Improve Service Life Research Articles

Study on Bending Resistance and Self-healing Property of SBS Modified Asphalt Mortar under Thermal Aging

At present, there are many studies on asphalt mixtures in China, but the research on asphalt mortar is not enough. In this paper, through trabecular bending tests of base asphalt mortar and SBS modified asphalt mortar under different aging degrees,and the change rules of mechanical properties of two kinds of asphalt mortar under different aging degrees were studied. By designing self-healing experiments of asphalt mortar specimens. The test results show that SBS modified asphalt mortar has better deformation resistance and load-bearing capacity than base asphalt mortar, SBS modified asphalt has better pavement performance, and the deformation resistance and stress relaxation performance of SBS modified asphalt mortar are greatly affected by short-term aging, which is the main factor affecting the healing degree. Therefore, controlling the short-term thermal aging of SBS modified asphalt mixture during paving and transportation is of great significance to the improvement of pavement service life.

A Methodology for the Application of Virtual Evaluation Methods within the Design Process of Cold Forged Steel Pinions

AbstractGears are essential machine elements in the drivetrain and transmission technology. The operational behaviour of a gear pairing is influenced by the design of the gear kinematics as well as the component properties. With regard to an improvement of performance and service life, the targeted modification of tooth geometry and component properties offers a promising approach. Thus, the achievable geometric and mechanical component properties are influenced by the manufacturing process, which must be taken into account in the design process. The application of virtual evaluation methods is suitable for this purpose. For the manufacturing of steel gears, cold forging provides the potential of achieving beneficial mechanical properties in a highly productive process. Major challenges for the industrial application are the short service life of the cost- intensive tools and the low geometric accuracy in comparison to machining processes. Within this study the design of the tooth geometry as well as the associated forming tool are investigated. The aim is to derive recommendations regarding an optimization of the resulting component properties and operational behaviour.

Tribological and microstructural investigation of hybrid AA8011/ZrB2-Si3N4 nanomaterials for service life improvement

The effect of ZrB2-Si3N4 particle reinforcement on the tribological behavior and microstructure of AA8011 alloy has been studied. ZrB2-Si3N4 particles were varied from 0 wt% to 20 wt% with an interval of 5 wt%. Dry sliding pin-on-disc tests at a room temperature condition were conducted to investigate the wear performances of the aluminium alloy/ ZrB2-Si3N4 composites. The tests were conducted at varying loads, from 20 to 40 N. The results depicted that the wear rates of the AA8011 alloy/ZrB2-Si3N4 composites are lower than that of the AA8011 and further decreases with increasing ZrB2-Si3N4 content, Also, the friction coefficient of the matrix alloy is higher than that of the composites and decreases with increasing ZrB2-Si3N4 content. This established the unique efficacy of ZrB2-Si3N4 effect on performance characteristics of aluminium series in application.

Optimization of energy consumption in coating removal for recycling scrap coated cemented carbide tools using hybrid laser-waterjet

In order to purified recovery of scrap cemented carbide, stripping of coatings was mandatory as engineering tools for improving service life were almost modified with anti-wear coatings. However, the low efficiency of current coating removal technologies leaded to the overmuch energy consumption, it was of great importance to achieve energy conservation to relieve the environment impact because of sustainable development. Reducing the energy consumption during processing could significantly improve the environmental performance of manufacturing systems. According to the energy consumption characteristics of hybrid laser-waterjet machine, a multi-objective optimization model for energy prediction with key parameters under actual constraints is constructed to trade off two responses: the cutting specific energy consumption (CSEC) and the processing time, which is transformed into a single-objective model and then solved by genetic algorithm. Simultaneously, the orthogonal experiment is proposed to identify the parametric influence on the multi-objective optimization and to validate the feasibility of the proposed model with the comparisons between single-objective and multi-objective optimization. Finally, the comparisons about energy consumption, carbon emission and the mechanical properties between high temperature oxidation method and hybrid laser-waterjet technology are carried out. The results indicate that larger feed speed and larger laser offset distance can benefit the energy conservation due to the shortened processing time. The multi-objective optimization model realizes about 80% of energy conservation compared to minimum CSEC, and 40% of which compared to minimum processing time. Contrasted to the energy conservation and substrate quality after processing, the hybrid laser-waterjet technology is much better than the high-temperature oxidation method.

Metallurgical changes of cryogenically treated Coated Carbide (KC-9225) and its performance during wet machining of Austenitic Stainless Steel – 310.

