The Experts below are selected from a list of 366 Experts worldwide ranked by ideXlab platform
J R Barber - One of the best experts on this subject based on the ideXlab platform.
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fracture mechanics implications for apparent static friction coefficient in contact problems involving slip weakening laws
Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2015Co-Authors: Antonio Papangelo, M Ciavarella, J R BarberAbstract:We consider the effect of differing coefficients of static and dynamic friction coefficients on the behaviour of contacts involving Microslip. The classic solutions of Cattaneo and Mindlin are unch...
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fracture mechanics implications for apparent static friction coefficient in contact problems involving slip weakening laws
arXiv: Soft Condensed Matter, 2015Co-Authors: Antonio Papangelo, M Ciavarella, J R BarberAbstract:We consider the effect of differing coefficients of static and dynamic friction coefficients on the behaviour of contacts involving Microslip. The classic solutions of Cattaneo and Mindlin are unchanged if the transition in coefficients is abrupt, but if it occurs over some small slip distance, the solution has some mathematical similarities with those governing the normal tractions in adhesive contact problems. In particular, if the transition to dynamic slip occurs over a sufficiently small area, we can identify a `JKR' approximation, where the transition region is condensed to a line. A local singularity in shear traction is then predicted, with a stress-intensity factor that is proportional to the the square root of the local contact pressure and to a certain integral of the friction coefficient-slip distance relation. We can also define an equivalent of the `small-scale yielding' criterion, which enables us to assess when the singular solution provides a good approximation. One consequence of the results is that the static coefficient of friction determined from force measurements in experiments is significantly smaller than the value that holds at the microscale.
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effect of small harmonic oscillations during the steady rolling of a cylinder on a plane
International Journal of Mechanical Sciences, 2008Co-Authors: J R Barber, M Ciavarella, L Afferrante, A SackfieldAbstract:If a wheel rolling over a rail transmits a tangential traction, frictional Microslip occurs in part of the contact area, resulting in energy dissipation and localized wear. If the applied forces oscillate in time, the resulting wear will be non-uniform, resulting in ‘corrugations’ that can grow with progressive passes, depending on the dynamics of the overall system. In this paper, a linear perturbation method is used to obtain closed-form expressions for the receptance of a two-dimensional rolling contact subjected to small oscillations in normal force and rotational speed superposed on a mean value in the limit of large coefficient of friction. Corresponding expressions are also obtained for the amplitude and phase of the energy dissipation in the contact, which is expected to correlate with the local wear rate. The results are compared with a simpler Winkler model of the contact and with other models that have been used for the analysis of rail corrugation. Surprisingly good agreement is obtained with numerical results due to Gross-Thebing for the receptances due to oscillations in rotational speed.
M Ciavarella - One of the best experts on this subject based on the ideXlab platform.
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fracture mechanics implications for apparent static friction coefficient in contact problems involving slip weakening laws
Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2015Co-Authors: Antonio Papangelo, M Ciavarella, J R BarberAbstract:We consider the effect of differing coefficients of static and dynamic friction coefficients on the behaviour of contacts involving Microslip. The classic solutions of Cattaneo and Mindlin are unch...
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fracture mechanics implications for apparent static friction coefficient in contact problems involving slip weakening laws
arXiv: Soft Condensed Matter, 2015Co-Authors: Antonio Papangelo, M Ciavarella, J R BarberAbstract:We consider the effect of differing coefficients of static and dynamic friction coefficients on the behaviour of contacts involving Microslip. The classic solutions of Cattaneo and Mindlin are unchanged if the transition in coefficients is abrupt, but if it occurs over some small slip distance, the solution has some mathematical similarities with those governing the normal tractions in adhesive contact problems. In particular, if the transition to dynamic slip occurs over a sufficiently small area, we can identify a `JKR' approximation, where the transition region is condensed to a line. A local singularity in shear traction is then predicted, with a stress-intensity factor that is proportional to the the square root of the local contact pressure and to a certain integral of the friction coefficient-slip distance relation. We can also define an equivalent of the `small-scale yielding' criterion, which enables us to assess when the singular solution provides a good approximation. One consequence of the results is that the static coefficient of friction determined from force measurements in experiments is significantly smaller than the value that holds at the microscale.
