Service Life Of Critical Components Research Articles

Fault diagnosis of rotating machinery using novel self-attention mechanism TCN with soft thresholding method

Rotating machinery (e.g. rolling bearings and gearboxes) is usually operated in high-risk and vulnerable environments such as time-varying loads and poor lubrication. Timely assessment of the operational status of rotating machinery is crucial to prevent damage caused by potential failure and shutdown, which significantly enhances the reliability of mechanical systems, prolongs the service life of critical components in rotating machinery, and minimizes unnecessary maintenance costs. In this regard, in this paper, a novel approach named self-attention mechanism combining time convolutional network with soft thresholding algorithm (SAM-TCN-ST) is proposed for fault intelligent recognition of rotating machinery. Specifically, the vibration signals are transformed into time-frequency graphs with distinct features utilizing the continuous wavelet transform, and then the proposed SAM-TCN-ST algorithm is employed for capturing essential data characteristics and classification performance. Eventually, datasets from rolling bearings and gearboxes are used to verify the accuracy and effectiveness of the proposed method compared with state-of-the-art benchmark networks such as pure TCN, convolutional neural networks and long short-term memory models. Experimental results demonstrate that the recognition accuracy rate of the proposed SAM-TCN-ST is higher than that obtained from the benchmark methods. This research presents an intelligent and viable solution for achieving real-time monitoring of the status and detecting faults in rotating machinery, thereby expectedly enhancing the reliability of mechanical systems. Consequently, the proposed SAM-TCN-ST algorithm holds significant potential for applications in prognostic and health management practices related to rotating machinery.

High-Temperature Oxidation Behavior of Plasma-Sprayed CoCrAlTaY-30Al2O3 Cermet Coating at 1050 °C

Cermet coatings with ceramic and metal characteristics will play an increasingly important role in extending the service life of critical components in harsh service environments. In this paper, CoCrAlTaY-30Al2O3 (wt.%) cermet coating was prepared by air plasma spraying technique. The effect of powder feeding rate on the microstructure and mechanical properties of the coating and its high-temperature oxidation behavior was investigated. The results showed that the CoCrAlTaY-30Al2O3 spraying powder mainly consisted of Al5Co2, α-Al2O3, Co, Cr7C3, and TaC in five phases. The microstructure of cermet coating was uniform and its porosity was relatively low. The coating was mainly composed of Al5Co2, Cr, and Al2O3 phases, and the change of powder feeding rate had no obvious effect on the phase composition of the coating. When the powder feeding rate was 32 g/min, the minimum porosity of the coating was (3.68 ± 0.86)%, and the maximum Vickers hardness and binding strength were (664.9 ± 55.9) HV0.3 and (78.6 ± 6.6) MPa, respectively. The oxidation rate constant kp1 of the coating at 1050 °C was 0.066 mg2∙cm−4∙h−1, and the fitted curve R2 value was 0.99547. In the oxidization initial stages, the alloy elements Co, Al, and Cr in the cermet coating were rapidly oxidized to form CoO, Al2O3, and Cr2O3. Then Al2O3 and Cr2O3 reacted with CoO to form Co(Al,Cr)2O4 spinel oxides. The θ-Al2O3 phase was formed after initial oxidation while the θ-Al2O3 phase was completely transformed into α-Al2O3 after 200 h. The oxide film mainly contained Co(Cr,Al)2O4, Cr2O3, and α-Al2O3 phases.

Improved wear resistance of directed energy deposited Fe-Ni-Cr alloy via closed-loop controlling laser power

Wear resistance influences the service life of critical components and limits the widespread application, and the thermal accumulation is a key factor affecting wear property in the coating preparation. In this work, the effects of thermal accumulation and suppression of the melt pool on wear performance were compared. We proposed a closed-loop control method based on proportion integration differentiation (PID) algorithm to improve the wear resistance by adjusting the laser power and controlling the melt pool size (MPS) in real time. The results demonstrated that the cross-growth of large-sized dendrites in the traditional mode resulted in poor wear performance. In contrast, dense equiaxial crystals without preferential orientation were formed in the closed-loop control mode, which caused the formation of a dense and homogenized coating. The grain refinement strengthening and increased microhardness led to the significant reduction of the wear rate to ~3.0·10−6 mm3/Nm, which was an-order-of magnitude lower than that in the traditional mode.