Various methods are employed to produce premium line of cutting tool materials with enhanced mechanical properties and improved service life. Cryogenic Treatment is one of those methods which has been considered for its benefits as a suitable add-on process. In this experimental investigation, Coated Tungsten-Carbide (KC9225) was taken as the cutting tool material and it was subjected to Deep Cryogenic-Treatment to analyse the several changes that might have taken place in its behaviour before and after the treatment. The treatment was carried out by a Dip-Stick arrangement where the temperature was gradually brought down to 100 K at the rate of ± 2 K/min. Tempering was also performed using the Dilatometer and the temperature was raised (~2 K/min) to 473 K. The changes in its mechanical properties both qualitatively as well quantitatively were investigated. Machining performance of the tool was also studied by performing wet turning on Austenitic Stainless Steel-310 where cutting force values were found to reduce by 3 to 71% in different cases thus proving its superiority as compared to the untreated tool.

A Wiener process–based remaining life prediction method for light-emitting diode driving power in rail vehicle carriage

Remaining life prediction is an effective way to optimize maintenance strategy and improve service life for light-emitting diode driving power in rail vehicle carriage. In this article, a Wiener process–based remaining life prediction method is proposed with the analysis of performance degradation data of light-emitting diode driving power in rail vehicle carriage. First, the temperature and humidity stress accelerated degradation tests are put forward in order to measure the output current of light-emitting diode driving power. Based on the output current, the accelerated degradation model is established. The drift and diffusion coefficients of the Wiener process are then obtained without prior information. Finally, the reliability of light-emitting diode driving power in rail vehicle carriage is assessed and the remaining lifetime is predicted after updating the degradation model parameters with Bayesian inference. The results show that the proposed method can improve the precision of assessment and reduce the uncertainty of prediction significantly. It also provides a potential solution for life prediction of other similar products.

Research on Cooling Technology of Shredder Cutting Tool With Ultrasonic Vibration-Assisted Cutting

To improve service life of shredder cutters, new technologies such as ultrasonic vibrationassisted cutting and cooling technology (jet and spray) are introduced into the design of the cutter for a two-axis horizontal shredder. Ultrasonic vibration-assisted cutting technology is theoretical analyzed, and result shows that the effect of friction reduction only happens when the speed of cutting is less than vibration speed. Therefore, the vibration-assisted cutting get a friction reduction of 52.5% and a cutting temperature reduction of 10.5% when the vibration-assisted cutting with an amplitude of 25 μm and a frequency of 20 kHz is performed on the shredder with the rotational speed of 60 r/min. Three cooling methods are proposed to lower the temperature of shredder tools such as air jet cooling, water jet cooling, and spray cooling. They are all simulated with Ansys-fluent software on the basis of the Lagrangian model. Simulation results show that water jet cooling can realize better cooling effect, whereas its cooling effect will not improve obviously until the jet diameter increases to around 4 mm. In addition, the cooling effect of the spray with vibration cutting which has less coolant consumption is very close to that of the water jet without vibration cutting. Therefore, the mode of spray cooling with vibration cutting can be used instead of the mode of water jet cooling for higher coolant utilization. By comparing with the traditional cutting of shredder, the spray cooling with vibration cutting has a cutting temperature reduction of 65%.

Effect of Oxidative Aging on the Engineering Properties of DGAMs

Short and long term aging were conducted on the dense graded asphalt mixtures (DGAMs) containing 40-50 penetration grade asphalt cement binders. The short term oven aging (STOA) was conducted on loose mixtures at temperature of 135 °C for four hours and at temperature of 154 °C for two hours, whereas, the long term oven aging (LTOA) was conducted at temperature of 85 °C and at two periods of time between four and eight days. Marshall properties, tensile and compressive strength at 25 and 60°C, flexural strength at 0 and -10°C, cohesion at 60°C, tensile strength ratio, and index of retained strength were carried out on unaged and aged DGAM. A mechanistic-empirical design approach using BISAR program was adopted for estimating the improvement in service life of the pavement or reduction in thickness of DGAM and base layer for the same service life due to the aging of DGAM. The results showed that the STOA and LTOA: (1) increases resistance of DGAM against permanent deformation, stripping, and flexural strength; (2) increases traffic benefit ratio between 10 and 20%; (3) reduces the thickness of the surface layer between 8 and 14%; and (4) the base thickness reduces between 35% and 57%.

