Golam Newaz

Piston Ring-Cylinder Bore Friction Modeling in Mixed Lubrication Regime: Part I—Analytical Results

An axi-symmetric, hydrodynamic, mixed lubrication model has been developed using the averaged Reynolds equation and asperity contact approach in order to simulate frictional performance of piston ring and cylinder liner contact. The friction force between piston ring and cylinder bore is predicted considering rupture location, surface flow factors, surface roughness and metal-to-metal contact loading. A fully flooded inlet boundary condition and Reynolds boundary conditions for cavitation outlet zone are assumed. Reynolds boundary conditions have been modified for non-cavitation zones. The pressure distribution along the ring thickness and the lubricant film thickness are determined for each crank angle degree. Predicted friction force is presented for the first compression ring of a typical diesel engine as a function of crank angle position.

Acoustic chaos for enhanced detectability of cracks by sonic infrared imaging

The technique of sonic infrared imaging (SIR) consists of the excitation of an object with a short pulse of 15 to 40 kHz sound, in combination with IR imaging of the object’s surface temperature as a function of time. Sonic infrared imaging is effective for detecting surface and subsurface cracks. The recent discovery of acoustic chaos has provided a means of greatly enhancing the effectiveness of SIR. We describe the properties of chaotic sound in the context of SIR crack detection, and show examples of the enhancement of the detectability of cracks through the use of chaotic sound.

Low cycle fatigue life estimation for ductile metals using a nonlinear continuum damage mechanics model

Abstract Continuum damage mechanics is an effective approach to model ductile failure. The same concepts can be extended to the low cycle fatigue damage process, where plasticity is still the key mechanism for crack initiation. In addition, in low cycle fatigue a relevant part of life is spent by the material to initiate a macroscopic crack that leads to complete failure. In this paper, the nonlinear damage model, initially proposed by Bonora, N. (1997) A non-linear CDM model for ductile fracture Engineering Fracture Mechanics (in press), is extended to the case of cyclic loading. Three possible formulations are proposed and discussed that take into account in different ways the accumulation of damage, plastic strain and the material cyclic properties change. Fully coupled life model was used to predict low cycle fatigue life in AI 2024 T3 alloy and HY80 low carbon steel. Comparison with a large fatigue experimental data set is also presented.

A comprehensive review of surface modification for neural cell adhesion and patterning

This comprehensive literature review covers recent studies on patterning neuronal cells by topographical modifications on material surfaces targeted for neural prostheses. We explore different materials that are used as the candidate surface for neuronal cell adhesion. Cell-material interactions are identified in both cases where the material surface was in direct contact with cells and where the materials were coated to facilitate cell adhesion. Commonly used coating materials and coating methods are discussed. The existing hypotheses behind mechanism of the response of neuronal cells to a specific topography are presented briefly. A few selected important studies have been presented to show the range of techniques employed and the extent of the research area.

Mechanics of damage initiation and growth in a TBC/superalloy system

Creep analysis was used to estimate stresses in different layers especially in bond coat and the thermally grown oxide (TGO) layer to determine the role of creep on damage initiation in the TBC system. Microcracks were observed to initiate near the bond coat/TGO interface after only a few thermal cycles. The origin of these microcracks can be attributed to the buildup of thermal stresses that may magnify due to asperity of the TGO layer and the bond coat. The TGO/bond coat interface was modeled as a rough periodic surface. Finite element calculations were conducted to determine the magnitude of stresses at the bond coat/oxide interface (modeled as a sine wave). It was found that large normal interface stresses arise at the peaks, while large shear stresses arise at the mean line of the rough interface. These residual stresses can exceed the interfacial tensile or shear strength of TGO. Effect of oxide layer growth between bond coat and Thermal barrier coating (TBC) was modeled as volume increase and subsequently as an induced pressure across the interface inside the crack. Mixed-mode fracture analysis of a thin circular delamination in an axisymmetric multi-layer circular plate was developed to assess growth.

