查看更多>>摘要：Climate change severely impacts the architectural heritage. Old buildings may have survived many large storms and heavy snows in the past, but extremes have increased recently. Meanwhile, the condition of historical structures gradually degrades even if they have had regular maintenance. Church towers are strongly affected: they are subject to increased wind compared to the other parts of the building. They are in a high location and gain less attention because of their out-ofthe-way position. On 17th September 2017, a massive storm in the Banat region, Romania, caused several church towers to collapse: the towers of Toager, Remetea Mare, Donceni and Ghilad fell down to pieces that day. The collapse of the tower of Dumbrava was one of the buildings involved, this study aims to clarify whether the poor condition of the building, or the flaw of the original design was the main reason for the failure in this village. The structural analysis of such historical timber structures can be problematic as the weak joints of the structure limit the load-bearing capacitance in an exceptionally low level if the traditional elastic analysis is used. The present paper points out that the plastic limit analysis can give a more realistic breaking load level for the high order statically indeterminate carpenter roofs.
Sattar, MohsinOthman, A. R.Kamaruddin, S.Akhtar, Maaz...
30页
查看更多>>摘要：Traditionally, the detection of the creep responses has been carried out using empirical methods containing multiple adjustable parameters. This makes it very difficult to estimate the material' creep behaviour outside the original data set. In recent years, the researchers have devised simple models for the prediction of creep properties, covering dislocation, particle and solid solution hardening. There are no adjustable parameters in these versions, these models are further explored in this study in order to establish an optimized solution for the creep analysis. This paper presents a review of the five established models which are Norton Bailey, Omega, KachanovRabotnov, Theta projection and Sine hyperbolic models. In depth analysis of these five creep models was conducted, highlighting the significance of their application and the demerits of their usage. First, creep phenomenon was explained, followed by creep mechanism and creep crack growth characterization. Historical development of the models was explained briefly followed by creep material models limitations. With the help of case studies, pros and cons of using the models were further highlighted and comparison was drawn among the models. Finally, future development of creep prediction models and their scope came into limelight. It is anticipated that this review paper will become a reliable reference for the selection of creep prediction models.
查看更多>>摘要：Corrosion and corrosion fatigue experiments were conducted on a butt weld constructed of G20Mn5QT cast steel and Q355D steel in a dry-wet cycle with 3.5 wt% NaCl solution. The microstructural characterization was analyzed using SEM. The butt weld suffered from pitting corrosion in a dry-wet cycle. Chloride ion erosion and defects (welding defects and casting defects) have important influences on pitting corrosion. Internal defects and corrosion pits are the main cause of corrosion fatigue failure of the butt weld specimens. Drying time accelerates pitting corrosion and corrosion fatigue progression without changing the corrosion and corrosion fatigue mechanism in 3.5 wt% NaCl solution. The three-parameter Weibull model has good applicability for evaluating the corrosion fatigue behavior of G20Mn5QT cast steel and Q355D steel butt welds in simulated seawater.
查看更多>>摘要：The interturn faults of voltage transformers will cause inaccurate data collection, wrong decision and wrong action of relay protection in power system. It is necessary to put forward an effective on method about the voltage transformer assessment. Two novel sensitive methods based on the excitation current and the phase difference between primary voltage and the excitation current (phase difference) for identifying interturn faults during energization of voltage transformer are presented. The kirchhoff's voltage equation (KVE) are provided by calculating the excitation current and phase difference between primary voltage and excitation current (phase difference). The proposed method was analyzed during the simulations and experimental tests were also carried out in laboratory to validate the results. The results indicate that the severity of interturn fault is positively correlated with the excitation current, and negatively correlated with the phase difference. Furthermore, the phase difference can effectively detect early interturn fault of voltage transformer.
查看更多>>摘要：During the operation of the reservoir, due to the periodic fluctuation of the reservoir water level, a certain depth of fluctuation zone of the reservoir bank slope will be formed. The fine particles in the soil of the fluctuation zone will erode and migrate with the seepage of the reservoir water, resulting in the deterioration of soil strength parameters in different degrees, and even affecting the stability of the bank slope in severe cases. Because of the continuous particle size distribution and large porosity of gravel soil bank slope, under the periodic seepage of reservoir water, it is more likely to have serious particle loss, and the accumulated soil strength degradation caused by particle loss will further cause bank deformation, even instability. This paper carries out periodic pressure permeability tests on gravel soil samples to obtain the change law of particle loss rate and the degradation law of strength characteristics, and researches its influence on the slope stability. The research results show that the periodic seepage will degrade the strength of gravelly soil. With the increase of infiltration times, the deterioration range gradually decreases and the strength tends to be stable.
查看更多>>摘要：Flue gas turbine is a kind of typical rotating machinery. It uses the flue gas expansion which contains a lot of heat energy and pressure energy generated in the catalytic cracking process to drive the axial-flow compressor or generator to rotate. Due to the complex structure, bad oper-ating environment, poor stability, and large vibration of the flue gas turbine, its failure rate is high, which causes immeasurable economic losses and safety hazards. Therefore, how to effec-tively obtain, extract and identify the fault information of flue gas turbine is a difficult problem in the field of fault diagnosis technology. In this paper, aiming at two kinds of faults in the tp9-90 flue gas turbine system, i.e., rotor misalignment and unbalance causing excessive vibration, the corresponding geometric model and mathematical model are established, and the fault mecha-nism is revealed. Through on-line monitoring of flue gas turbine rotor vibration signal, the running state of flue gas turbine is comprehensively analyzed, and the technological trans-formation is carried out according to the fault causes, the improved flue gas machine runs smoothly, and the vibration and failure rate are obviously reduced. This study provides an important reference for condition monitoring and fault diagnosis of flue gas turbines.
