Purpose




The purpose of this paper is to present the results of the application of various models to estimate the reliability in railway repairable systems.




Design/methodology/approach




The methodology proposed by the International Electrotechnical Commission (IEC), using homogeneous Poisson process (HPP) and non-homogeneous Poisson process (NHPP) models, is adopted. Additionally, renewal process (RP) models, not covered by the IEC, are used, with a complementary analysis to characterize the failure intensity thereby obtained.




Findings




The findings show the impact of the recurrent failures in the times between failures (TBF) for rejection of the HPP and NHPP models. For systems not exhibiting a trend, RP models are presented, with TBF described by three-parameter lognormal or generalized logistic distributions, together with a methodology for generating clusters.




Research limitations/implications




For those systems that do not exhibit a trend, TBF is assumed to be independent and identically distributed (i.i.d.), and therefore, RP models of “perfect repair” have to be used.




Practical implications




Maintenance managers must refocus their efforts to study the reliability of individual repairable systems and their recurrent failures, instead of collections, in order to customize maintenance to the needs of each system.




Originality/value




The stochastic process models were applied for the first time to electric traction systems in 23 trains and to 40 escalators with ten years of operating data in a railway company. A practical application of the IEC models is presented for the first time.

Reliability analysis in railway repairable systems

In the current research, the influence of multi-pass of friction stir welding and SiC microparticles on the tensile strength, microhardness, and %strain of dissimilar reinforced joints of AA6082 and AA5083 was examined. A tool rotating speed of 900 rpm, a transverse speed of 45 mm/min, a tool tilt angle of 2º and 8% volume percentage of SiC microparticles were considered as parameters for multi-pass FSW. The finding demonstrated that increasing the number of FSW passes from one to three augmented the dispersion pattern of SiC microparticles. The grain refinement of multi-pass reinforced joints was achieved by the pinning effect of SiC microparticles and dynamic recrystallization. The three-passes FSWed reinforced joint exhibited the highest tensile strength (247.17 MPa), % strain (13.1%), and microhardness (126.6 HV) due to the higher grain refinement. 

/pdf/influence-of-sic-microparticles-and-multi-pass-fsw-on-weld-1h99tbpy.pdf

Influence of SiC Microparticles and Multi-Pass FSW on Weld Quality of the AA6082 and AA5083 Dissimilar Joints

The hydraulic system plays an important role in supplying power and its transition to other working parts of a coal shearer machine. In this paper, the reliability of the hydraulic system of a drum shearer was analyzed. A case study was done in the Tabas Coal Mine in Iran for failure data collection. The results of the statistical analysis show that the time between failures (TBF) data of this system followed the 3-parameters Weibull distribution. There is about a 54% chance that the hydraulic system of the drum shearer will not fail for the first 50 h of operation. The developed model shows that the reliability of the hydraulic system reduces to a zero value after approximately 1 650 hours of operation. The failure rate of this system decreases when time increases. Therefore, corrective maintenance (run-to-failure) was selected as the best maintenance strategy for it.

Reliability modeling of hydraulic system of drum shearer machine

Abstract In the current work, quadratic mathematical models at a 95% confidence level were developed to predict the optimum value of output responses such as the tensile strength, microhardness, and % strain of SiC particles-based friction stir welded composite joints of AA6061 and AA7075. Tool rotating speed, transverse speed, and volume percentage of SiC particles were considered as processing variables to multi-optimize the output responses using the desirability function in the Response surface methodology. ANOVA analysis was carried out to confirm the validity and adequacy of the developed model. The developed models showed that rotating speed is the most influential and transverse speed is the least influential variable. The highest tensile strength of 263 MPa, microhardness of 189 HV, and % strain of 29.4% was found at a rotating speed (RS) of 1200 rpm, transverse speed (TS) of 30 mm/min, and 10% volume percentage of SiC particles. The optimized processing variables, including transverse speed, rotating speed, and volume percentage of SiC particles, were found to be 32 mm/min, 1164 rpm, and 8.7%, respectively. The value of multi-optimized output responses, including tensile strength, % strain, and microhardness, was found to be 252 MPa, 26.7%, and 178 HV, respectively.

