Operational Service Life Research Articles

Study of laser texturing assisted abrasive flow finishing for enhancing surface quality and microgeometry of spur gears

This paper reports on study of laser texturing assisted abrasive flow finishing (LT-AFF) process of the hobbed spur gear (HSG) to further improve their microgeometry, surface finish, micohardness, microstructure, wear resistance, and material removal rate (MRR) as compared to AFF process. Preliminary experiments were conducted to identify optimum values of power and focal length of the continuous fiber laser of 1064-nm wavelength, and number of passes for laser texturing of the HSG made of 20MnCr5 alloy steel. Identified optimum values were used to produce homothetic texture on flank surfaces of HSG in a direction perpendicular to the lay profile generated by hobbing. Influence of laser texturing was studied by comparing deviations in microgeometry, average and maximum surface roughness values, microhardness, wear resistance, and MRR of HSG directly finished by AFF and laser-textured hobbed spur gears (LTHSG) finished by AFF. Previously optimized value of viscosity of AFF medium was used during finishing of HSG and LTHSG. Deviations in total profile, total lead and total pitch, and radial runout were used to indicate deviation in microgeometry of the spur gears. Results reveal that AFF of LTHSG reduced surface roughness and errors in microgeometry and improved microhardness, microstructure, wear resistance, and MRR than direct of AFF of HSG. Improved microgeometry and surface quality of spur gears will lead to their increased operating performance and service life thus reducing their running noise and vibrations and preventing their premature and failures. This research proves that productivity of AFF process can be improved significantly by laser texturing for finishing the spur gears.

Study on Bogie Frame Reliability of Urban Railway Vehicles

The planning and design of the urban railway lines is an important part of the medium-distance railways, and the construction of the domestic urban railways is developed rapidly. As an important part of the urban railway, the rail vehicle has become one of the research and development priorities of the key enterprises. As the main load-bearing structure of railway vehicle bogies, the bogie frame reliability is crucial to the operational safety and service life of vehicles. In view of this, the reliability of the domestic newly designed urban vehicle bogie frame is analyzed based on UIC standards, which provides effective support for the design of urban vehicles.

Application of tuned-mass system on railway catenary to improve dynamic performance

Finding a simple and practical method to improve the dynamic behaviour of a specific structure is always desirable in civil and mechanical engineering. The railway catenary system is the overhead power line above the track, interacting together with the train-based pantograph to transfer electric power. Due to vertical stiffness variation and a propagating wave along the catenary, the fluctuation of the contact force becomes significant with operational speed increasing. Therefore, this has become one of the key factors which limits the operational speed and service life of key components. Wire misalignment, structural errors and uneven mass distribution of the catenary can further deteriorate the contact stability. In order to achieve a higher speed on existing lines, the catenary needs large-scale modification implying long out-off-service time. From the designing aspect, all components directly fixed to the catenary, like clamps, steady arms and other fittings, are made as light and small as possible to minimize disturbances. However, in other engineering applications, some well-designed additional mass systems are adopted aiming to improve their dynamic performance. In order to take advantage of these unavoidable masses on the catenary, an investigation on lumped-mass distribution in single-pantograph and multi-pantograph operations is performed with help of a 3D pantograph-catenary finite element (FE) model. The results show that a rightly-tuned mass, here the implementing location and the elasticity of its connection, can positively change the dynamic performance without implementing large-scale modification to the existing system. Through a brief discussion on the mechanism of this positive effect, this paper proposes that applying some artificial tuned-mass system can be a possible method to overcome unfavourable working conditions or even allow speed increase on existing lines.

