Solid State Phenomena Vol. 223

Abstract: The influence of material anisotropy on the exploitation performance of structural elements is recognized still insufficiently. The state seems to be the more evident if we consider that each type of materials inhomogeneity is not neutral in relation to its properties. In this field, carefully selected characteristics – the kind of microstructure diagnostics – delivers valuable data for the identification and quantification of desired material parameters deciding its usability. A separate problem is a spatial distribution of the parameters, which is an important feature of advanced, multi-functional materials with gradient-or/and layered structure. Further stages of the microstructure diagnostics covering the prediction of material behaviour in exploitation conditions and the estimation of the time of safe exploitation are still challenging research problems.The enumerated aspects of materials diagnostics require experimental data registered for the representative sample and suitable methods of data processing. Laboratory techniques and modelling procedures utilized in contemporary materials engineering deliver a wide range of computer-aided methodology, enabling one to obtain valuable characteristics of material, including crystallographic texture, residual stresses, phase composition, and crystallite size. In addition to methodological, experimental conditions play an important role in the outlined microstructure diagnostics. Both aspects are evident in the case of the identification of a subtle field of stresses resisted in the near-surface layer or in coating-substrate interface where a non-destructive way of examination is demanded. This work presents a selected non-destructive investigation of degraded areas of materials, recognized as critical from the viewpoint of the behaviour of a specific structural element in exploitation conditions.

Abstract: Research of residual stresses in steel at different depths from its surface is presented in this paper. The material used for research was AISI 310S heat resistant steel (containing approx. 0.2%C, 25%Cr and 20%Ni) in form of a rolled steel sheet with a thickness of 2mm. Stress measurements were conducted with the use of K_αCo radiation by the sin²ψ method in three directions, including the direction of the sheet's rolling (φ = 0°). For the purpose of measuring stresses at different depths from the surface, the steel underwent the process of electropolishing in electrolyte based on perchloric acid at 32 V for various durations (every 1-5 s) to the maximum depth of 35 μm. The set residual stress distributions vary depending on the direction of the test. The strongest stresses are on the steel's surface, and stresses have the widest range (from compressing to streching ones) in the area under the surface, which occurred in the rolling direction, and the narrowest range in its transverse direction. A correlation was discovered in the distribution of compression stresses and microhardness in the outer layer of the steel to a depth of 10 μm, where the role of plastic deformation in shaping the qualities of the steel outweighs the influence of structure content. This was proven using polar figures.

Abstract: Selected results of experimental research showing possibilities to combined accelerated methods, i.e. thermographic determination of the fatigue curve and estimating the fatigue limit, were presented in this paper. The tests were performed using the reversed bending fatigue-testing machine with a rotational frequency of 77 Hz. The main item of the test station was the thermographic camera. Test specimens were made of C45 (1.0503) steel drawn bars. The full tests results were presented for the fatigue S-N curve (23 specimens at 10 load levels) and fatigue limit by the Staircase method (25 specimens) based on 10⁷ cycles to failure was determination. The accelerated test for determining the slope of the S-N curve and the fatigue limit were made by a single specimen based on gradually increasing loading. Methods previously presented in the literature are based on the phenomenon of temperature stabilization during most of the fatigue process. The results presented in this work did not show the occurrence of such a phenomenon. For that reason, the new approach to the determination of the slope of S-N curve was proposed. Combined application of both experimental methods, Locati and thermographic, with a new approach to the determination of this slope might allow one to develop automatic equipment for the accelerated determination of the fatigue limit which would contribute to significant reduction of the test costs and time, thus increasing availability of such tests.

Abstract: Web guiding used in roll-to-roll material processing machinery is connected with a number of issues including the maintenance of the web tension, the precision of the lateral web displacement, the accuracy of transport positioning of the web, and the selection of web transport velocity. The article presents the precision of the lateral web displacement issue during the start-stop work mode of the web transport. A model of a system for automatic web guiding is shown. The requirements of the lateral web guiding for transporting material over rollers in a processing machine working in a start-stop mode are presented. The control system is discussed, particularly its hardware structure and behaviour. The obtained functionality of the control system enables its application in roll-to-roll material processing machines, working either in the start-stop mode or continuously.