查看更多>>摘要：Natural rock mass generally contains discontinuous structural planes, such as joints, fractures and faults, which have great influence on the occurrence of rockburst. The rockburst mechanism of rock mass with structural planes in underground chamber excavation is studied by means of model test and numerical simulation in this paper. Firstly, quartz sand, barite powder, gypsum powder, cement and water are selected as raw materials to configure the similar materials suitable for the rockburst model test. Secondly, four working conditions of none structural plane, single structural plane, multiple structural planes and through structural plane are designed, and the corresponding rockburst model tests are carried out. The stress and displacement laws of surrounding rock during excavation are analyzed. Finally, the numerical calculation of chamber excavation is conducted under the above four working conditions and the model test is verified. The failure modes and laws of surrounding rock mass with different structural planes during chamber excavation are obtained. The results show that: (i) After the tunnel excavation in rock mass with single structural plane, the tension of structural plane and the expansion of fractures occur, accompanied by small-scale rockburst. (ii) After the tunnel excavation in rock mass with multiple structural planes, the stress level of surrounding rock mass decreases significantly and no rockburst occurs, but the surrounding rock is prone to large-scale collapse or spalling. (iii) After the tunnel excavation in rock mass with through structural plane, the fractures appear in the vault and arch bottom and expand rapidly, accompanied by rockburst phenomena such as granules ejection. The research results of this paper are of great significance for understanding the deformation and failure mechanism of rock mass with structural planes in the underground chamber excavation.
De Maio, UmbertoGreco, FabrizioLeonetti, LorenzoBlasi, Paolo Nevone...
18页
查看更多>>摘要：The cracking behavior analysis, in terms of crack spacing and crack width prediction, is essential to assess the damage and durability of a reinforced concrete (RC) structure. However, available numerical models cannot give satisfactory results in the cracking prediction due to the continuum representation of the concrete material often adopted in the numerical framework. Based on the cohesive finite element method, an interelement fracture model has been proposed here to investigate the cracking behavior, as well as its influence on the load-carrying capacity, of RC structural elements under static loading conditions. This fracture model is employed together with an embedded truss model for the rebars allowing them to be crossed by the cracks. Cracking analyses are performed on RC members subjected to tension and flexural loads. Comparisons with available experimental and numerical results have highlighted the effectiveness of the proposed model to investigate the cracking behavior in RC structures.
查看更多>>摘要：The premature cracking failure of a driven gear occurred in a high-speed railway gearbox of a certain line after running 600,000 km. The comprehensive analysis methods, such as physical and chemical inspection, morphology observation and inspection of the meshing surface, magnetic particle inspection, Barkhausen noise analysis (BNA) inspection, etc., were used to analyze the abnormal failure of the gear. The results showed that the failure mechanism of the gear was rolling contact fatigue (RCF), which was mainly caused by the reduced hardness and contact fatigue strength of the meshing surface from grinding burn due to improper grinding process. Both sides of the microcracks bore the internal extrusion pressure under the oil wedge effect, leading to the fatigue growth of the cracks and subsequent peeling failure. Based on the analysis results, the root causes were finally found and the pertinent prevention measures for the similar gears in service were proposed.
查看更多>>摘要：In order to further understand the failure mechanism of superheater tubes of waste heat boiler in a complex environment, sample sections cut down from the failed and non-failed tubes had been investigated by using visual observation, micro-zone analysis and Stress calculation check. Results showed that S content of 15MoG slightly exceeded the standard, and the main composition of corrosion products were related to the oxygen, sulfur, chlorine, sodium, potassium, calcium. Ash samples on the failed tube and at the bottom of the furnace were analyzed by EDS and XRD. The on-site operation and shutdown of the boiler were also considered. The failure mechanism was corrosion thinning raised by high temperature oxidation corrosion, sulfide corrosion, chloride corrosion, and dew point corrosion. The prerequisite of corrosion was that corrosive medium, over-temperature operation, severe fouling deposits were present simultaneously. Measures to limit these factors which can alleviate corrosion thinning are suggested and put forward.
查看更多>>摘要：In the present study, distribution characteristics and biodiversity of microbial communities from four real sewer pipes in urban residential area were studied. The differences of microbial community were observed in spatial distribution. The genus of Mycobacterium, Acidiphilium and Acidithiobacillus were mainly detected in the upper and middle part. Methanthrix, Longilinea and Desulfobulbus were dominant in the bottom part. Total nitrogen, sulfate and oxidation-reduction potential were identified to be the crucial driving factors in the formation of microbial community. The corrosion differences in different sites primarily resulted from the differences of microbial communities in upper parts. From the evaluation of microbial induced concrete corrosion, sulfate-reducing bacteria and fermentation bacteria in bottom part and sulfur-oxidizing bacteria in upper part played a major role. Further, the middle and end of the sewer pipes faced greater risk of concrete corrosion than the beginning parts.