An Efficient Chloride Ingress Model for Long-Term Lifetime Assessment of Reinforced Concrete Structures Under Realistic Climate and Exposure Conditions

Chloride penetration is among the main causes of corrosion initiation in reinforced concrete (RC) structures producing premature degradations. Weather and exposure conditions directly affect chloride ingress mechanisms and therefore the operational service life and safety of RC structures. Consequently, comprehensive chloride ingress models are useful tools to estimate corrosion initiation risks and minimize maintenance costs for RC structures placed under chloride-contaminated environments. This paper first presents a coupled thermo-hydro-chemical model for predicting chloride penetration into concrete that accounts for realistic weather conditions. This complete numerical model takes into account multiple factors affecting chloride ingress such as diffusion, convection, chloride binding, ionic interaction, and concrete aging. Since the complete model could be computationally expensive for long-term assessment, this study also proposes model simplifications in order to reduce the computational cost. Long-term chloride assessments of complete and reduced models are compared for three locations in France (Brest, Strasbourg and Nice) characterized by different weather and exposure conditions (tidal zone, de-icing salts and salt spray). The comparative study indicates that the reduced model is computationally efficient and accurate for long-term chloride ingress modeling in comparison to the complete one. Given that long-term assessment requires larger climate databases, this research also studies how climate models may affect chloride ingress assessment. The results indicate that the selection of climate models as well as the considered training periods introduce significant errors for mid- and long- term chloride ingress assessment.

Improving the Efficiency of Earth Monitoring Missions by Equipping Small Spacecraft AIST-2 with Electric Propulsion

The paper considers the problem of equipping a small spacecraft (SS) of the AIST-2 series with electric propulsion for orbital plane maneuvers, such as station keeping and attitude control. Solution of this problem will increase the satellite's operational service life on a low-Earth orbit and, in future, allow attitude control of a satellite constellation.

Modal testing circuit board assembly of an electronic apparatus by laser vibrometry

The operating capacity and service life of printed circuit boards in various electronic equipment and devices depends on their ability to resist vibroacoustic loads, including vibration and acoustic noises. In this paper, non-contact laser vibrometry has been applied to perform the modal analysis of a circuit board assembly in order to identify its vulnerable spots and to find solutions to protect the assembly from external vibroacoustic loads. A broadband periodic chirp signal was used to excite vibration, which enabled a rapid generation of results. The paper provides data on eigenfrequencies, vibration velocity fields, and vibration displacement profiles. Frequency ranges have been determined in which eigenfrequencies with the highest vibration amplification lie. The obtained data can be used to develop a quality control technique for printed circuit boards and to optimize their construction as early as the design stage.

Measurement and simulation of impact wear damage to industrial conveyor belts

Increasing the reliability of commercial conveyor belt systems results in an improvement of the service life and the economics of the belts as well as other technological components. The operational service life of a conveyor belt depends on several factors, such as the type of transported material, operating conditions, conveyor belt quality, and belt material properties. Important factors also include the methods used for conveyor belt storage. Long-term storage, which is not compliant with the applicable standards, contributes to the shortening of a belt’s service life. The main objective of this article is to identify the effects of selected factors (i.e. storage, drop height, type of transported material) on the wear of rubber-textile conveyor belts. These experiments involved testing unused conveyor belts in two different phases of their life cycle: (1) a conveyor belt stored for 24 months, and (2) an unstored conveyor belt, put into service right from the factory, i.e. in the beginning of its life cycle. In total, 42 test samples were used. An analysis of the relative risk, and the use of decision trees, established the relationship between the selected variables.

Retardation of heat exchanger surfaces mineral fouling by water-based diethylenetriamine pentaacetate-treated CNT nanofluids

Mineral scale deposition on heat exchanging surfaces increases the thermal resistance and reduces the operating service life. The effect is usually intensified at higher temperatures due to the inverse temperature solubility characteristics of some minerals in the cooling water. Scale formation build up when dissolved salt crystallize from solution onto the heated surface, forming an adherent deposit. It is very important for heat transfer applications to cope with the fouling problems in industry. In this present study, a set of fouling experiments was conducted to evaluate the mitigation of calcium carbonate scaling by applying DTPA-treated MWCNT-based water nanofluids on heat exchanger surfaces. Investigation of additive DTPA-treated MWCNT-based water nanofluids (benign to the environment) on fouling rate of deposition was performed. 300mgL−1 of artificially-hardened calcium carbonate solution was prepared as a fouling solution for deposit analysis. Assessment of the deposition of calcium carbonate on the heat exchanger surface with respect to the inhibition of crystal growth was conducted by Scanning Electron Microscope (SEM). The results showed that the formation of calcium carbonate crystals can be retarded significantly by adding MWCNT-DTPA additives as inhibition in the solution.

