查看更多>>摘要：The fracture toughness resistance curve (e.g., J -R curve and crack tip opening displacement (CTOD) or delta-R curve) is important in facilitating strain-based design and integrity assessment of oil and gas pipelines, where influence of ground movement and presence of planar weld flaws must be accounted for. In the present study, duplicate single edge notched bend (SE(B)) and clamped single edge notched tension (SE(T)) specimens with two different initial crack lengths were tested at room temperature for longitudinally-oriented specimens machined from X60 and X100 pipe steels where the notch is along the through-thickness direction. The results showed the expected trends of higher fracture toughness resistance curves for shallow-cracked over deep -cracked specimen types and tension over bending loading modes. Eleven constraint parameters (i.e., Q(HRR), Q(SSY), Q(LM), Q(BM), A(2), A(2BM), h, T-z, C-p, A(p), V-p) were calculated based on 3-D finite element analysis for all tested SE(B) and SE(T) specimens. The results indicated that the shallow-cracked SE(B) specimens exhibit a constraint condition similar to the intrinsically low-constraint deep-cracked SE(T) specimens made of the X60 pipe steel. Among all of the constraint parameters, the A(p )parameter based on the equivalent plastic strain isoline was found to correlate the best to the material fracture toughness for currently tested specimens. Furthermore, a linear master curve between various critical fracture toughness values and A(p) parameter was obtained for all the tested specimens with different crack lengths, loading modes and pipe steels.
查看更多>>摘要：The intake of water diversion project is generally located on the bank slope above the large reservoir or deep water area of a river. Due to the influence of water level change and hydraulic action, the rock mass of bank slope is seriously weathered and broken, leading that the rock mass has low strength and is easy to collapse or landslide. In this paper, the water intake engineering of the long-distance diversion project in central Shanxi Province is selected as the research object. The multi-point displacement meter is used to monitor the slope deformation after anchorage and concrete retaining wall support. Based on the FLAC(3D) V 6.0 software, the numerical simulation of the excavation process of the steep reinforced river bank slope is carried out, and the long-term deformation of the slope is predicted. The excavation scheme of retaining outer thin-walled rock wall as water cofferdam is proposed. The excavation process of foundation pit, which is supported with concrete-filled steel tubular pile reinforcing cofferdam and concrete supporting beam, is simulated. It is found that the upper part of the steep slope supported by anchor cable and concrete retaining wall is stable, and the large deformation and plastic failure of the water-retaining thin rock wall are mainly affected by the disturbance of foundation pit excavation. The concrete-filled steel tubular pile support avoids the collapse of the reserved thin-walled cofferdam, and the horizontal beam in the foundation pit improves the stress state of the external wall of the foundation pit. The research results of this paper reveal the evolution mechanism of rock mass deformation and failure during excavation of foundation pit on steep bank slope, and provide guidance for excavation and support of foundation pit for similar bank slope.
查看更多>>摘要：This paper aims to describe the observed damage and crack propagation in patrimonial masonry buildings of Puebla and Morelos, Mexico due to both September 7 (M-w = 8.2) and 19 (M-w = 7.1) 2017 earthquakes. Historical masonry buildings are earthquake prone structures due to the missing structural integrity by the low tensile strength of masonry, heavy inertial forces, large openings and structural elements with different in-plane and out-of-plane behavior, especially when detached from the rest of the building. The two large seismic events damaged 2340 architectural heritage buildings, mainly in the States of Puebla, Morelos and Mexico. The observed damages during post-earthquake investigations ranged from moderate to heavy, with partial and total collapses, mainly in vaulted systems and bell towers. The presented damage identification and failure propagation description allowed to generate practical schematic representations of crack patterns in several structural elements such as domes, vaulted covers, facades, bell towers and so on, providing valuable information that can be useful to propose suitable rehabilitation and retrofitting works. The 2017 earthquakes also generated uncountable damages in different cultural assets including retables, painted murals and bells, being of great cultural and historical value. The main causes of the observed damages in masonry structures are also due to the lack of maintenance, previous structural modifications and inadequate interventions. Continuous and correct maintenance of structures is indispensable to reduce the possible damages due to earthquakes. Thus, a detailed structural assessment of the buildings is always necessary to carry out an adequate intervention according to the criteria of restoration.
查看更多>>摘要：A severe accident of surrounding soil failure occurred during the construction of Zizhi Tunnel, a shallow tunnel in very soft ground using the shallow tunneling method in Hangzhou, China. We provide an in-depth comparison with careful evaluation of three design variation plans through 3D numerical analyses on the stress distribution inside the advance core, ground deformation, and soil arching over the tunnel crown. Consequently, the third support design scheme, i.e., soil reinforcement using sub-horizontal Metro Jet System (MJS) piles, is recommended as it leads to the smallest disturbance to the surrounding ground, and is the most favorable for the soil arching formation. We also find that the advance core's stability is crucial for preventing the face failure and reducing the surface settlement. Finally, the effectiveness of world's first successful example of applying sub-horizontal MJS piles to reinforce tunnel excavation in very soft soil is verified by the field monitoring data.
Rincon-Casado, A.Julia-Lerma, J. M.Garcia-Vallejo, D.Dominguez, J....