Controllable excimer-laser fabrication of conical nano-tips on silicon thin films

We have found conditions for the reproducible, direct laser fabrication of sharp conical tips with heights of about 1 μm and apical radii of curvature of several tens of nanometers. An individual cone is formed when single-crystalline silicon on a silica substrate is irradiated with a single pulse from a KrF excimer laser, homogenized and shaped to a circular spot several microns in diameter. Atomic force microscopy and field-emission scanning electron microscopy were used to characterize these structures. A simple mechanism of formation based on movement of melted material is proposed. Our results suggest that this technique could produce even smaller structures by optimizing the laser processing geometry.

Piston Ring-Cylinder Bore Friction Modeling in Mixed Lubrication Regime: Part II—Correlation With Bench Test Data

A bench friction test system for piston ring and liner contact, which has high stroke length and large contact width has been used to verify the analytical mixed lubrication model presented in a companion paper (Part 1). This test system controls the speed, temperature and lubricant amount and records the friction force, loading force, crank angle signal and contact temperature data simultaneously. The effects of running speed, applied normal load, contact temperature and surface roughness on friction coefficient have been investigated for conventional cast-iron cylinder bores. Friction coefficient predictions are presented as a function of crank angle position and results are compared with bench test data. Analytical results correlated well with bench test results.

Nanopatterning effects on astrocyte reactivity.

An array of design strategies have been targeted toward minimizing failure of implanted microelectrodes by minimizing the chronic glial scar around the microelectrode under chronic conditions. Current approaches toward inhibiting the initiation of glial scarring range from altering the geometry, roughness, size, shape, and materials of the device. Studies have shown materials which mimic the nanotopography of the natural environment in vivo will consequently result in an improved biocompatible response. Nanofabrication of electrode arrays is being pursued in the field of neuronal electrophysiology to increase sampling capabilities. Literature shows a gap in research of nanotopography influence in the reduction of astrogliosis. The aim of this study was to determine optimal feature sizes for neural electrode fabrication, which was defined as eliciting a nonreactive astrocytic response. Nanopatterned surfaces were fabricated with nanoimprint lithography on poly(methyl methacrylate) surfaces. The rate of protein adsorption, quantity of protein adsorption, cell alignment, morphology, adhesion, proliferation, viability, and gene expression was compared between nanopatterned surfaces of different dimensions and non-nanopatterned control surfaces. Results of this study revealed that 3600 nanopatterned surfaces elicited less of a response when compared with the other patterned and non-nanopatterned surfaces. The surface instigated cell alignment along the nanopattern, less protein adsorption, less cell adhesion, proliferation and viability, inhibition of glial fibrillary acidic protein, and mitogen-activated protein kinase kinase 1 compared with all other substrates tested.

Study of the effect of crack closure in Sonic Infrared Imaging

Sonic infrared (SIR) imaging is a novel hybrid technology that employs ultrasonic excitation and infrared imaging to detect defects in materials. There are several parameters can affect the detectability of a defect in Sonic IR. One is the closure status of a defect, say a crack in a material. We have studied the relationship between the heating in a crack and crack closure. The crack closure was realized by applying a variety of clamping forces on the crack. In this paper, we provide quantitative results of the study on infrared signal levels at different status of crack closure. The temperature profile of a fixed point at the crack during the excitation period was presented. The thermal energy transformed from the kinetic movement was analysed over a fixed region for all clamping cases. Meanwhile, the crack energy at two fixed points crossing the crack was also studied.

Finite element modeling of the heating of cracks during sonic infrared imaging

We describe a finite element model that calculates the energy dissipation to be expected in a crack during sonic infrared (SIR) imaging. These calculations confirm the experimental result that the presence of acoustic chaos enhances the heating and thereby enhances the probability of crack detection using SIR. Although thermoplastic contributions are allowed in the calculation, under the assumed conditions of sonic excitation, which mimic those of typical SIR experiments, the heating appears to be dominated by frictional effects.