METAL STRUCTURES SURVIVABILITY ASSESSMENT WHEN SIMULATING SERVICE CONDITIONS

Purpose. The research is aimed at improving the quality and reliability of measures of primary and secondary protection of metal structures at manufacturing companies, to prolong the service life of cyclically loaded structures of production facilities taking into account the corrosion level of danger. Methodology. Authors proposed to use the principles of process approach for statement and realization of management problems of operational service life in corrosion environments. The principles of ensuring reliability on the level of corrosion danger include justification of stages sequence for survivability assessment of a structural metalwork based on the strategy of DMAIC (define, measure, analyze, improve, control): definitions, measurements, analysis, improvement and monitoring of measures of primary and secondary corrosion protection. Findings. Providing control measures from corrosion according to the criterion of corrosion danger allows providing requirements of reliability of structural metalwork based on calculated provisions of the limiting conditions method and solving the problems of management in technological safety during the expected service life of structural objects. Originality. The developed strategy of maintenance of the industrial facilities on an actual state includes the process approach to resource management by creation of system for the account and the functional controlling, risk analysis and regulation of technological safety in production facilities of the enterprises. Realization of the principles of process approach to management of technological safety at the object level is directed to perfecting of tools and methods of anticorrosive protection, extension of a resource taking into account indexes of survivability (,) and justification of program measures to ensure the reliability of enterprises(PER). Practical value. On the basis of process approach to quality and reliability management, generalizations of the natural and numerical researches directed to justification of design solutions of primary and secondary protection of a metalwork at the given level of corrosion danger of a metalwork the organizational measures of PER including assessment of integral characteristics of constructional suitability, technological rationality and risk analysis of signs corrosion danger of objects are developed.

A data mining approach for machine fault diagnosis based on associated frequency patterns

Bearings play a crucial role in rotational machines and their failure is one of the foremost causes of breakdowns in rotary machinery. Their functionality is directly relevant to the operational performance, service life and efficiency of these machines. Therefore, bearing fault identification is very significant. The accuracy of fault or anomaly detection by the current techniques is not adequate. We propose a data mining-based framework for fault identification and anomaly detection from machine vibration data. In this framework, to capture the useful knowledge from the vibration data stream (VDS), we first pre-process the data using Fast Fourier Transform (FFT) to extract the frequency signature and then build a compact tree called SAFP-tree (sliding window associated frequency pattern tree), and propose a mining algorithm called SAFP. Our SAFP algorithm can mine associated frequency patterns (i.e., fault frequency signatures) in the current window of VDS and use them to identify faults in the bearing data. Finally, SAFP is further enhanced to SAFP-AD for anomaly detection by determining the normal behavior measure (NBM) from the extracted frequency patterns. The results show that our technique is very efficient in identifying faults and detecting anomalies over VDS and can be used for remote machine health diagnosis.

Performance monitoring of large-scale autonomously healed concrete beams under four-point bending through multiple non-destructive testing methods

Concrete is still the leading structural material due to its low production cost and great structural design flexibility. Although it is distinguished by such a high durability and compressive strength, it is vulnerable in a series of ambient and operational degradation factors which all too frequently result in crack formation that can adversely affect its mechanical performance. The autonomous healing system, using encapsulated polyurethane-based, expansive, healing agent embedded in concrete, is triggered by the crack formation and propagation and promises material repair and operational service life extension. As shown in our previous studies, the formed cracks on small-scale concrete beams are sealed and repaired by filling them with the healing agent. In the present study, the crack formation and propagation in autonomously healed, large-scale concrete beams are thoroughly monitored through a combination of non-destructive testing (NDT) methods. The ultrasonic pulse velocity (UPV), using embedded low-cost and aggregate-size piezoelectric transducers, the acoustic emission (AE) and the digital image correlation (DIC) are the NDT methods which are comprehensively used. The integrated ultrasonic, acoustic and optical monitoring system introduces an experimental configuration that detects and locates the four-point bending mode fracture on large-scale concrete beams, detects the healing activation process and evaluates the subsequent concrete repair.

