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Статті в журналах з теми "Shear friction; shear-sliding mechanism; size effect"
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Fuqiang, Li, Qin Guangpeng, Liu Yonggang, Wang Qichen, Wang Ying, and Hou Fengjun. "Study on the Mechanism of Gas Ignition by Friction Effect of Hard Quartz Sandstone Instability." Geofluids 2020 (December 22, 2020): 1–17. http://dx.doi.org/10.1155/2020/8867343.
Повний текст джерелаАнотація:
When the upper part of a high gas coal seam has hard and thick sandstone roof, the gas explosion accident in goaf is even caused by roof collapse. Taking the mining of 1007 working face of 10 coal seam under Xia KuoTan Coal Mine as the engineering background, using the method of indoor experiment and theoretical analysis, the possibility of rock friction effect igniting gas is studied. Under the engineering geological conditions, the results show that the heat produced by the friction process of hard sandstone can ignite gas. According to the 3DEC numerical simulation, the instability characteristics of the overburden hard rock are studied. The results show that the size of the slab instability area is not changed when the length of the working face increases. When the thickness of the roof is increased, the area of sliding instability is increased and the degree of sliding instability is more intense. At the boundary of the tunnel, the overlying strata are subjected to the largest shear stress, and it tends to form a friction surface with greater slip instability.
2
Ren, Minghui, Guangsi Zhao, Xianhao Qiu, Qinghua Xue, and Meiting Chen. "A Systematic Method to Evaluate the Shear Properties of Soil-Rock Mixture considering the Rock Size Effect." Advances in Civil Engineering 2018 (September 5, 2018): 1–9. http://dx.doi.org/10.1155/2018/6509728.
Повний текст джерелаАнотація:
The soil-rock mixture (S-RM) is widely applied in the geotechnical engineering due to its better mechanical properties. The shear strength, an essential aspect of S-RM which governs the stability and the deformation, is rather necessary to be revealed properly. The extraordinary issue of S-RM compared to fine-grained soils is the grain size effect on the strength analysis. This paper proposes a systematic method to obtain the realistic shear strength of S-RM by detecting the rock size effect. Firstly, based on fractal theory, the rock size was determined as 5 mm by the multifractal property of granular size distribution. Then, based on 2 selected specimen sizes combining the engineering dimension, shear gaps (T) effect and specimen size effect on the shear strength of S-RM have been investigated. It is shown that the gap of the direct shear test decides the physical mechanism of particles forming the shear resistance of S-RM based on the variation of apparent cohesion and mobilized internal friction angle. Specimen size effect is weakened by the gap effect considering the boundary effect. Realistic and stable shear strength parameters of S-RM have been researched by a reasonable gap (0.2–0.4D, where D is the largest particle size).
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Fu, Hongyuan, and Caiying Chen. "Effect of Nanotalc on the Shear Strength of Disintegrated Carbonaceous Mudstone." Journal of Nanoscience and Nanotechnology 20, no. 8 (August 1, 2020): 5049–54. http://dx.doi.org/10.1166/jnn.2020.18490.
Повний текст джерелаАнотація:
This work was aimed to improve the shear strength of disintegrated carbonaceous mudstone (DCM) with nanotalc (NT). A series of direct shear tests were carried out on the NT-modified DCM specimens to determine their shear strengths at various NT concentrations. Subsequently, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were performed to reveal the underlying mechanism which the results showed that shear strength was first increased and then decreased with increasing certain NT concentration. Moreover, the increase in NT concentration also resulted in rise in cohesion and reduction in angle of internal friction. The optimum NT concentration for shear strength improvement of DCM is 4%. This improvement of shear strength is achieved because NT can fill the pores in DCM and its products can bind with particles. This results in formation of large aggregates owing to the small size, strong adsorption capacity and cation-exchange capacity.
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Zhang, Jingwei, Jia Li, Julong Wang, and Shuaiqi Xu. "Characteristics of the Interface between Bamboo Grids and Reinforced Soil of High-Filled Embankments in Loess Areas." Advances in Civil Engineering 2021 (July 19, 2021): 1–13. http://dx.doi.org/10.1155/2021/5135756.
