Jan DuszaLucia HegedusovaMonika KasiarovaErika Csehova...
761-764页
查看更多>>摘要：The paper deals with the determination of the characteristic strength δ_(0,bend) and δ_(0,cont) as well as the Weibull moduli m_(bend) and m_(cont) of the Si_3N_4+SiC micro/nanocomposite determined by the four-point bending test and the contact test using opposite spheres both applied to specimens of different size, respectively. Material failure in the bending and contact modes is caused by the presence of processing defects as fracture origins, and by the formation of cone cracks, respectively, where a stable growth of the cone cracks initiated during contact loading is assumed to be a reason of δ_(0,cont) >>δ_(0,bend), m_(cont)>>m_(bend). A microstructural analysis of the processing flaws, and a mathematical analysis of the propagation of the cone cracks regarding different dimensions of a specimen are also presented.
查看更多>>摘要：This study is focused on examining the effect of cracks on chloride penetration into concrete. In order to get reliable results, short-term and long term experiments were set up and chloride penetration behaviour through cracks was examined. It was noticed that chloride penetration through cracks tends to decrease with time. One of the explanations is crack-healing. Especially, this trend was obvious in concrete samples with larger crack width. However, measuring the border between chloride contaminated zone and healthy zone was clear in concrete of short-term experiment, while it was ambiguous in long term experiment.
查看更多>>摘要：The paper is devoted to numerical modelling of R-curve behaviour in laminates with strong interfaces, in particular multilayers made of alumina (A) and zirconia (Z). Contrary to previous studies based upon the application of approximate weight function method originally developed for homogeneous specimens, a full field analysis by FE of a three-point bending test of a sandwich beam is attempted and compared with the results obtained by approximate weight function method. Also the crack penetration across the layer interfaces is discussed, particularly in the case of a weak singularity.
查看更多>>摘要：Due to the stress concentration effect around the hole, cracks are likely to initiate at the hole under the action of fatigue loading. This paper is specifically concerned with cracks emanating from a surface semi-spherical cavity in a finite body by using the boundary element software FRANC3D developed by a fracture mechanics investigation group of Cor-nell University. The numerical results can reveal the effect of the geometry of the surface cavity on the stress intensity factors.
查看更多>>摘要：On 12 May 2008, a magnitude 8.0 earthquake happened in Wenchuan, China .It was the most serious earthquake in china since 1949, causing very huge casualties and engineering damages. The complex building of the Xuankou secondary school in Yingxiu town was designed by the Code for Seismic Design of Buildings of China (GB50011-2001), the seismic fortification intensity of the buildings was 7 degree. In the earthquake, it was destroyed most seriously, and the engineering damage was characteristic. In the paper, the properly of material nonlinearity was considered ,the nonlinear analysis model of infilled frame structure was established, the time history analysis and nonlinear static analysis were used during inelastic stage, the main cause of structural destruction was obtained, the influence of the infill wall on the structure was discussed.Therefore ,the results can provide valuable reference for the seismic design of infilled frame structure.
查看更多>>摘要：High-resolution elastoplastic simulations of a plane-strain tensile crack under cyclic loading visualised the Laird-Smith mechanism of fatigue crack growth, which manifested the effects of ΔK and overload, but no signs of crack closure. Simulations discarded the supposed mechanism of plasticity-induced crack closure (PICC) via out-of-plane stretching of material elements filling-in the crack and coming in contact at unloading. Specimen compliance curves turned out to be nonlinear merely by virtue of plasticity with no contribution of crack closure. Thus the results manifested the ambiguity of main justifications about the phenomenon of PICC.
查看更多>>摘要：This study is focused on modification of a conventional bumper damper to increase its energy absorbability. This bumper damper device is currently used on passenger vehicles for reducing structural damage, as well as part of the pedestrian protection system. A hollow aluminium cylinder with 2mm in thickness was subjected to a range of experiments. The energy absorption takes place as a ram displaces along the cylinder's bore, where the outer diameter of the ram is slightly wider than the inner diameter of this cylinder.Results from laboratory experiments and ANSYS finite element software showed that the hollow cylinder absorbs 3.2 kJ energy, after the ram was displaced 80mm inside the cylinder. The damper is modified by attaching two metallic rings with 1mm thickness outside the cylinder surface to increase its crashworthiness, the addition of these rings resulted in increase of 16% in energy absorption.
查看更多>>摘要：Thermoplastic elastomers are a relatively new group of engineering materials and are increasingly used in various technical applications (i.e., seals, gaskets, damping elements, and membranes) where the fatigue resistance plays an important role. The fracture behavior of elastomers is often characterized using the tearing energy concept, T. However, hardly any data are available for these types of materials. Hence, an unfilled and a filled thermoplastic polyurethane (TPU) type were investigated under cyclic loading conditions. The pure shear specimen configuration was used in the experimental part of this study. Crack growth kinetics curves were determined and the cycle number and the tests frequency dependence of these curves investigated. While a stable crack growth process was observed at 2 Hz the crack growth became unstable above specific test amplitude at 10 Hz.
查看更多>>摘要：In this paper, the influence of deep cryogenic treatment (DCT) on mechanical properties of two commercial steels is analysed. Hardened AISI 302 stainless steel and 18NiCrMo5 carburized steel specimens were subjected to DCT after standard treatments. For both materials, the fatigue behaviour is a key property considering their usual applications requirements. Surface hardness, tensile properties and axial fatigue resistance of both materials were measured and compared with and without DCT. From the analysis of the experimental results and from their interpretation in the light of the previous literature, some useful indications are obtained about the DCT potential fallout on design and construction of structural components.
查看更多>>摘要：The aim of this work is to investigate the (rolling) contact fatigue behaviour of transmission spur gears coated with PVD (Physical Vapour deposition) thin hard films. Numerical models of coated steel and titanium spur gears were developed. The effect of the residual stress gradient induced by the coating deposition process was considered in the calculations. A theoretical-numerical procedure was arranged to foresee the crack propagation direction. Such a procedure could represent a powerful tool to predict the (rolling) contact fatigue resistance of PVD-coated gears.
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