查看更多>>摘要：Blade defects such as scratch and deformation always cause performance degradation or even failure of gas turbine, and furtherly threat energy safety. Therefore, defect detection of individual blades is important in gas turbine maintenance. Currently, defect detection is mostly manually implemented, so it is necessary to design an automatic method to reduce labor costs. However, most available detection methods require CAD models or prior shapes of blades, which might not always be acquirable for gas turbine users. Besides, those methods are not suitable for practical use because of their high demands for detection equipment. In this paper, a simple but efficient 3D vision-based defect detection process using point clouds is proposed to detect scratches and deformation accurately. First, sliding sampling window is used to reduce the computation burden in each detection process. Second, a pipeline of detection algorithms based on underline surface analysis is proposed to extract local geometry features and predict potential defects. Last, a filtering algorithm is introduced to reduce false detections. The whole process is carried on with real defective blades, and its effects are both intuitively and quantitatively evaluated. The results show that a multi-step detection process based on FPFH is able to detect both scratch and deformation accurately, which will be suitable for practical application.
查看更多>>摘要：Insulated rail joints (IRJs), safety critical components of railway track, are used to locate trains and broken rails using electrical signalling systems. The bending rigidity of the rail at an IRJ is only 2/3(rds) as that of continuous rail. As a result, stress singularity problems occur at IRJs which therefore degrade faster compared to the continuous rail. Both railhead top surface and subsurface damage occurs and accelerates the initiation of cracks. Head hardened rails are used to overcome these problems. A thorough study addresses the damage pattern in the railhead sub-surface using a 3D finite element analysis (FEA) employing vertical wheel loadings considering three endpost materials: fibre glass (fb), nylon 66 (ny) and polytetrafluoroethylene (ptfe). A new damage parameter, the vertical residual stress component, is proposed to assess new patterns of railhead damage considering plastic deformation. To rank the influential stress related damage parameters, two other parameters are also considered, namely residual von-Mises and longitudinal stress components. Of these, the residual von-Mises stress component is more prominent with regard to the top surface and sub-surface damage, whereas the longitudinal stress component is responsible for top surface material damage. From these damage patterns, a progressive change in the hardness distribution of railhead material can evolve.
查看更多>>摘要：Mash seam welding of the tail end and head end of cold-rolled coils is performed to maintain continuity in the Continuous Galvanizing Line (CGL). Failure of the weld can lead to mill stoppage causing huge productivity loss of up to 48 h for one such breakdown and causing damage to the mechanical systems. The failure of the weld is a result of defects present along the fusion line such as lack of fusion, craters due to expulsion, shrinkage cavity and cracks. Improper welding parameters can lead to the formation of the above defects and can remain undetected during the subsequent processing. Hence a non-destructive weld inspection system was developed to detect defects. Additionally, the ultrasonic-based weld inspection system with a machine learning algorithm was developed to gather and train the scan data for accurate prediction of weld defects and prevent catastrophic failure due to weld breakage.
Carneiro Neto, R. M.Akhavan-Safar, A.Sampaio, E. M.Assis, J. T....
9页
查看更多>>摘要：The behavior of polymeric adhesives is time and temperature dependent, as they are considered viscoelastic materials. These materials can undergo creep deformation even at low stress levels and room temperature. This way, a viscous flow can occur at the adhesive layer and it can lead to viscous deformation, causing a modification in the adhesive properties. The current work aims to investigate the shear creep fracture energy of an epoxy adhesive using end notched flexure (ENF) samples creep tested until failure. The endurance creep limit for cracked bonded joints subjected to pure shear loading conditions is also investigated using ENF samples, representing the maximum creep load which ENF bonded joints can sustain without creep fracture after a specified time. The GIICr-life curve was obtained where the GIIcr is the mode II creep fracture energy. Results showed that small changes in creep load can significantly change the creep endurance limit. Creep fracture energy can be employed for joint design against creep service loads.
Shojaei, Mohammad RezaKhayati, Gholam RezaKorasani, Seyed Mohammad JavadHarnashki, Roya Kafi...
25页
查看更多>>摘要：The presence of nodules on the surface of cathode copper plates was the most important reason for the failure of the punch of mechanical clinching of copper cathode sheets. This study demonstrated a comprehensive investigation into the nodulation growth of copper cathodes in the electrorefining plant based on metallographic analysis. More than 15 random samples were selected from the top, middle, and bottom of the cathodes produced in the Khatoon Abad copper refinery, Iran. Studies were carried out based on the determination of growth modes including field oriented isolated crystal (FT), basis-oriented reproduction (BR), field-oriented texture (FT), and unoriented dispersion (UD). A scanning electron microscope equipped with the EDS spectrometer was used to determine the elemental analysis of the origin of each nodule and investigate the effect of entrapped slimes impurities on the nodules' microstructure. The results confirmed that the physical and chemical adsorption of inhibitors including Fe, Ni and Mn as hydrated phases on the preferred active sites restricted the FT growth mode at the first stages of crystallization. Then, it enhanced the local current density and cathodic polarization promoting the UD growth mode. The same mechanisms occurred when as-received-casted anodes replaced the cathode and caused the formation of cavity at the preferred active site and intense nodulation at the border of the sample. Analysis of this site of nodules' root revealed that the aggregation of inhibitors at the lower preferred active sites, i.e., lower than 5 mm, provided the possibility of large local current density, polarization and encourage the formation of brittle deposition as MeOH. In this case, the formation of the spongy nodule was dominant.
