The Experts below are selected from a list of 89220 Experts worldwide ranked by ideXlab platform
A Mugadu - One of the best experts on this subject based on the ideXlab platform.
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the influence of an edge radius on the local stress field at the edge of a complete fretting contact
International Journal of Solids and Structures, 2002Co-Authors: A. Sackfield, A Mugadu, David A. HillsAbstract:The state of stress adjacent to the corner of a complete or almost complete fretting contact pad is studied using the corresponding Muskhelishvili potentials. Three potential are employed; that for a semi-infinite rigid punch, that for a finite square-ended rigid punch, and that for a punch having a flat form with radiused corners. It is shown that the Asymptotic stress field (the semi-infinite punch) matches the finite punch well over a large region. Further, the edge radius which can be tolerated, but still giving rise to a local stress field which can be approximated by the Asymptotic solution is found. The implication of these results for the application of an Asymptotic Approach to the design of almost complete fretting contacts is described.
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a generalised stress intensity Approach to characterising the process zone in complete fretting contacts
International Journal of Solids and Structures, 2002Co-Authors: A MugaduAbstract:The known analytical contact solution for the stress field induced by a rigid, square-ended punch, sliding on an elastic half-plane defines the stress state everywhere in the half-plane. An Asymptotic Approach is then used to determine the characteristic stress field at the edge of the contact, which is matched with the contact solution. Hence, the regions over which the Asymptotic solution is valid are found. Using a method analogous to the crack-tip stress field, a generalised stress intensity factor is defined, with the aim of providing a single variable characterisation of the stress state at the punch corner. The crack initiation process zone for a fretting fatigue crack is therefore captured, and the conditions for small scale yielding explicitly found.
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an Asymptotic Approach to crack initiation in fretting fatigue of complete contacts
Journal of The Mechanics and Physics of Solids, 2002Co-Authors: A Mugadu, D A Hills, L LimmerAbstract:Abstract The stress state near the corner of a complete contact subject to fretting action is studied using an Asymptotic analysis. The spatial distribution of stress, together with the generalised stress intensity factor defining the severity of the stress state are found, and the implications for experimental determination of crack initiation conditions discussed.
D A Hills - One of the best experts on this subject based on the ideXlab platform.
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explicit and Asymptotic solutions for frictional incomplete half plane contacts subject to general oscillatory loading in the steady state
Journal of The Mechanics and Physics of Solids, 2021Co-Authors: H Andresen, R M N Fleury, M R Moore, D A HillsAbstract:Abstract This contribution presents an Asymptotic formulation for the stick-slip behaviour of incomplete contacts under oscillatory variation of normal load, moment, shear load and differential bulk tension. The Asymptotic description allows us not only to approximate the size of the slip zones during the steady-state of a cyclic problem without knowledge of the geometry or contact law, but provides a solution when all known analytical solutions for incomplete contacts reach their limitations, that is, in the presence of a varying moment and a differential bulk tension large enough to reverse the direction of slip at one end of the contact. An insightful comparison between the mathematically explicit analytical solution and the Asymptotic Approach is drawn using the example geometry of a shallow wedge.
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correlation of fretting fatigue experimental results using an Asymptotic Approach
International Journal of Fatigue, 2012Co-Authors: D A Hills, A Thaitirarot, J R Barber, Daniele DiniAbstract:Abstract Small refinements are made to the bounded Asymptotic forms recently developed to encapsulate the state of slip and stress at the edges of incomplete contacts. They are then used to re-analyse several sets of publicly available fretting fatigue data. Several different combinations of the asymptotes are used and it is shown that two are viable and give big improvements upon stress-based criteria. These procedures provide a practical method for both designing against fretting fatigue and quantifying nucleation times when fretting is unavoidable.
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an Asymptotic Approach to crack initiation in fretting fatigue of complete contacts
Journal of The Mechanics and Physics of Solids, 2002Co-Authors: A Mugadu, D A Hills, L LimmerAbstract:Abstract The stress state near the corner of a complete contact subject to fretting action is studied using an Asymptotic analysis. The spatial distribution of stress, together with the generalised stress intensity factor defining the severity of the stress state are found, and the implications for experimental determination of crack initiation conditions discussed.
Jamal Najim - One of the best experts on this subject based on the ideXlab platform.
