Solid State Phenomena Vol. 240

Abstract: The development of measurement methods, and in particular digital image correlation (DIC) systems, which are designed to measure of entire displacements and deformations fields, opens up new areas of research. In general, the materials constitutive relations are formulated in such a way that material parameters could be determined with relatively simple experimental tests carried out on samples with uniform (approximately) stress and strain fields. Then it is possible to apply them to complex boundary value problems formulated e.g. in the small or large deformation theories. The application of DIC allows to verify the accuracy of their predictions by comparing the results of the experiment with solutions to boundary value problems obtained using the finite element method (FEM).

Abstract: The paper attempts to clarify the differences between theoretical and experimental values of elastic bearing capacity for shields with openings under tension. The discrepancies occur between the experimental and the FEM calculations results which were realized by team of Institute of Applied Mechanics of Cracow University of Technology.For the purpose of comparative analysis one performed FEM calculations of the 15CrMo steel shield of geometry which was the geometry of shields being the subject of the experiments. The material model assumed in the FEM calculations was the elastic-plastic steel with the small linear reinforcement. In the calculations it was failed to obtain analogous plastic deformation schemes as in the experiments. There was obtained a similarity between the plastic zones shape and dimensions obtained from FEM calculations and for plastic zones shape and dimensions from experiments for loadings which exceed the experimental elastic bearing capacity for about 20%.

Abstract: The paper presents a method based on FEM analysis of determining the strain hardening of elements after the thermochemical treatment. A computational algorithm, which takes into account two factors, has been suggested. Firstly, the gradient of material properties resulting from the changes in the carbon content in the surface layer after the carburizing process. Secondly, the phase transformations occurring during the hardening of the material. The proposed flowchart did not include the flow effect, which greatly reduced the computation time by eliminating tedious CFD calculations. Thanks to an original program Converter coupled with a commercial software's SimHard, SimCarb J Math Pro and Ansys the carburizing process followed by quenching in gases was modeled. In parallel to the numerical calculations the results were verified experimentally. The results of FEM analysis for the tube made of stainless EN 16CrMn5 subjected to three processes of thermochemical treatment have also been presented in the paper. The experimental results were compared with the numerical simulations and a satisfactory convergence has been achieved.

Abstract: In this paper we present a calibration method, which enables a combining of 3D Digital Image Correlation and termographic systems for simultaneous measurements of displacements, strains and temperature. It concerns a model of a calibration target, that works for visible and infrared light spectrum and calibration method. The working system was applied for three interesting cases: monitoring of a tank filled with liquid, a heated plexi board and a human arm during muscle contraction.

Abstract: The aim of the research, presented in the paper, is to show and to assess the porosity structure in accordance to the dimensions of carbon dioxide particle. The characteristic surface morphology of the sample and the visualisation of the coal porous structure have been obtained using the atomic force microscope (AFM). The presented study of the coal microstructure is a part of the concepts of the project which aim is to develop the guidelines for design of the innovative technology of shale gas recovery with the use of liquid CO₂. The technology will be based on Military University of Technology invention which considers gaseous hydrocarbons recovery from at least two levels of lateral wellbores with the use of supercritical CO₂, what will result with wellbore productivity increase, because CO₂ will cause desorption of CH₄ from the porous structure of shale rock and the thermodynamic transformation of CO₂ in the reservoir will help the rock fracturing. The heat energy added for the fracturing process will be taken from the surrounding rock mass.

Abstract: The paper presents a description of the stand for rock material fracturing in laboratory conditions. Requirements to be met by fracturing stands were formulated. Proper operation of the test stand was verified by marble sample fracturing. Many of technical details of the developed stand were given, which may be useful for readers designing their own stands.

Abstract: Thermomechanical conditions in which the elements of modern aircraft engines work, require the use of protective coatings. The coatings increase the creep strength and also the local thermal stress in the near-surface areas due to the differing thermal expansion of particular material layers. For this reason it is necessary to develop a method for evaluating the operating properties of nickel superalloys with the aluminide layer, taking into consideration the surface processes related to the thermo-mechanical fatigue, taking place during the operation. In the presented work the assessment of the influence of the aluminium-coated layer, deposited on the nickel alloy specimens in the chemical deposition process (CVD) on the changes of the damage parameter in cyclic load conditions was carried out. The damage parameter was defined as a total strain in consecutive load cycles. The dynamics of damage development was analysed for two specimen lots (4 with the layer and 4 without it) displaying axial symmetry with a narrowing in the measured section. The results obtained were correlated with the results of fractography studies using SEM. The results obtained were used for the determination of the relationship between the damage parameter being the sum of the average strain and the strain amplitude, and the number of cycles, until the specimen is destroyed.

Abstract: When a material is subjected to a cyclic loading at high values of stress or strain, both thermal and damage develop together with cyclic plastic strain. These processes are often accompanied by damage deactivation characterized by actual state of micro-cracks, which are generally active under tension and passive under compression. In classical formulation damage deactivation occurs instantly when loading changes sign and consequently leads to non-smooth path separating both load ranges. The real materials, however, do not exhibit such bilinear paths. Therefore, the more realistic model based on continuous damage deactivation is proposed, in which micro-cracks close gradually, see Cegielski and Ganczarski [2, 3, 4], Hansen and Schreyer [5]. Simultaneously, thermo-mechanical coupling may play essential role in processes of cyclic plasticity hence present formulation comprises an additional heat transfer equation.

Abstract: This work presents results of fatigue tests of P91 steel specimens under constant-amplitude and programmed loading in temperature T=600°C. Two strain levels, applied in different order, were used for programmed loading. The loading program level changes were introduced for different levels of damage. The tests provided the basis for analysis of strain energy ΔW_pl in the function of the number of load cycles under constant-amplitude and programmed loading. It has been found that that the form of a loading program has an influence on the life and value of energy cumulated in the specimen until crack initiation. Verification of Palmgren Miner hypothesis revealed that its effectiveness depends on the loading program and temperature.

Abstract: Metal matrix composites (MMCs) with aluminium alloy AA2124 matrix reinforced with 17 and 25% of SiC were investigated. Symmetric tension-compression fatigue tests at ambient temperature and tensile creep tests at elevated temperature were carried out. Specimens were subjected to fatigue or creep loading conditions. Tests were stopped after given number of cycles or strain values respectively. Electronic Speckle Pattern Interferometry (ESPI) was used in order to detect damage under fatigue and creep conditions. Strain fields were observed on specimens’ surfaces to localise strain concentrations that would indicate areas of damage development.