Повний текст джерелаАнотація:
There are a large number of high-filled and deep-dug highways in loess areas. The differential settlement between the filled and undisturbed soils is the main cause of damage. Bamboo grids are good reinforcement and flexural tensile materials for highway subgrades, and the properties of the interface between the bamboo grid and loess soil affect the safety and stability of embankments. First, the feasibility of bamboo grid application in high-filled embankments in loess areas was verified based on a durability analysis and test of the mechanical properties of bamboo. Then, a series of large-scale direct shear tests were carried out to determine the shear properties of the interface between bamboo grids and loess soils. The influential factors of vertical stress, shear rate, grid spacing, and compactness on the shear properties were studied, and the related mechanism was discussed. The results show that bamboo grids enhance the shear strength of loess soils more than geogrids under different vertical stresses because of the passive friction resistance between the vertical and horizontal ribs and soil particles, the bite force of particle skeletons, and the surface friction of grids. Bamboo grids enhance the stability and shear resistance of soils because of their good deformation performance, and thus, the shear rate effect within 7 mm/min can be negligible. The greater the relative compaction of the subgrade soil, the better the reinforcement effect owing to the greater cohesive force, greater internal friction angle, and better bite force. The variation in grid spacing changes the embedded effect of soil, side friction resistance, and size of the contact area. The shear resistance has an optimal value, which first increases and then decreases. Therefore, in practical applications, it is necessary to test the optimal bamboo grid spacing for a project.
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Wang, Yongxin, Shengjun Shao, and Zhi Wang. "Effect of Particle Breakage and Shape on the Mechanical Behaviors of Granular Materials." Advances in Civil Engineering 2019 (October 27, 2019): 1–15. http://dx.doi.org/10.1155/2019/7248427.
Повний текст джерелаАнотація:
The particle breakage property under loading is an important factor affecting the nonlinearity of the shear strength and stress-strain curves of coarse-grained soils. The macromechanical behaviors of coarse granular materials under consolidation and drainage shearing were tested by using a large true triaxial apparatus. The particle breakage mechanism has been analyzed by the fluctuation change of stress-strain curve and particle composition change. It was shown that the particle shape is an extremely important microproperty of the influence of granular material breakage. The variation rules of the internal friction angle and interlocking strength with the index of fine-grained breakage were sorted out, and the critical particle size for measuring the two friction modes under the given gradation was determined to be 1 mm. In addition, the numerical analysis was conducted by simulating the microshape parameters of particles. The conclusion is as follows: (1) The effect of shape parameters on shear strength can be simulated using the smoothness index Fd. (2) Compared with spherical particles, irregular-shaped particles lead to a decrease in the number of strong force chains. Moreover, more coordination numbers are needed to maintain a stable configuration, and the shear strength is improved.
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Gessesse, Y. B., and M. H. Attia. "On the Mechanics of Crack Initiation and Propagation in Elasto-Plastic Materials in Impact Fretting Wear." Journal of Tribology 126, no. 2 (April 1, 2004): 395–403. http://dx.doi.org/10.1115/1.1491975.
Повний текст джерелаАнотація:
Normal and oblique impact wear processes are characterized by unique features, which include the development of some residual stress components that vanish in unidirectional sliding. Parametric finite element analyses were conducted to estimate the likelihood locations for crack initiation, and the subsequent direction and rate of crack propagation in an elasto-plastic material with bi-linear isotropic hardening properties. The results showed that the increase in contact pressure can cause a significant increase in the size of the plastically deformed crack initiation zone and allows it to reach the surface. Such behavior is not predicted under continuous sliding conditions. The presence of surface friction forces in oblique impact, can also result in the development of a secondary region of high tensile stresses at the contact area. Using the crack tip slip displacement CTSD method, the rate of crack growth was found to be linearly proportional to the crack length, and significantly dependent on the contact pressure and the coefficient of friction at the crack surface. The small effect of the coefficient of friction at the micro-contact area on wear suggests that the effect of shear traction is mainly due to the increase in the depth of the crack nucleation zone. As expected, the increase of the material flow stress with strain-hardening has a wear reducing effect.
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Panin, Sergey V., Lyudmila A. Kornienko, Vladislav O. Alexenko, Dmitry G. Buslovich, Svetlana A. Bochkareva, and Boris A. Lyukshin. "Increasing Wear Resistance of UHMWPE by Loading Enforcing Carbon Fibers: Effect of Irreversible and Elastic Deformation, Friction Heating, and Filler Size." Materials 13, no. 2 (January 11, 2020): 338. http://dx.doi.org/10.3390/ma13020338.