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On the Capacity Achieving Covariance Matrix for Rician MIMO Channels: An Asymptotic Approach
IEEE Transactions on Information Theory, 2010Co-Authors: Julien Dumont, Philippe Loubaton, Samson Lasaulce, Walid Hachem, Jamal NajimAbstract:In this paper, the capacity-achieving input covariance matrices for coherent block-fading correlated multiple input multiple output (MIMO) Rician channels are determined. In contrast with the Rayleigh and uncorrelated Rician cases, no closed-form expressions for the eigenvectors of the optimum input covariance matrix are available. Classically, both the eigenvectors and eigenvalues are computed numerically and the corresponding optimization algorithms remain computationally very demanding. In the Asymptotic regime where the number of transmit and receive antennas converge to infinity at the same rate, new results related to the accuracy of the approximation of the average mutual information are provided. Based on the accuracy of this approximation, an attractive optimization algorithm is proposed and analyzed. This algorithm is shown to yield an effective way to compute the capacity achieving matrix for the average mutual information and numerical simulation results show that, even for a moderate number of transmit and receive antennas, the new Approach provides the same results as direct maximization Approaches of the average mutual information.
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on the capacity achieving covariance matrix for rician mimo channels an Asymptotic Approach
arXiv: Probability, 2007Co-Authors: Julien Dumont, Philippe Loubaton, Samson Lasaulce, Walid Hachem, Jamal NajimAbstract:The capacity-achieving input covariance matrices for coherent block-fading correlated MIMO Rician channels are determined. In this case, no closed-form expressions for the eigenvectors of the optimum input covariance matrix are available. An approximation of the average mutual information is evaluated in this paper in the Asymptotic regime where the number of transmit and receive antennas converge to $+\infty$. New results related to the accuracy of the corresponding large system approximation are provided. An attractive optimization algorithm of this approximation is proposed and we establish that it yields an effective way to compute the capacity achieving covariance matrix for the average mutual information. Finally, numerical simulation results show that, even for a moderate number of transmit and receive antennas, the new Approach provides the same results as direct maximization Approaches of the average mutual information, while being much more computationally attractive.
Daniele Dini - One of the best experts on this subject based on the ideXlab platform.
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partial slip incomplete contacts under constant normal load and subject to periodic loading
International Journal of Mechanical Sciences, 2016Co-Authors: David A. Hills, R M N Fleury, Daniele DiniAbstract:Abstract We present a general formulation for the stick slip behaviour of incomplete contact under oscillating loading, but with a constant normal load. An Asymptotic description of the contact traction very close to the contact edges is used. The slip zones present in the steady state with cyclically varying bulk tension and shear force (with an arbitrary phase shift) are found. The range of the variation of the state of stress near both of the contact edges and the respective slip zone sizes are defined in terms of the loading parameters, including the phase angle. The quality of the approximations used by the Asymptotic Approach and the range of applicability of the method is also analysed in detail in this paper.
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correlation of fretting fatigue experimental results using an Asymptotic Approach
International Journal of Fatigue, 2012Co-Authors: D A Hills, A Thaitirarot, J R Barber, Daniele DiniAbstract:Abstract Small refinements are made to the bounded Asymptotic forms recently developed to encapsulate the state of slip and stress at the edges of incomplete contacts. They are then used to re-analyse several sets of publicly available fretting fatigue data. Several different combinations of the asymptotes are used and it is shown that two are viable and give big improvements upon stress-based criteria. These procedures provide a practical method for both designing against fretting fatigue and quantifying nucleation times when fretting is unavoidable.
David A. Hills - One of the best experts on this subject based on the ideXlab platform.
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partial slip incomplete contacts under constant normal load and subject to periodic loading
International Journal of Mechanical Sciences, 2016Co-Authors: David A. Hills, R M N Fleury, Daniele DiniAbstract:Abstract We present a general formulation for the stick slip behaviour of incomplete contact under oscillating loading, but with a constant normal load. An Asymptotic description of the contact traction very close to the contact edges is used. The slip zones present in the steady state with cyclically varying bulk tension and shear force (with an arbitrary phase shift) are found. The range of the variation of the state of stress near both of the contact edges and the respective slip zone sizes are defined in terms of the loading parameters, including the phase angle. The quality of the approximations used by the Asymptotic Approach and the range of applicability of the method is also analysed in detail in this paper.
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the influence of an edge radius on the local stress field at the edge of a complete fretting contact
International Journal of Solids and Structures, 2002Co-Authors: A. Sackfield, A Mugadu, David A. HillsAbstract:The state of stress adjacent to the corner of a complete or almost complete fretting contact pad is studied using the corresponding Muskhelishvili potentials. Three potential are employed; that for a semi-infinite rigid punch, that for a finite square-ended rigid punch, and that for a punch having a flat form with radiused corners. It is shown that the Asymptotic stress field (the semi-infinite punch) matches the finite punch well over a large region. Further, the edge radius which can be tolerated, but still giving rise to a local stress field which can be approximated by the Asymptotic solution is found. The implication of these results for the application of an Asymptotic Approach to the design of almost complete fretting contacts is described.