15页
查看更多>>摘要：This study presents an experimental methodology aimed at estimating the residual fatigue life of in-service wind turbine bolts. The main objective is to assess the residual life of the bolts to plan their replacement and to avoid unexpected breakages of wind turbine blade connections. To develop the methodology, M16 bolts of quality 10.9 with controlled predamage were used, simulating in-service operating conditions. The fatigue tests were carried out taking care to place the nut at the point on the bolt that produces the highest damage at the same point where the predamage was performed. In addition, the influence of a possible angular positioning error on the residual fatigue life has been investigated. The residual fatigue life is estimated from the difference in fatigue life of new bolt tests and the fatigue life of predamaged bolt tests, simulating service conditions. Special care has been taken to guarantee that the most damaged zone of the bolt in service is also in the position that produces the highest damage during tests. An experimental procedure for determining the fatigue life of a new bolt from tests conducted on a bolt under the same operating conditions was developed. The developed methodology has been applied to M20 bolts belonging to real turbines in service.
查看更多>>摘要：The failure of a stay cable on the Saint-Nazaire bridge is investigated in detail. In 2000, fatigue cracks that had cut many wires led to a first replacement, alike to the initial, of the H32 stay cable. Examination of the deposited locked coil strand showed that fretting fatigue was involved in the wire breaks. The cause of the failures at the anchorages is discussed/studied in depth in the paper. Bending moments of the rigid cable, at its exit from the anchorage socket were proven to be the source of the fatigue stress due to vibrations induced by vortex detachments (VIV: Vortex Induced Vibrations). As wires ruptures occurred again in 2017 in the new H32 stay cable at the same place, further studies on dampers were carried out. After numerical simulations, the "Stockbridge " damper became a good candidate for attenuating the amplitude of vibrations. It could indeed be designed to fit the required frequency range between 30 and 35 Hz.
Gomes Dobrovolski, Mateus EdilsonNeneve, Bruno LeandroDias, Roberto LuizGodinho, Jayson Pereira...
15页
查看更多>>摘要：The service life of wastewater treatment plants is often impaired by the biogenic deterioration caused by sulfuric acid (H2SO4). This study used fly ash (as a Portland cement replacement) and different contents of neutral sodium silicate (0%-10%) as mitigating solutions. One group was immersed in lime-saturated water for 182 days, and the other was submitted to a 0.5% H2SO4 solution for the same interval. The microstructural analysis (SEM/XRD) confirmed the con-sumption of calcium-based compounds during the pozzolanic reaction, the Na2SiO3 hydration, and the H(2)SO(4 )attack. The neutralized depths measured after spraying phenolphthalein reiterated this trend. The H2SO4 front progressed inwards, promoting gradual peeling and the formation of gypsite. The slow diffusion of H2SO4 did not impair the early-age compressive strength, but the depletion of the alkaline reserve hindered the results in the long term. Therefore, Na2SiO3 was not a viable mitigating solution against the H2SO4 attack, contrary to fly ash.
查看更多>>摘要：Crankshaft fracture is a typical failure form of reciprocating high-pressure plunger pump. Different from traditional power machinery, the number of plungers in plunger pumps is usually odd, which leads to unbalanced radial force of the crankshaft and greatly increases the risk of failure. The crankshaft of a 250 kW high-pressure plunger pump was fractured, and the fracture morphology was river-shaped, which was a typical fatigue failure. To trace the failure of the crankshaft, a Constructure-Kinematics-Materials-Craftsmanship (CKMC) method was brought out. The microstructure of the damage zone was observed, and a three-dimensional transient finite element model was established to find the most dangerous zone and damage mechanism. The results show that high-cycle fatigue of fillet zone is the main reason for crankshaft fatigue failure. Material defects and lack of nitrided layer at fillet are the key factors to accelerate crankshaft failure. Finally, recommendations for preventing future failures were presented.
查看更多>>摘要：With the improvement of family life quality and the implementation of energy-saving green household appliances, the volume of refrigerator increases rapidly and the energy efficiency ratio continues to decrease. However, the compressor size is required to be smaller, and the startup and shutdown are more frequent, which aggravates the wear of crankshaft connecting rod. Here, the failure compressor (300 ppm) provided by the manufacturer was disassembled and analyzed. The results showed that there were abrasive wear and adhesive wear on the surface of crankshaft and connecting rod. The source of solid particles in compressor was further analyzed, and the process control measures were proposed. In addition, combined with its failure mechanism and pro-duction process, the crankshaft surface composite treatment process was designed and bench test was carried out, which shows excellent anti-wear and self-lubricating performance.
Poursaeidi, EsmaeilFar, Amin AziziRahimi, JavadSigaroodi, Mohammad Rasoul Javadi...
19页
查看更多>>摘要：In this study, numerical and experimental methods were used to investigate the combined effect of internal cooling channels and thermal barrier coating on temperature distribution and, ultimately, fracture of a real GEF9 turbine blade. The blade comprises TBC layers and internal cooling channels, damaged after 66,000 h of operation. Observations showed blockage of the cooling channels for the fractured blade. The blade temperature distribution was calculated before and after blockage using CFD, and simulation results were used to design the experimental tests. The results show that blockage leads to about a 100-degree increase in blade temperature, 5-mu m growth in TGO, and changes in the coating porosity fraction. This causes an increase in ceramic layer stress and the TBC delamination. With the spallation of the TBC layer, the blade is exposed to higher temperatures. Finally, the blade failed due to overheating, accompanied by centrifugal forces related to the blade rotation.
NSTL
Elsevier