Повний текст джерелаАнотація:
The aim of the study was to develop a design methodology for the UltraHigh Molecular Weight Polyethylene (UHMWPE)-based composites used in friction units. To achieve this, stress–strain analysis was done using computer simulation of the triboloading processes. In addition, the effects of carbon fiber size used as reinforcing fillers on formation of the subsurface layer structures at the tribological contacts as well as composite wear resistance were evaluated. A structural analysis of the friction surfaces and the subsurface layers of UHMWPE as well as the UHMWPE-based composites loaded with the carbon fibers of various (nano-, micro-, millimeter) sizes in a wide range of tribological loading conditions was performed. It was shown that, under the “moderate” tribological loading conditions (60 N, 0.3 m/s), the carbon nanofibers (with a loading degree up to 0.5 wt.%) were the most efficient filler. The latter acted as a solid lubricant. As a result, wear resistance increased by 2.7 times. Under the “heavy” test conditions (140 N, 0.5 m/s), the chopped carbon fibers with a length of 2 mm and the optimal loading degree of 10 wt.% were more efficient. The mechanism is underlined by perceiving the action of compressive and shear loads from the counterpart and protecting the tribological contact surface from intense wear. In doing so, wear resistance had doubled, and other mechanical properties had also improved. It was found that simultaneous loading of UHMWPE with Carbon Nano Fibers (CNF) as a solid lubricant and Long Carbon Fibers (LCF) as reinforcing carbon fibers, provided the prescribed mechanical and tribological properties in the entire investigated range of the “load–sliding speed” conditions of tribological loading.
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Lv, Beifeng, Yinuo Zhao, Na Li, Yanfei Yu, Yanting Wu, and Miaojie Gu. "Triaxial Mechanical Properties and Mechanism of Waterborne Polyurethane-Reinforced Road Demolition Waste as Road Bases." Polymers 14, no. 13 (July 3, 2022): 2725. http://dx.doi.org/10.3390/polym14132725.
Повний текст джерелаАнотація:
The recycling and reuse of construction waste have not only effectively protected natural resources but also promoted the sustainable development of the environment. Therefore, in this article, waterborne polyurethane (WPU) as a promising new polymer reinforcement material was proposed to reinforce the road demolition waste (RDW), and the mechanical performance of WPU-reinforced RDW (named PURD) was investigated using triaxial unconsolidated and undrained shear (UU) and Scanning Electron Microscope (SEM) tests. The results showed that under the same curing time and confining pressure, the shear strength of PURD increased with the increase in WPU content. When the WPU content was 6%, the WPU presented the best reinforcement effect on RA. The failure strain of PURD increased with the increase in confining pressure, but increased first and then reduced with the increase in WPU content. The specimens with 5% WPU content showed the best ductility. At the curing time of 7 and 28 days, the internal friction angle and cohesion of PURD increased with the increase in WPU content, and they reached a maximum when the WPU content was 6%. The internal friction angle barely budged, but the cohesion increased obviously. The enhancement effect of WPU was attributed to the spatial reticular membrane structure produced by wrapping and bonding particles with the WPU film. Microscopic analysis showed that with the increase in WPU content, the internal pore and crack size of PURD gradually decreased. As the WPU content increased, the WPU film became increasingly thicker, which increased the adhesion between WPU and RA particles and made the structure of PURD become increasingly denser.
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Tamadon, A., D. J. Pons, and D. Clucas. "EBSD Characterization of Bobbin Friction Stir Welding of AA6082-T6 Aluminium Alloy." Advances in Materials Science 20, no. 4 (December 1, 2020): 49–74. http://dx.doi.org/10.2478/adms-2020-0022.
Повний текст джерелаАнотація:
Abstract Electron Backscatter Diffraction (EBSD) was used to determine microstructural evolution in AA6082-T6 welds processed by the Bobbin Friction Stir Welding (BFSW). This revealed details of grain-boundaries in different regions of the weld microstructure. Different polycrystalline transformations were observed through the weld texture. The Stirring Zone (SZ) underwent severe grain fragmentation and a uniform Dynamic Recrystallisation (DRX). The transition region experienced stored strain which changed the grain size and morphology via sub-grain-boundary transformations. Other observations were of micro-cracks, the presence of oxidization, and the presence of strain hardening associated with precipitates. Flow-arms in welds are caused by DRX processes including shear, and low and high angle grain boundaries. Welding variables affect internal flow which affects microstructural integrity. The shear deformation induced by the pin causes a non-uniform thermal and strain gradient across the weld region, leading to formation of mixed state transformation of grain morphologies through the polycrystalline structure. The grain boundary mapping represents the differences in DRX mechanism I different regions of the weld, elucidates by the consequences of the thermomechanical nature of the weld. The EBSD micrographs indicated that the localised stored strain at the boundary regions of the weld (e.g. flow-arms) has a more distinct effect in emergence of thermomechanical nonuniformities within the DRX microstructure.
