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M. A. Hamilton

Bio: M. A. Hamilton is an academic researcher from University of Florida. The author has contributed to research in topics: Dry lubricant & Tribometer. The author has an hindex of 7, co-authored 9 publications receiving 276 citations.

Papers
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Journal ArticleDOI
05 Oct 2012-Science
TL;DR: It is shown that hadrosaurids broke from the primitive reptilian archetype and evolved a six-tissue dental composition that is among the most sophisticated known, three-dimensional wear models incorporating fossilized wear properties reveal how these tissues interacted for grinding and ecological specialization.
Abstract: Mammalian grinding dentitions are composed of four major tissues that wear differentially, creating coarse surfaces for pulverizing tough plants and liberating nutrients. Although such dentition evolved repeatedly in mammals (such as horses, bison, and elephants), a similar innovation occurred much earlier (~85 million years ago) within the duck-billed dinosaur group Hadrosauridae, fueling their 35-million-year occupation of Laurasian megaherbivorous niches. How this complexity was achieved is unknown, as reptilian teeth are generally two-tissue structures presumably lacking biomechanical attributes for grinding. Here we show that hadrosaurids broke from the primitive reptilian archetype and evolved a six-tissue dental composition that is among the most sophisticated known. Three-dimensional wear models incorporating fossilized wear properties reveal how these tissues interacted for grinding and ecological specialization.

95 citations

Journal ArticleDOI
TL;DR: In this article, a series of experiments on thin coatings of molybdenum disulfide were conducted to explore the nature of friction, and in particular thermally activated friction in macroscopic tribology.
Abstract: Studies to explore the nature of friction, and in particular thermally activated friction in macroscopic tribology, have lead to a series of experiments on thin coatings of molybdenum disulfide. Coatings of predominately molybdenum disulfide were selected for these experiments; five different coatings were used: MoS2/Ni, MoS2/Ti, MoS2/Sb2O3, MoS2/C/Sb2O3, and MoS2/Au/Sb2O3. The temperatures were varied over a range from −80 °C to 180 °C. The friction coefficients tended to increase with decreasing temperature. Activation energies were estimated to be between 2 and 10 kJ/mol from data fitting with an Arrhenius function. Subsequent room temperature wear rate measurements of these films under dry nitrogen conditions at ambient temperature demonstrated that the steady-state wear behavior of these coatings varied dramatically over a range of K = 7 × 10−6 to 2 × 10−8 mm3/(Nm). It was further shown that an inverse relationship between wear rate and the sensitivity of friction coefficient with temperature exists. The highest wear-rate coatings showed nearly athermal friction behavior, while the most wear resistant coatings showed thermally activated behavior. Finally, it is hypothesized that thermally activated behavior in macroscopic tribology is reserved for systems with stable interfaces and ultra-low wear, and athermal behavior is characteristic to systems experiencing gross wear.

60 citations

Journal ArticleDOI
TL;DR: In this article, a dynamic contact model was used to calculate contact pressures and slip velocities on individual surface elements from this kinematic data, and the most significant degree of crossing motion intensity was observed in the lateral compartments for both gait and stair-rise activities.
Abstract: This manuscript describes a formulaic method to predict the severity of crossing motions experienced by ultra-high-molecular-weight polyethylene (UHMWPE) under sliding conditions across a bearing surface. A statistical model for evaluating the distribution of sliding about this orientation is described. This model compares favorably to published experimental data on UHMWPE under multidirectional pin-on-disk testing. These algorithms are applied to the tibial component of a total knee replacement using patient-specific kinematics for gait and stair-rise activities collected using fluoroscopy. A dynamic contact model is used to calculate contact pressures and slip velocities on individual surface elements from this kinematic data. The most significant degree of crossing motion intensity was observed in the lateral compartments for both gait and stair-rise activities. This coincided with the location of maximum tribological intensity. The maximum crossing motions are characteristic of 4 and 9 deg of bidirectional crossing motion for gait and stair, respectively.

60 citations

Journal ArticleDOI
10 May 2007-Wear
TL;DR: In this paper, a survey of filled polyetheretherketone composites was conducted and a wide variety of available nanoparticles and microparticles were used during this exploratory activity.

45 citations

Journal ArticleDOI
TL;DR: In this article, a nearly ideal two-dimensional scotch yoke mechanism was constructed to test a model of wear depth as a function cycle number, and experiments show a linear progression of wear over two distinct regions, suggesting a sudden transition in wear modes just after 1.5 million cycles.
Abstract: A nearly ideal two-dimensional scotch yoke mechanism was constructed to test a model of wear depth as a function cycle number. Model variables include the reciprocating mass, a two dimensional wear-rate, crank radius, and angular velocity. The model originally developed by T. A. Blanchet (1997), was nondimensionalized and simplified under conditions of large numbers of cycles, to predict the importance of including coupling based solely on a ratio of maximum allowable wear depth to the crank radius. Experiments show a linear progression of wear over two distinct regions, suggesting a sudden transition in wear modes just after 1.5 million cycles. The need for cycle or time dependent wear rates in analysis, which is a potentially far more significant source of error, is clearly illustrated by the experiment and discussed.

