查看更多>>摘要：Containment structures shall remain viable even after strong ground motions to save lives and valuables. Therefore, the current study exploits the prestressing effect to mitigate seismic damage and prevent function and structural failure during seismic events. The seismic response of the studied reinforced concrete containment (RCC) structure is well captured and investigated. The results reveal that the prestressing could significantly mitigate the seismic damage and the RCC structure's bottom is the most vulnerable region. Hence, the prestressing value might be designed to mitigate the seismic damage of the RCC structure not only to keep its integrity under over-pressure. Moreover, damage assessment using different damage indices has been presented, and a modification for the Park-Ang damage index has been formulated. Furthermore, a new formula has been proposed to predict the RCC structure's damage ratio accurately, and a new classifi-cation for the damage states has been developed to identify the performance level.
查看更多>>摘要：To solve the failure problems encountered in the tunnels constructed by shallow tunnelling method in loose granular stratum, taking a tunnel construction project on the Sichuan-Tibet 318 Highway Line in China as an example. Failure phenomena, characteristics, and modes were systematically analyzed during tunnel construction. Then, the evolution at different failure modes was analyzed through DEM calculation and the prevention mechanism was discussed. Finally, corresponding construction countermeasures were put forward from the aspects of pre-support, excavation, bolt driving, and collapse prevention. The results show that: (1) The convention-ally strong support system cannot play an active role in the tunnel. The core problems in con-struction are how to reduce the disturbance of excavation to surrounding rock and realize the restraint of the support system to the surrounding rock in the arch-foot area. (2) According to the loss of the surrounding rock, the failure modes can be divided into two types: I-the rapid development failure from vault collapse and II-the lag failure of ground cavity moving up. Construction optimization aims at avoiding the mode-I and alleviating the mode-II. (3) For the mode-I, maintaining the stability of the initial ground-arch is the practical measure; For the mode -II, when the cavity area is more significant than 5 m2, it must be filled in time. (4) The field deformation data of surrounding rock after treatment shows that the effect of the proposed countermeasures is remarkable, which can provide valuable references for the tunnel design, construction, and disaster control in a similar area.
查看更多>>摘要：A numerical methodology is endeavoured to infuse the inherent heterogeneity of reinforced concrete (RC) when subjected to low-velocity impact loading contrary to the existing practice of homogenized model. Coarse aggregates are inserted as a form of inclusion with varying shape, material properties and arranged randomly across the volume. Weibull statistics has been used to quantify the random variation of material properties. A suitable damage plasticity model is used with mapped inelastic and cracking behaviour for a given grade of concrete. After validating the present model with experimental evidences in literature, the plastic work done and the energy dissipation are investigated. It was observed that the plastic work accumulation at supports loses its symmetric pattern, particularly at time-instant of maximum deformation, when present formulation of heterogeneity is considered. This significantly affects the damage accumulation and nucleation of cracks during the impact event as observed in the global failure patterns across sections at different longitudinal locations.
查看更多>>摘要：Several cracks were observed on the fifth tenon tooth root of some second stage high pressure turbine blades of an aero-engine after ground test run. Surface and sectional morphologies of cracks, recrystallization and microstructure of the near-surface were utilized to explore surface integrity of the tenon tooth root. Besides, the finite element analysis was carried out to estimate the static strength and temperature field of the turbine blade. The results showed that most of the cracks were along the near-surface carbides, where undergone grinding burn with the formation of the white layer and fine secondary gamma ' phases, and then cracks fatigue propagated during operating. Some cracks above the microporosities were ascribed to the local stress concentration when contacting with the grinding wheel during the creep feed grinding. The recrystallization occurred on the tenon teeth surface during annealing at 1000 degrees C for four hours after grinding, and related cracks were not observed in the recrystallized fine grains layer during operating.
查看更多>>摘要：Based on the Finite Element Method (FEM) and the Smooth Particle Hydrodynamics (SPH) coupling method, this paper established full-size multi-physical field coupling model of debris flow impacting pipeline. By simplifying mud into Bingham fluid, this paper studied the dynamic response law of pipeline with defect and intact pipeline (pipeline without defect) under the joint action of mud and block stone, established the displacement equations of the pipeline under impact, thus obtained the displacement, stress and strain characteristics of different pipeline positions at different impact moment. The results showed that numerical simulation of dispersing mud into SPH particles can well simulate the movement process of mud splashing and detour flow. The maximum displacement occurred in the middle part of the pipeline. For the intact pipeline, the main failure was caused by the instantaneous impact of the mud, however, for the pipeline with defect, the dominant failure factor changed from the mud impact to the stone impact. This study provided a new pathway and theoretical reference for disaster prevention and control of pipelines in debris flow section.
