The Experts below are selected from a list of 741 Experts worldwide ranked by ideXlab platform
Aimy Bazylak - One of the best experts on this subject based on the ideXlab platform.
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the impact of fibre surface morphology on the effective thermal conductivity of a polymer electrolyte membrane fuel cell gas diffusion layer
Journal of Power Sources, 2014Co-Authors: S J Botelho, Aimy BazylakAbstract:Abstract In this work, the effect of fibre surface morphology on the effective thermal conductivity of the gas diffusion layer of a polymer electrolyte membrane fuel cell is presented. Atomic force microscopy was used to measure the fibre surface roughness and Asperity Height distributions for various fibres for Toray carbon paper. Hertzian contact mechanics was used to determine individual micro-contact areas and thermal resistances, and results were compared with the smooth cylinder approximation. The effective thermal contact resistance between rough fibres was determined using resistance network theory. The thermal contact resistance and total contact area were determined for various angles of fibre orientation and contact forces; results are presented as empirical formulations. It was found that the effective thermal contact resistance is significantly affected by fibre roughness features when compared to the smooth fibre case, which is often used in the literature. The analysis conducted provides an alternative to computationally expensive surface feature analyses by providing a tool which can be used to implement the nano-scale features of gas diffusion layer fibres into existing effective thermal conductivity models.
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the impact of fibre surface morphology on the effective thermal conductivity of a pem fuel cell gas diffusion layer
224th ECS Meeting (October 27 – November 1 2013), 2013Co-Authors: S J Botelho, Aimy BazylakAbstract:In this work, the preliminary findings for determining the effect of fibre surface morphology on the effective thermal conductivity of the gas diffusion layer of a polymer electrolyte membrane fuel cell is presented. Atomic force microscopy was used to measure the fibre surface roughness and Asperity Height distribution for various fibres and locations along each fibre for Toray carbon paper TGP-H-120. The thermal contact resistance was measured using preliminary methods, which will be further advanced in the near future. Hertzian contact mechanics was used to validate the results obtained, and to compare with smooth fibre thermal contact resistance for rough and smooth fibres. The thermal contact resistance was determined for various angles of fibre orientation and contact forces; it was determined that values for rough fibre contact are on average twice that of the contact of smooth fibres.
Naj Aziz - One of the best experts on this subject based on the ideXlab platform.
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Effects of cyclic loading on the shear behaviour of infilled rock joints under constant normal stiffness conditions
Rock Mechanics and Rock Engineering, 2013Co-Authors: Ali Mirzaghorbanali, Jan Nemcik, Naj AzizAbstract:The variation of the shear strength of infilled rock joints under cyclic loading and constant normal stiffness conditions is studied. To simulate the joints, triangular asperities inclined at angles of 9.5° and 18.5° to the shear movement were cast using high-strength gypsum plaster and infilled with clayey sand. These joints were sheared cyclically under constant normal stiffness conditions. It was found that, for a particular normal stiffness, the shear strength is a function of the initial normal stress, initial Asperity angle, joint surface friction angle, infill thickness, infill friction angle, loading direction and number of loading cycles. Based on the experimental results, a mathematical model is proposed to evaluate the shear strength of infilled rock joints in cyclic loading conditions. The proposed model takes into consideration different initial Asperity angles, initial normal stresses and ratios of infill thickness to Asperity Height.
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shear behaviour of idealized infilled joints under constant normal stiffness
Geotechnique, 1999Co-Authors: Buddhima Indraratna, Asadul Haque, Naj AzizAbstract:The shear behaviour of soft joints containing infill materials was investigated in the laboratory under constant normal stiffness (CNS) conditions. Tests were conducted on joints with asperities having inclinations of 9·5° (type 1) and 18·5° (type II), under a given range of initial normal stresses (σno) 0·30 to 1·10 MPa, and at a constant normal stiffness of 8·5, Kn/mm. It was found that the shear strength of joints decreases considerably even with the addition of a thin layer of infill. Results also show that the effect of asperities on shear strength is significant up to an Asperity Height to infill thickness (t/a) ratio of 1·4—1·8, whereas the shear behaviour is controlled by the infill alone beyond this critical ratio. The shear displacement corresponding to the peak shear stress is considerably reduced once the infill starts to govern the shear behaviour of the joint. In this study, the drop in peak shear stress under CNS conditions has been modelled by a hyperbolic relationship. In relation to ‘cle...