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Yang, Xiaoyun, Yan Zhang, and Zhuhan Li. "Embankment Displacement PLAXIS Simulation and Microstructural Behavior of Treated-Coal Gangue." Minerals 10, no. 3 (February 28, 2020): 218. http://dx.doi.org/10.3390/min10030218.
Повний текст джерелаАнотація:
The purpose of this study is to investigate the displacement of coal gangue filling material in road construction and microstructural behavior of treated coal gangue by considering the environmental factors of aqueous solutions with different acidity. The displacement analysis of the coal gangue embankment model has been done by means of the finite element method PLAXIS. Furthermore, using the scanning electron microscope, the energy dispersive system, and the Raman spectrometer to analyze the microscopic mechanism in the view of microstructure, elements, the integrity of carbon structure and the stability of chemical bonds of coal gangue. The results show that the larger displacement of the treated coal gangue subgrade is within 4.0 m below the top of the subgrade, and the maximum displacement value is about 7 mm, which is less than the displacement of untreated coal gangue sample. While the treated A-CG and T-CG grain size, surface area and internal friction angle increase, the unstable carbon structure is destroyed, so its shear strength, compression performance, and consolidation effect are improved. S-CG particles are coated with Na-Si-Al gel, which enhances the density, viscosity and shear strength, thus ensuring the stability of the coal gangue subgrade. The treated coal gangue subgrade slope foot displacement, boundary shear stress and safety factor are all meet the specification requirements.
Дисертації з теми "Shear friction; shear-sliding mechanism; size effect"
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Chen, Yongjian. "Quantifying the compressive ductility of concrete in RC members through shear friction mechanics." Thesis, 2015. http://hdl.handle.net/2440/95248.
Повний текст джерелаАнотація:
This thesis contains a series of journal papers in which the compressive ductility of concrete in RC members has been quantified through shear friction mechanics. Firstly, the size dependent stress‐strain models for unconfined and actively confined concrete are derived based on the fundamental mechanics of shear friction theory. At this stage, the shear friction properties, that is the relationship between the shear stress, normal stress, crack widening and interface slip across the sliding plane, are not specifically required. It is shown how the stress‐strain from cylinder tests of one specific length can be modified to determine that for any size of cylinder. Moreover, it is shown that the proposed approach can be used to make existing generic stress/axial‐strain relationships size dependent and these size dependent relationships can be directly used to determine the corresponding size dependent stress/lateral‐strain relationship. Being mechanics based, size dependent stress‐strain models reduce the reliance on vast experimental testing as only one size of specimen needs be tested to obtain stress‐strain relationships for all sizes. Secondly, the shear friction properties, that is the relationship between the shear stress, normal stress, crack widening and interface slip across the sliding plane is derived and presented in a generic form suitable for application. These generic shear‐friction material properties are then used to simulate and quantify the shear‐sliding behaviour of initially uncracked concrete generally obtained directly from relatively expensive tests. In addition, it is also shown how these shear‐sliding capacities can then be used to quantify the shear capacity of RC beams without stirrups and without the need for size factors as the mechanics based approach automatically, through mechanics, allows for member size. Thirdly, the generic shear‐friction material properties derived in Chapter 3 are used to simulate passive confinement in FRP confined cylinders. Importantly, two distinct cylinder failure modes have been identified and examined: that of the circumferential wedge that is common in standard cylinders with aspect ratios of 2:1; and that of the single sliding plane that occurs at higher aspect ratios. It shows the mechanics solutions for the influence of specimen size, that is both diameter and height, on the stress‐strain relationship of axially loaded FRP confined concrete cylindrical specimens and how small scale FRP wrapped specimens suitable for compression testing can be designed so that the stress/strain relationship of the full scale member under pure compression can be extracted from those of the small test specimen. Finally, a series test of steel tube confined concrete columns is designed to verify the accuracy of the size effect expressions proposed in previous chapters. Importantly, it shows that because the standard material test always adopts small scale 2:1 aspect ratio specimens, the majority failure mode in material test specimens is the circumferential wedge failure. Consequently it is for this wedge failure mode that most axial‐stress/global-axial‐strain relationships are developed. However, similar to the specimens studied in this test program, the aspect ratio of most practical steel tube confinement columns is more than 2. Hence only in a minority of cases does the circumferential wedge failure occur in practice. Therefore, the empirical or semi‐empirical equations developed from small scale concrete specimens are not truly representative of the actual behaviour of full‐scale columns which have aspect ratios markedly different from the 2:1 ratio most commonly tested.Thesis (Ph.D.) -- University of Adelaide, School of Civil, Environmental and Mining Engineering, 2015
Тези доповідей конференцій з теми "Shear friction; shear-sliding mechanism; size effect"
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Xu, H., and K. Komvopoulos. "Fracture Mechanics Analysis of Asperity Cracking Due to Repetitive Sliding Contact." In STLE/ASME 2010 International Joint Tribology Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ijtc2010-41162.