查看更多>>摘要：The perovskite solar cell (PSC) is one of the most promising game-changers in the electro-optic market. This paper examines the nonlinear dynamic performance and stability of the PSC on elastic foundations under different support conditions subjected to various biaxial impacts. By incorporating the third-order shear deformation theory (TSDT) and von-K ' arm ' an geometric nonlinearity, the governing equations of the nonlinear dynamic analysis are deduced by employing the Galerkin method. By using the fourth-order Runge-Kutta approach, the nonlinear governing equations can be solved and subsequently, the dynamic buckling behaviour of the structure can be assessed. Multifaceted effects of the velocity impacts, boundary conditions, dynamic buckling criteria, initial imperfections, damping, elastic foundations, plate theories, and impulse loadings on mechanical performance and dynamic stability of the novel PSC are investigated in the numerical study. These numerical investigations inspire the holistic design of practical energy-harvesting devices with strengthened structure capacity against external impulses.
查看更多>>摘要：Adobe bricks have been used in construction since ancient times, due to their low cost, good performance and the ease of assembly and elaboration of these elements in construction. However, the low ductility and resistance of adobe could harm the structural behaviour of buildings, especially taller buildings. The addition of additives, in the form of abundant high-density polyethylene (HDPE) fibres, could improve the mechanical properties from a seismic and structural point of view. These improved adobes could replace factory bricks, whose mechanical deficiencies are similar to adobe (stiffness and flexural strength), and they could reduce the high cost of buildings today. This work analyses and compares the performance and structural performance that these elements acquire in framed buildings, compared to traditional adobe, incorporating different percentages of high-density polyethylene fibres (HDPE) in low-rise buildings (of 2 and 4 storeys), which are very abundant in areas of high seismicity. For this, models of structural frames are analysed, adding adobe walls using the mechanical results carried out in a laboratory at the University of Talca (Chile). The addition of a small percentage (0.6% and 1.2%) of HDPE in the traditional adobe, improves the ductility and the structural performance of the frames.
查看更多>>摘要：Considering the continuity of production in petrochemical plants and the harmfulness of leakage, any slight defect in the system may lead to dramatic accidents. Therefore, we used systematic characterization methods to analyze the causes of leakage near the weld of outdoor pressure pipe in a petrochemical plant. It is found that the crack extends from the outside into the inside surface of the pipe wall, and there are massive corrosion products on the crack surface. Furthermore, the damaged parts observed of the external insulating layer are wet and accumulate chlorine, which from the corrosive environment to the pipe material. Finally, it is concluded that microcracks originate from pitting pits and gradually expand to the inner surface with the coaction of internal pressure of the pipe up to 12 MPa. The reason of pipe leakage is the interaction of pitting corrosion, transgranular corrosion, and stress corrosion cracking.
查看更多>>摘要：This paper relates to experimental and numerical analyses of damage of a thin-walled laminated angle column. Limit and post-buckling states of the simply-supported column under uniform compression were investigated. Geometric imperfections of real samples were identified by 3D scanning. Flexible pads were used to prevent stress concentration where the column contacts with the rigid support plates. First, experiments were conducted on a testing machine using the Aramis system for column strain measurement. After that, a numerical model reflecting the real system was designed in Abaqus. A progressive damage analysis of the thin-walled angle columns was performed by the finite element method. Experimental and numerical post-buckling equilibrium paths were compared. Numerical and experimental results showed high agreement, both in qualitative and quantitative terms. The same failure mechanism was obtained in the experiments and in the numerical analysis, i.e. flange damage (crack) in the column centre.
查看更多>>摘要：This paper presents a proposition of innovative thermoplastics bio-resorbable composite materials based on polylactic acid. The compositions were prepared as an alternative to traditional biodegradable polymers, using grounded and dried plant waste in the form of buckwheat husks and dried onion husks. The main goal of the research was to develop new biopolymers prepared by extrusion for a wide range of industrial applications. Composite samples were made with the addition of 10, 20 and 30 wt% of onion or buckwheat husks and their mechanical and thermophysical properties were examined, with particular emphasis on the degree of crystallinity. The conducted tests showed that increasing the amount of filler decreases the mechanical properties of the composite, with the exception of the elongation at break, which slightly increased. Moreover, the 10% addition of waste positively influences the increase in the degree of crystallinity of the samples.
NSTL
Elsevier