18 citations


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Journal ArticleDOI
TL;DR: In this article, the authors present a focused review of solid lubrication with molybdenum disulfide by highlighting its structure, synthesis, applications and the fundamental mechanisms underlying its lubricative properties, together with a discussion of their environmental and temperature dependence.
Abstract: Molybdenum disulfide (MoS2) is one of the most broadly utilized solid lubricants with a wide range of applications, including but not limited to those in the aerospace/space industry. Here we present a focused review of solid lubrication with MoS2 by highlighting its structure, synthesis, applications and the fundamental mechanisms underlying its lubricative properties, together with a discussion of their environmental and temperature dependence. The review also includes an extensive overview of the structure and tribological properties of doped MoS2, followed by a discussion of potential future research directions.

257 citations

Journal ArticleDOI
TL;DR: In this article, the effects of edge structures on the edge stability, and electronic and magnetic properties of MoS2 nanoribbons by first-principles calculations were studied. And the authors predicted that S-terminated zigzag nanors are the most stable even without hydrogen saturation because of their low and negative edge energies.
Abstract: Two-dimensional materials have various applications in next-generation nanodevices because of their easy fabrication and particular properties. In this work, we studied the effects of edge structures on the edge stability, and electronic and magnetic properties of MoS2 nanoribbons by first-principles calculations. We predicted that S-terminated zigzag nanoribbons are the most stable even without hydrogen saturation because of their low and negative edge energies, although hydrogen saturation of the edge states can stabilize other nanoribbons with different edge structures. MoS2 zigzag nanoribbons are metallic and ferromagnetic. Importantly, their conductivity may be semiconducting (n- or p-type) or half metallic by controlling the edge structures saturated with H atoms. The magnetic states of the MoS2 zigzag nanoribbons are enhanced by H-saturation and are much stronger than those of graphene zigzag nanoribbons. The armchair nanoribbons are semiconducting, with bandgaps increased by the hydrogen saturation of their edge states, and are nonmagnetic. These MoS2 nanoribbons with versatile functions may have applications in spintronics, nanodevices, and energy harvesting.

245 citations

Journal ArticleDOI
TL;DR: In this paper, the effects of strain on the electronic and magnetic properties of MoS2 nanoribbons were investigated and it was shown that they are stretchable up to a strain of 10%.
Abstract: First-principles calculations are carried out to study the effects of strain on the electronic and magnetic properties of MoS2 nanoribbons. We predict that MoS2 nanoribbons are stretchable up to a strain of 10%. The band structures of the nonmagnetic armchair MoS2 nanoribbons change from direct character to indirect with the increase of strain due to the shift of the energy states near the Fermi level. The ferromagnetic states of metallic zigzag MoS2 nanoribbons are greatly improved because the energy difference between the nonmagnetic and magnetic states is increased up to 4.9 times, and the magnetic moments are increased up to 2 times under a strain up to 10%. Our calculations show that the electronic and magnetic properties of MoS2 nanoribbons can be controlled by applying strain, indicating their potential applications to spintronics and photovoltaic cells.

217 citations

Journal ArticleDOI
TL;DR: In this article, a review of advances in the design and exploration of hard coatings with high temperature adaptive behavior in tribological contacts is reviewed, where advances with ab initio modeling of intrinsically layered solids point to new compositions for thermally stable, easy to shear ceramic coatings, load and temperature-adaptive surfaces with arrays of compliant carbon and boron nitride nanotubes as well as low friction two-dimensional structures.
Abstract: Progress in the design and exploration of hard coatings with high temperature adaptive behavior in tribological contacts is reviewed. When coupled with most recent surface engineering strategies for high temperature contact thermal management, this progress opens a huge opportunity for adaptive coating applications on machine parts, where oils and coolants are commonly used. The adaptive mechanisms discussed here include metal diffusion and formation of lubricant phases at worn surfaces, thermally- and mechanically-induced phase transitions in hexagonal solids, contact surface tribo-chemical evolutions to form phases with low melting point, formation of easy to shear solid oxides, and others. All of these adaptive mechanisms are combined in nanocomposite coatings with synergistic self-adaptation of surface structure and chemistry to lubricate from ambient temperatures to 1000 °C and provide surface chemical and structural reversibility during temperature cycling to maintain low friction coefficients. The review also highlights emerging surface adaptive concepts, where advances with ab initio modeling of intrinsically layered solids point to new compositions for thermally stable, easy to shear ceramic coatings, load- and temperature-adaptive surfaces with arrays of compliant carbon and boron nitride nanotubes as well as low friction two-dimensional structures. Approaches for self-regulation of coating thermal conductivity, heat flow, and thermal spike mitigations are discussed in the context of surface structure evolution and phase transitions. Future progress is linked to the development of in situ exploration techniques, capable of identifying adaptive surface chemistry and structural evolutions in broad temperature regimes. When combined with predictive modeling, such approaches drastically accelerate adaptive coating developments. The review identifies opportunities, strategies, and challenges for designs and applications of hard coatings with high temperature adaptive lubrication and contact thermal management.

185 citations