查看更多>>摘要：Leaf spring is often used in commercial vehicles' suspension systems to ensure ride comfort and support dynamic wheel loads. In this study, we found a failure phenomenon in a two-layer leaf spring where the fatigue fracture occurred on the companion spring leaf. The decarbonization layer was observed on the surface of the leaf with a 100 mu m thickness. The Vickers hardness of the leaf was reduced from - 550 Hv of the inner material to - 500 Hv at the surface region. The decarbonization layers led to fatigue fracture initiation, propagation, and total failure of the spring. Two-dimensional (2-D) finite element simulations were conducted to illustrate the effects of the decarbonization layer and the surface defects. Also, the fracture process was represented in the three-dimensional (3-D) simulation. We conclude that either additional surface treatments or installing rubber pads between each leaf will be helpful to raise the leaf spring's durability.
查看更多>>摘要：Thermal effect is an important cause of engineering failure of gear system. However, the lack of accurate model limits the research on the thermal behavior of gear transmission system. Here, based on the linear thermal expansion theory, involute profile theory and energy method, the thermal expansion model, the mesh stiffness model, the load sharing ratio model and the loaded static transmission error model of spur gears are proposed which comprehensively consider the thermal changes of material properties, theoretical involute, thermal profile error and actual contact positions. The corresponding finite element models are established to verify the accuracy of the proposed model and published models. The results indicate that the proposed model is accurate enough. The increase of temperature leads to the decrease of mesh stiffness, the unevenness of load sharing ratio and the increase of loaded static transmission error, accompanied by the phenomenon of earlier meshing. The hub bore radius has obvious influences on the thermal profile error and mesh stiffness, and the load torque also has apparent influences on mesh stiffness. The research provides supports for gear thermal effect analysis and gear system design.
查看更多>>摘要：Thermal effect is an important cause of engineering failure of gear system. However, the lack of accurate model limits the research on the thermal behavior of gear transmission system. Here, based on the linear thermal expansion theory, involute profile theory and energy method, the thermal expansion model, the mesh stiffness model, the load sharing ratio model and the loaded static transmission error model of spur gears are proposed which comprehensively consider the thermal changes of material properties, theoretical involute, thermal profile error and actual contact positions. The corresponding finite element models are established to verify the accuracy of the proposed model and published models. The results indicate that the proposed model is accurate enough. The increase of temperature leads to the decrease of mesh stiffness, the unevenness of load sharing ratio and the increase of loaded static transmission error, accompanied by the phenomenon of earlier meshing. The hub bore radius has obvious influences on the thermal profile error and mesh stiffness, and the load torque also has apparent influences on mesh stiffness. The research provides supports for gear thermal effect analysis and gear system design.
查看更多>>摘要：Management of corrosion, and repair and restoration of corrosion-affected structures pose a daunting challenge to the aircraft industry. This paper presents analytical studies to examine and quantify the effects of corrosion of Al-alloys on the fatigue life of aircraft structures. Two scenarios are considered: (i) fatigue of a pre-corroded material and (ii) fatigue in a corrosive environment. The corrosion damage is idealized using standard crack models, and cycle-by-cycle fatigue crack growth analysis is carried out for an aircraft horizontal stabilizer under spectrum loading conditions. A few aircraft operational scenarios are considered, and fatigue life calculations presented. The zone which experiences 18% lower stress than the maximum stress zone is shown to turn fatigue critical if vulnerable to corrosion. The results point to the risk posed by corroded zones if missed while focusing attention on high stress zones. The computations indicate that an exposure of even 25% of operational life to corrosive environment can reduce life by 40-55%. The study quantifies the significance of corrosion while arriving at design safe life, remaining useful life and maintenance intervals.
Soltanloo, MostafaBabaee, Mohammad HosseinYeganeh, Sayyed Ehsan HosseiniShafiei, Ali...
18页
查看更多>>摘要：This paper focuses on failure analysis of a boiler waterwall tube, ASTM A213 Grade T2 steel, used in a 325 MW fuel oil-fired thermal power plant. The influence of fire/waterside factors on the failure was identified through multiple characterization techniques. Preliminary macroscopic observations revealed uniform heavy deposition and repair welding indications on the fireside surface of the failed tube. Moreover, a longitudinally hemielliptical inner groove along with excessive weld metal penetration and discrete cavities were observed along the crown of the tube, leading to local wall thinning down to around 50% of its nominal thickness. No noticeable hardness and microstructural variations such as pearlite colonies decomposition caused by long term overheating and formation of decarburized layer were detected. According to the results of micro-zone analyses, considerable quantity of sodium vanadium oxide compounds accumulated throughout the fireside surface of the tube was due to poor fuel quality used. The authors postulated that evaporation at the waterline of the approximately filled tube resulted in water/ steam stratification and localized caustic constituents concentration within the inner groove like NaOH and alkaline producing salts containing Na, Mg, Ca and P elements entered into the water/ steam cycle through condenser copper-based tube leakages. This trend solubilized protective magnetite film locally and, consequently, triggered caustic corrosion of the bare steel.
NSTL
Elsevier