Comparative study of materials for friction pairs in a new high water-based hydraulic motor with low speed and high pressure

PurposeAiming at improving the mechanical efficiency, the applicability and the working life of high water-based hydraulic motor (HWBHM) under working conditions at low speed and high pressure, the friction performance of different matching materials for piston slipper – crankshaft pair with high water-based hydraulic fluid (HWBHF) under working conditions at low speed and high pressure – were studied.Design/methodology/approachThe friction experiments for different materials (316L, 316L with surface coating OVINO – tetrahedral amorphous carbon [TAC; 316L-TAC] – 316L with surface coating OVINO-graphite intercalated compound [GIC; 316L-GIC] and polyetheretherketone [PEEK] reinforced with 30 per cent carbon fiber [PEEK-30CF]) under HWBHF lubrication were implemented on a pin-disk friction abrasion machine to determine the variations of coefficient of friction (CoF) and wear rate for each matching materials. In addition, the roughness and the morphology of worn surface of different matching materials were quantitatively characterized.FindingsThe study revealed that material combinations have different friction performances. Test results showed that the abrasion of matching type stainless steel (SS) and SS is rather serious, and the method of surface coating could improve the friction performance of SS when friction with other materials. For matching type of SS with surface treatment (SS-ST) and SS-ST, 316L-GIC and 316L-GIC have relatively stable CoF, and the wear rate was smaller than other matching materials, while 316L-TAC and 316L-TAC has the smaller CoF than that of 316L-GIC. Matching materials 316L-GIC with PEEK-30CF of matching type SS-ST and PEEK-30CF has more stable COF and better wear resistance than those of other matching materials.Originality/valueThis research has laid a foundation for the improvement of service life and working efficiency of friction pair in HWBHM under working conditions at low speed and high pressure.

Nanostructured copper-carbon nanotubes composites for aircraft applications

PurposeThe reliable performance of critical components working under extreme conditions is paramount to the safe operation of aircraft, and material selection is critical. Copper alloys are an obvious choice for such applications whenever a combination of transport, mechanical and tribological properties is required. However, low strength and hardness issues require development of new copper alloys and composites to improve service life and reliability. This study aims to investigate the effect of carbon nanotubes as reinforcement phase in copper-matrix composites.Design/methodology/approachThe development of novel copper-based composites refined to the nanoscale was envisaged through mechanical milling of mixtures containing copper and carbon nanotubes (2 Wt.%). Milling took place in a planetary ball mill for times varying between 1 h and 16 h at 400 rpm. A ball-to-powder ratio of 20:1 and alumina vial and copper spheres were used under dry conditions or with addition of isopropyl alcohol. Scanning electron microscopy/energy dispersive spectroscopy, size distribution, Raman spectroscopy and X-ray diffraction were used to study the produced powders.FindingsAttained results show that mechanical milling of the studied system produces nanostructured powders containing second-phase carbon nanotubes homogeneously distributed in the metallic matrix, together with severe copper grain refinement. This should correspond to increased residual microstresses, envisaging significant improvement of mechanical properties of the produced copper composites.Originality/valueThe novelty of the work resides in the use of carbon nanotubes for the reinforcement of copper, and on the systematic microstructural characterisation of the produced composites.

Aging exploration of long term multistressed HTV-silicone rubber/silica/alumina composites for high voltage insulation

Aging due to environmental stresses is main problem of silicone rubber insulators. The main intention of this research is to obtain silica/alumina based HTV-SiR composite with improved aging performance. For this purpose one nano with 15% nano silica (SN) and three hybrid composites based on 20% micro silica and 2% (S2), 4% (S4) and 6% (S6) silica each along-with neat sample (SN) of High Temperature Vulcanized Silicone Rubber (HTV-SiR) are prepared and exposed to accelerated multistress laboratory aging for 13.5 lab years. For this purpose, an environmental chamber is designed and fabricated including multiple stresses such as acid rain, heat, UV radiations, salt fog etc. For aging investigation; leakage current values are recorded after each weathering cycle. Similarly, STRI classification method was applied for hydrophobicity analysis. AC dielectric strength was investigated according to ASTM D-149 standard. Fourier Transform Infrared Spectroscopy (FTIR) was performed in order to follow the structural changes in all samples. After the laboratory weathering, it was observed that all the hybrid composites showed improved leakage current, hydrophobicity, and dielectric strength. S4 and S6 showed 23.7 kV mm−1 and 23.3 kV mm−1 of dielectric strengths, both these samples showed final HC-2 hydrophobicity class and nearly 2 μA of leakage currents. FTIR results also showed that the siloxane backbone and other important hydrocarbons remained in intact in the case of these hybrid composites. It was also emerged that higher loadings of nano-silica do not improve service life of HTV-SiR.

Modified Bond Coatings Improve Service Life of Plasma Sprayed Thermal Barrier Coatings and Protective Performance of Overlay Coatings

Abstract New thermal and cold spray technologies are being developed to extend the lifespan of thermal barrier coating (TBC) systems at elevated temperatures. This article describes the relevant attributes of coating technologies such as high velocity air fuel, high velocity air plasma spray, and high pressure cold spray for use in TBC systems.