S J Botelho - One of the best experts on this subject based on the ideXlab platform.
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the impact of fibre surface morphology on the effective thermal conductivity of a polymer electrolyte membrane fuel cell gas diffusion layer
Journal of Power Sources, 2014Co-Authors: S J Botelho, Aimy BazylakAbstract:Abstract In this work, the effect of fibre surface morphology on the effective thermal conductivity of the gas diffusion layer of a polymer electrolyte membrane fuel cell is presented. Atomic force microscopy was used to measure the fibre surface roughness and Asperity Height distributions for various fibres for Toray carbon paper. Hertzian contact mechanics was used to determine individual micro-contact areas and thermal resistances, and results were compared with the smooth cylinder approximation. The effective thermal contact resistance between rough fibres was determined using resistance network theory. The thermal contact resistance and total contact area were determined for various angles of fibre orientation and contact forces; results are presented as empirical formulations. It was found that the effective thermal contact resistance is significantly affected by fibre roughness features when compared to the smooth fibre case, which is often used in the literature. The analysis conducted provides an alternative to computationally expensive surface feature analyses by providing a tool which can be used to implement the nano-scale features of gas diffusion layer fibres into existing effective thermal conductivity models.
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the impact of fibre surface morphology on the effective thermal conductivity of a pem fuel cell gas diffusion layer
224th ECS Meeting (October 27 – November 1 2013), 2013Co-Authors: S J Botelho, Aimy BazylakAbstract:In this work, the preliminary findings for determining the effect of fibre surface morphology on the effective thermal conductivity of the gas diffusion layer of a polymer electrolyte membrane fuel cell is presented. Atomic force microscopy was used to measure the fibre surface roughness and Asperity Height distribution for various fibres and locations along each fibre for Toray carbon paper TGP-H-120. The thermal contact resistance was measured using preliminary methods, which will be further advanced in the near future. Hertzian contact mechanics was used to validate the results obtained, and to compare with smooth fibre thermal contact resistance for rough and smooth fibres. The thermal contact resistance was determined for various angles of fibre orientation and contact forces; it was determined that values for rough fibre contact are on average twice that of the contact of smooth fibres.
Ming Liu - One of the best experts on this subject based on the ideXlab platform.
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finite element analysis of large contact deformation of an elastic plastic sinusoidal Asperity and a rigid flat
International Journal of Solids and Structures, 2014Co-Authors: Ming LiuAbstract:Abstract Normal contact deformation of an Asperity and a rigid flat is studied within an axisymmetric finite element model. The Asperity features a sinusoidal profile and is elastic–plastic with linear strain hardening. Influences of geometrical (Asperity Height and width) and loading (the maximum interference) parameters on frictionless contact responses are explored for both loading and unloading. Dimensionless expressions for contact size and pressures covering a large range of interference and Asperity ratio values are obtained in power-law forms. Results show the mean contact pressure after fully-plastic contact reaches a plateau only for small Asperity ratios, while it continues increasing for large Asperity ratios. The residual depth is found to be associated with plastically dissipated energy.
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Finite element analysis of large contact deformation of an elastic–plastic sinusoidal Asperity and a rigid flat
International Journal of Solids and Structures, 2014Co-Authors: Ming LiuAbstract:Normal contact deformation of an Asperity and a rigid flat is studied within an axisymmetric finite element model. The Asperity features a sinusoidal profile and is elastic–plastic with linear strain hardening. Influences of geometrical (Asperity Height and width) and loading (the maximum interference) parameters on frictionless contact responses are explored for both loading and unloading. Dimensionless expressions for contact size and pressures covering a large range of interference and Asperity ratio values are obtained in power-law forms. Results show the mean contact pressure after fully-plastic contact reaches a plateau only for small Asperity ratios, while it continues increasing for large Asperity ratios. The residual depth is found to be associated with plastically dissipated energy.
Nemcik Jan - One of the best experts on this subject based on the ideXlab platform.