Optimization of processing variables of friction stir welded dissimilar composite joints of AA6061 and AA7075 using response surface methodology

In this study, the friction stir welding between AA5083 and AA7075 is modeled using numerical methods, and the role of parameters affecting the process, such as welding speed and rotation speed on material flow, temperature, and strain, is studied. The temperature, strain, and material mixing were analyzed while welding AA7075 to AA5083 alloys using a Coupled Eulerian-Lagrangian (CEL) approach. It was discovered that the CEL approach had accurately anticipated the mixing of materials in the stir zone (SZ) by comparing the SZ of the samples fabricated experimentally and modeled by simulation. Results show that the temperature and strain increase dramatically as the rotation speed increases from 500 to 900 rev min−1. The material flow obtained from the simulation shows that with increasing rotational speed or decreasing welding speed, AA7075 is more stretched towards AA5083 in the sheet’s higher surfaces, indicating an increase in material flow intensity. Better material mixing and increased material flow allowed for the achievement of the maximum tensile strength at the welding and rotation speeds of 36 mm min−1 and 900 rev min−1.

Investigation of the effect of welding and rotational speed on strain and temperature during friction stir welding of AA5083 and AA7075 using the CEL approach

Abstract Friction stir welding (FSW) is gaining attention over fusion welding is due to exceptional advantages. The advantages in FSW are superior joint properties, less preparation time, fumeless. FSW welding is widely employed in the automotive and aerospace sectors to join similar and dissimilar aluminium components. Many research articles have published particle reinforced Aluminium composite (AMC) FSW welding and reported improvement in mechanical properties. The paper focuses on the parameters used during welding to obtain good weld quality. The FSW joint efficiency of (AMC) varies between 80 and 95 percent, and joint efficiency is obtained by selecting the optimal combination of tool rotation speed, welding speed, and applied axial load. The tool rotation speed varies between 600 and 1200 rpm, with a 30–110 mm/min welding speed for uniform grain size in the joint using moderate axial loads. The tool profile and process parameters significantly impact welded joints' hardness and tensile behavior. The paper outlines the FSW process, operating ranges, and type of tools been used, which may be helpful for future research in the domain.

Influence of process parameters and its effects on friction stir welding of dissimilar aluminium alloy and its composites – a review

The current study investigates the exfoliation corrosion behavior of friction stir welded aluminum composite. The stir casting method was employed to fabricate chromium oxide (2 and 4% wt) reinforced Al 6061 composites. The fabricated composite samples are friction stir welded with two process parameters. The solution immersion tests were performed for two intervals per the ASTM G34 (24 h, 48 h), and the weight loss method was employed. The corrosion sample is analyzed by optical microscope FESEM and surface roughness. The gelatinous corrosion product formed over the surface can apply pressure over the grains resulting in the formation of pits. The intergranular corrosion (IGC) is formed by continuous penetration of the solution and the pits. The grains suffering from IGC are more susceptible to pit. The weight-loss method is not sufficient to predict the damage induced by the exco solution. Evaluating the pit depth can help to know the severity of corrosion. The measurement of the pit is difficult due to its irregular nature. The surface roughness instrument is used, and the damage is represented in average roughness (Ra) and average depth (Rz). The exposure duration and welding parameters play a significant role in corrosion. More material is lost at higher process parameters and extended hours of the test, forming higher surface deterioration.

Exfoliation corrosion susceptibility on friction stir welded aluminium 6061/Cr2O3 composite

Effect of Al2TiO5 Particulates on the Microstructural and Mechanical Characteristics of AA5052 Composites

Aluminum (Al) alloys are reinforced with carbides and oxides to enhance their properties. Al composites are developed to meet current automotive, shipbuilding, and aviation requirements. In the current study, aluminum 6061 is reinforced with B4C and Cr2O3 separately to fabricate Al6061 + B4C and Al 6061 + Cr2O3 aluminum metal matrix composites (Al MMC). The Al composites were fabricated by stir casting with a wt % in steps of 2%, 4%, and 6%. Joining of Al MMC is essential to develop valuable components. The developed composites were welded using friction stir welding (FSW). FSW is recognized and widely used for joining Al MMC due to premium weld quality with minimum defects. The present study aims to analyze the effect of process parameters and predictive accuracy of the artificial neural network (ANN) and response surface methodology (RSM). The parameters selected for the study are tool rotational speed, tool travel speed, and reinforcement wt %. The FSW was performed based on the experimental design developed by the design expert software. Through RSM analysis, it was found that both the independent factors (tool rotational and tool transverse speed) and the interaction of factors jointly contribute to the FSW joint properties. The higher ultimate strength of 139 MPa and lower tensile strength of 48 MPa are found. As the tool travel speed increase from 20 to 25 mm min−1, ultimate tensile strength increase by about 59%. The average accuracy of RSM was 98.26 and of ANN was 94.86.

https://iopscience.iop.org/article/10.1088/2631-8695/acb6d1/pdf

Analysis of tensile strength on friction stir welded Al 6061 composite reinforced with B4C and Cr2O3 using RSM and ANN

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