Short‐beam three‐point bend test study in syntactic foam. Part III: Effects of interface modification on strength and fractographic features

Syntactic foam slabs having uncoated microballoons and paraffin oil surface‐treated microballoons were fabricated and tested for short‐beam three‐point bend test. The work points to the role of paraffin oil coating first weakening the interface between the microballoons and the matrix and hence lowering the efficiency of load transfer from matrix to the fillers (i.e., microballoons). This led to an overall decrement of 71% in the experimentally measured strength value compared to the deduced value for uncoated microballoons' specimens. The large strengths for uncoated microballoons specimens can be traced to the presence of the curvilinear marks in the matrix that, incidentally, are absent in the case of paraffin oil coated specimens. These observations are revealed distinctly in the microscopy of test‐failed specimens. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 687–693, 2005     

Oviposition Preference and Performance of a Specialist Herbivore Is Modulated by Natural Enemies,Larval Odors,and Immune Status

Journal of Chemical Ecology - Insect herbivores frequently must balance host plant quality and the risk of attack by their natural enemies when making oviposition decisions. Yet, which factor is...     

An index to characterize gas-solid and solid-solid mixing from average volume fraction fields

A mixing index based on solid volume fraction fields is developed for gas-solid flows. Conventional mixing indices are based on particle realizations of granular mixing and are applicable to experimental data or discrete element method simulations. However, these indices cannot be used as-is for multifluid models, and an index for characterizing mixing in gas-solid flows from continuous fields is needed. The performance of the new mixing index is tested in two applications. The first is a 3D simulation of the mixing of biomass and sand in a fluidized bed reactor, and the second is a 2D simulation of binary particle segregation in a fluidized bed. The simulations are performed using OpenFOAM®. The mixing index is used to quantify gas-solid mixing using solid volume fractions and solid-solid mixing using solid fractions. The formulation of conventional mixing indices is extended to be used with solid volume fractions fields, and methods for performance improvement are presented.     

Microchemical and microstructural studies in a PTA weld overlay of Ni-Cr-Si-B alloy on AISI 304L stainless steel

Ni-Cr-Si-B alloy coatings deposited on AISI 304L stainless steel substrate using plasma transferred arc welding process were studied with respect to the microchemical and microstructural modifications that take place during the process. The coating was characterized for (1) interface integrity and dilution (2) type, morphology and distribution of secondary phases in the coating (3) elemental redistribution between substrate and coating and (4) different phases that form during the deposition process. Formation of a transition zone of only 760 μm width was understood in terms of interdiffusion of Fe and Ni across the interface. Preferential redistribution of carbon to the surface of the coating was observed. It was explained on the basis of difference in thermodynamic activity. Apart from γ-Ni solid solution, the other primary phases identified in Ni-Cr-Si-B alloy were Cr₂B, Cr₇C₃ and Cr₃C₂. The observed changes in microstructure, microchemistry and hardness have been understood based on the phase transitions of the Ni rich alloy during solidification and cooling on the substrate.     

Gas-Sensing Properties of Zinc Ferrite Nanoparticles Synthesized by the Molten-Salt Route

Zinc ferrite (ZnFe₂O₄) nanoparticles have been synthesized at 700°C using sodium chloride as a growth inhibitor. Single-phase formation of spinel zinc ferrite having crystallite size in the range of 15–20 nm was observed by XRD and confirmed by TEM. In the present work, the gas-sensing properties of these zinc ferrite nanoparticles toward ethanol, LPG, H₂, NO _x . SO _x , and H₂S have been studied. It was found that they exhibit excellent selective sensitivity toward 200 ppm of H₂S at the operating temperature of 250°C, and thus this nanosized ferrite is expected to be useful in an industrial application as a potential H₂S gas sensor.     

Machining Performance and Surface Integrity of AISI D2 Die Steel Machined Using Electrical Discharge Surface Grinding Process

The aim of this study is to establish optimum machining conditions for EDSG of AISI D2 die steel through an experimental investigation using Taguchi Methodology. To achieve combined grinding and electrical discharge machining, metal matrix composite electrodes (Cu-SiC_p) were processed through powder metallurgy route. A rotary spindle attachment was developed to perform the EDSG experimental runs on EDM machine. Relationships were developed between various input parameters such as peak current, speed, pulse-on time, pulse-off time, abrasive particle size, and abrasive particle concentration, and output characteristics such as material removal rate and surface roughness. The optimized parameters were further validated by conducting confirmation experiments.     

