Materials Science Forum Vols. 537-538

Abstract: In our study we summarise the materials and manufacturing technologies of coronary stents used nowadays. Different testing methods for stent’s features are presented and main expansion features such as recoil and foreshortening are determined. The most frequent failures caused by the expansion of the coronary stents are also shown.

Abstract: Results of the X-ray diffraction (done by computer quantitative phase analysis) and metallographic miscroscopy (colour etching and computer image analysis) inspections aimed at determining the residual austenite content of modern TRIP steel sheets produced at Dunaferr.

Abstract: Fracture of ferritic reactor pressure vessel steels is determined by temperature and specimen size. In low temperature fracture occurs by cleavage, with elevation of temperature and decrease of specimen size the ratio of ductile tearing prior to cleavage increases and, in the end, fracture will have a ductile character. There is a temperature interval where both fracture mechanisms are present. Hypothesis of the traditional (global) assessment method has been that the shift of the fracture toughness reference curves due to neutron irradiation is equal with the shift of the ductile-to-brittle transition temperature measured by the Charpy impact test. Local assessment approaches based on the „weakest link” statistical theory recommend the direct measurement of fracture mechanics parameters to structural integrity evaluation. The paper describes the main features of both global and local approaches, analyzing the micro structural aspects of the most known micromechanical models of local approach and drawing conclusions concerning their applicability.

Abstract: In this paper, the influence of the microstructure on the fatigue behaviour of specimens from defined rim positions of original railway wheels R7 (SAE 1050) and tyres B6 (SAE 1065) is characterised under constant and variable amplitude loading. Due to the industrial heat treatment and the component size, the ferrite fraction and the cementite lamellae spacing of the ferriticpearlitic microstructures increase with increasing tread distance. The microstructural gradients influence the fatigue behaviour in a characteristic manner. Mechanical stress-strain hysteresis, temperature and electrical resistance measurements were performed. Temperature and electrical resistance data represent the actual fatigue state in highly stressed volume parts and are not related to a gauge length. Furthermore the electrical resistance is qualified to detect a proceeding fatigue damage in load-free specimens and components. For variable amplitude loading a new testing procedure was applied, which combines any kind of near-service load spectrum with short single step measuring sequences. The plastic strain amplitude, the temperature and the electrical resistance data of each single step sequence are plotted in cyclic ‘deformation’ curves and represent the sum of microstructural changes caused by near-service loading. The substitution of the plastic strain amplitude by the changes of the temperature and the electrical resistance leads to modified Morrow and Manson-Coffin curves. Electron microscopic investigations allow to interpret the measured fatigue data on the basis of microstructural details.

Abstract: The paper reviews the whole design process of large−scale trusses of overhead lines for power transmission. It describes the modules of the system of interactive computer programs made by the authors. According to the iterative nature of the design process special graphic support helps the interaction of the designer. The effect of assumptions used during the design process, imperfections due to the fabrications and erection of the structures can only be detected by the loading tests carried out on newly designed set of towers. Some experiences learned by these tests are also detailed in the paper.

Abstract: Six different theoretical equations are compared in the present paper with experimental data, measured for 28 binary liquid metallic systems. General conclusions are drawn on the ability of the different theoretical models to describe the concentration and temperature dependence of the viscosity of liquid alloys. A new equation is derived, being able to predict the viscosity in multicomponents alloy even if the viscosities of the pure components are not known.

Abstract: Knowledge of the TTT (Time-Temperature-Transformation) or CCT (Continuous- Cooling-Transformation) diagrams of steels is an important factor in the thermo-mechanical processing of steels. Much experimental work has been undertaken to determine such diagrams. Significant works have been written which can calculate TTT and CCT diagrams for steels. The aim of the present work is to show the developed model that can provide accurate enough TTT and CCT diagrams for steel 42 CrMo4 (where the austenitisation temperature was 1050°C). The calculated results are compared by the experimental results. The developed TTT phase transformation diagrams based on FEM-based phase elements and the star-like cooling simulation make it possible to create virtual CCT diagram data.

Abstract: The TTT (Time-Temperature-Transformation) phase transformation diagrams based on FEM based phase elements make it possible to create virtual TTT diagrams. In this case the virtual TTT diagrams are results of multiple linear regression calculations. The basic TTT diagrams are created on the basis of measured published data. Two created virtual TTT diagrams are presented for two different austenitisation temperatures. The results of calculations are compared to the measured ones.

Abstract: A novel numerical approach for testing and evaluation of quenching media and quenching systems is outlined. The technique proposed is based on determination of heat transfer coefficient from temperature signals recorded and applying it as input for simulation of quenching process. The evaluation method is based on the calculated microstructural and mechanical properties of cylindrical samples.

Abstract: Rollers of three different material structures were examined: rollers consisting of pure EP resin; homogeneous EP/SiC composite rollers containing 5 vol.% SiC; and EP/SiC composite rollers with functionally gradient (FG) material structure. Wear tests were performed on the rollers. The wear tests showed that rollers of gradient structure are the most wear-resistant of all. Microhardness measurements were performed on the materials of the three different rollers. SEM images were made of the surface of wear traces. In order to get to know better the effect of SiC reinforcement particles on the wear mechanism, microhardness measurements were simulated by 3D FE micro-models. The SEM images and the FE models were used to explain the excellent wear behavior of the tread of rollers with gradient material distribution.