Review on hardfacing as method of improving the service life of critical components subjected to wear in service

A review on hardfacing is presented. Hardfacing involves applying a consumable with desired wear properties over a soft base metal surface to enhance resistance to different wear mechanisms. Substrate materials used for hardfacing are mainly steel, while the alloys of carbide forming elements dominate the surfacing consumables. Powder metallurgy, atomisation and granulation are methods of producing hardfacing alloy powder. Most welding methods were identified to be successfully used in applying consumable on substrate surfaces. Dilution decreases with increase in the number of hardfacing layers. Buffers, butters and build-up metals are used to compensate for composition differences to prevent spalling, overcome welding difficulties and make up for badly worn surfaces, respectively. Waffle, stringer and dot patterns are the existing hardfacing deposit patterns. Benefits of hardfacing include: reduced downtime, inventory and maintenance cost, increased plant availability and productivity, and a good number of service life extensions through timely reparation.Keywords: Hardfacing, wear, substrate, consumable, service life extension, composition compensation

Significance of Fatigue Damage from Overload Trucks on Bridge Load Rating

Overload trucks constitute a major portion of truck load populations on highways. Specific to bridges, the increase in the frequency of overloads may trigger shortening of service life of critical components because of fatigue damage, considering the fact that fatigue damage accelerates at higher loads. This is especially important to older bridges that have been designed for loads lower than the standard for current highway bridge design in the United States. As the number of requests for special permits to use bridges by overload trucks increases, the accumulated damage may substantially reduce the service life of bridges resulting in costly repair and replacements. In this paper, the significance of overloads in causing fatigue damage to bridges is discussed. Samples of truck load data have been compiled and used to determine the contribution of overloads to fatigue damage for steel girder bridges made up of welded cover plates. The paper discusses using the expected fatigue life expended (FLE) as an index to determine the impact of overloads on bridge fatigue damage. The FLE is then determined to be an important factor that can be used to modify bridge rating equations as a way of controlling the number of overload permits for a given bridge.

State Assessment of Ukrainian and Other Countries Power Equipments

The power capacity growth to meet increasing electricity demand is complicated by a significant number of power units having operating lifetime expired. However, the domestic and foreign practice shows that the actual operating life of power units is often substantially longer than it is claimed by manufacturers. Lifetime extension of existing power units is a common international practice ensuring power generation at the achieved level until new power generating capacity is put into operation. The article provides analysis of the current state of power equipment of Ukrainian thermal and nuclear power plants. The main differences and problems in assessment of remaining service life of critical components of TPP and NPP units are comprehensively considered. A comparative analysis of domestic and foreign methods for equipment remaining life assessment is provided. The main problem of ensuring sustainable unit performance is raised within the article.

Diffusion Mechanisms in Binary ‘Steel–coating’ Systems Under Long–term High Temperature Exposures

The processes of mutual element diffusion in coating and matrix are the one of significant factors affecting the service life of critical components and assemblies, including products with coatings. These processes render a direct influence on the corrosion resistance and wear of parts, operating at high temperatures in aggressive environments, such as the petrochemical industry. The paper proposes a method for calculating the concentrational distribution of elements in matrix and its coating at high temperature gradients and internal stresses. Concentrational mechanism of diffusion and thermal diffusion by the vacancy mechanism are the dominant mass transfer processes of the coating elements at the binary ‘steel–coating’ system heated to 1173K (1073–1173K is the temperature of the pyrolysis under industrial conditions). Both transfer mechanisms are directed into the matrix depth which leads to an intensive relocation of coating atoms to its internal surface layers. The focus of this study was to perform an analysis of the coating concentrational profiles, obtained on the basis of thermal diffusion and vacancy mechanisms of mass transfer taking into account internal stresses in the crystal lattice of matrix.

