Papers by Keyword: Damage Mechanism

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Authors: Gabriella Zsoldos, Pál Bárczy, Tamas J. Szabo
Abstract: During this study the distortion phenomenon was investigated on selected UHMWPE cups removed from patients, using 3dimensional measurement method. The cups investigated were machined by Metrimed Ltd. from ram extruded Chirulen 1020 type UHMWPE rods. The samples were measured with a 3D touch coordinate measurement device with an accuracy of 3 microns.
521
Authors: Yue Jun Zhang, Jin Fang Peng, Zhen Bing Cai, Min Hao Zhu
Abstract: A railway axle operated over 6×105 km has been detected by varied micro-examination methods in detail. The examination of Leeb hardness tester results showed that the hardness of the press-fit seats presented higher hardness than that of other sites. According to the micro morphological analyses by optical microscope (OM), scanning electron microscope (SEM), energy dispersive X-ray spectrum (EDX), and profilometer on the surface at different press-fit seats, the most severe damage band was occurred at the inner edge of wheel seat near the gear seat. The transmission electron microscope (TEM) results indicated that the dislocation density of subsurface, beneath the axle surface about 20 μm, was much higher with a great deal of dislocation tangles, pile-ups and cellular structure formation. However, when the examination depth increased to 100 μm, no cellular structure can be founded, the dislocation density was very low, so the damage depth was less than 100 μm.
1393
Authors: Daniele Ferretti, Eva Coisson, Marco Rozzi
Abstract: The present paper concentrates on the numerical modelling of masonry vaults, adopting a type of analysis first developed at the University of Parma for applied mechanics, based on the use of non-smooth dynamics software, through a Differential Variational Inequalities (DVI) formulation specifically developed for the 3D discrete elements method. It allows to follow large displacements and the opening and closure of cracks in dynamic field, typical of the masonry vaulted structures. Once the modelling instrument was calibrated, thanks to the comparison with the recurrent damage mechanisms previously analysed, it was also applied to foresee the behavior of the same structure with different actions and with different types of strengthening. The development of damage mechanisms, both in quasi-static cases (for insufficient lateral confinement or for possible soil settlements) and in the occurrence of seismic events, make this type of structures very difficult to be modelled precisely with other methods. Given the three-dimensional CAD model of a vault modeled with a great number of masonry units with specific positions and pattern, the method proved to be able to reproduce the behavior of the structure under both static and seismic loads, showing the mechanism of collapse, the network of contact forces, the displacements and other useful data. The aim is to inspect the possible influences in the structural behavior given by the discrete geometry and the changes in the mechanisms development given by different strengthening interventions. Once the modeling instrument will be calibrated, also through the comparison with real cases and with the results obtained through limit analysis, it will be possible to adopt it as a base also for the prevision of the future behavior of the vaults subjected to strengthening, avoiding uncalibrated and uncritical applications of materials based more on trends rather than on a thorough analysis for the specific case.
52
Authors: Irina Pushkareva, Abdelkrim Redjaïmia, Antoine Moulin, Nathalie Valle
Abstract: A detailed analysis of the evolution of industrial Dual Phase (DP) steel microstructures is carried out as a function of various annealing and tempering conditions. Advanced characterization techniques such as Parallel Electron Energy Loss Spectroscopy (PEELS) in the TEM and high spatial resolution Secondary Ion Mass Spectrometry (NanoSIMS) are employed in order to provide qualitative and quantitative measurements of local carbon concentration in the martensite. For certain annealing and tempering conditions, it is observed that local variations in carbon levels have occurred inside the individual martensite islands. These carbon variations strongly influence the damage behaviour of the steel. During tensile tests, a clear dependence of the damage mode on the local martensite carbon content is observed. Better knowledge of the relationship between the microstructure evolution at the sub-grain level and the damage behaviour can facilitate the design of DP steels with improved damage resistance.
839
Authors: Xian Kai Bao, Yi Li
Abstract: Aiming at the surrounding damage and instability in underground excavation and operation, an analysis of surrounding rock damage modes and an exploration of damage mechanism are done and an conclusion of control principles and means for surrounding rock deformation and damage is made in the thesis. The result dovetailed with engineering and provides reference for engineering design and operation.