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Numerical Simulation of Unsaturated Infilled Joints in Shear
'Sociological Research Online', 2018Co-Authors: Gong Libin, Nemcik Jan, Ren TingAbstract:Rock discontinuities filled with soil-like materials commonly exist in rock masses, where the infill material is usually unsaturated, and the joint could have a much higher shear strength compared with fully saturated conditions. Understanding the shear behavior of unsaturated infilled joints is important when assessing ground stability such as in open cut mines or underground excavations. However so far, research on this topic is rare and not mature. This paper investigates the shear behaviour of unsaturated infilled joints in the numerical software FLAC. The FLAC soil-water retention and permeability models were modified in FISH subroutine to consider infill porosity change. A series of constant water content direct shear tests on infilled joints under various ratios of infill thickness to Asperity Height (t/a) were numerically conducted. Results highlight the necessity of correcting the intrinsic models in FLAC, and indicate that t/a ratio has a distinct influence on small-strain shear behaviour. Shear induced variations of fundamental infill parameters (e.g. matric suction, degree of saturation and saturated permeability) are discussed
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Laboratory tests on thin spray-on liner penetrated rock joints in direct shear
'Sociological Research Online', 2015Co-Authors: Qiao Qiuqiu, Nemcik Jan, Porter Ian, Baafi ErnestAbstract:To study the shear behaviour of TSL penetrated rock joints, the direct shear test was adopted. The effects of surface roughness, penetrated thickness to Asperity Height ratio, shear rate, and normal load on the shear behaviour of TSL penetrated rock joints were investigated in this study
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A model for water flow through rock fractures based on friction factor
'Springer Science and Business Media LLC', 2015Co-Authors: Zhang Zhenyu, Qiao Qiuqiu, Nemcik Jan, Geng XueyuAbstract:Rock fracture roughness and tortuosity caused by contact asperities produce extra resistance for fluid flow in comparison with the channel consisting of two smooth parallel plates. To characterise the role of roughness and tortuosity in water flow through rock fractures, the existing studies of the effect of fracture roughness and contact area (tortuosity) on fluid flow through rock fractures were firstly reviewed. Then, an explicit flow model was derived using the friction factor predictor previously proposed according to the flow data of sandstone fractures. Regarding the introduced relative roughness of rock fracture as the correction variable, the developed flow model can be considered as a corrected form of classic cubic law, where the relative roughness is defined as the ratio of the averaged peak Asperity Height to equivalent hydraulic aperture. Sensitivity analysis shows that the cubic law can overestimate the flow rate by 10 % when the relative roughness increases to 70.7. With further increase in relative roughness up to 300, which usually represents tight rock fractures, the flow rate is only approximately 64 % of that predicted by cubic law. The verification of this friction factor to granite and limestone fractures shows that the used friction factor predictor is in good accordance with the experimental data
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A study on the shear behaviour of infilled rock joints under cyclic loading and constant normal stiffness conditions
'University of Wollongong Library', 2014Co-Authors: Mirzaghorbanali Ali, Nemcik Jan, Aziz NajAbstract:Shear behaviour of infilled rock joints under cyclic loading and constant normal stiffness conditions were studied. The experiments were carried out in a cyclic loading direct shear apparatus. The laboratory studies were conducted using saw tooth shaped asperities cast in high strength gypsum plaster. Two types of triangular asperities inclined at 9.5° (Type I) and 18.5° (Type II) from the shearing direction were considered for testing. Clayey sand (75% fine sand and 25% Kaolinite) at initial moisture content of 12.5% was selected as the infill material. Profile of shear planes and strength envelopes for different conditions of infill thickness to Asperity Height ratio, initial normal stress, and initial Asperity angle were investigated
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Effects of cyclic loading on the shear behaviour of infilled rock joints under constant normal stiffness conditions
'Sociological Research Online', 2014Co-Authors: Mirzaghorbanali Ali, Nemcik Jan, Aziz NajAbstract:The variation of the shear strength of infilled rock joints under cyclic loading and constant normal stiffness conditions is studied. To simulate the joints, triangular asperities inclined at angles of 9.5 and 18.5 degrees to the shear movement were cast using high-strength gypsum plaster and infilled with clayey sand. These joints were sheared cyclically under constant normal stiffness conditions. It was found that, for a particular normal stiffness, the shear strength is a function of the initial normal stress, initial Asperity angle, joint surface friction angle, infill thickness, infill friction angle, loading direction and number of loading cycles. Based on the experimental results, a mathematical model is proposed to evaluate the shear strength of infilled rock joints in cyclic loading conditions. The proposed model takes into consideration different initial Asperity angles, initial normal stresses and ratios of infill thickness to Asperity Height