Visnadi, Lais BittencourtFilho, Roberto Rema GaudeosoCastro, Helio Fiori de
25页
查看更多>>摘要：Fault diagnosis is a mandatory process in modern industry management, because it may reduce costs due to unexpected failures that may occur in machines. It is proposed to study the dynamic effect in the rotor response of gear tooth crack caused by bending stress. As the bearings are the common location to install sensors as accelerometers, the response in their corresponding degrees of freedom is considered. A geared rotor model is assumed for the simulations. This model embraces a detailed finite element discretization, which contemplates five degrees of freedom per node, including torsional rotation. In addition, a time-varying mesh stiffness calculated by the potential energy method is adopted to represent the tooth contact. A crack model is assumed with three input parameters (initial position, propagation angle and depth). A design of experiments was set up to show the influence of each parameter on the system response for three different mean depths. The results analysis pointed out that for a precise parameter identification, all three parameters should be taken into account, because they affect the system response and they also present combined influence.
查看更多>>摘要：This paper aims at influence of relative density on deformation and failure characteristics for a shield tunnel in sandy cobble strata. A series of model tests were performed for tunnels with different relative densities of 0.35, 0.55, and 0.75. The evolution law of the stratum deformation during the instability process of the tunnel face was analyzed. The soil disturbance range of tunnel face instability with different relative densities was explored. The results show that relative density has a significant impact on the extent of surface subsidence. The stratum deformation caused by the instability of tunnel face in the medium dense and dense sandy cobble strata only occurs significantly behind the tunnel face, while the stratum with loose sandy cobble has sig-nificant stratum deformation behind and in front of the tunnel face. The method of improving the relative density can be used to reduce the deformation of the sandy cobble strata.
查看更多>>摘要：Ultra-high pressure fracturing technology has become more and more important in China's deep Shale Gas extraction. In recent years, fracturing manifold failure accidents have happened frequently and service life has shortened drastically. There are more than 94% of failure accidents that are caused by vibration fatigue of the union joint. In this paper, it was established as a 3d finite element model of the union joint based on finite element theory and fatigue theory. The author proposed a safety evaluation method based on fatigue life, and compared it with that based on strength. The results show that vibration is the key factor affecting fatigue life, and the fatigue life-based safety evaluation method is more suitable to describe the union joint safety. Therefore, set fatigue life as optimization goal and the key parameters of the union joint thread are optimized by orthogonal optimization method. The optimal results are obtained from the study range, namely that the thread turns 8, the pitch is 10.47 mm, the bearing surface angle is 24.5?, and the guide surface angle is 24.5?. In comparison to the initial union joint, the fatigue life of the optimized union joint is increased by two orders of magnitude. These studies improve the fatigue performance of the union joint and have important guiding significance for improving the safety evaluation level of the fracturing manifold system in this paper.
查看更多>>摘要：Failure analyses with 10 leaked and 10 non-leaked Cu tubes for a fire sprinkler system were conducted to understand the cause of pitting corrosion. Water analysis revealed that the water in the leaked tubes was more corrosive than that in the non-leaked tubes. Surface analysis revealed that the leakage due to the pitting corrosion occurred with carbonaceous residue and deposits in the presence of trapped air in the tube. Furthermore, the chloric residue in the as-received Cu tube induced localized corrosion on the Cu.
查看更多>>摘要：The tunnel face stability is a key issue to ensure the engineering safety. Combined with model tests and numerical simulations, this paper focuses on progressive settlement characteristics of sandy cobble strata for shield tunnels during the instability process. Burial depths are the main parameter in this study, and ratios of burial depth and tunnel diameter were set as 0.5, 1.0 and 2.0, respectively. The results show that the surface settlement value decreases with the increase of the burial depth ratio. In addition, the time of local instability is negatively correlated with the burial depth ratio. The soil disturbance range of tunnel face instability with relatively large burial depth is significantly smaller than that with small burial depth. This provides a reference for the research on the strata deformation caused by the instability of the tunnel face in the sandy cobble strata.
NSTL
Elsevier