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effect of small harmonic oscillations during the steady rolling of a cylinder on a plane
International Journal of Mechanical Sciences, 2008Co-Authors: J R Barber, M Ciavarella, L Afferrante, A SackfieldAbstract:If a wheel rolling over a rail transmits a tangential traction, frictional Microslip occurs in part of the contact area, resulting in energy dissipation and localized wear. If the applied forces oscillate in time, the resulting wear will be non-uniform, resulting in ‘corrugations’ that can grow with progressive passes, depending on the dynamics of the overall system. In this paper, a linear perturbation method is used to obtain closed-form expressions for the receptance of a two-dimensional rolling contact subjected to small oscillations in normal force and rotational speed superposed on a mean value in the limit of large coefficient of friction. Corresponding expressions are also obtained for the amplitude and phase of the energy dissipation in the contact, which is expected to correlate with the local wear rate. The results are compared with a simpler Winkler model of the contact and with other models that have been used for the analysis of rail corrugation. Surprisingly good agreement is obtained with numerical results due to Gross-Thebing for the receptances due to oscillations in rotational speed.
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a review of analytical aspects of fretting fatigue with extension to damage parameters and application to dovetail joints
International Journal of Solids and Structures, 2001Co-Authors: M Ciavarella, G DemelioAbstract:Abstract Recent advances by the authors in analytical methods for the analysis of plane fretting fatigue (FF) contact problems are described, and new consequences for FF damage are derived. Constant normal load and oscillating tangential load (the celebrated Cattaneo–Mindlin case) are considered with in-phase oscillating moderate bulk stresses, for an arbitrary spline rotated geometry and, in particular, the flat punch with rounded corners in view of application to the dovetail joints. Extremely simple, new results are found for initiation parameters such as tangential Microslip and frictional energy, which have been used under certain conditions as threshold parameters for FF. Finally, it is shown that for an “almost flat” geometry, the surface damage parameters decrease, but the tensile stress concentration increases, although it becomes more localized, suggesting that for cracks eventually initiated, the likelihood of self-arrest is higher than in the equivalent Hertzian case with same loads. This seems to interpret recent experiments, although it is not clear whether the optimal geometry in terms of FF life is the perfectly flat one, or an intermediate one.
Y Zhou - One of the best experts on this subject based on the ideXlab platform.
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Footprint Study of Ultrasonic Wedge-Bonding with Aluminum Wire on Copper Substrate
2015Co-Authors: I Lum, Michael Mayer, Y ZhouAbstract:The effects of the process parameters of ultrasonic power and normal bonding force on bond formation at ambient temperatures have been investigated with scanning electron microscopy (SEM) and energy-dispersive x-ray (EDX) anal-ysis. A model was developed based on classical Microslip theory1 to explain the general phenomena observed in the evolution of bond footprints left on the substrate. Modifications to the model are made due to the inherent differences in geometry between ball-bonding and wedge-bonding. Classical Microslip theory describes circular contacts undergoing elastic deformation. It is shown in this work that a similar Microslip phenomenon occurs for elliptical wire-to-flat contacts with plastically deformed wire. It is shown that relative motion exists at the bonding interface as peripheral Microslip at lower powers, tran-sitioning into gross sliding at higher powers. With increased normal bonding forces, the transition point into gross sliding occurs at higher ultrasonic bond-ing powers. These results indicate that the bonding mechanisms in aluminum wire wedge-bonding are very similar to those of gold ball-bonding, both on copper substrate. In ultrasonic wedge-bonding onto copper substrates, the ultra-sonic energy is essential in forming bonding by creating relative interfacial motion, which removes the surface oxides. Key words: Wire-bonding mechanism, copper substrates, aluminum wire, ultrasonic power, friction, wea
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Bonding mechanism in ultrasonic gold ball bonds on copper substrate. Metall Mater Trans A 2005;A36:1279