Повний текст джерелаАнотація:
Asperity failure due to repetitive sliding is a common process of wear particle formation. Linear elastic fracture mechanics and the finite element method (FEM) were used to analyze asperity cracking due to sliding against another rigid asperity. The maximum ranges of the tensile and shear stress intensity factors (SIFs) were used to determine the crack growth direction and the dominant mode of fracture. Simulations of repetitive sliding showed a strong dependence of the wear particle size and wear rate on the direction and rate of crack growth. The maximum ranges of tensile and shear SIFs were used to determine the dominant mode of crack growth. The effects of asperity interaction depth, sliding friction, initial crack position, crack-face friction, and material properties on crack growth direction, dominant fracture mode, and crack growth rate are discussed in the context of FEM results. It is shown that the asperity interaction depth and sliding friction exhibit the most pronounced effects on the crack growth direction and growth rate. A transition from shear- to tensile-dominant mode of crack growth was observed with the increase of the asperity interaction depth and/or sliding friction coefficient. Crack-face opening, slip, and stick mechanisms are discussed in the light of crack mechanism maps constructed for different asperity interaction depths and sliding friction coefficients.
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Pustogvar, Anna, Knut V. Høyland, Arttu Polojärvi, and Ida M. Bueide. "Laboratory Scale Direct Shear Box Experiments on Ice Rubble: The Effect of Block to Box Size Ratio." In ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/omae2014-23646.
Повний текст джерелаАнотація:
Direct shear box experiments on rubble ice were performed in the cold laboratory of Norwegian University of Science and Technology (NTNU) in order to estimate effect of the specimen scale on the resulting mechanical properties of the material. In total 23 tests were performed, including 18 tests on dry rubble and 5 tests with having the box and the rubble submerged in saline water for 30 minutes before testing. Experiments with two ice block sizes, different gradation and two different values of confining pressures were conducted. From the shear force records measured during the experiments, values for peak friction angles and cohesion of the ice rubble were derived. In addition to these, the dilation angle of the ice rubble was estimated using the video recordings from the tests. The results from the experiments and a review on earlier experiments also presented here suggest that there is a relation between the size of the ice blocks and material properties yielded by the experiments. The results further show that the rubble dilation and the load limiting mechanism in the experiment should be carefully studied and reported in the experiments in order to gain understanding on rubble behavior.
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Coppejans, Okko, and Noud Werter. "Discretization Challenges in Crash Simulations: Mesh, Geometry and Failure Criterion Effects From the Energy Perspective." In ASME 2022 41st International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/omae2022-79655.
Повний текст джерелаАнотація:
Abstract The simulation of collisions of ships using FEA has a long history of rules and guidelines to which such simulations should conform. Nevertheless, there are still subjects that lack thorough understanding in literature and standards. With the rise in popularity of stress state dependent failure criteria and the ability to simulate with smaller element sizes, new questions arise. This paper is part of an ongoing sensitivity study of the effect parameters such as element size, choice of failure criterion, geometric placement of the striking vessel and friction have on the dissipated energy in a collision simulation. It is shown that the use of different mesh sizes and different failure criteria results in different failure mechanisms and deformation patterns and have a great effect on dissipated energy. The stress states in which most of the plastic work is performed (and therefore energy is dissipated) are shown to be in the triaxiality range of 0.27–0.35. The energy contributions of the regions above that, towards equi-biaxial tension, and below that, towards pure shear, are very significant on first contact and shape the initial deformation mechanism. Furthermore it is shown that the placement of the incoming V-bow with respect to element boundaries significantly influences the energy absorption. The parameters influencing energy dissipation are numerous and just a very small selection is discussed in this paper. No perfect deterministic approach is presented in this paper, but a base for a probabilistic approach is given.