查看更多>>摘要：Steam generation from hot reformer effluent in a hydrogen unit of a petroleum refinery increases the refinery margin. Upstream and downstream piping in hydrogen plant were constructed by SA335 P22 (AS) and type SS304L (SS) materials, respectively. This paper reports failure of dissimilar pipe weld after six months of high pressure steam service. Visual inspection indicates several ratchet marks initiated from outer wall surface at heat affected zone (HAZ) of AS pipe accompanied with brittle fracture. Further, failed samples were examined for chemical analysis, micro-hardness, fractography & elemental analysis and microstructural analysis. Fractographic results indicated that the dissimilar weld was failed due to thermal fatigue. Moreover, microstructural analysis revealed the presence of martensite in AS HAZ region with higher micro-hardness. In-spite of fixed operating temperature at 600 degrees C, there was a difference in thermal expansion that induced large strain gradient at interface and result in low cycle thermal fatigue failure. Type 308L filler metal was directly employed for dissimilar welding without buttering at interface layer was the main cause of failure. The principal factors that were responsible for Dissimilar Metal Weld (DMW) failure are discussed with respect to Schaeffler diagram and correct welding procedure for failure prevention is proposed. It is further recommended to employ 309/309L filler metal at interface layer according to ASME codes & standards to avoid DMW failure.
查看更多>>摘要：For vehicles and vessels like cars and ships, the practical environmental conditions encountered are consequences of dynamic and static operation, include moving off and stopping. Therefore, it is necessary to perform dynamic atmospheric exposure corrosion tests on metal materials under vehicle operating conditions. In this paper, a carbon steel dynamic atmospheric corrosion test was designed considering vehicle operating conditions. After completion of the corrosion test, the corrosion data was collected, processed and predicted by a series of methods and algorithms. Firstly, multiple dedicated test vehicles operating in Tianjin were chosen as carriers for carbon steel dynamic atmospheric corrosion test. Secondly, the driving characteristics data was collected using an on-board positioning data collection and transmission system. Then, the dynamic fuzzy clustering algorithm was introduced to identify the key influencing factors in the parameters of vehicle driving characteristics and to optimize data dimension, the two key index parameters of the vehicle driving characteristics identified being the average vehicle speed and dynamic/static ratio. During the atmospheric corrosion test, a time-weighted weighting algorithm model was constructed and applied to the previously collected meteorological and pollutant data in order to fit the sampling interval of corrosion data. Finally, four models including GA-SVR, unoptimized SVR, GA-BPNN and unoptimized BPNN were constructed to predict the corrosion rate of carbon steel in the dynamic environment. The final results show that the root mean square error and average relative error reached their minimum for GA-SVR with the prediction result R-2 = 0.9771, all indicators suggest that GA-SVR holds an advantage over the three models including SVR, GA-BPNN and BPNN.
查看更多>>摘要：Recent earthquakes have highlighted that historical fortified masonry constructions may suffer extensive damage, even under low-to-moderate seismic actions, and corner towers may be one of the most vulnerable structural elements. An accurate assessment of the structural seismic performance is one of the most effective tools to deeply understand and identify the main structural weaknesses of such a building typology. To this aim, the need to properly simulate the dynamic behavior of large complex masonry buildings can strongly limit the application of simplified analysis methods widely used in common practice and largely presented in the literature. The objective of this study is to provide a comprehensive numerical insight into the earthquake response and seismic vulnerability of historical fortified masonry palaces with corner towers using non-linear dynamic analyses and a macro-modelling FE-based approach, which is able to take into account the complex interactions between different macro-elements and the characteristics of the seismic action. After a knowledge phase of the geometrical and constructive features of the two palaces under study, detailed three-dimensional FE models have been developed and predictive non-linear dynamic analyses have been performed to assess damage patterns and identify the most critical macro-elements. The numerical analyses highlight that the seismic response and damage distributions are significantly influenced by the geometrical features and main dynamic properties of the two palaces. A fundamental role is also played by the interactions of the different macro-elements with the adjacent structural parts. The results of the non-linear dynamic analyses point out that the two palaces are highly vulnerable to seismic actions, highlighting the onset of possible local collapse mechanisms and recurrent damage concentrations. For both the palaces, the most critical elements are the corner towers that present remarkable cracks patterns along the height, in the connection regions with the adjacent walls, in the upper part and in the vaults. Widespread damage is also observed in the macro-elements that are characterized by high slenderness, large openings and small walls thickness, and in the large vaults of the two palaces. A clear correlation between large displacements and high values of energy density dissipated by tensile damage is generally observed for the main critical macro elements of both the palaces. The main outcomes presented in this study may also represent a useful insight to improve the knowledge and better understand the earthquake response and seismic vulnerability of similar historical fortified masonry palaces located in the same region, providing valuable information for practical applications in seismic risk assessment and mitigation at territorial scale.
查看更多>>摘要：Premature failure of conjunction gear in vehicle was reported frequently. The fractured of tooth of the conjunction gear in a vehicle was detected. Marco and micro analysis, chemical composition and mechanical test were employed to determine the causes of the failure of the conjunction gear. The analysis results showed that the lower hardening depth layer was formed in the tooth of conjunction gear due to the inappropriate heat treatment. And the micro cracks were formed on the surface of tooth of the conjunction gear on the action of the impact load. In addition, the upper bainit of material was formed based on the unqualified heat treatment, which reduced the impact toughness of material and accelerated the growth of cracks. The element segregation caused the brittleness of material was increased and the resisting propagation ability of micro crack was reduced. Finally, the tooth of the conjunction gear was fractured. The improvement scheme was proposed to prevent the similar failure based on the results of the study.
NSTL
Elsevier