On the search for optimal damage precursors

A new approach to predict the service life of critical components via study of damage precursors is emerging and is the topic of this article. To date, most service life predictions are based on measurements of damage indicators and their growth toward criticality or failure, for example, fatigue crack length and material loss due to corrosion or wear. This makes lifetime estimates based on measurements of damage, for example, around half-life, or even at 80% life, difficult and inaccurate. To improve the accuracy and reliability of lifetime prediction, efforts are now underway to determine the state awareness of a critical component during service, based on property characterizations, in addition to the measurements of the direct damage indicators, such as crack length, acoustic emission, ultrasound signals, and eddy current measurements. These characterizations will include indirect damage indicators, that is, precursors and allied or affiliated damage indicators. For affiliated damage indicators, residual stress relaxation or development, phase changes, electrical property (resistivity, dielectric constant, permeability), and microstructural characterization must be considered. The selection of the optimal combination of direct and indirect damage indicators will be application specific. It is proposed to assess the efficacy of damage indicators on the basis of their Di/Df versus Ni/Nf, that is, damage ratio versus life fraction curves (referred to as damage indicator ratio curves), searching for indicators with damage indicator ratio curves that best meet the needs of the application.

Life extending control of helicopter based on dynamic inversion

The purpose of using life extending control for Black Hawk UH-60 helicopter is to make a trade-off between the handling qualities and the service life of critical components. An increase in service life span results in enhanced safety and the reduction in maintenance costs. This paper presents a design methodology of life extending control for structural durability and high performance of mechanical system, which is based on an explicit dynamic inversion control scheme. A real-time nonlinear fatigue crack growth model is built to predict fatigue damage resulting from the impact of cyclic bending stress on rotor shaft, which serves as an indicator of service life. The 4-axis gain-scheduled flight controller, whose gains are adjusted as a function of damage and flight velocity, is designed to regulate roll attitude, pitch attitude, vertical velocity and yaw rate. The nonlinear system simulation results show that the responses can meet the requirements on ADS-33 Level 1 handling qualities and that the 4-axis decoupling control is realized. As the damage increases, the tracking performance is slightly degraded, which results in smaller transients in bending moment response.

Remanufacturing with ECH – A Concept

A concept of remanufacturing is develops for expensive saving for new components. The cost of spare parts for aerospace and automobile engine are very high, in many cases repair of parts is cost effective. A lot of components are reused, which results in decreasing the amount of materials, energy and waste. This paper aims to find the remanufacturing possibilities with electrochemical honing (ECH) process, for difficult to machined alloy of engine parts. ECH process have their own advantages to remove any hard material with controlled surface generation with excellent surface finish. Furthermore, it provides highest productivity and increasing the service life of critical components. This paper presents a unexplored concept with some direction for future research with an objective to mature the remanufacturing engineering.

Hybrid life-extending control of mechanical systems: experimental validation of the concept

The goal of life-extending control is to achieve high performance of complex dynamical systems (e.g., aircraft, spacecraft, and energy-conversion systems) without overstraining the mechanical structures and the potential benefit is an increase in the service life of critical components with no significant loss of performance. This paper presents a two-tier architecture and a design methodology of hybrid (i.e., combined discrete-event and continuously varying) life-extending control for structural durability and high performance of mechanical systems. A feedback controller at the lower tier is designed with due consideration to robust performance and damage mitigation. A variable-structure stochastic automaton is employed at the lower tier for status evaluation of structural damage while the overall system performance is maintained by the supervisory level discrete-event controller at the upper tier. Experimental results on a laboratory test apparatus are presented for validation of the proposed concept of hybrid life-extending control.

Protective Coatings by Plasma Spraying: A Review

In recent years, the use of plasma-sprayed protective coatings has gained increasing acceptance for prolonging the service life of critical components exposed to aggressive environments during normal operation. This paper is aimed at providing an overview of the current state-of-the-art of the plasma coating technology. It includes a brief discussion of the various important aspects associated with the development of reliable protective coatings as well as their evaluation, and outlines some noteworthy advances made in the field of plasma spray materials and equipment in the past few years. The various factors influencing the coating quality are identified and the wide-ranging utility of plasma-sprayed coatings is also highlighted.