Key Engineering Materials Vol. 586

Abstract: One of the ways to increase service life of the abrasive wear parts are new developed as-cast steels with ceramic phase. Expensive wear resistant high chromium cast iron can be exchanged by Fe – B alloys. The mechanical properties of the borides in the Fe – B cast iron depend on alloying elements like chromium or nickel. A set of sample with different content of carbon, chromium, nickel and boron has been prepared. Chemical composition (GDOES) and microstructure of the as-cast alloys have been investigated as well as the hardness and Young modulus of the borides. Our results shown that mechanical properties of borides depends both on chromium and carbon content.

Abstract: The paper deals with determination of mechanical properties of active solders type Sn3.5Ag4Ti(Ce,Ga), Sn2Ti, Bi25In18Sn and Sn2La by use of “Small Punch Test” (SPT). Reference curves were plotted for determination of mechanical properties of the mentioned solders, which allowed mutual comparison of measured results from SPT test with the results obtained from standard tests. On comparison of SPT results with the results of standard methods agreement of both results is obvious. It may be thus concluded that SPT technique can be used for assessment of mechanical properties for a wide scope of soldering materials.

Abstract: Titanium is material which is used in many areas of human activity. Therefore it is necessary to join it with other material. It is very difficult to welding Ti with other metals by conventional fusion welding methods. There exist special joining technologies of heterogeneous materials which is possible to use. This is usually a joining of materials in the solid state, as diffusion welding, friction welding or explosion welding. This contribution deals with diffusion welding of titanium alloy Ti6Al4V and stainless austenitic steel 1.4301. There are described mechanical properties (as is reduced modulus Er and indentation hardness HIT) and changes of chemical composition of join due to diffusion of elements.

Abstract: The glass-cement plates have made great progress today. They extend the possibilities of technical requirements in solutions of complex structures. The higher aesthetic requirements are available with the plates and in another point of view they contribute significantly to economic aspect in construction. The article describes the tests of high temperatures resistances of glass-cement plates. The first part is focused on determining the values of tensile strength in bending for samples subjected to annealing at temperatures 200, 300, 400 and 500 ° C in endurance at the highest temperature level for 24 hours. The results will be compared with values obtained for the reference samples. The bending strength was performed according to the norm ČSN EN 1170-4 Precast concrete products - Test method for glass-fibre reinforced cement - Part 4: Measuring bending strength, "Simplified bending test" method. The mean strength in bending of reference samples was equal to 11.3 MPa. The strength is decreasing with temperature of firing and dependence is very closed to linear relationship with slope approx. 1.87 MPa per 100 °C. Furthermore, the thermal dilatometric analysis was performed on the plates in the temperatures till 540 °C in the second part.

Abstract: In the case of material parameters required for evaluation of built heritage preservation state, knowledge of the least possible volume of removed sample is essential in order to minimize damage accumulation to the buildings. These requirements lead to determination of representative volume element (RVE) that was in this paper calculated using combination of image and signal processing techniques. Then, a detailed map of material properties was created using nanoindentation to evaluate local characteristics of the material. Furthermore, atomic composition of samples was quantified by energy dispersive spectrometry (EDX) detector for scanning electron microscopy (SEM) device. Presented method based on combination of SEM, EDX and nanoindentation techniques demonstrates possibility of effective testing in the field of historical buildings preservation.

Abstract: When the depth-sensing (nano)indentation is applied to sintered samples, measured properties, which are expected to represent the material of an individual grain, seem to depend on the overall porosity of the macroscopic sample. To understand such a result, it is assumed that while the nanoindenter penetrates into the surface grain and probes the properties of its material, the grain itself serves as another, larger indenter indenting the rest of sample and probing the properties that represent the bulk of material rather than individual grains. Load vs. displacement curve reflects the synergetic response of these two “indenters” and so it contains information about the sample’s mechanical properties at both microscopic and macroscopic scales. Obtained theoretical results agree qualitatively with the experimental data (the dependence of the indentation modulus on the porosity of sample; the indentation size effect).

Abstract: In this paper a particulate composites with polypropylene matrix and rigid mineral fillers are studied. The polymer particulate composites are frequently used in many engineering applications. Due to the physical and chemical interaction between matrix and particles a third phase (generally called interphase) is formed. The composite is modeled as a three-phase continuum. The properties of particles and interphase have a significant effect on the global behavior of the composite. On the basis of fracture mechanics methodology the interaction of micro-crack propagation in the matrix filled by rigid particles covered by the very soft interphase is analyzed. The effect of the composite structure on their mechanical properties is studied here from the theoretical point of view. The properties of particles and matrix were determined experimentally. Conclusions of this paper can contribute to a better understanding of the behavior of micro-crack in polymer particulate composites with respect to interphase.

Abstract: The experimental study deals with the effect of modification of the surface layer by irradiation cross-linking on the mechanical properties of the Poly (methyl methacrylate) - PMMA tested using the instrumented microhardness test. The surface layer of PMMA specimen made by injection technology was modified by irradiation cross-linking using beta irradiation, which significantly influences mechanical properties of the surface layer. Compared to the heat and chemical-heat treatment of metal materials (e.g. hardening, nitridation, case hardening), cross-linking in polymers affects the surfaces in micro layers. These mechanical changes of the surface layer are observed in the instrumented microhardness test. Our research confirms the comparable properties of surface layer of irradiated PMMA with highly efficient polymers. The subject of this research is the influence of irradiation dosage on the changes of mechanical properties of PMMA.

Abstract: Local polymerization stress occurs due to polymerization shrinkage of resin based composites adhesively bonded to tooth tissues. Shrinkage causes local displacements of cavity walls, with possible occurrence of micro-cracks in the enamel, dentin and/or material itself. In order to design a cavity for experimental testing of polymerization shrinkage of dental composites using 3D optical analysis, in this paper finite element method (FEM) was used to analyze numerical models with different cavity radiuses. 3D optical strain and displacement analysis of composite materials and cavity walls is limited by equipment sensitivity i.e. 0.01% for strain and 1 micron for displacement. This paper presents the development of 3D computer premolar models with varying cavity radiuses, and local stress, strain and displacement analysis using FEM. Model verification was performed by comparing obtained results with data from the scientific literature. Using the FEM analysis of local strains, displacements and stresses exerted on cavity walls, it was concluded that the model with 1 mm radius was optimal for experimental optical 3D displacement analysis.

Abstract: This paper aims to apply time-temperature superposition to short-term microindentation data measured at different temperatures, and to compare the viscoelastic compliance master curve that is found with data derived earlier from standard macro creep measurements in pressure. Using a sharp standard Berkovich indenter a successful application of this geometry in characterizing time-dependent mechanical properties of viscoelastic materials is confirmed.