Research of Influence of Quality of Materials on a Road Marking of Highways

In research work importance of control of a condition of maintained objects, regular inspection of their technical condition and the proved assignment of geometrical parameters and operating modes is emphasized. Attracting of new methods of the organization of movement can considerably affect safety of traffic. Drawing of a road marking - the complex process demanding qualification and presence of qualitative materials. The marking possesses great value for safety of traffic; therefore of its creation is demanded much. At a stage of preparation there is an estimation of a condition of road and load to which it is exposed. Depending on these parameters materials for creation of a road marking are selected. The insufficient attention to details of a road marking can lead to decrease of operational parameters and service life.

New machine tool motorized spindle integrated with one electromagnetic ring balancer driven by optimal square wave

Machine tool motorized spindle usually encounters mass imbalance in the operational process. In order to enhance the machining efficiency and precision, on-line active unbalance compensation technique is becoming the first choice of vibration suppression for machine tool spindle. This paper proposes a new motorized spindle integrated with one electromagnetic ring balancer. Firstly, the three-dimension structural design of the integrated spindle is described in detail. Then, the balancing principle of electromagnetic ring balancer is set forth. In order to disclose the structural characteristic and determine the reasonable square wave drive parameters, the finite element calculations are carried out to obtain the relationship between the torque and rotational angle of counterweight disk when coil is not electrified, and the movement curve when coil is applied different currents. Based on the steady-state and transient electromagnetic field simulations, a specific spindle prototype with one electromagnetic ring balancer is developed. For the prototype, vibration test rig is built to verify the balancer design correctness, fabrication quality and vibration reduction effectiveness. The experimental results show that the proposed balancer has a smooth movement process under square wave drive, a desired unbalance response and the spindle vibration can be effectively reduced in a semiautomatic balance way, which is very beneficial to the improvement of operational precision and service life of machine tool motorized spindle.

A method of diagnostics of induction-motor rotor eccentricity

Electroenergetics and industry mainly use induction motors (IMs) as drives of mechanisms. One method to improve their operational reliability and service life is effective and timely diagnosis of abnormal operating modes, in particular, rotor eccentricity. However, for a number of reasons, it has not before been possible to develop a diagnostic system that would allow one to effectively identify the rotor static eccentricity during an operational process. To solve this problem, a method of diagnostics of rotor eccentricity in IM has been proposed that uses a stator current, and the amount of eccentricity is determined by the operative value of additional current. It is proposed to carry out IM diagnostics in an idling regime in two stages. At the first stage, the reference values of a harmonics of stator current’s components of additional current, its operative value, and dependence from the rotor eccentricity are determined and saved for a fully functioning machine. At the second stage, the values of a harmonics of stator current’s and components of additional current are determined. The operative value of additional current is calculated taking into account the relation of the received harmonics to their reference value, and the shift of a rotor is determined by reference dependence.

Grain Coarsening Characteristics of Modern Nb Microalloyed Steels

Modern steelmaking technologies utilizing microalloyed steel designs have been responsible for enormous economic benefits for both the steelmaker and fabricator. What has not been acknowledged is the environmental benefit that high strength steels have produced in terms of reduced steel usage in major infrastructure projects. The judicial use of microalloying has the potential to further reduce total tonnage requirements while delivering enhanced operational performance and service life. Various projects around the world have begun to recognize these recent microalloying developments. This paper will present the grain coarsening behavior of the new generation of Nb bearing steels, which have been used in major international steel fabrication projects.

