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641.
Inadequate control of weld metal composition due to vaporization of volatile alloying elements is a serious problem in the
welding of many important engineering alloys. Effectiveness of surface active elements such as oxygen or sulfur in blocking
vaporization sites on the weld pool surface was investigated. Several iron samples doped with oxygen or sulfur were exposed
to a carbon dioxide laser beam in pulsed mode. The time average metal vaporization rates and the emission spectra were compared
with those obtained from ultra pure iron samples. Since the weld pool surface area and temperature distribution are affected
by oxygen and sulfur, the true effects of these elements on metal vaporization rates cannot be easily evaluated from welding
data. Therefore, rates of isothermal vaporization of iron and copper drops doped with oxygen or sulfur were determined both
in the presence and the absence of low pressure argon plasma. These rates were compared with the rates of vaporization of
ultrapure metal drops. Presence of sulfur or oxygen in metals always resulted in increased metal vaporization rates. The results
are analyzed on the basis of interfacial phenomena. 相似文献
642.
Recently, commercial Zn-Al foundry alloys such as ZA-27 have found increasing use for many applications and have competed effectively against copper, aluminium and iron-based foundry alloys. However, the elevated temperature (> 100°C) properties of zinc-aluminium alloys are unsatisfactory and restrict their use in some applications. One viable approach to improving the elevated temperature properties is to reinforce the zinc-aluminium alloys with alumina fibres. In this investigation, the mechanical properties of a Zn-Al alloy reinforced with alumina fibres were evaluated. Tensile, compression and impact properties were determined at 25, 100 and 150°C. Lubricated wear tests were also performed on the unreinforced alloy and composites. It was found that although fibre reinforcement did result in some improvement of tensile and compression properties at elevated temperatures, the composites had poor toughness and ductility. The presence of a brittle SiO2 layer at the fibre/matrix interfaces resulted in fibre/matrix decohesion under tensile loading, impairing the performance of the reinforced materials. Some improvement in wear resistance was noted for the composite materials but fibre reinforcement did not yield significant improvement in fatigue resistance. 相似文献
643.
The paper describes a theoretical study of normal impact between solids with small-scale surface asperities. An elastic-plastic impact model is used to study the normal impact between rough surfaces in presence of surface forces. The well-established elastic and plastic adhesion indices are used to consider the different conditions arising out of varying impact velocity and material parameters. The study shows that the coefficient of restitution is affected by material-properties, surface-topography and impact velocity. Results clearly indicate that high impact velocity is desirable in order to achieve low coefficient of restitution. However, there are certain combinations of material properties and surface conditions, given by the choice of adhesion indices, where coefficient of restitution falls to a very low value. 相似文献
644.
S. K. Swain S. Sahoo D. K. Mohapatra B. K. Mishra S. Lenka P. L. Nayak 《应用聚合物科学杂志》1994,54(10):1413-1421
A number of resins were synthesized by reacting cardanol, a byproduct of the cashew industry, with furfural and substituted aromatic compounds in the presence of acid and basic catalysts. The resins were characterized by IR and NMR spectra and shown to be selective ion exchangers for certain metal ions. A batch equilibrium method was used for studying the selectivity of the metal ions. The thermal behavior of the resins was also studied. A plausible degradation mechanism is suggested. © 1994 John Wiley & Sons, Inc. 相似文献
645.
646.
The structure and mechanical properties of Sn-Zn unidirectionally frozen eutectic alloys have been examined over the growth range 5 to 4000mm h–1. The structure is predominantly broken-lamellar below 750mm h–1 but becomes increasingly fibrous at higher growth rates. The yield and ultimate strengths when tested in tension and compression were found to increase monotonically with growth rates up to 1000 mm h–1 above which they assumed near constant values. This behaviour is attributed to some loss of axial growth at higher growth rates. The hardness measured on transverse sections increased over the entire growth rate range. Annealing at near eutectic temperatures followed by quenching increased the strength of alloys grown at less than 750 mm h–1 and decreased that of those grown at higher rates. Similar behaviour was observed in selected Cd-Zn eutectic alloys. The increase in strength is attributed to solid solution hardening and the reduction to structural degradation during annealing. The Sn-rich matrix in this broken-lamellar eutectic appears to contribute significant strengthening to the composite. 相似文献
647.
Epoxy resins were prepared using various molar ratios of epichlorohydrin and bisphenol-A and then cured with four different hardeners: diaminodiphenyl methane (DADPM), dithioterephthalic acid (DTTPH), dimethylamino propylamine (DMAPA) and diethylene triamine (DT). The thermal behaviour of these epoxy resins was studied. From the energy of activation data it was observed that DADPM gives the highest thermal stability of all these curing agents. Dielectric constant measurements of uncured resins were made at 30°C and at a frequency of 2.5 × 103 Hz. The higher activation energies of the resins are related to the polarity of the hydroxyl moiety in the epoxy resins. 相似文献
648.
649.
In this paper, we address a real life waste collection vehicle routing problem with time windows (VRPTW) with consideration of multiple disposal trips and drivers’ lunch breaks. Solomon's well-known insertion algorithm is extended for the problem. While minimizing the number of vehicles and total traveling time is the major objective of vehicle routing problems in the literature, here we also consider the route compactness and workload balancing of a solution since they are very important aspects in practical applications. In order to improve the route compactness and workload balancing, a capacitated clustering-based waste collection VRPTW algorithm is developed. The proposed algorithms have been successfully implemented and deployed for the real life waste collection problems at Waste Management, Inc. A set of waste collection VRPTW benchmark problems is also presented in this paper.Waste collection problems are frequently considered as arc routing problems without time windows. However, that point of view can be applied only to residential waste collection problems. In the waste collection industry, there are three major areas: commercial waste collection, residential waste collection and roll-on-roll-off. In this paper, we mainly focus on the commercial waste collection problem. The problem can be characterized as a variant of VRPTW since commercial waste collection stops may have time windows. The major variation from a standard VRPTW is due to disposal operations and driver's lunch break. When a vehicle is full, it needs to go to one of the disposal facilities (landfill or transfer station). Each vehicle can, and typically does, make multiple disposal trips per day. The purpose of this paper is to introduce the waste collection VRPTW, benchmark problem sets, and a solution approach for the problem. The proposed algorithms have been successfully implemented and deployed for the real life waste collection problems of Waste Management, the leading provider of comprehensive waste management services in North America with nearly 26,000 collection and transfer vehicles. 相似文献
650.
Marginal glass forming Al-based alloys have attracted considerable attention due to the occurrence of a primary crystallization reaction that yields a microstructure consisting of uniformly dispersed Al-nanocrystals embedded in an amorphous matrix. Rapidly solidified Al-alloys ribbons containing 8 at.% Ni and 4-6 at.% La were prepared by single roller melt-spinning technique. As-melt-spun and annealed ribbons were investigated by means of differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and hardness measurements. XRD studies revealed that ribbons are fully amorphous in the as-melt-spun state. DSC studies showed that crystallization proceeds in two or three stages that are sensitively influenced by La content. Crystallizations kinetics were analysed by Kissinger and Johnson-Mehl-Avrami approaches. Microhardness of all the ribbons was examined at different temperatures and correlated with the corresponding structural evolution. 相似文献