Temperature-dependent mechanical and long crack behavior of zirconium diboride–silicon carbide composite

Hot pressed ZrB2–20 vol.% SiC ultra-high temperature ceramic composites have been prepared for strength and fracture investigations. Two composites fabricated under differing hot pressing temperatures with (ZSB) and without (ZS) B4C sintering aids were selected for room temperature modulus of rupture (MOR) strength and single-edge-notch bend (SENB) fracture toughness experiments. Structure property relationships were examined for both composites. MOR and stiffness temperature dependence was also investigated up to 1500 °C. Long crack propagation studies were conducted up to 1400 °C using the double cantilevered beam geometry with half-chevron-notch initiation zones. Residual Boron-rich carbide maximum particle sizes were found to be strength limiting in ZSB billets while SiC controlled strength in ZS billets. Flexure strength decreased linearly with temperature from 1000 to 1500 °C with no visible plastic deformation prior to fracture. Similar stiffness decreases were observed with a transition temperature range of 1100–1200 °C. Long crack studies produced R-curves that show no significant toughening behavior at room temperature with some modest rising R-curve behavior appearing at higher temperatures. These studies also show the plateau toughness increases with temperature up to 1200 °C. This is supported by an observed transition from primarily transgranular fracture at room temperature to primarily intergranular fracture at high temperatures. Wake zone toughening is evident up to 1000 °C with K_R rise from 0.1 to 0.5 MPa√m. Beyond 1000 °C fracture mechanism transitions to include creep zone development ahead of crack tip with wake zone toughening vanishing.     

Some uncollected writings reprinted from early publications

Abstract

It is rather odd to write about amateur photography in Germany, when such a thing hardly exists; and still I venture to say a few words about its future, as it is almost certain that Berlin, Germany's centre for science, has given it an impetus, which promises to bring forth a host of well-trained workers. Thanks to the munificence of the city, which devoted upwards of £1,000,000 to the purpose, a new technical high school was erected and opened about two years ago. The building is a grand work of architectural art, unsurpassed by any educational institution on the face of the globe, both in exterior and interior beauty, and practicality. It is of enormous dimensions, and the 800 or 900 students who now occupy it are quite lost within its walls, as the building can accommodate 2000 or more.     

REFORMING OF N-OCTANE ON A Pt/Al2O 3 CATALYST. 1. PRODUCT DISTRIBUTION AND KINETIC ANALYSIS.

The conversion of n-octane on Pt/Al₂O₃ catalyst to hydrocracked products, isooctane, ethylbenzene, o-,p-,m-xylene and toluene was investigated in hydrogen in a Berty CSTR at three different partial pressures of n-octane, 101·325 KPa total pressure, temperatures between 400°C-460°C and W/F values up to 0·33gmincm^-3. The hydrocracked products were the most predominant. Of the other products, isooctane was present in the highest yield. A sequence of elementary steps based on the suggested reaction network of Ako and Susu (1986) was found to predict the experimental conversion-W/F data with the conversion of adsorbed isooctane to adsorbed o-xylene as the rate determining step. The activation energies for the forward and backward reactions of this step were determined to be 21·2 and 14·3 Kcal/gmol, respectively.     

Characterisation of natural organic matter from the Nordic typing project water samples by chemometric analysis of their near infrared spectral profiles

Natural organic matter (NOM) from nine different water sources located in the southern part of Norway selected for the “NOM typing project” was characterised by using near infrared spectroscopy and multivariate data analysis.

The near infrared profiles of these NOM samples were corrected for multiple scattering effect and differentiated twice before subjecting them for multivariate data analysis. The preprocessed profiles were first subjected to multivariate calibration using partial least squares (PLS) technique against earlier determined values of four different biopolymer input (carbohydrates, N-acetyl amino sugars, proteins and polyhydroxy aromatics) of the NOM as dependent variables. The profiles were then classified using principal component analysis (PCA).

The PLS calibration models obtained demonstrate that the biopolymer input of the NOM samples can be predicted with acceptable precision.

The PCA reveals that the samples fall into three different groups. This classification agrees with earlier classifications carried out by using variables that were determined by alternative expensive and time-consuming analytical techniques.     

Estimating an Endogenous Growth Model with Public Capital and Government Borrowing: U.S. and Germany 1960–1995

The paper presents and estimates an endogenous growth model with publiccapital and government borrowing. Government behavior (tax rates, spending andborrowing) does not follow optimizing rules but is restricted by two fiscalregimes (rules). In the strict fiscal regime government borrowing is used forpublic investment only. In the less strict regime it can also be used forpublic investment and to a certain degree for the debt service. The growthrate differs in our model variants according to which rule is adopted.Moreover, the growth maximizing income tax rate is different from zero. Forthe two relevant fiscal regimes, which correspond roughly to the cases of theU.S. and Germany, the model is estimated by employing time series data from1960.4 to 1992.1 and 1966.1 to 1995.1 respectively. The results suggest anexplanation for the different time paths of economic variables in the Americanand German economies in the post-war period.     

Transformation approach to numerically integrating PDEs by means of WDF principles

As has been shown, attractive methods for numerically integrating partial differential equations (PDEs) resulting from physical problems can be obtained by simulating the actual physical passive (conservation of energy) dynamical system by means of a discrete passive dynamical system, and this in such a way that the full parallelism and the exclusively local nature of the interconnections (principle of action at proximity) are preserved. An alternative approach for developing such methods is presented which, while still using principles of the same type as those on which multidimensional wave digital filters (WDFs) are based, involves appropriate transformations of the original coordinates of the physical problem at hand. This alternative approach is not only easier to apply than the one referred to above but also more general; it is illustrated on the one hand by the same examples as those that have been used for the other approach, and on the other by showing the applicability to Maxwell's equations.