Effect of thermal residual stresses on fatigue crack opening and propagation behavior in an Al/SiC p metal matrix composite

The effects of a thermal residual stress field on fatigue crack growth in a silicon carbide particle-reinforced aluminum alloy have been measured. Stress fields were introduced into plates of material by means of a quench from a solution heat-treatment temperature. Measurements using neutron diffraction have shown that this introduces an approximately parabolic stress field into the plates, varying from compressive at the surfaces to tensile in the center. Long fatigue cracks were grown in specimens cut from as-quenched plates and in specimens which were given a stress-relieving overaging heat treatment prior to testing. Crack closure levels for these cracks were determined as a function of the position of the crack tip in the residual stress field, and these are shown to differ between as-quenched and stress-relieved samples. By monitoring the compliance of the specimens during fatigue cycling, the degree to which the residual stresses close the crack has been evaluated. formerly Research Student, Department of Materials Science and Metallurgy, University of Cambridge formerly Lecturer, Department of Materials Science and Metallurgy, University of Cambridge This article is based on a presentation made in the symposium entitled “Creep and Fatigue in Metal Matrix Composites” at the 1994 TMS/ASM Spring meeting, held February 28–March 3, 1994, in San Francisco, California, under the auspices of the Joint TMS-SMD/ASM-MSD Composite Materials Committee.     

PALAEOZOIC TECTONIC HISTORY OF SE TURKEY

A review of published data for the Palaeozoic of SE Turkey, together with facies distribution and palaeo-fault maps derived from regional field data, are used to interpret the Palaeozoic tectonic history of the region.
Intracratonic rifting events in the Early Cambrian and the Early Ordovician led to syn-rift deposition within fault-bounded basins. Marine transgressions across the region in the mid-Cambrian and mid-to-Late Ordovician were probably influenced by regional thermal subsidence after each rifting event, in addition to (glacio-)eustatic mechanisms. Marine transgressions in the Early Silurian and Early Carboniferous are thought to have been entirely eustatic in origin.
Poorly-constrained, Late Palaeozoic facies variations across the region can be related to uplift during the Caledonian and Hercynian orogenic episodes. Widespread tilting and erosion before the Cretaceous, which has removed much of the Late Palaeozoic record from this region, resulted from uplift at the edges of a major rift system which was initiated during the Triassic-to-Jurassic opening of the Southern Neotethys.     

Works of adhesion at the carbon fiber-liquid interface determined using a modified wetting technique

Works of adhesion W_SL between aqueous solutions with pH values in the range from 1 to 14 and carbon fibers from different sources, which were additionally treated in an inert atmosphere or in oxygen, were measured by use of a microbalance. These works of adhesion W_SL were found to show distinct stepwise dependencies on the pH value. The works of adhesion W_SL are attributed to dispersion interactions W_SL¹ and various acid-base interactions w_sl^ab—in the latter case between the acidic and basic surface groups of carbon and the various basic and acidic aqueous solutions.     

Comparison of capillary gas chromatographic method and automated spectrophotofluorometric methods for measuring content uniformity of conjugated oestrogens in pharmaceutical preparations

To measure the content uniformity of conjugated cestrogens tablets, the USP XXII monograph specifies a capillary gas chromatographic method. This involves separation of the trimethylsilyl derivatives of the various oestrogens found in a typical conjugated oestrogens tablet using a fused-silica 0V 225 bonded phase column. Hydrogen is used as the carrier gas with FID detection. A more rapid spectrophotofluorometric method of analysis has been developed in which the oestrogens are extracted from the dosage form into water, then transferred into organic solvent as the dicyclohexylamine complex. Fluorescence is developed by heating the solution of the complex in the presence of 70% sulphuric acid. The chemistry and detection are carried out using a segmented-flow analyser.The spectrophotofluorometric method is preferred as a routine control for content uniformity because considerable time is saved during sample preparation and analysis compared to gas chromatography. Coefficients of variation show that both methods produce acceptable results. These results fall well within the USP XXII [1] monograph, limits and also well within the tighter limits imposed by the USP XXII, section 905.     

Toward a theory of robust compensation for systems with unknownparasitics

The problem of designing a robust compensator based on a plant model with order uncertainty is considered. The uncertainty is characterized mathematically as a class of generalized singular perturbations of the plant. The case of static compensation is examined. A necessary and sufficient condition is established under which actual closed-loop behavior is close to that predicted by the plant model under sufficiently small singular perturbations. The condition is shown to be generic     

POEMS: program for outliers elimination in multidimensional space

A Program for Outliers Elimination in Multidimensional Space (POEMS), which allows the user to eliminate outliers from training spaces as a prior step to any statistical study, is presented. Even though the program can be applied to any scientific field, the characteristics of POEMS makes it particularly suitable for 'series design' on Quantitative Structure-Activity Relationships studies.     

The Macintosh Programmer's Workshop

The authors discuss the Macintosh Programmer's Workshop (MPW), a Macintosh development environment that includes a comprehensive set of programming tools and handles several languages. It also combines the graphical interface common to all Macintosh applications, a command language similar to the Unix shell languages, and Smalltalk's immediate execution of commands in any window. They focus on the program-development environment rather than on the tools in that environment. They give the history of MPW, and describe its design goals. The bulk of the article is a discussion of MPW's design