Periodically Forced Nonlinear Oscillators With Hysteretic Damping

We perform a detailed study of the dynamics of a nonlinear, one-dimensional oscillator driven by a periodic force under hysteretic damping, whose linear version was originally proposed and analyzed by Bishop in [1]. We first add a small quadratic stiffness term in the constitutive equation and construct the periodic solution of the problem by a systematic perturbation method, neglecting transient terms as $t\rightarrow \infty$. We then repeat the analysis replacing the quadratic by a cubic term, which does not allow the solutions to escape to infinity. In both cases, we examine the dependence of the amplitude of the periodic solution on the different parameters of the model and discuss the differences with the linear model. We point out certain undesirable features of the solutions, which have also been alluded to in the literature for the linear Bishop's model, but persist in the nonlinear case as well. Finally, we discuss an alternative hysteretic damping oscillator model first proposed by Reid [2], which appears to be free from these difficulties and exhibits remarkably rich dynamical properties when extended in the nonlinear regime.Comment: Accepted for publication in the Journal of Computational and Nonlinear Dynamic

Manufacturing of ultra-fine particle coal fly ash–A380 aluminum matrix composites with improved mechanical properties by improved ring milling and oscillating microgrid mixing

An experimental study is presented of ultra-fine coal fly ash (CFA) aluminum matrix composites produced by successive high-power ring milling of CFA, oscillating microgrid mixing of the CFA–aluminum melt, gravity casting and rapid cooling. Samples corresponding to different CFA concentrations and particle size distributions (1 μm average, or less) are produced and subjected to microstructural and mechanical characterization, including tensile, compressive, impact, hardness and wear testing. While the usual trade-off between increased strength and hardness and reduced ductility and toughness is observed, the obtained ultra-fine particle composites are confirmed to have overall improved mechanical properties compared to composites with larger size particles previously produced by ball milling

FABRICATION OF HIGHLY COMPACTED GREEN BODY USING MULTI-SIZED AL POWDER UNDER A CENTRIFUGAL FORCE

This study investigates the application of centrifugal force for the compaction of metal powder. Previous studies using the centrifugal force for manufacturing the green bodies were focused on fine powders with narrow particle size distribution or binary mixtures. This study explores the particle packing of multi-sized powder. Aluminum alloy powder with a particle size less than 100 μm and polymer binder were admixed and compacted in the centrifugal casting with ranging magnitudes of centripetal acceleration. Three different centrifugal forces were tested: 700, 1800, and 3700 G. The microstructure of the green bodies was then observed on the SEM micrographs. The obtained green bodies had high packing densities ranging from 62 to 69%. The packing density and median particle size increase at the positions further away from the center of rotation of the centrifuge with an increase of centrifugal force. The effect of centrifugal force on the segregation of particles was investigated through the quasi-binary segregation index. The segregation phenomena was not observed at 700 G, but clear particle segregation was found at higher centrifugal forces. The increase of the centrifugal force resulted in higher segregation with finer particles moving to the inner part of the spinning mold, with a significant change in the size of particles located closer to the center of rotation. Overall, the centrifugal process was found to produce highly compacted green bodies while yielding a segregation effect due to wide particle size distribution

HEAT TRANSFER THROUGH HYDROGENATED GRAPHENE SUPERLATTICE NANORIBBONS: A COMPUTATIONAL STUDY

Optimization of thermal conductivity of nanomaterials enables the fabrication of tailor-made nanodevices for thermoelectric applications. Superlattice nanostructures are correspondingly introduced to minimize the thermal conductivity of nanomaterials. Herein we computationally estimate the effect of total length and superlattice period ( lp ) on the thermal conductivity of graphene/ graphane superlattice nanoribbons using molecular dynamics simulation. The intrinsic thermal conductivity ( ) is demonstrated to be dependent on lp . The of the superlattice, nanoribbons decreased by approximately 96% and 88% compared to that of pristine graphene and graphane, respectively. By modifying the overall length of the developed structure, we identified the ballisticdiffusive transition regime at 120 nm. Further study of the superlattice periods yielded a minimal thermal conductivity value of 144 W m− 1 k− 1 at lp = 3.4 nm. This superlattice characteristic is connected to the phonon coherent length, specifically, the length of the turning point at which the wave-like behavior of phonons starts to dominate the particle-like behavior. Our results highlight a roadmap for thermal conductivity value control via appropriate adjustments of the superlattice period

A Gaussian decision-support tool for engineering design process

Decision-making in design is of great importance, resulting in success or failure of a system (Liu et al., 2010; Roozenburg and Eekels, 1995; Spitas, 2011a). This paper describes a robust decision-support tool for engineering design process, which can be used throughout the design process in either the concept or knowledge space described in Hatchuel and Weil (2009). The tool is graphical and designed to communicate efficiently with different fields of expertise. It takes into account the Gaussian form of expert lack of certainty and generates the concept or model uncertainty which is necessary for a robust design. Recently, this tool was successfully used by an interdisciplinary design team consisting of different experience level and diverse design knowledge as described in this paper

Parametric Quasi-Static Study of the Effect of Misalignments on the Path of Contact, Transmission Error, and Contact Pressure of Crowned Spur and Helical Gear Teeth Using a Novel Rapidly Convergent Method

Quasi-static modelling of non-conjugate contact of tooth-modified spur and helical gears has been studied at length, but existing models are hindered by convergence problems and require a brute-force numerical approach. Here, a novel, computationally efficient, and stable and unconditionally convergent model is developed for non-conjugate tooth contact in three dimensions and applied to crowned spur and helical gears to assess parametrically the sensitivity of various in- and out-of-plane misalignments on the path of contact, transmission error, and contact pressure. Performance metrics are defined, and comparisons are made between three different crowning modification functions