查看更多>>摘要：? 2022 Elsevier LtdM400 alloy distributor used to disperse acid gas containing HCl and H2S in the stabilizer top gas scrubber suffers from severe corrosion attack at the connection between distribution pipe, branch pipe and distribution hole during service. The failure analysis is carried out through experimental and numerical simulation methods. The results show that the acidic gas has scouring effect, and the corrosion products in the front gas transmission pipeline are brought into distributor by high-speed airflow and promote its corrosion. In addition, dew-point corrosion on the scrubber wall and the entrance of oxidized Fe3+ into the distributor, further aggravate its erosion corrosion. The erosion corrosion of the distributor and the dew-point corrosion of the scrubber wall build a vicious cycle in common, which eventually leads to the failure of the distributor. A series of protection suggestions are put forward to mitigate and avoid similar incidents.
查看更多>>摘要：? 2022 Elsevier LtdThermal barrier coatings (TBCs) have been widely used in high-power engine components because of their excellent thermal insulation properties. In this study, microcrack growth and fatigue life analysis of TBCs were carried out based on thermal shock tests of TBCs samples. Scanning electron microscopy (SEM) was used to observe the spallation and vertical crack growth behavior of TBCs during the tests. The fatigue life prediction model applied to piston TBCs was developed by modifying the Paris equation with the sintering of the coating and the effect of a thermally grown oxide (TGO) layer being considered. The model was calibrated by conducting tests on piston TBCs, and the forecasting error was less than 15%, indicating that the prediction model is both practical and effective. The results of this study provide a service life evaluation and test method for TBCs on pistons, which can be utilized to guide piston TBCs design.
查看更多>>摘要：? 2022 Elsevier LtdThis paper investigates the mechanism of failures of API-grade seamless pipes. Two failures occurred, the pipe with the first failure had a 4.7 m long longitudinal crack, which occurred catastrophically. The pipe with the second failure had a small leakage. Pressure in the pipes due to hydraulic oil remains at 30–140 bar. The occurrence of large longitudinal crack at such low pressure and 25–40 °C of ambient temperature in the seamless low carbon steel hydraulic pipe requires a very high strain rate exerting on the pipe or hydrogen-induced-cracking (HIC) etc. Chemical analysis, tensile testing, hardness, visual observations, optical and electron microscopy, and Energy dispersive spectroscopy (EDS) were used to thoroughly evaluate the root cause of this failure and its mechanism. Results showed hydraulic pipe failed by HIC due to the presence of severe Sulphide inclusions. The most probable source of hydrogen in the pipe was hydraulic oil. Some mitigation measures were also proposed to prevent such failures in the hydraulic pipes of the unit.
查看更多>>摘要：? 2022 Elsevier LtdThe safety of operation and the extension of the aircraft life cycle cannot be ensured without the use of methods and means of technical diagnostics. Monitoring and diagnostics of the technical condition of aircraft components is therefore one of the most important task. The main problem being addressed is the monitoring of the manifestations of the incipient degradation of piston hydraulic pumps, which are critical elements in terms of flight safety. The main research question is: what changes in the physical parameters occur in the process of degradation of the hydraulic pump components and how they affect the life cycle of the pump? The research methodology is based on quantitative methods of data obtained by measuring the physical parameters of the pump such as vibration, acoustic emissions, flow and fluid pressure and temperature. The obtained results show that there is agreement of the initial degradation manifestations, but only for certain physical parameters of the hydraulic pump. This finding is significant in that the outlet pressure from the pump does not necessarily signal the initial stage of its degradation. From the point of view of the safety of the hydraulic system and the mission of the aircraft, we consider this to be an important and originality knowledge.
查看更多>>摘要：? 2022 Elsevier LtdEarly delamination of the nitrided tappet inserts in the valve train of a high speed and heavy duty diesel engine occurred and thus the failure mechanism of early delamination was investigated with the method of numerical simulation and experiment at first. Additionally, the countermeasure was put forward and identified using a valve train bench test rig. Flying off of the tappet in valve train took place, causing repeated impact forces between the interfaces of the tappet and cam. Early delamination of the compound layer (CL) was formed once the surface crack connected with the subsurface crack. Removal of the CL of the nitrided tappet inserts was verified as an effective countermeasure for avoiding the early delamination as well as protecting the matching part, which suggests the hard and brittle CL of the nitrided part should be removed under a heavy load condition especially accompanying with repeated impact forces.
