Magnesium — an old material with new applications

Magnesium alloys have been made more competitive for engineering applications through developments in alloys and casting techniques. The properties of magnesium alloys and the advantages of die casting are described. High strength-to-weight ratios allow thin-section designs which retain good fatigue and creep resistance and are suitable for EMI shielding applications. Machining, joining, surface treatment and corrosion resistance of alloys are considered.     

Deficiencies of polypropylene in its use as a food-packaging material — a review

The outstanding chemical and physical qualities of polypropylene (PP) combined with an attractive price have made it one of the protagonists in the food-packaging industry. Like other polymers, however, PP tends to lose some of its constituents to the packed product, by migration, and when submitted to thermal, oxidative or radiation stresses PP starts to degrade. These processes are of concern when food is packed in the plastic, for they can cause PP to impart off-odour and off-taste to the packed product and in the worst case can give rise to toxicity of the food. This paper reviews the work that has been done on these processes and considers the recycling of PP for food-packaging use.     

Synthesis and characterization of Yb3+,Tm3+:Ba2YF7 nanocrystalline with efficient upconversion fluorescence

A novel upconversion luminescence nanocrystals Yb³⁺,Tm³⁺:Ba₂YF₇ were synthesized via the hydrothermal method. They have uniform morphology with a mean size of 30 nm even if annealed at 600 °C. Pumped by 980 nm laser diode the as-synthesized powers emit ultraviolet/blue light, which is in the range of the specific upconversion luminescent spectra of Tm³⁺ ions. After post-annealing at 600 °C in an argon atmosphere for 2 h, their upconversion luminescence intensity is 5 multiple improved and the ultraviolet/blue light can even be seen by the naked eyes under a low excitation power of 20 mW. This indicates that Ba₂YF₇ is a very effective luminescent host material. Excitation power dependences of individual upconversion emission intensity are plotted, which partly uncover the upconversion luminescence mechanism of Tm³⁺ ions.     

Inclusion Complexation of Lorazepam with β — Cyclodextrin

The preparation of an inclusion complex of Lorazepam, a benzodiazepine antianxiety agent with β -cyclodextrin is described. The inclusion compound was prepared by the homogeneous coprecipitation method in the molar ratio of 1:2 of the drug and β -cyclodextrin respectively. The formation of inclusion complex was evaluated by UV spectral studies, IR studies, X-ray diffractometry, and Differential Thermal Analysis. The solubility and in-vitro drug release studies indicated that the complex form of the drug significantly increase the solubility and the dissolution rate compared to the free form. Tablets prepared with Lorazepam- β -cyclodextrin complex also showed a significant increase in dissolution of the drug indicating that P-cyclodextrin plays an important role in the solubilization of the drug.     

Dynamic elasto-plastic response of beams — A new model

A new approximate model to analyze the dynamic elasto-plastic large deformation response of beams is presented. The model beam is composed of two rigid parts interconnected by a gap of zero width which is built of fibers having an imaginary length. The imaginary length governs the strains and stresses in the beam, for equal deflections in the real and model beams, and is found to be almost constant in the elastic and elasto-plastic domains. The deflected shape is triangular because interest is focused on midspan deflection, while advanced existing models [13] can be used to determine the deflected shape. Comparison of predicted final deflections with test results show very good correspondence. Apart from the final deflection, which may easily be measured in tests, the model also calculates the time dependence of the dynamic reactions, bending moment and membrane force, displacement, velocity and acceleration as well as stress and strain distributions at selected times. Calculation of a complete response time history requires only a few seconds. The proposed model is extendable to various boundary conditions and load distributions and might be generalized to include strain hardening and rate effects.     

Soft PVD Coatings — a new coating family for high performance cutting tools

The joint effort of a cutting tool manufacturer and a coating specialist led to the development of a soft solid lubricant based cutting tool coating (Patents pending!). It is applied by an advanced sputtering technique as a very thin uniform coating with a good adherence to the tools. It has a low coefficient of friction and a low affinity to alloy materials like aluminum, titanium and precious metals. These factors and others allow the machining at high spindle speed and feed rates with an excellent workpiece surface finish. Values can be maintained which are far superior to even those permitted for cemented carbide tools. In some cases, productivity and tool life can be increased by a factor of up to 20.     

Hermetic compressors — a case study

Since the energy crisis, Danfoss have been working systematically on their hermetic compressors for household refigerators and freezers. Significant savings in energy consumption have been achieved, both from improvements to existing designs and from a new design of the smallest compressors.The improvements and results achieved are presented here.     

Reliability growth—a new graphical model

A new reliability growth model is presented which is simpler to plot and fits the data more closely than the Duane model over the range of Duane slopes normally observed during a reliability growth programme. The model is derived from variance stabilization transformation theory. The problem, inherent in Duane's model, of providing too much influence to earlier failures is overcome. A method is also presented of comparing different models which have different y‐axes. Extensive simulations were conducted and the results indicate that for Duane slopes less than 0.5 the new model is more effective. The leverage and influence aspects of both models are evaluated by means of Cook's distance. Finally, two published datasets are analysed and the findings confirm the simulation results. Copyright © 1999 John Wiley & Sons, Ltd.