查看更多>>摘要：This paper studied the function failure of a quartz flexible accelerometer servo circuit manufactured by a thick-film hybrid integrated process. The circuit adopts the epoxy glue bonding process of the metal shell and the ceramic cover plate to encapsulate, and it is a non-airtight package. After the circuit is powered on, the quiescent current output is abnormal, and the DC voltage output is constant high potential, the acceleration detection function cannot be realized. In response to this phenomenon, the fault tree method is used to locate the failure location, and the fault is located at the abnormal function of the differential capacitor voltage converter chip. Using microscopic analysis and characterization methods, it can be seen that the hydrolysis and corrosion of the surface of differential capacitance-to-voltage converter chip causes leakage in the active area inside the chip, leads to the function failure of the circuit. The above research is of great significance to the design, storage and application of non-hermetic hybrid integrated circuits.
查看更多>>摘要：A modified layer of a certain thickness is produced on the surface of 18CrNiMo7-6 alloy steel after carburizing and quenching that greatly affects the microstructure and fatigue properties of the material. In this work, the fatigue performance of each layer was studied. The fatigue fracture and tensile fracture were compared under different depths of the modified layer. The fatigue fractures of the modified layer for different stresses were analyzed. As the depth of the modified layer increased, the slope of the S-N curve gradually decreased. As the depth of the modified layer increased, the fracture mode changed from brittle fracture to brittle-ductile mixed fracture, the shear lip became thicker, and the dimple became larger. There was no fiat area in the tensile fracture. At the same depth of the modified layer, a smaller stress amplitude, led to a larger proportion of the crack propagation area.
查看更多>>摘要：The aim of this study is to analyze the local change in stress-strain and damage behavior in an inlet groove structure of a power plant component under the effect of the crack geometrical constraint. A robust constitutive model is used to describe the inelastic behavior of advanced 9-12% Cr heat-resistant steels at high temperature. Steam temperature and loading profiles corresponding to the idealized startup, holding and shutdown sequence of the structure are assumed. Thirteen cycles of this sequence are chosen for the loading conditions. Transient heat transfer analysis is conducted to estimate the thermal field throughout the structure. Structural analysis is then performed using the material constitutive model. The results show that the crack geometrical constraint not only changes the stress-strain behavior, but also the damage distribution. Compared to the results without the crack effect, the damage locations demonstrate a major change. Specifically, the damage starts underneath the surface of the groove structure. This is attributed to the more complex multi-axial features in the regions close to the surface of the structure.
查看更多>>摘要：Cargo operations on tanker vessels involve high risks to crew and the marine environment. At the time of loading and unloading of cargoes and tank cleaning operations, consequences of accidents may be severe such as loss of lives, property loss and marine pollution. One of the most critical accidents is an explosion which may advance to a large fire. An explosion may occur due to flammable and combustible materials, electric arcs, dangerous operations, like hot work on deck, or static electricity. This study focuses on the issue of static electricity, which is one of the serious threats onboard and can cause large explosions under hazardous conditions if a discharge is in contact with nearby flammable gases or air mixture. In a bow-tie structure, static electricity-related explosion and fire accident was determined as the top event. In the fault tree diagram, intermediate events were considered as the flammable atmosphere in a tank, operational failures, technical failures, and unsafe practices which cover direct human errors. Fuzzy logic and Cognitive Reliability and Error Analysis Method (CREAM) were used for quantitative failure analysis, and the probability of accident risk was found as 6.31E-02. Findings show that the most critical contributions to the top event are minimal cut sets of lack of monitoring cargo tank atmosphere, inadequate actions for reducing the O2 level in tank, failure to understand safety data sheets, failure to follow procedures, non-bonded ullage & sample apparatus. The research provides a significant contribution to the literature and gives information regarding static electricity risks to ship officers, tanker safety superintendents and other maritime authorities to improve the safety of cargo operations.
查看更多>>摘要：The crack initiation and propagation on the cage bridge surface can change the cage structural stiffness and clearances, which may lead to the cage failure ahead of time and affect the dynamics of planet roller bearing. To detect the initial cage crack failure in the planet roller bearing, the dynamic characteristics of the cage with crack should be studied. In this study, an equivalent stiffness model for the cage bridge is presented to investigate the crack depth and location effects on the cage bridge structural stiffness and impact forces. A dynamic model of the planet roller bearing considering the cage crack is proposed to simulate the dynamic behavior of the planet roller bearing elements. The impact forces on cage bridge surfaces are analyzed, and the vibrations of the cage are discussed.
查看更多>>摘要：In the present work, the fracture toughness and tensile property of 40CrNiMoA high-strength steel were systematically investigated, The experimental results reveal that the ultimate tensile strength of 40CrNiMoA steel decreases gradually with improving the tempering temperature, while the fracture toughness reveals a reverse trend to the tensile strength. The fractography shows the consistency of quasi-static fracture characteristic in the tensile and K_(IC) specimens. The complicated fracture mechanism of 40CrNiMoA steel is mainly attributed to the various micro-structures: grain size, dislocation density and precipitated carbides. Additionally, based on the macro/micro- fracture mechanisms and energy principle, we proposed the relation between fracture toughness and macroscopic tensile parameters. The new model would provide an effective strategy to predict the fracture toughness of high-strength steels, which can be further applied to other engineering materials such as aluminum and titanium alloys.