查看更多>>摘要：? 2022 Elsevier LtdThe work herein presented aims to analyse an existing failure in a ball mill of a cement production line. This equipment has the function of grinding the mixture of clinker and selected additions to produce cement. The ball mill understudy has a length of 16.2 m between supports, and the formation of cracks was noticed approximately midspan near a maintenance manhole. The failure is recurrent and responsible for reducing the period between overhauls. The cracks were detected using dye penetrant liquids and repaired by a rewelding procedure using PERMA E622 electrode. Numerical simulations were carried out using the Finite Element Method, and displacements and stresses induced in the structure were calculated. The maximum stress values were registered in the region where the failure occurred, near through-holes used to bolt the ball mill's cladding plates. The ball mill was redesigned to ensure high endurance for the equipment. Therefore, internal and/or external reinforcement rings were inserted in the structure, and the maximum stresses calculated were reduced by 32%, increasing approximately five times the fatigue life predicted for the ball mill.
查看更多>>摘要：? 2022As in every manufacturing process, fused deposition modeling (FDM) is strongly related to its operational parameters. 3D-printed components are anisotropic and brittle and this imposes the need to investigate the effect of FDM-related parameters to improve functionality and strength. In this paper the flexural strength of polyethylene terephthalate glycol (PET-G) is studied by testing different levels for five important process-related parameters; the height of each layer, density of infill, angle of deposited material, printing speed and printing temperature. A response surface experiment with 27 runs was conducted to obtain results for flexural strength (MPa) and proceed with the examination of the effect of each parameter on the response using statistical analysis. The experiments were performed according to ASTM D790 standard. Experimental observations dealing with fructure mechanics and failure modes were recorded and analysed. Based on the analysis of variance (ANOVA) a full quadratic regression equation was generated and verified for its efficiency. Finally the model was implemented as an objective function for a modern population-based algorithm known as grey wolf algorithm (GWO). It was shown that the algorithm can suggest good combination for parameter settings to maintain good flexural strength with a gain close to 15% compared to the highest value obtained by the series of experiments conducted.
查看更多>>摘要：? 2022 Elsevier LtdThe paper emphasizes the fact that in the case of composite materials which are characterized by anisotropy, unlike classic isotropic materials, the modulus of elasticity changes its value when the degree of damage changes. Moreover, a decrease in this modulus can characterize the degree of material damage. The literature on this phenomenon was analyzed. However, the vast majority of studies leading to the description of changes in the stiffness of the material have so far been carried out only for uniaxial tension–compression. One case was also found where the authors performed a similar analysis for the material subjected to torsion. It was found that such analysis has not yet been performed for pendulum bending, which is a very common type of load in structural elements. Based on the authors’ own experimental research for cyclic pendulum bending and double-sided torsion of specimens made of polyamide PA6, reinforced with continuous glass fibers, it was found that, as in the case of uniaxial tension–compression, as the degree of damage increases, there is also a decrease in both Young's modulus for bending and the shear modulus for torsion.
查看更多>>摘要：? 2022 Elsevier LtdThe uniaxial tension, strain-controlled and stress-controlled cyclic deformation experiments of U75VG rail steel at various loading rates were carried out. Experimental results show that the U75VG rail steel shows obvious rate-dependent tension, cyclic softening feature and ratcheting behavior. Moreover, based on the rate-dependent experimental results, a new cyclic visco-plastic constitutive model was established by introducing the rate-dependent isotopic resistance and ratcheting factor into isotropic and kinematic hardening rules, respectively. Compared with the classic cyclic visco-plastic model, the proposed model can reasonably simulate the tension, strain-controlled and stress-controlled cyclic deformation behaviors at different loading rates. Finally, the prediction capacity of ratcheting behavior under a wide range of loading rates was demonstrated.
查看更多>>摘要：? 2022 Elsevier LtdThe steel reinforced concrete(SRC) column is a key bearing part of some kinds of buildings and bridges, and its failure is usually the main cause of progressive structural collapse. To evaluate the column as-built performance, this paper reports the impact behavior of seven SRC columns with built-in L-shaped steels under out-of-plane lateral multiple impacts and the corresponding residual axial mechanical properties. The column is first subjected to three repeated impact loading under the same impact energy to study its impact resistance. Subsequently, the axial compression test is carried out to explore residual behavior. The influences of impact height, stirrup ratio and axial compression ratio on its performance are considered and discussed in detail. Results indicate that the column does not collapse or perforate after three times of impact, showing good impact resistance. Flexural-shear failure is the main failure mode under the first impact. And columns with large axial pressure gradually experience local punching failure from overall failure because the axial pressure inhibits the oblique crack. With the increase of impact times, the peak impact loads of the hammer reduced while the mid-span displacement of the specimen increased continuously. And the performance of column deteriorates sharply after two impact damages. The static tests showed that the residual axial bearing capacity was deeply influenced by the induced residual deformation. Both the impact behavior and residual mechanical properties were improved with the increase of stirrup ratio. In addition, the deformation of specimen after impact damage caused the constraint effect of stirrup in the initial stage of axial compression test, leading to the difference in the ascending stage of load displacement curves.
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