2015Co-Authors: I Lum, Jae Pil Jung, Y ZhouAbstract:The effects of process parameters on bond formation in thermosonic gold ball bonding on a copper substrate at ambient temperatures have been investigated with scanning electron microscopy (SEM). A model was developed based on classical Microslip theory to explain the general phenomena observed in the evolution of bond footprints left on the substrate. The specific effects of ultrasonic energy and complex stress distributions arising from tool geometry must be taken into consideration and were incorporated into the model. It was shown that relative motion existed at the bonding interface as Microslip at lower powers, transitioning into gross sliding at higher powers. With increased normal bonding forces, the transition point into gross sliding occurred at higher ultrasonic bonding powers. I
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footprint study of ultrasonic wedge bonding with aluminum wire on copper substrate
Journal of Electronic Materials, 2006Co-Authors: Michael Mayer, Y ZhouAbstract:The effects of the process parameters of ultrasonic power and normal bonding force on bond formation at ambient temperatures have been investigated with scanning electron microscopy (SEM) and energy-dispersive x-ray (EDX) analysis. A model was developed based on classical Microslip theory1 to explain the general phenomena observed in the evolution of bond footprints left on the substrate. Modifications to the model are made due to the inherent differences in geometry between ball-bonding and wedge-bonding. Classical Microslip theory describes circular contacts undergoing elastic deformation. It is shown in this work that a similar Microslip phenomenon occurs for elliptical wire-to-flat contacts with plastically deformed wire. It is shown that relative motion exists at the bonding interface as peripheral Microslip at lower powers, transitioning into gross sliding at higher powers. With increased normal bonding forces, the transition point into gross sliding occurs at higher ultrasonic bonding powers. These results indicate that the bonding mechanisms in aluminum wire wedge-bonding are very similar to those of gold ball-bonding, both on copper substrate. In ultrasonic wedge-bonding onto copper substrates, the ultrasonic energy is essential in forming bonding by creating relative interfacial motion, which removes the surface oxides.
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bonding mechanism in ultrasonic gold ball bonds on copper substrate
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2005Co-Authors: I Lum, Jae Pil Jung, Y ZhouAbstract:The effects of process parameters on bond formation in thermosonic gold ball bonding on a copper substrate at ambient temperatures have been investigated with scanning electron microscopy (SEM). A model was developed based on classical Microslip theory to explain the general phenomena observed in the evolution of bond footprints left on the substrate. The specific effects of ultrasonic energy and complex stress distributions arising from tool geometry must be taken into consideration and were incorporated into the model. It was shown that relative motion existed at the bonding interface as Microslip at lower powers, transitioning into gross sliding at higher powers. With increased normal bonding forces, the transition point into gross sliding occurred at higher ultrasonic bonding powers.
Patrick Ragot - One of the best experts on this subject based on the ideXlab platform.
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Slip-shakedown analysis of a system of circular beams in frictional contact
International Journal of Solids and Structures, 2008Co-Authors: N. Antoni, Quoc Son Nguyen, Patrick RagotAbstract:In automotive components, the cumulative Microslip phenomenon is often observed for engine assemblies. This phenomenon results in an accumulation of the relative slips in a preferred tangential direction on the contact interface of two solids under cyclic loadings. A significant relative displacement may occur and leads to the assembly failure. In particular, a global rotation of the bearing shell may result from this mechanism of cumulated slips in conrod big end systems. To discuss this rotation problem, a model of two circular beams in frictional contact and submitted to a periodical rotating load is considered here. The aim is to give some simplified estimates of the critical rotation load based on a slip-shakedown analysis. The discussion holds for Tresca friction and can be extended to Coulomb friction under the assumption of small coupling. The static and kinematic slip-shakedown approaches are discussed. The obtained analytical results are shown to be in agreement with the finite element computations.