Retrofitting Steam Turbines with Expired Service Life

Many pieces of equipment installed at thermal power stations (TPS) have an expired service life or are close to expiry and are obsolete. In addition, the structure of heat consumption by end users has changed. Among the ways for solving the problem of aging equipment is the retrofitting of turbines that allows for service life recovery and improvement of their performance to the modern level. The service life is recovered through replacement of high-temperature assemblies and parts of a turbine, and the performance is improved by retrofitting and major overhaul of low-temperature assemblies. Implementation of modern engineering solutions and numerical methods in designing upgraded flow paths of steam turbines considerably improves the turbine effectiveness. New flow paths include sabre-like guide vanes, integrally-machined shrouds, and effective honeycomb or axial-radial seals. The flow paths are designed using optimization and hydraulic simulation methods as well as approaches for improving the performance on the turbine blading and internal steam flow paths. Retrofitting of turbines should be performed to meet the customers' needs. The feasibility of implementation of one or another alternative must be determined on a case-by-case basis depending on the turbine conditions, the availability of reserves for generating live steam and supplying circulation water, and the demands and capacities for generation and delivery of power and heat. The main principle of retrofitting is to retain the foundation and the auxiliary and heat-exchange equipment that is fit for further operation. With the example of PT-60-130 and T-100-130, the experience is presented of a comprehensive approach to retrofitting considering the customer’s current needs and the actual equipment conditions. Due to the use of modern engineering solutions and procedures, retrofitting yields updating and upgrading of the turbine at a relatively low cost.

Simulation Analysis of Cylinder Impact Performance Influenced by Shaft Sleeve Structure

To study the cylinder motion characteristics, cylinder and shaft sleeve stress characteristics of cylinder stroke and return process influenced by different shaft sleeve structure, the cylinders with non-chamfering shaft sleeve, C0.3 chamfering shaft sleeve and R0.3 round corner shaft sleeve were used for simulation of cylinder stroke and return process. The results show that the piston velocity curves of three kinds of shaft sleeve are identical. Maximum stress of different shaft sleeves fluctuates and maximum stress elements of C0.3 and R0.3 shaft sleeve are similar. When cylinder strokes, maximum stress of cylinder occurs at the end of piston rod connected to the load; the stress of C0.3 shaft sleeve is the lowest. When cylinder returns, maximum stress of cylinder occurs at the shaft sleeve; the stress of C0.3 and R0.3 shaft sleeve differ little and are both lower than that of non-chamfering shaft sleeve. It provides a reference for structure optimization and service life improvement of the cylinder shaft sleeve.

Fatigue cracking simulation of aged asphalt pavements using a viscoelastic continuum damage model

Few information in the literature indicates how aging affects the service life of asphalt pavements. This work presents linear viscoelasticity and damage characterisation of an asphalt mixture at four aging states, and simulation of pavements fatigue performance. E* tests were performed in sinusoidal compression. Controlled crosshead tension-compression testing was used for damage characterisation. Aged materials were obtained by heating loose asphalt mixture at two temperatures (85°C and 135°C) and aging times (2 and 45 days). Two simulated pavements were studied for comparing behaviour at different ages using Layered Viscoelastic Pavement Analysis for Critical Distresses (LVECD). Results showed that the effect of aging seems to improve service life. It was also observed that simulating the asphalt layer as composed by two half-layers (aged at the top and unaged at the bottom) did not lead to significantly different results with respect to fatigue performance of an evenly aged layer.

Efficient Use of Water Resources in the Steel Industry

In the steel sector water management aims at improving the sustainability of the production cycle, resulting in resource efficiency benefits and in reduced water demand and costs. To be reused, water needs to be cooled and desalinized to avoid salt concentration in water circulation systems. The presented work includes two case studies carried out in an integrated steelmaking plant, respectively, to evaluate the possible implementation of ultrafiltration and reverse osmosis to reduce salt concentration in water streams and to investigate, through modelling and simulation, a process integration solution to improve water efficiency. Results showed that most salts are removed by reverse osmosis and that its coupling with ultrafiltration allows obtaining very high quality water; reuse of desalinated wastewater resulted in being more suitable and economically viable than its discharge. Moreover, modelling and simulation showed that the considered blowdown could be reused without significant changes in the receiving water network area. The industrial implementation of water recovery solutions can lead to a decrease of fresh water consumption, effluent discharge, and to improvement of product quality and equipment service life. The considered desalination technologies are transferable and easily implementable, and modelling and simulation are very useful in order to evaluate process modifications before real implementation.