查看更多>>摘要：Fretting fatigue of dovetail structure of aero-engine compressor is a very complex phenomenon, which is affected by different factors such as temperature, load, friction coefficient, and arc radius, etc. Aiming at the problem of the high-temperature fretting fatigue life prediction of dovetail structure, the high-temperature effect on fretting fatigue life is analyzed, and then the fretting fatigue life prediction model is established considering the temperature effect by introducing temperature equivalent factor based on the circular flat contact theory and continuous damage mechanics theory. Besides, the criterion of fretting fatigue cracks initiation failure is proposed based on the displacement-strain joint monitoring method in the fretting fatigue tests. The experiment results show that the proposed fretting fatigue life prediction model has a high life prediction ability within ± 2.0 times error band. It is found that the traditional damage mechanics accumulation model cannot reflect the change of fretting fatigue damage only by changing the material performance parameters in a high-temperature environment, needing temperature correction and the proposed fretting fatigue life prediction model considering temperature effect in the exponential form of temperature ratio is feasible.
查看更多>>摘要：Corrosion, friction and wear of wire ropes always exist in multi-layer winding systems. They lead to the lubrication failure and service performance degradation of wire rope. To reveal the tribological properties of wire rope in service, the coefficient of friction (COF), friction temperature rise and surface wear characteristics of wire rope with different lubrication and corrosion conditions were investigated. The experimental results show that friction parameters of the lubricated wire ropes are relatively small, which are obviously affected by the sliding stroke and velocity. The COF fluctuates between approximately 0.15 and 0.28, and the friction temperature rise is reduced to below 7 °C. Additionally, the corrosion solutions degenerate the anti-friction and anti-wear properties of the lubricating grease and oil. The COF and friction temperature rise of the oil lubricated wire rope increase greatly when the rope sample is corroded by sea-water and dilute sulfuric acid solution. The sliding wear mechanism and lubrication stage of the lubricated wire ropes is adhesive wear and boundary lubrication, respectively. Furthermore, dilute sulfuric acid solution is the most harmful to the friction-reduction and wear-resistance of the lubricating grease and oil used for wire rope, followed by sea-water solution and fresh water solution.
Afzal Ahmed SoomroAinul Akmar MokhtarJundika Chandra Kurnia
26页
查看更多>>摘要：Hydrocarbon fluid integrity evaluation in oil and gas pipelines is important for anticipating HSE measures. Ignoring corrosion is unavoidable and may have severe personal, economic, and environmental consequences. To anticipate corrosion's unexpected behavior, most research relies on deterministic and probabilistic models. However, machine learning-based approaches are better suited to the complex and extensive nature of degraded oil and gas pipelines. Also, using machine learning to assess integrity is a new study field. As a result, the literature lacks a comprehensive evaluation of current research issues. This study's goal is to evaluate the current state of machine learning (methods, variables, and datasets) and propose future directions for practitioners and academics. Currently, machine learning techniques are favored for predicting the integrity of damaged oil and gas pipelines. ANN, SVM, and hybrid models outperform due to the combined strength of the constituent models. Given the benefits of both, most popular machine learning researchers favor hybrid models over standalone models. We found that most current research utilizes field data, simulation data, and experimental data, with field data being the most often used. Temperature, pH, pressure, and velocity are input characteristics that have been included in most studies, demonstrating their importance in corroded oil and gas pipeline integrity assessment. This study also identified research gaps and shortcomings such as data availability, accuracy, and validation. Finally, some future suggestions and recommendations are proposed.
查看更多>>摘要：To explore the prestressed modal characteristics of the last stage blade in steam turbine under low volume flow conditions, the fluid-structure interaction (FSI) method of ANSYS mechanical + CFX is adopted to consider the effect of flow field on the strength performance of the rotor blade. The cyclic symmetry analysis is adopted to calculate the strength performance and modal characteristics of the rotor blade. The results show that the flow field of the last stage is composed of backflow vortex, separation vortex and tip clearance vortex under low volume flow conditions. The tip clearance vortex has high circumferential velocity and temperature. The maximum deformation of the rotor blade is on the leading edge of the blade at 80% span, and the maximum equivalent stress is on the suction surface at 90% span. With the decrease of the steam flow, the temperature at the blade tip increases significantly, which increases the maximum deformation and the equivalent stress of the rotor blade. The plastic deformation occurs when the steam flow is reduced to 15% turbine heat acceptance (THA). In addition, the elastic modulus of blade material decreases with the increase of temperature, which leads to the decrease of natural frequencies. From 35 %THA to 5% THA condition, the natural frequencies of the blade decrease by 34-136 Hz. This study provides a theoretical reference for the identification, diagnosis and prediction of the vibration of the last stage blade under low volume flow conditions.
NSTL
Elsevier