requirements. These recommendations are applied to an existing concrete gravity dam and the results are compared with other international guidelines.

Transverse Stiffener Requirements in Straight and Horizontally Curved Steel I-Girders

Prior research has demonstrated that transverse stiffeners in straight I-girders are loaded predominantly by bending induced by their restraint of web lateral deflections at the shear strength limit state, not by in-plane tension field forces. This is at odds with present specification approaches for the design of these components. Furthermore, recent studies have confirmed that curved I-girders are capable of developing substantial shear postbuckling resistance due to tension field action and have demonstrated that the AASHTO LRFD equations for the tension field resistance in straight I-girders may be applied to curved I-girders within specific limits. However, the corresponding demands on transverse stiffeners in curved I-girders are still largely unknown. In this paper, the behavior of one- and two-sided transverse stiffeners in straight and horizontally curved steel I-girders is investigated by full nonlinear finite element analysis. New recommendations are developed for design of transverse stiffener...

Viscoplastic Lubrication Analysis in a Metal-Rolling Inlet Zone Using Parametric Quadratic Programming

A mathematical programming solution based on finite element method is used to analyze wall slip of viscoplastic lubrication in a metal-rolling inlet zone. Slip velocity can be directly obtained by parametric quadratic programming without an iterative process between the oil film pressure and the slip velocity. It is found that wall slip causes the oil film thickness to decrease dramatically. The initial limiting shear strength and proportional constant of the viscoplastic lubricant have a larger effect on the oil film pressure than the rolling speed. The nonsensitivity of oil film thickness to the rolling speed is a great particular advantage to metal-rolling processing.

Closure to “Plastic Limit, Liquid Limit and Undrained Shear Strength of Soil—Reappraisal” by Binu Sharma and Padma K. Bora

Closure to “Plastic Limit, Liquid Limit and Undrained Shear Strength of Soil—Reappraisal” by Binu Sharma and Padma K. Bora

Discussion of “Plastic Limit, Liquid Limit, and Undrained Shear Strength of Soil—Reappraisal” by Binu Sharma and Padma K. Bora

Discussion of “Plastic Limit, Liquid Limit, and Undrained Shear Strength of Soil—Reappraisal” by Binu Sharma and Padma K. Bora

Performance and Seismic Vulnerability of Masonry Housing Types Used in Chile

Masonry is the most used construction material, especially for residential dwellings built in all regions of Chile, up to four stories high. The masonry wall's reinforcement of these buildings can be classified into three types: confined, reinforced and hybrid. Although buildings with confined masonry walls have limited shear strength and ductility, they have demonstrated acceptable seismic behavior. Experience for buildings with the other two types of reinforcement has been different; during the 1985 Llolleo earthquake several buildings had severe damage due to design and construction deficiencies. In this paper a description of key structural features, construction process, seismic resilient features and deficiencies of masonry housing types used in government-subsidized low-income dwellings is provided. In addition, various seismic vulnerability indices that characterize their seismic behavior are calculated. The evolution over time of such indices shows that nowadays a large amount of buildings are likely to be damaged after a severe earthquake.

Plastic Limit, Liquid Limit and Undrained Shear Strength of Soil—Reappraisal

The concept that plasticity index of soils can be defined as a range of water contents producing a 100-fold variation in undrained shear strength has been experimentally verified with the help of a large number of tests on soils of diverse nature. This has led to the redefinition of the plastic limit as the water content at which undrained shear strength is around 170 kN/m2. Undrained shear strength of a soil at the liquid limit can be considered to be around 1.7 kN/m2. Accordingly, both the liquid limit and the plastic limit have been determined in the present work by a single consistent method, i.e., the Swedish fall cone method. The undrained shear strength-water content relationship has been found to be log-linear for a wide range of water contents beginning from lower than the plastic limit to higher than the liquid limit. This resulted in the formulation of an expression for predicting undrained shear strength of a remolded soil at any water content based solely on its liquid limit and plastic limit.

Experimental observation of a dimple-wedge elastohydrodynamic lubricating film

One of the main features of typical elastohydrodynamic lubricating (EHL) contacts is the unique horseshoe film shape, which can be readily observed by using interferometry and quite accurately modelled by the well-established EHL theory. However, an anomalous EHL film, characterized by a wedge shape together with a tiny dimple at the inlet region, is observed under pure sliding conditions with ultra slow speeds of 3–800 μm/s in an optical EHL test rig. The variations of the wedge and the inlet dimple with different sliding speeds and loads are investigated using a series of polybutene oils of high viscosities. It is found that the inclination of the wedge is dependent on sliding speeds, loads and oil viscosities. The dimple always occurs at the inlet. The appearance of an inlet dimple together with a wedge film shape is reported for the first time. The phenomenon can be attributed to a non-Newtonian characteristic of the lubricant: the limiting shear strength. Additionally, the influence of starvation on the film shape is also examined.

Comparative Evaluation of MoS2 and WS2 as Powder Lubricants in High Speed, Multi-Pad Journal Bearings

As part of a program to develop solid/powder-lubricated journal bearings, a comparative evaluation has been performed to aid in determining whether MoS2 and WS2 powder are suitable lubricants for high-speed, extreme-environment multi-pad journal bearings. Plots of traction coefficients, friction, frictional power loss, and bearing pad temperature are presented as a means for comparing various powder lubricants. This paper primarily focuses on experiments carried out on a three-pad journal bearing and a disk-on-disk tribometer. Results showed that MoS2 traction curves resemble that of SAE 10 synthetic oil. Unlike liquid lubricants, powder films have a limiting shear strength property. Once the powder reaches this limiting value, the maximum traction coefficient is limited and the powder essentially shears along sliding walls. Experimental traction data shows evidence of this property in various powders. The thermal performance of the bearing was evaluated at speeds up to 30,000 rpm and loads up to 236 N. Although WS2 displayed constant friction coefficient and low temperature with increasing dimensionless load, MoS2 exhibited frictional behavior resembling that of a hydrodynamic lubricating film. In this paper, an attempt has been made to provide a criterion for the selection of solid lubricants for use in those tribosystems that may be operated in a high speed/load regime (i.e., high strain rates) as an alternative yard stick to conventional comparative approaches.