W. Kromp

Plastic deformation under simultaneous cyclic and unidirectional loading at low and ultrasonic frequencies

Abstract Whenever cyclic strain is superimposed on undirectional loading, the inherent asymmetry of plastic deformation causes an apparent decrease in the externally observable load. This facilitation of deformation can be spectacular at ultrasonic frequencies. Since ultrasound is used for both materials testing and metal forming, the actual stresses reached within the samples must be of concern. The stress dip might be caused by strain-induced recovery, by microstructural changes or by elastic stress relaxation. Aluminum alloy samples were simultaneously exposed to static and vibratory loading at 0.5, 1, 10, 50 and 20 000 Hz. No frequency influence was observed at room temperature. The stress dip is caused by elastic relaxation.

Determination of magnification and resonance length of samples used in ultrasonic fatigue tests

Abstract For ultrasonic fatigue tests various dumb-bell shaped specimens are used. For different sample shapes formulae are given, which allow a quick estimate of the resonance length and magnification factor. The calculations are based on the fact that the equation of motion can be solved explicitly when the shape of the stepped part, which, in longitudinal section, is usually part of a circle, is approximated by an exponential or catenoidal curve. The applicability of the presented method is discussed.

Hydrogen effects on low-cycle fatigue of the single-crystal nickel-base superalloy CMSX-2

The effects of hydrogen on the low-cycle fatigue behavior of CMSX-2 [001]-oriented single crystals were examined. Fatigue tests were conducted under constant plastic strain amplitude control. Cyclic stress-strain curves and fatigue life data at different plastic strain amplitudes were determined for hydrogen-free and hydrogen-charged specimens. Two charging procedures, leading to different hydrogen concentrations, were applied. Hydrogen was found to decrease significantly the number of cycles to failure under the various experimental conditions. The increasing hydrogen concentration and ratio of the hydrogen to nonhydrogen-containing volume were found to shorten fatigue life in hydrogen-charged specimens. Based on the analysis of cyclic stress-strain curves and optical and transmission electron microscopy (TEM), it was established that hydrogen enhanced strain localization and promoted crystallographic, stage I cracking, leading to embrittlement. The overall fracture mechanism is discussed in conjunction with Duquette and Gell’s stage I fracture model.[16]

Risks due to beyond design base accidents of nuclear power plants in Europe—the methodology of riskmap

International treaties on liability in the case of nuclear accidents set a limit on the repair payments to be made by the operators of nuclear power plants to countries adversely affected by nuclear fall-out which is independent of the actual risk incurred by the individual countries. A map of the risk due to beyond design base accidents of nuclear power plants in Europe could give an indication which countries are likely to profit by joining the treaties and which are not. Such a riskmap for effects based on the deposition of the long-lived radionuclide Cs-137 is being developed for commercial nuclear power plants in Europe. Dispersion and deposition calculations are based on meteorological data of 1 year. The modular design allows scenario calculations for different assumptions concerning source terms and frequencies of beyond design base accidents of individual power plants or plant types as well as a sensitivity analysis of the results.

Transverse expansion of 2-D carbon/carbon laminates as a consequence of delamination

Abstract This paper shows that from simple measurements of stress/strain curves of a damaged specimen of carbon-fibre-reinforced carbon (C/C) material one can estimate not only qualitatively, but even quantitatively the size of a delamination. By this method a delamination can be detected before the specimen is destroyed. This effect is visible only in composites containing satin texture woven material. The driving forces for the delamination are discussed and an experimental verification is presented.

flexRISK – Flexible Tools for Assessment of Nuclear Risk in Europe

flexRISK studies the geographical distribution of the risk due to severe accidents in nuclear facilities, especially nuclear power plants (NPP) in Europe. Starting with source terms and accident frequencies, the large-scale dispersion of radionuclides in the atmosphere is simulated for about 1,000 meteorological situations. Together with the subsequent calculation of resulting radiation doses the consequences of severe accidents can be estimated. In this contribution, a description of the flexRISK project is provided.

Ultrasonic fatigue tests with stabilized amplitude and controlled temperature

Abstract An attachment for fatigue testing was developed, complementary to a commercially available ultrasonic generator with a power of 200 W. The fundamental improvements are: a control system which stabilizes the fatigue amplitude, and a programming attachment which supplies ultrasonic fatigue pulses in order to prevent undesirable temperature rises caused by internal friction. Similar attachments were developed for generators with powers of 400, 1 000 and 2 500 W. These improved fatigue testing machines permit investigations concerning the fatigue behaviour of metals with a remarkably high degree of damping.

IN VITRO RETENTION OF RADIONUCLIDES BY THE MYCELIUM OF EDIBLE FUNGI :BASIS FOR SUBSEQUENT RISK ASSESSMENT

The accident at the Chernobyl reactor on 26 April 1986 distributed considerable amounts of radioactive material over a large area of Europe. The accident has stimulated sampling and thorough measurements of radionuclide contamination in all types of forest resources from timber to forest by-products — such as mushrooms and berries. Many authors [1 — 3] have reported that macromycete fungi are absolute accumulators of 137Cs in forests because the specific activity in fungal fruit bodies exceeds both the activity in plants, which are usually involved in symbiotic relations with soil fungi, and the activity in the substratum on which they develop. It has been suggested that the consumption of wild-growing mushrooms is a risky activity [4]. From the viewpoint of risk perception, edible mushrooms play an important role even in modern society - far beyond their value as a food supply. The search for and gathering of edible mushrooms are one of the last opportunities for urbanised humans to satisfy their drive as hunters and collectors in nature and thus form an important part of our cultural heritage.