Fabrication of fluorescent dyes supported on porous boron nitride nanosheets and their excellent photoluminescence properties

Fluorescent dyes rhodamine B (RhB) was successfully introduced into the porous boron nitride nanosheets to obtain an effective and rare-earth free light composite conversion materials. X-ray powder diffractions, photoluminescence spectra, etc., were used to investigate the optical performance and thermal stability of these organic-dye-impregnated phosphor composites. The experimental results evidently showed that, compared with the optical properties of RhB in aqueous solution, the composite phosphors possessed more excellent optical performance and higher thermal stability due to their structural defects, surface hydroxyl groups and nanosize pore channel. In addition, the phosphor composites exhibited greatly improved service life and had a broad visible emission wavelengths of 540–680 nm under the 363 nm light excitation. We believe that the reported work should open the way toward the practical application of organic-dye-impregnated phosphor composites in the field of illumination light source.

Frictional Performance Assessment of Cemented Carbide Surfaces Textured by Laser

Cemented carbides are advanced engineering materials often used in industry for manufacturing cutting tools or supporting parts in tribological system. In order to improve service life, special attention has been paid to change surface conditions by means of different methods, since surface modification can be beneficial to reduce the friction between the contact surfaces as well as to avoid unintended damage. Laser surface texturing is one of the newly developed surface modification methods. It has been successfully introduced to fabricate some basic patterns on cemented carbide surfaces. In this work, Direct Laser Interference Patterning Technique (DLIP) is implemented to produce special line-like patterns on a cobalt (Co) and nickel (Ni) based cemented tungsten carbide grade. It is proven that the laser-produced patterns have high geometrical precision and quality stability. Furthermore, tribology testing using a nano-tribometer unit shows that friction is reduced by the line-like patterns, as compared to the polished one, under both lubricated and dry testing regimes, and the reduction is more pronounced in the latter case.

Surface hardening of 30CrMnSiA steel using continuous electron beam

Abstract 30CrMnSiA high strength low alloy (HSLA) carbon structural steel is typically applied in equipment manufacturing and aerospace industries. In this work, the effects of continuous electron beam treatment on the surface hardening and microstructure modifications of 30CrMnSiA are investigated experimentally via a multi-purpose electron beam machine Pro-beam system. Micro hardness value in the electron beam treated area shows a double to triple increase, from 208 HV 0.2 on the base metal to 520 HV 0.2 on the irradiated area, while the surface roughness is relatively unchanged. Surface hardening parameters and mechanisms are clarified by investigation of the microstructural modification and the phase transformation both pre and post irradiation. The base metal is composed of ferrite and troostite. After continuous electron beam irradiation, the micro structure of the electron beam hardened area is composed of acicular lower bainite, feathered upper bainite and part of lath martensite. The optimal input energy density for 30CrMnSiA steel in this study is of 2.5 kJ/cm2 to attain the proper hardened depth and peak hardness without the surface quality deterioration. When the input irradiation energy exceeds 2.5 kJ/cm2 the convective mixing of the melted zone will become dominant. In the area with convective mixing, the cooling rate is relatively lower, thus the micro hardness is lower. The surface quality will deteriorate. Chemical composition and surface roughness pre and post electron beam treatment are also compared. The technology discussed give a picture of the potential of electron beam surface treatment for improving service life and reliability of the 30CrMnSiA steel.

A time-variant model of surface chloride build-up for improved service life predictions

Current service life models for predicting the time to chloride-induced corrosion initiation of steel reinforcement in concrete structures are based on a hypothesized surface chloride concentration, Cs, as a boundary condition. This is either assumed to be constant or varies with time, generally disregarding other factors that influence Cs. For example, Fickian models use a constant Cs and existing time-variant models assume Cs is only a function of time. In this paper, an improved time-variant Cs model is hypothesized using general physical concepts and is then validated by an empirical study. The proposed model, as opposed to the existing time-variant models, not only accounts for the variability of Cs with exposure time but also incorporates the effects of time to exposure and the effects of the concentration of chlorides in the exposure environment. The model assumes that Cs is sigmoidal in shape with an asymptote that is a function of the concentration of chlorides in the environment. The input variables for the proposed model were selected based on best subset sampling analysis on the results of the experimental work to determine the influence of water-to-cement ratio, time to exposure, the concentration of chlorides in the exposure environment, and exposure time on Cs. The accuracy of the proposed model is assessed versus existing time-variant Cs models and the results indicate that the proposed model better predicts the Cs in concrete exposed to chlorides. Moreover, results of service life predictions using the proposed model show that the proposed model yields more accurate results, better protecting owners from financial and engineering risks.