High temperature mechanical strength and microstructural stability of advanced 9-12%Cr steels and ODS steels.
The present study proposes a comparison between several martensitic and ferritic steels in terms of creep strength and cyclic softening effect. The damage mechanisms are identified using fractographic observations and the microstructural evolutions are observed by TEM. The effects of a modified chemical composition on the high temperature mechanical behaviour are studied.
High temperature fatigue: behaviour of three typical classes of structural materials
Abstract The goals of this paper are: (i) to review the mechanisms of cyclic deformation, damage accumulation and crack propagation in three types of materials widely used in power generation industries, i.e. Cr–Mo steels, austenitic stainless steels and superalloys used in jet engine turbines (both Ni base and Fe–Ni base) when they are tested at elevated temperature; (ii) to relate these mechanisms to engineering applications; (iii) to review life prediction methodologies including thermomechanical fatigue (TMF); and (iv) to point out current and likely future trends in the development of more fatigue resistant materials and life prediction methods. The emphasis is laid on the creep–fatigue–oxidation behaviour of the two first classes of materials, i.e. 9–12% martensitic Cr steels and austenitic stainless steels. As the major issue for the design of components used in power generation industries is the extrapolation of short term laboratory data to much longer times, only physically based models for life prediction are examined. In Ni base superalloys, the emphasis is laid on the effect of oxidation on fatigue crack growth rate at elevated temperature and on their behaviour in TMF
In search of optimum chest radiography techniques.
A nation-wide study of chest radiography in Sweden had previously revealed a large variation in the physical and technical factors involved, in particular the radiation dose. In this study the image quality could not be assessed unambiguously. The aim of the present study was to try to establish a correlation between visual grading of radiographs and physical and technical factors in order to find the optimum chest X-ray system. The physical and technical performance of 24 chest units was evaluated. Radiographs were taken of an anthropomorphic chest phantom supplied with test structures simulating various pathologies. Image quality was assessed by visual grading analysis of the radiographs. The physical and technical parameters of the units rated best were used to exemplify good radiographic practice. The results were in agreement with the recommendations issued by the Commission of the European Communities (CEC). It was also shown that low radiation dose is compatible with high-quality radiographic imaging of the chest.