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Gupta, V., Dan Potter, and Serge Hoart. "Mechanisms-Based Failure Laws for Graphite/Epoxy Laminates Under Compression." In ASME 1998 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/imece1998-1160.
Повний текст джерелаАнотація:
Abstract Micromechanisms of failure were studied to determine the influence of specimen size and fiber constraint effects with end loading, and with a view to develop the failure laws. For this study, [±10]12s and [±15]12s, [±30]12s, and [±45]12s specimens with various aspect rations (height/width) were tested with an end loading fixture. Failure modes varied depending on the fiber orientation of the laminate layers to the loading axis. Failure transitioned from shear slipping along the fibers in the [±45]12s and [±30]12s samples to global delamination in the [10]12s samples. Geometry and size effects were also investigated by comparing samples with various aspect ratios. In addition to simply changing the geometry of the samples, adjusting the aspect ratio varied the amount of fibers constrained at the specimen ends against the platen interfaces. For all of the fiber orientations tests, low aspect ratio specimens had a lower elastic modulus but a higher ultimate strength compared to the larger aspect ratio specimens. Stress concentration and fiber constraint effects introduced by the end loading explain these results. These effects highlight the importance of specimen geometry and fixturing considerations for off-axis compression testing and the sensitivity of stress/strain behavior to specimen size. Biaxial compression testing was also conducted on [±45]12s and [±30]12s samples with a cruciform material testing machine. Samples were loaded with platens slightly smaller than the sample widths. The confinement ratio R, the ratio of stress applied to the secondary to primary sample axes, was varied from 0.25 to 1 to measure the sensitivity of sample failure mechanisms and stress/strain behavior to different stress states. Failure modes for both fiber orientations transitioned from the uniaxial failure mode to massive delamination with an increasing confinement ratio. Results indicate that the shear stress oriented along the fiber direction dictates failure for confinement ratios from 0 to 0.5, since the shear stress at failure is relatively constant. Above R = 0.5, failure moves toward delamination since the fiber aligned axial stresses that produce buckling begin to dominate the decreasing shear stresses along the fibers. These investigations lead to further understanding of the coupling between failure modes and stress/strain results for biaxial compression testing to allow development of failure models. A simple local matrix shear criterion in the micromechanical model captured the nucleation of fiber-aligned longitudinal cracks rather well. The saturation cracking state that ensured was determined in terms of the length of the two wing-cracks that nucleated from the edges of the main longitudinal crack due to its mode-III sliding along the fiber axis direction. The stress intensity factor at the wing crack tip was determined in terms of the friction sliding resistance, matrix fracture toughness, and the attendant compressive stress state near the main sliding crack. The model captured the results obtained with different biaxiality ratios and also explained the changes in the failure model to axial delamination.
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Yang, J., and K. Komvopoulos. "A Mechanics Approach to Static Friction of Elastic-Plastic Fractal Surfaces." In ASME/STLE 2004 International Joint Tribology Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/trib2004-64271.
Повний текст джерелаАнотація:
A contact mechanics theory of static friction is presented for isotropic rough surfaces exhibiting fractal behavior. The analysis is based on a piece-wise power-law size distribution and a normal slope distribution of the asperity contacts and elastic-fully plastic deformation models. Numerical integration yields solutions for the normal and friction forces in terms of fractal parameters, elastic-plastic material properties, and interfacial shear strength. The variation of the static coefficient of friction with normal load is related to the effect of the surface topography on the dominant deformation mode at the asperity contacts. Plastic deformation of the smaller asperity contacts dominates at low loads and elastic deformation of the larger asperity contacts at high loads. The critical load signifying the transition from predominantly plastic to elastic deformation depends on the fractal parameters and material properties. In the low-load range, the static coefficient of friction decreases with the increase of the load, while in the high-load range it increases relatively faster with the load. Numerical results for copper fractal surfaces illustrate the effects of normal load, surface topography, and interfacial shear strength on the static coefficient of friction.
