Residual Stresses VII, ICRS7

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Authors: Janez Grum, Roman Šturm
Abstract: Laser remelting process is a very promising hardening method for ferrous and nonferrous alloys, which do not show a homogeneous microstructural state after having been heattreated in a traditional way. Consequently, the alloys concerned do not achieve the required hardness of the surface layer and do not provide the required wear resistance either. The paper deals with residual stresses of thin flat specimens of nodular cast iron 500-7 in the laser remelting process. In the process of gradual remelting of the specimen surface, that is during its heating and cooling, volume changes of the specimen occur due to thermal and microstructural changes. For a better knowledge of volume changes in the thin surface layer of the specimen, the latter were evaluated by residual-stress measurement in the thin modified surface layer after the remelting process. In laser remelting of a workpiece such remelting conditions should be ensured that a uniform thickness of the modified layer could be obtained in spite of several laser-beam passages across the workpiece surface. Because of a multiple laser-beam passage across the workpiece surface, the state of internal stress in the workpiece changes. Optimal laser surface remelting conditions on the basis of knowing the residual stresses were chosen, while the way of guiding the laser beam over the surface of flat samples and degree of overlapping were varied.
Authors: Janez Grum, Martin Zupančič
Abstract: Nickel maraging steels in the as-delivered state show a microstructure consisting primarily of oversaturated lath martensite. The final mechanical properties are achieved with precipitation annealing, during which the dissolved alloying elements start to precipitate. The newly-formed precipitated phases efficiently hinder shifts of dislocations, which results in considerable changes of the mechanical properties. Strength and hardness thus essentially increase whereas the material shows a relatively high fracture toughness. The precipitated phases formed during precipitation annealing also cause some distortion of a workpiece and transformational residual stresses on the micro and macro scales. Linear strains after precipitation annealing range from -0.05% to -0.1% and depend primarily on temperature/time conditions during the precipitation process. The non-homogenous annealing such as laser annealing produces temperature-induced residual stresses which are combined with transformational stresses. These stresses are expected to be lower and much more different than the stresses occuring in comparable classical heat-treated steels, however they cannot be neglected due to the exceptional performance of maraging steels and also their employment with high-demanding products. The results of the residual stress measurements after laser-induced and classical heat treatments of Ni-Co-Mo maraging steel with 12% nickel are presented.
Authors: Zheng Qiang Zhu, Li Gong Chen, De Lin Rao
Authors: Changfu Ding, Song Feng Tian, Kuifang Wan, Li Sun
Abstract: With the coal-fired units developing toward large capacity and high parameter, the safety and the economic operation is very important. The cracks on the cylinder and rotor that produce during performance are analyzed. It is pointed out that residual stress is an important factor affecting the fault and should be noticed in practice. And residual stress monitoring online has good prospects of development in this field.
Authors: T. Erbacher, Michael Ott, Tilmann Beck, Otmar Vöhringer
Abstract: Al2O3 ceramic plates of diameter 166 mm and thickness 5 mm were subjected to frictional loading regimes. The resultant residual stress effect in the material was analyzed using the sin2y and AP methods based on a modified measurement condition for the pole angle y and the azimuth angle F on a 4 cycle goniometer. Furthermore, the frictional loading of the Al2O3 plates lead to clear differences in the residual stress state near the surface. An underlying correlation was observed between the residual stress state of the Al2O3 material and its residual strength with this effect being ascribed to the magnitude of frictional load applied.
Authors: A. Ottlik, Volker Schulze, L. Pintschovius, Hermann Müller, Detlef Löhe
Abstract: Brazing of cemented carbides to steel bodies gives rise to the development of complex stress states and distortions which influence the fatigue behaviour of the parts. It is quite important to estimate the residual stresses with numerical methods whose agreement is to be guaranteed with experimental characterization of the brazed parts. In this work FEM simulations and X-ray as well as neutron stress analysis were used to examine the residual stresses of brazed samples. Joints with different geometries and dimensions made of cemented carbide and different steels showing different phase transformation behaviours were investigated.
Authors: Udo Brückner, Alexander Epishin, Thomas Link, Bernard Fedelich, Pedro D. Portella
Authors: B. Kasanická, Thomas Wroblewski, Volker Schulze, Detlef Löhe
Abstract: Analysis of the residual stress state, the microstructure and surface topography of ceramic microcomponents made of Y2O3-stabilized ZrO2 produced by micro powder injection moulding were performed. During the production of the microspecimens sintering conditions were varied. The measurement of residual stresses has been carried out using the MAXIM (MAterials XRay IMaging) diffractometer at HASYLAB beamline G3 at DESY in Hamburg (Germany). The microstructure and surface topography of differently moulded specimens were examined using a scanning electron microscope (SEM) and a confocal white light microscope type NANOFOCUS. The findings are used to establish correlations between process parameters and characteristics of the microcomponents. These will allow to improve the production process with respect to the mechanical properties of the microcomponents.
Authors: Henryk Tomaszewski, K. Godwod, Ryszard Diduszko, F. Carrois, J.M. Duchazeaubeneix
Abstract: Modification of material surface layers by conventional shot peening is commonly used to improve the strength of metal components. As it occurred high compressive stresses up to 2.0 GPa may be introduced also to near surface region of alumina ceramics by this technique. Two alumina ceramics were given to ultrasonic shot peening which is a new, compact and small consuming of shot media method developed by Sonats company. This process is named Stressonic®. The dependence between diameter of tungsten balls, treatment time (at constant mass of balls in the housing and vibration amplitude) and level of compressive stresses introduced was determined. High microplastic deformation in shot peened surface layer of alumina was observed by X-ray diffraction. An increase of surface resistance to fracture of ceramics with increasing level of compressive stresses was also found.
Authors: Cahit Can Aydiner, Ersan Üstündag
Abstract: Bulk metallic glasses (BMGs) are attractive structural materials that develop residual stresses during processing due to thermal tempering. In this process, compressive surface stresses are generated within thin layers balanced with tension in the interior. In the present study, stress generation was analyzed experimentally and theoretically in a BMG plate and a cylinder. The residual stresses were measured using the crack compliance method. It was shown that high stresses can be attained in metallic glasses due to thermal tempering: over −300 MPa compression on the surface balanced by +150 MPa tension in the middle. The experimental data were then compared to the predictions of a viscoelastic model that took into account the equilibrium viscosity of BMG as a function of temperature. The model was shown to be accurate within 5 to 25% of the experimental stress data. It is therefore a powerful tool for estimating processing-induced residual stresses in bulk metallic glasses.

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