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Slip-shakedown analysis of a system of circular beams in frictional contact
Int. J. Solids & Structures, 2008Co-Authors: Nicolas Antoni, Quoc Son Nguyen, Patrick RagotAbstract:In automotive components, the cumulative Microslip phenomenon is often observed for engine assemblies. This phenomenon results in an accumulation of the relative slips in a preferred tangential direction on the contact interface of two solids under cyclic loadings. A significant relative displacement may occur and leads to the assembly failure. In particular, a global rotation of the bearing shell may result from this mechanism of cumulated slips in conrod systems. To discuss this rotation problem, a model of two circular beams in frictional contact and submitted to a periodical rotating load is considered here. The aim is to give some simplified estimates of the critical rotation load based on a slip-shakedown analysis. The discussion holds for Tresca friction and can be extended to Coulomb friction under the assumption of small coupling. The static and kinematic slip-shakedown approaches are discussed. The obtained analytical results are shown to be in agreement with the finite element computations.
Joss Blandhawthorn - One of the best experts on this subject based on the ideXlab platform.
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microslit nod shuffle spectroscopy a technique for achieving very high densities of spectra
Publications of the Astronomical Society of the Pacific, 2001Co-Authors: Karl Glazebrook, Joss BlandhawthornAbstract:We describe a new approach to obtaining very high surface densities of optical spectra in astronomical observations with extremely accurate subtraction of night sky emission. The observing technique requires that the telescope is nodded rapidly between targets and adjacent sky positions; object and sky spectra are recorded on adjacent regions of a low-noise CCD through charge shuffling. This permits the use of extremely high densities of small slit apertures ("microslits") since an extended slit is not required for sky interpolation. The overall multiobject advantage of this technique is as large as 2.9 times that of conventional multislit observing for an instrument configuration which has an underfilled CCD detector and is always greater than 1.5 for high target densities. The "nod-shuffle" technique has been practically implemented at the Anglo-Australian Telescope as the "LDSS++ project" and achieves sky subtraction accuracies as good as 0.04%, with even better performance possible. This is a factor of 10 better than is routinely achieved with long slits. LDSS++ has been used in various observational modes, which we describe, and for a wide variety of astronomical projects. The nod-shuffle approach should be of great benefit to most spectroscopic (e.g., long slit, fiber, integral field) methods and would allow much deeper spectroscopy on very large telescopes (10 m or greater) than is currently possible. Finally, we discuss the prospects of using nod-shuffle to pursue extremely long spectroscopic exposures (many days) and of mimicking nod-shuffle observations with infrared arrays.
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microslit nod shuffle spectroscopy a technique for achieving very high densities of spectra
arXiv: Astrophysics, 2000Co-Authors: Karl Glazebrook, Joss BlandhawthornAbstract:We describe a new approach to obtaining very high surface densities of optical spectra in astronomical observations with extremely accurate subtraction of night sky emission. The observing technique requires that the telescope is nodded rapidly between targets and adjacent sky positions; object and sky spectra are recorded on adjacent regions of a low-noise CCD through charge shuffling. This permits the use of extremely high densities of small slit apertures (`microslits') since an extended slit is not required for sky interpolation. The overall multi-object advantage of this technique is as large as 2.9x that of conventional multi-slit observing for an instrument configuration which has an underfilled CCD detector and is always >1.5 for high target densities. The `nod-shuffle' technique has been practically implemented at the Anglo-Australian Telescope as the `LDSS++ project' and achieves sky-subtraction accuracies as good as 0.04%, with even better performance possible. This is a factor of ten better than is routinely achieved with long-slits. LDSS++ has been used in various observational modes, which we describe, and for a wide variety of astronomical projects. The nod-shuffle approach should be of great benefit to most spectroscopic (e.g. long-slit, fiber, integral field) methods and would allow much deeper spectroscopy on very large telescopes (10m or greater) than is currently possible. Finally we discuss the prospects of using nod-shuffle to pursue extremely long spectroscopic exposures (many days) and of mimicking nod-shuffle observations with infrared arrays.