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Rosenkrantz, Adam, and John Tichy. "Particle Flow Behavior in a Shear Cell Device." In ASME/STLE 2011 International Joint Tribology Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ijtc2011-61155.
Повний текст джерелаАнотація:
This presentation describes ongoing research performed on a simple shear cell apparatus, previously described [1]. As a complement, discrete particle simulations and continuum models have been used to predict normal and shear forces in the ongoing experiments. The trends and orders-of-magnitude of the models and experiment are in basic agreement. Theoretical models used are constructed with basic principles, rather than curve fitting, to obtain effective properties of the mixture such as viscosity or conductivity. The experiment itself serves to determine the effects of shear rate, packing fraction, particle size and film thickness on the load carrying normal stress. Additionally, the frictional shear stress can be investigated. The working particulate medium within the apparatus consists of glass of aluminum spheres, poly-dispersed over four size increments, all less than 1.00 mm diameter. The upper annular disk is held stationary in a rotational sense by a force transducer, and applies predetermined normal stress values which vary according to a system of interchangeable counterweights. The lower transfer surface and the sidewalls of the annular ring are rotated by applied mechanical torque. Experimental trials consist of shear initiation, after which the trough velocity, film thickness, supporting load, and frictional torque are measured. From these measurements one can calculate the average shear rate, the average load-carrying normal stress, the average frictional shear stress, and the solids volume fraction. Such third body granular flow may apply to some solid lubrication mechanisms, and to applications such as smart clutches and dampers. The continuum theory presented is unique in that it addresses solid-like behavior and its transition to fluidized behavior. The discrete particle dynamics rely on the conceptual models of Iordanoff and colleagues [2]. Our findings are that the two theoretical predictions agree reasonably with the experimental results, suggesting validity of the approach. These results are promising, and may be used to further develop high level predictive models. Furthermore, similar methods of small scale experimental particle simulation can be used to develop simpler more usable continuum approaches.
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Manjunathaiah, Jairam, and William J. Endres. "A New Model and Analysis of Orthogonal Machining With an Edge Radiused Tool." In ASME 1998 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/imece1998-1037.
Повний текст джерелаАнотація:
Abstract A new machining process model that explicitly includes the effects of the edge hone is presented. A force balance is conducted on the lower boundary of the deformation zone leading to a machining force model. The machining force components are an explicit function of the edge radius and shear angle. An increase in edge radius leads to not only increased ploughing forces but also an increase in the chip formation forces due to an average rake angle effect. Previous attempts at assessing the ploughing components as the force intercept at zero uncut chip thickness, which attribute to the ploughing mechanism all the changes in forces that occur with changes in edge radius, are seen to be erroneous in view of this model. Calculation of shear stress on the lower boundary of the deformation zone using the new machining force model indicates that the apparent size effect is mainly due to deformation below the tool (ploughing) and a larger chip formation component due to a lower shear angle. The shear strain rate is substantially higher at smaller uncut chip thickness resulting in a mild effect of strain-rate hardening. Frictional conditions do not exhibit change with uncut chip thickness if an average rake formulation is used.
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Jordon, J. B. "The Effect of Microstructural and Geometrical Features on Fatigue Performance in Mg AZ31 Friction Stir Spot Welds." In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-65280.
Повний текст джерелаАнотація:
The relationship of microstructural and geometrical features to fatigue performance is investigated in friction stir spot welds made using AZ31 magnesium alloy sheets. Lap-shear coupons were spot welded using two sets of welding parameters. Optical microscopy of the initial state of the microstructure of each set of spot welds revealed differences in the hook formation, sheet thickness in the weld zone, and nugget diameter. Both sets of welds were fatigue tested in load control until failure at various load ratios. Optical microscopy of the failed coupons revealed differences in the fracture mode between the two sets of coupons. A linear elastic fracture mechanics model was used to correlate the fatigue life in the two processes. The fatigue model, which is a function of hook size, sheet thickness, and nugget diameter, showed good correlation to the experimental results. The model was also employed to show that the fatigue of the friction stir spot welds was most sensitive to the sheet thickness in the weld zone, followed by hook height, and then nugget diameter.
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Takata, Rosalind, Yong Li, and Victor W. Wong. "Effects of Liner Surface Texturing on Ring/Liner Friction in Large-Bore IC Engines." In ASME 2006 Internal Combustion Engine Division Fall Technical Conference. ASMEDC, 2006. http://dx.doi.org/10.1115/icef2006-1525.
