Papers by Keyword: Indentation

Abstract: This study investigates the indentation fracture toughness (IFT) of six HVOF-applied cermet coatings. The materials tested were WC-42CrC-16Ni and Cr₃C₂-37WC-18NiCoCr. For each material, three coatings were produced using varying deposition parameters. IFT was measured under a 100 N load, and the K_iC values were calculated using the method proposed by Chicot. For the Cr₃C₂-37WC-18M coating, the K_iC value increased with higher oxygen and kerosene flow rates. Conversely, for the WC-42CrC-16Ni coating, higher K_iC values were observed at lower oxygen and kerosene flow rates.

Abstract: In physics and mechanics, plasticity is defined as the ability of a material to undergo irreversible (plastic) deformation. Conventionally, the plastic strain at fracture in tensile tests, δ, has been used as a quantitative measure of plasticity. However, δ does not follow the scientific definition of plasticity. The influence of structural factors, temperature and strain rate on the value of δ were not elaborated over many decades. This lack of well-founded quantitative characteristic hindered efforts to control and to increase plasticity of materials. The plasticity characteristic that corresponds to the scientific definition of this quantity, δ* = plastic strain ε_р/ total strain ε_t, has been successfully used by many scientists to determine plasticity δ* by indentation. In the present work, the technique for the determination of the plasticity characteristic δ* during mechanical compression and tensile tests of metallic alloys has been introduced for the first time. In this case, δ* is determined more precisely than by indentation, and the second deformation curve δ*=f*(ε_t) is constructed. A theory of the influence of structural factors (grain size, dislocation density, disperse particles of the second phase) on the plasticity characteristic δ* has now been developed, making it possible to estimate the influence of the indicated factors on δ* and to design alloys with an optimal combination of strength and plasticity. The discovered correlation of the values of δ* and δ for steels and for aluminum alloys allows us to use the developed theory to calculate the influence of the structural factors on d for these materials as well.

Abstract: The article is devoted to improving the accuracy measuring hardness metals based on the principle similarity mechanical. Hardness test homogeneous solid by means indentation static tip rigid into its flat surface by a force normal to this plane is considered. Volumes that have experienced plastic and elastic deformation in the process of the indentation do not have distinct and definite boundaries. Deformation degree within these volumes is as variable as the stresses causing it. The application relationship empirical between the applied static load and the restored indent diameter indent is shown.

Abstract: Mechanical properties of surface layers of aluminum alloys before and after friction tests are studied by nanoindentation. The influence of the composition of the alloys on these properties is analyzed. It is obtained that as a result of wear and tear, relatively compliant layer is formed on the surface of one of the alloys. Another sample demonstrates relatively rigid film at the surface of the friction path. Conclusions about different mechanisms of the wear and tear of alloys are made based on the analysis.

Abstract: Influence of residual welding stresses on the hardness values of the weld metal is studied. The investigations were carried out on 5V titanium alloy welded joints, obtained by electron-beam welding and argon-arc welding (TIG-welding). It is shown that the nature of the residual stresses distribution depends on the parameters of welding and affects the hardness values of the weld metal. It is shown, that the difference between the hardness values of the metal after welding and the metal after partial relief of residual stresses on the investigated alloy is up to 90 MPa, which is about 3% of the weld metal hardness level.

Abstract: Comparative studies of wear resistance during dry friction of vacuum ion-plasma coatings of nitride systems TiAlN and CrAlSiN are carried out. The structural parameters, coating thickness, and physical and mechanical properties were chosen as comparison parameters. A fundamental difference in the wear mechanisms of the coatings is demonstrated. In the TiAlN-system coatings develop an oxidative wear mechanism due to their insufficient heat resistance. The CrAlSiN-system coatings have maximum resistance to plastic deformation. And they are wear out according to the fatigue mechanism, which is typical for coatings with a high level of mechanical properties.

Abstract: This paper presents a hierarchical multi-scale modelling approach devoted to investigating the mechanical behaviour of cement-bound gravels. Material studied is based on Non-Hazardous Waste Incineration (NHWI) bottom ashes. The elastic moduli of NHWI particles have been previously determined by an original indentation campaign never conducted so far on these types of aggregates. The results of the experimental campaign serve as input data to the developed numerical strategy. The modelling is based on the definition of Representative Elementary Volumes (REV) considering all the heterogeneities of the material. The "virtual laboratory" set up made it possible to determine the mechanical parameters characterizing the gravel treated with 3% of cement. The high value obtained of the internal friction angle (76 °) gives the material a good bearing capacity. The classification in mechanical classes 3 and 4 when the Young's modulus of the NHWI particles varies from 20 to 80 GPa proves the feasibility of the reuse of this type of industrial by-products in this sector of activity. The present modelling approach is validated by means of comparisons with experimental results of the literature.

Abstract: The advantages of supplementary cementitious materials (SCM) use in concrete, such as reduced cement consumption and overall material improvement (durability, chemical resistance, etc.), are widely known. Our research focuses on two major factors connected to high performance concrete (HPC) containing SCM, the content of selected SCM and the homogenization process used for concrete mixture. Both of these aspects of this research were addressed by the authors from macro-level of the material. In this contribution, the focus is directed on microscopical performance of concrete mixtures with highest macro-mechanical features with respect to both homogenization procedure and SCM containment.

Abstract: The fan blades and turbine blades in a jet engine are seriously damaged by high velocity impingements of various foreign objects. In this study, a prediction method of indentation size formed by a high-velocity impingement of a solid sphere (PMIS) was developed from a theoretical model based on an expanding cavity model and energy conservation before and after impingement. The Johnson-Cook constitutive equation was employed to introduce effects of work hardening, strain rate hardening and thermal softening into the cavity model. As a result, the distribution of equivalent plastic strain, equivalent plastic strain rate, temperature and equivalent von Mises stress estimated using the expanding cavity model was in good agreement with the data obtained from the finite element analysis. In addition, it has been demonstrated that PMIS can accurately predict the radius of indentation formed on various metallic materials subjected to the impingement of a solid sphere with the radii of 0.75, 1.5 and 3 mm at several impact velocities from 50 to 300 m/s.

Abstract: The paper describes an experimental program focused on the research of high performance concrete with partial replacement of cement by fly ash. Four mixtures were investigated: reference mixture and mixtures with 10 %, 20 % and 30 % cement weight replaced by fly ash. In the first stage, the effect of cement replacement was observed. The second phase aimed at the influence of homogenization process for the selected 30% replacement on concrete properties. The analysis of macroscopic properties followed compressive strength, elastic modulus and depth of penetration of water under pressure. Microscopic analysis concentrated on the study of elastic modulus, porosity and mineralogical composition of cement matrix using scanning electron microscopy, spectral analysis and nanoindentation. The macroscopic results showed that the replacement of cement by fly ash notably improved compressive strength of concrete and significantly decreased the depth of penetration of water under pressure, while the improvement rate increased with increasing cement replacement (strength improved by 18 %, depth of penetration by 95 % at 30% replacement). Static elastic modulus was practically unaffected. Microscopic investigation showed impact of fly ash on both structure and phase mechanical performance of the material.