Mechanism and preventive measures for die soldering during Al casting in a ferrous mold

This work provides a comprehensive understanding of the reactions at the ferrous die/molten metal interface in a metal mold casting operation. The literature has shown that several important factors influence reactions at the ferrous die/molten aluminum interface, including temperature of the melt, temperature of the die, alloy chemistry of the melt and die, die surface engineering, topographical features, and coatings. This article discusses the effect of the more critical factors on soldering, based on the authors’ investigations. Inaddition, based on a mechanistic understanding of the interface reactions between ferrous die and molten aluminum, recommendations are given for specific processing issues to alleviate soldering during die casting of aluminum alloys.     

Non-uniform Euler-Bernoulli beams under a single moving oscillator: An approximate analytical solution in time domain

Dynamic responses of simply supported non-uniform beams traversed by a moving oscillator are analysed in this paper. An approximate analytical method based on Rayleigh-Ritz (R-R) formulation is developed. The fundamental approximate mode obtained from R-R method is used in the present formulation to determine the responses of the beam and the oscillator. Effects of surface irregularities on the displacement and acceleration responses of the beam and the vehicle are also analysed. The results are compared with those obtained using Finite element method (FEM). A numerical example is provided to illustrate the validity of the present method which shows that the proposed method is simple, computationally more efficient compared to FEM and gives fairly good results. Though the single-mode approach used in the present paper is a classical one and numerous studies on the responses of uniform beams under moving loads have been reported in the past, its application to non-uniform beams (for which there does not exist any closed form expression for mode shapes) under a moving load, especially a moving oscillator, is presented for the first time.     

Technical review: Improvement of mechanical properties and suitability towards armor applications – Alumina composites

Ceramic Matrix Composites (CMCs) have many interesting properties, mainly light weight, cost efficiency, low density, high compressive strength, high hardness and durability. Hence, they emerged as a boon to the development of personnel armors in the past. The current work aims to review various new methodologies adapted for the reinforcement of Alumina (Al₂O₃) CMCs in recent times, including some of the interesting results obtained with respect to mechanical properties, suitability of the synthesized composites for armor applications, and the upcoming reinforcement trends. Finally, studies related to reinforcement in Al₂O₃ CMCs, specifically towards armor applications have been consolidated to arrive at some of the important inferences for concluding reasonably.     

Solar hydrogen generation from organic substance using earth abundant CuS–NiO heterojunction semiconductor photocatalyst

This work explores the critical role of NiO co-catalyst assembled on the surface of a CuS primary photocatalyst which effectively improves interface properties and enhances solar-to-hydrogen production by prolonging lifetime of photo-excitons generated at the CuS surface. The nanoscale CuS/NiO heterojunction is formulated using hydrothermal and wet impregnation methods. The resultant CuS/NiO composite shows optical absorbance between 380 and 780 nm region. The type-II energetic structure formed at CuS/NiO heterojunction facilitates rapid charge separation and as a result, the CuS/NiO composite exhibits 13 folds higher photocatalytic water splitting performance than CuO and NiO. The champion CuO/NiO photocatalyst is first identified by screening the catalysts using a preliminary water splitting test reaction under natural Sunlight irradiation. After the optimization of the catalyst, it was further explored for enhanced photocatalytic hydrogen production using different organic substances dispersed in water (alcohols, amine and organic acids). The champion CuS/NiO catalyst (CPN-2) exhibited the photocatalytic hydrogen production rate of 52.3 mmol h^?1.g^?1_cat in the presence of lactic acid-based aqueous electrolyte and, it is superior than hydrogen production rate obtained in the presence of other organic substances (triethanolamine, glycerol, ethylene glycol, methanol) tested under identical experimental conditions. These results indicate that the energetic structure of CuS/NiO photocatalyst is favorable for photocatalytic oxidation or reforming of lactic acid. The oxidation of lactic acid contributes both protons and electrons for enhanced hydrogen generation as well as protects CuS from photocorrosion. The modification of surface property and energetic structure of CuS photocatalyst by the NiO co-catalyst improves photogenerated charge carrier separation and in turn enhances the solar-to-hydrogen generation efficiency. The recyclability tests showed the potential of CPN-2 photocatalyst for prolonged photocatalytic hydrogen production while continuous supply of lactic acid feedstock is available.