Повний текст джерелаАнотація:
Well-designed surface texturing may be used to reduce ring/liner friction and increase efficiency in internal combustion engines. This study investigated the effects of textures of either grooves or dimples on ring/liner friction, in the hydrodynamic and mixed regimes. Existing MIT models were used to conduct this research. The ring-pack model is based on averaged flow-factor Reynolds analysis, and is used in conjunction with a deterministic model for flow factor calculation. Although this advanced model is applicable in a wide range of cases, the surface textures studied here are very different than a typical liner surface, and can be represented only approximately by the averaged analysis upon which the ring simulation is based. For this reason, this analysis of surface features has focused on a parametric study, the goal of which is to analyze trends relating ring/liner friction to surface parameters, and to make a general evaluation of the potential of surface texturing to reduce ring-pack losses. In the hydrodynamic and mixed regimes, surface texturing affects the fluid pressure in the lubricant between ring and liner, thus affecting the ability of the oil film to support the ring load. If the effect of the texturing is to impede the flow of lubricant, the result will be an increase in oil film thickness. This causes friction reduction in two ways: if asperity contact was present, it is reduced; and the increase in film thickness causes a decrease in shear rate, thus decreasing oil shear stress. It was found that surfaces with both dimpled and grooved textures could cause friction reduction through this mechanism, with deeper features and more transverse groove patterns causing the greatest reduction. Friction also decreased with increasing area ratio (the percentage of the surface that is occupied by the surface features) for both grooves and dimples, and was only slightly dependent on groove width and dimple diameter. Because the effect of the surface texturing is on hydrodynamic effects in the oil, it is strongly coupled with lubricant properties. If surface texturing and lubricant viscosity are optimized together side effects such as oil consumption and wear can be mitigated, while friction can be reduced even further than it is via surface texturing alone. This possibility was also briefly considered in this study.
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Takata, Rosalind, and Victor W. Wong. "Effects of Lubricant Viscosity on Ring/Liner Friction in Advanced Reciprocating Engine Systems." In ASME 2006 Internal Combustion Engine Division Fall Technical Conference. ASMEDC, 2006. http://dx.doi.org/10.1115/icef2006-1526.
Повний текст джерелаАнотація:
The piston ring-pack contributes a large portion of the mechanical losses in an internal combustion engine. In this study, the effects of lubricant viscosity are evaluated with the goal of reducing these mechanical losses. Oil viscosity affects friction directly in the hydrodynamic regime, where hydrodynamic friction increases with viscosity. It also influences boundary friction indirectly via oil film thickness — higher viscosity causes oil films to be thicker, which reduces asperity contact. At the optimum viscosity (the viscosity at which minimum friction losses are incurred) there is a balance between these hydrodynamic and boundary effects. As piston speed, ring loading, and other parameters change during the engine cycle, the optimum oil viscosity also changes. If the variation of viscosity could be controlled during the cycle, it could be maintained at an optimum at all times. In this study, several theoretical and realistic cases were studied to quantify the friction benefit that could be obtained if this were possible. Idealized cases with low viscosity near mid-stroke (to reduce hydrodynamic friction) and high viscosity near end-strokes (to reduce boundary contact) were considered, as were several more realistic cases based on temperature and shear-rate dependencies. It was found that, for the oil control ring studied, the effect on friction of keeping viscosity high near end-strokes is very small, and does not provide a substantial benefit (in terms of friction) over allowing viscosity to vary naturally with temperature and shear rate. Two mechanisms lead to the relatively small size of the friction benefit: the contribution to total cycle ring friction from the dead-center area is small, because of low piston speeds there; and any reduction in asperity contact due to increased viscosity is accompanied by an increase in hydrodynamic friction, which cancels out some of the benefit. Oil viscosity near mid-stroke, where most of the ring/liner friction is generated, is the dominant viscosity that controls the overall friction losses for the ring. Although its contribution to friction reduction is not large, maintaining high lubricant viscosity near dead-centers can lead to a reduction in wear in that region, because asperity contact decreases. For the ring-pack studied, a friction reduction of ∼7% is predicted when viscosity is reduced in the mid-stroke region (based on OCR effects alone). If end-stroke viscosity is also kept high, the end-stroke regions, where current engines experience the most wear, will see a reduction in asperity contact (although there will still be a slight wear increase in the mid-stroke). An end-stroke wear reduction of up to 25% is predicted by the current model.