The possibilities of fracture mechanics as applied to problems of strength, service life, and substantiation of safe operation of heat-generating and mechanical equipment

The fundamentals of fracture mechanics are briefly outlined, and its possibilities as a tool for estimating the longevity and bearing capacity of equipment components the metal of which contains cracklike flaws are pointed out. Experimentally obtained kinetic crack resistance diagrams lying at the heart of methods for determining the survivability of structures are given for some steels. Practical application of the methods of fracture mechanics is demonstrated on a particular example of substantiating temporary operability of a boiler drum having cracklike flaws near the holes for water downtake pipes.

A review of milk fouling on heat exchanger surfaces

Formation of deposits on heat exchanger surfaces during operation rapidly increases the thermal resistance and reduces the operating service life. Product quality is deteriorated by fouling, which causes reduction of proper heating. The chemistry of fouling from milk fluids is qualitatively understood, and mathematical models for fouling at low temperatures exist, but the behavior of systems at ultrahigh temperature processing is still not clearly understood. The effect of whey protein fouling on heat transfer performance and pressure drop in heat exchangers was investigated by many researchers in diversified fields. Among them, adding additives, electromagnetic means, treating of heat exchanger surfaces and changing of heat exchanger configurations are notable. The present review highlighted information about previous work on fouling, parameters influencing fouling and its mitigation approach.

액체로켓엔진 터보펌프용 펌프의 축추력 조절에 관한 연구

The magnitude of the axial thrust acting on pump bearings has a great influence on the operational reliability and service life of a pump for turbopumps. In the present study, radial vanes are introduced to the pump casing to control the axial thrust by changing the cavity pressure between the impeller and the casing. To investigate the effect of the vanes on the axial thrust of the pump, experimental and computational studies were performed with and without the vanes. It is shown that the vanes reduce the cavity pressure by preventing the flow from rotating with the impeller. Experimental and computational results show similar trend for the axial thrust difference between two cases with and without the vanes. The results show that the cavity vanes are very effective in controlling the magnitude of the axial thrust.

Service life of RC structures: chloride induced corrosion: prescriptive versus performance-based methodologies

Reinforced concrete (RC) structures subjected to aggressive environmental exposure conditions are traditionally designed to satisfy safety, serviceability, durability and aesthetics requirements throughout their operational design service life. This is usually established using time-dependent mathematical models, developed through performance-based methodologies in guidelines and European and national standards. However, at present, in most cases, prescriptive methodologies are used. The objective of this paper is to compare, as regards chloride induced corrosion, defined target periods of service life according to a prescriptive methodology with service life results of a performance-based methodology. In the laboratory concrete specimens were manufactured having compositions according to a prescriptive specification. These specimens were tested in order to determine their performance properties (strength, chloride diffusion and capillary absorption). Test results were included in the mathematical models of the performance-based specifications. The classic safety factor and recent probabilistic approaches have been used to estimate the service life of each composition being compared to the target periods defined in the prescriptive specification. Numerical calculations show that the results of the Partial Safety Factor and a full probabilistic approach are distinctly different and consequently their convergence still needs to be improved, due to the complexity of the process of chloride penetration into the concrete, not only the model but also the input values. When compared to performance-based approaches it would be expected that the prescriptive methodology would be more conservative due to its less quantified information on concrete and environment properties, though in this study this was not always true.

Estimation of Electric Transformer Service Life from Oil Degradation Kinetics

Petroleum-based transformer oil performs the dual roles of insulator and electrolyte depending on charges in the oil. The availability of charges for conduction influences the level of voltage breakdown in the mineral oil and depends on the intensity of physicochemical processes such as redox action, hydrolysis, photodegradation, sludge/particle development, and gas formation arising from thermal, mechanical, chemical, and electrical stresses in the oil. Previous investigators have focused mostly on single oil aging indicators to build models for estimation of the aging rates of transformer oils, within a time frame that is too short relative to the operational service life of transformers. In this research, the interdependence of oil voltage breakdown and changes in oil physicochemical characteristics was investigated experimentally using T24 and T14 oils. Tests were performed with a DTS-100D oil tester for voltage breakdown and a HKV 4000 series high kinematic viscosity bath. The calculated activation e...