Key Engineering Materials Vol. 662

Abstract: Three cracked geometries loaded in mode I are investigated and the plastic zone size calculated. For estimation of the plastic zone size, two fracture criteria are used (Rankine and von Mises). Whereas the classical criteria give the same results (the stress intensity factor being identical for each geometry), the data from numerical simulations exhibit differences for various geometries. It is shown that the multi-parameter form of the criteria enables to obtain results that agree better to the numerical ones. Particularly, the Williams expansion is utilized for approximation of the stress components that serve as inputs for the fracture criteria. It is concluded that taking into account several more initial terms of the series can help to predict the plastic zone size more accurately.

Abstract: Local plastic deformation in cutting zone during turning is affected by technological conditions of the processes. Therefore it is needful to know detail structure changes of plastic deformed material during machining. It is localised, asymmetric deformation which operates at very large strains and exceptionally high strain rates. Three areas of intensive local plastic deformation in cutting zone were observed: the primary area of plastic deformation in shear plane, the secondary area of plastic deformation caused by friction of chip to tool face and the tertiary area of plastic deformation caused by friction of tool to machined surface. Local strain in these three areas was estimated by measurement of deformation of grains on metallographic cut. The effect of grains boundaries self-orientation caused by grains deformation was evaluated using stereology. But the orientation is not the same as deformation and so a correlation between the grain deformation and grain orientation was used. The turning piece was made of CK45 (1.0503) carbon steel. The specimen of cutting zone was obtained by using internal stress method.

Abstract: The presented article deals with the research of surface layer ́s micro-mechanical properties of modified LDPE by radiation cross-linking after temperature load. These micro-mechanical properties were measured by the DSI (Depth Sensing Indentation) method on samples which were non-irradiated and irradiated by different doses of the β – radiation and then were temperature loaded. The purpose of the article is to consider to what extent the irradiation process influences the resulting micro-mechanical properties measured by the DSI method. The LDPE tested showed significant changes of indentation hardness and modulus after temperature load.

Abstract: This paper deals with utilization of recycled irradiated high-density polyethylene (rHDPE_x) as a filler which was blended with non-modified high-density polyethylene (HDPE). Two blends were tested regarding the original state of the mixing components – HDPE granules/rHDPE_x grit and HDPE granules/rHDPE_x powder. Results show that the increasing amount of the rHDPE_x, regardless its form, results in worsening both observed parameters – hardness and micro-indentation hardness.

Abstract: The presented article deals with the research of micro-mechanical properties in the surface layer of modified Polypropylene filled by 25% of glass fibers. These micro-mechanical properties were measured by the Depth Sensing Indentation - DSI method on samples which were non-irradiated and irradiated by different doses of the β - radiation. Radiation doses used were 0, 66 and 99 kGy for filled Polypropylene with the 6% cross-linking agent (triallyl isocyanurate). The change of micromechanical properties is greatly manifested mainly in the surface layer of the modified polypropylene where a significant growth of microhardness values can be observed.

Abstract: Cross-linking is a process in which polymer chains are associated through chemical bonds. The cross-linking level can be adjusted by the irradiation dosage and often by means of a cross-linking booster. The polymer additional cross-linking influences the surface nanoand micro layers in the way comparable to metals during the thermal and chemical-thermal treatments. The aim of this paper is to study the effect of ionizing radiation with different doses (33, 66 and 99 kGy), on micro-mechanical properties of polyethylene (HDPE) and compare these results with those of non-irradiated samples. Influence of the cross-linking by β – radiation of the tested HDPE on micro-indentation test and morphology was investigated. Micro-mechanical properties increased with increasing value of the dose of irradiation material. The changes were examined and confirmed by X-ray diffraction.

Abstract: The possibility of the non-destructive testing of concrete surface morphology by means of a new-generation 3D laser scanner is presented. The test results for a reference concrete substrate surface and a sandblasted concrete substrate surface are reported. The effect of sandblasting on the morphology of the concrete surfaces of the substrates is highlighted. The results are presented as three-dimensional images and the values of the morphology parameters are compared in a table.

Abstract: The contribution deals with estimation of tensile properties and fatigue behavior based on hardness measurement. First of all the database of tensile and fatigue properties vs. hardness data was created for a group of steels, from literature survey and performed experiments. Tensile strength, yield strength, ductility and parameters of Ludwig-Hollomon equation in static and cyclic loading were extracted and fitted in relation to the hardness HB. The experimental materials were API 5 L grade steels – X60 and X70 after different deformation exposition. Measured tensile curve (SC) and cyclic deformation curve (CDC) were compared with predicted curves. Hardness was measured in-situ during cyclic loading. The maximum possible hardness values were experimentally determined. The results give a good agreement between estimated and measured data of both static tensile test and fatigue properties.

Abstract: Laser welding is one of advanced and promising joining technologies of metallic materials, characteristic by numerous advantages in comparison with conventional welding processes. The technology still can be considered as fairly new and so, investigations are needed to reach optimum properties of welds in specific application cases, depending on welding parameters. Certification welding procedures usually require to demonstrate sufficient microstructure, mechanical, impact loading and other characteristics, but not fatigue resistance, which is essential for welded dynamically loaded structures. The paper contains results of fatigue resistance investigation of laser welded 10 mm thick sheets of a carbon structural S 355 steel. High cycle fatigue tests were performed after optimizing laser welding parameters. Resulting endurance limit of the welds and heat affected zone was higher than that of basic material. However, high scatter of results and different damage mechanisms were shown for different load amplitudes. The results are discussed on the basis of fractographical analyses, which provided some quite interesting details about crack initiation mechanisms.

Abstract: Clinching is a simple, cheap and efficient method of joining that enables to join two or more sheets without any additional elements such as rivets, bolts or nuts. In addition, clinching does not require a surface preparation e.g. drilling (riveting), cleaning and roughening of the surface (adhesive boding) and other types of surface preparations (arc welding). Clinching is utilized in a wide range of applications and can be applied to different materials such as low carbon steel sheets, high-strength steel sheets, aluminium alloys, magnesium alloys. The paper presents the results of evaluation of clinched joint properties. The advanced high-strength steel sheet DP600 in combination with the drawing grade steel sheets DC06, DX51D+Z and high-strength low alloy steel sheet H220PD were used for experiments. The influence of position of the sheets relative to the punch and die of the tool on the carrying capacities of the clinched joints was observed as well. The tension test and microhardness test were used for the evaluation of clinched joint properties.