1367
Authors: Roman Petráš, Viktor Škorík, Jaroslav Polák
Abstract: Thermomechanical fatigue experiments were performed with austenitic stainless Sanicro 25 steel. Several amplitudes of mechanical strain in a wide temperature interval (250-700 °C) were applied to the specimens. Mechanical response was recorded and fatigue lives were obtained. Scanning electron microscopy combined with FIB technique was used to study the mechanism of crack initiation in in-phase and in out-of-phase thermomechanical cycling. Different mechanisms of the crack initiation were found in these two types of loading. During in-phase loading fatigue cracks start in grain boundaries by cracking of the oxide. Cracks grew preferentially along grain boundaries which resulted in rapid crack initiation and low fatigue life. In out-of-phase loading multiple cracks perpendicular to the stress axis developed only after sufficiently thick oxide layer was formed and cracked in low temperature loading half-cycle. The cracks in oxide allowed localized repeated oxidation and finally also cracking. The cracks grow transgranularly and result in longer fatigue life.
273
Authors: Jie Wei, Yu Hong Chen, Liang Jiang
Abstract: Short carbon fiber reinforced silicon carbide (SiC) composites were prepared with boron (B) and carbon (C) as sintering additives via pressureless sintering at 2150°C. The damage mechanism of fiber was investigated as following: (1) The carbon fiber was seriously physically damaged in the process of material mixing; (2) The chemical damage of the carbon fiber was happened in the reaction with matrix as the high sintering temperature; (3) Numerous cavities exist between the carbon fiber and the matrix leads to the weak interfacial strength.
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Authors: Zhuo Lin, Ming Tian, Dong Bai Chen, Chun Feng Li
Abstract: According to the analysis of the structure, topography, earthquake sequence, and earthquake hazards in September 2012 earthquake of Yiliang County, Yunnan Province, the mechanism of the earthquake damage is given. The low-cycle fatigue, shallow source, topography, population density, seismic capacity of the structure and seismic awareness of the residents is the main damage factor. This research provides a reference to the seismic design of analogous regions.
1426
Authors: Ivo Šulák, Karel Obrtlík, Ladislav Čelko, Pavel Gejdoš
Abstract: Thermal barrier coatings are widely used to protect the substrate from high temperature and extremely aggressive environments in gas engines. In the present article, authors have been studied degradation of complex thermal barrier coating system deposited on polycrystalline nickel superalloy IN 713LC. The substrate material was grit blasted with alumina (Al2O3) particles prior to air plasma deposition of CoNiCrAlY bond coat. Top coat consists of conventional zirconia (ZrO2) stabilized by yttria (Y2O3) -YSZ ceramic in combination with a eutectic nanocrystalline ceramic Eucor made of zirconia (ZrO2), alumina (Al2O3) and silicia (SiO2) –in the ratio of 50/50 in wt. %. The top coat was deposited using water stabilized plasma. Test specimens with the TBC coating system were fatigued under strain control condition in fully reversed symmetrical push-pull cycles at 900°C in air. The microstructure of TBC was characterized with scanning electron microscopy and energy dispersion X-ray analysis. The coating hardness and thickness were measured. Fracture surface and polished sections parallel to the specimen axis were examined to study damage mechanisms in coatings under cyclic loading at high temperature. TBC delamination was observed at the top coat/bond coat interface after cyclic loading at high temperature. Fatigue crack initiation sites are documented. Majority of fatigue cracks start from the surface and top coat/bond coat interface.
420
Authors: Jun Qi Lin, Xiao Qing Fang, Jin Long Liu
Abstract: The state of art of tunnel earthquake damages and tunnel earthquake damage mechanism are briefly introduced in this paper. According to tunnel’s traffic function and damage descriptions based on the investigation, tunnel damages are divided into five grades: no damage, minor damage, moderate damage, major damage and collapse, and their corresponding damage index range and characteristic values are defined. The influence of tunnel materials in Kobe earthquake and Chi-Chi earthquake are collected in this paper, and the damage grades are determined based on the performance in the earthquake. After comparative analysis, the seismic intensity, overburden depth, rock classification, distance to faults and the tunnel length are chosen as the seismic damage influence factors. A formula for tunnel seismic damage evaluation is deducted using these factors and the least square method and with the modification of construction time, seismic fortification intensity and portal stability. The damage of four tunnels is evaluated using the derived formula, and the results are the same with that of static and dynamic methods. It shows that the method provided in this paper is effective, reliable.
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