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Editorial Office

University of Ljubljana
Faculty of Mechanical Engineering
Journal of Mechanical Engineering

Aškerčeva 6,

SI-1000 Ljubljana
Slovenia

P: +386 1 4771 137
E: info@sv-jme.eu



The journal is subsidized by Slovenian Research Agency.

 
ISSN: 0039-2480

Journal of Mechanical Engineering 63 (2017) 5

 

 

 


 

Critical Failure Analysis of Superheater Tubes of Coal-Based Boiler

Authors - Gagan Kumar Gupta* – Somnath Chattopadhyaya


Abstract

This paper highlights a methodology for failure investigation of superheater tubes made of the material T-22 of a coal-based boiler. The process includes visual observation, the identification of sampling locations, the determination of the bulk chemical composition of the base alloy, microstructural investigation using optical microscopy, the exploration of finer structural details using a scanning electron microscope (SEM), the evaluation of hardness over samples obtained from different locations, the fractographic analysis of different failed locations, the X-ray diffraction (XRD) study of corrosion products adhered to inner surfaces, and the determination of the nature of the failure. Within a span of four months, three successive failures of superheater tubes were reported. The tubes were observed to have undergone significant wall thinning. Microscopic examinations using SEM on the failed region and a region some distance away on the as-received tubes were conducted in order to determine the failure mechanism. Layer-wise oxidation corrosion (exfoliation) in the inner surface was observed. Apart from major cracking, a number of nearly straight line crackings were observed in the longitudinal direction of both tubes. Close to cracking/bulging, void formation/de-cohesion of grain boundary indicated creep deformation under service exploitation. The failure mechanism was identified to be a result of excessive oxidation corrosion along the inside wall to reduce thickness, the spheroidization of alloy carbides and the coarsening of precipitate as well as creep void formation along grain boundary leading to inter-granular cracking with material flow near regions covered with thick scales. Moreover, there was a drastic reduction in bulk hardness of alloy and finally ‘thin lip fish mouth’ fractures

Keywords - coal based boiler, corrosion, creep, fractographic analysis, SEM, superheater tube

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 63(2017)5, 287-299, SI 43
DOI:10.5545/sv-jme.2016.4188

 

pdfCritical Failure Analysis of Superheater Tubes of Coal-Based Boiler (.pdf 2.1MB)

 


  

Influence of Quasi-Steady Wind Loads on the Fatigue Damage of Wind Turbine Gearboxes

Authors - Dong Xiang* – Li Jiang – Mengxing You – Yinhua Shen


Abstract

Quasi-steady wind varies both in time and space and has a great influence on a wind turbine gearbox’s fatigue life. Quasi-steady wind fields are described by mean wind speed and turbulence intensity, and the influence of these two parameters on wind turbine gearbox’s fatigue life is studied. Based on the two-step decoupled method (the first step is global analysis and the second is gearbox dynamic analysis), a model which can calculate the complex gearbox’s fatigue damage from gear’s dynamic force and SN parameters is established. The fatigue damage of every gear calculated from the established model is then analysed. The fatigue damage result under certain wind loads is first analysed, and the vulnerable gears among each stage are found. Then, how mean wind speed and turbulence intensity influences fatigue damage is studied, and the damage comparison factors are calculated, which finds the 3rd stage pinion to be the gear most sensitive to wind loads, and it requires more attention when designing gearboxes. Finally, the gears’ fatigue damage sensitivities to mean wind speed and turbulence intensity are analysed and the condition in which fatigue damage is more sensitive to wind loads is found, this is meaningful when designing pitch control systems

Keywords - quasi-steady wind load, fatigue life, wind turbine gearbox, LDD, FAST, ADAMS

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 63(2017)5, 300-313, SI 44
DOI:10.5545/sv-jme.2016.4224

 

pdfInfluence of Quasi-Steady Wind Loads on the Fatigue Damage of Wind Turbine Gearboxes (.pdf 4.9MB)

 


 

Drop-in Performance Analysis and Effect of IHX for an Automotive Air Conditioning System with R1234yf as a Replacement of R134a

Authors - Mehmet Direk* – Alper Kelesoglu – Ahmet Akin


Abstract

This paper presents the experimental comparative performance analysis of an automotive air conditioning (AAC) system using R1234yf and R134a. For this purpose, an AAC experiment setup used for R134a was built to obtain the drop-in performance of a new refrigerant R1234yf. Among the low global warming potential (GWP) refrigerants, R1234yf was particularly chosen due to its similar thermo-physical properties with R134a. However, the system with R1234yf could not perform as efficiently as R134a can. Therefore, an internal heat exchanger (IHX) was employed to enhance the performance of the R1234yf system. After that, the performances of R1234yf and R134a were compared under various compressor speeds and air stream temperatures. The results showed that the cooling capacity and COP of the system with R1234yf were 17.1 % and 12.4 %, respectively, lower compared to the one with R134a. However, when the IHX was introduced into the system with R1234yf, the cooling capacity and COP values were significantly enhanced by 7.9 % and 4.1 %, respectively.

Keywords - R134a, R1234yf, automotive air conditioning, internal heat exchanger

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 63(2017)5, 314-319, SI 45
DOI:10.5545/sv-jme.2016.4247

 

pdfDrop-in Performance Analysis and Effect of IHX for an Automotive Air Conditioning System with R1234yf as a Replacement of R134a (.pdf 561KB)

 


 

The Calculation of Meshing Efficiency of a New Type of Conical Involute Gear

Authors - Li Yu – Guangjian Wang* – Shuaidong Zou


Abstract

A new type of conical involute gear, proposed in this paper, can be applied in precise gear transmission for adjusting the backlash because of the special characteristics of its teeth. The meshing states of parallel external gear transmission based on the proposed gears are analysed and presented. The expressions of the length of contact and relative sliding velocity at any meshing position are derived. Then, the calculation formula of meshing efficiency is given by utilizing the piecewise equivalent method. Next, the variation of the length of contact line, unit load, meshing efficiency in a meshing period with different gear parameters and different operations are illustrated by employing numerical examples, and the influences of gear parameters and operations on meshing efficiency of the proposed gears are discussed based on the computing results. In the end, the applicability of the calculation is introduced

Keywords - conical involute gear, gear transmission, tangential modification, meshing efficiency


Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 63(2017)5, 320-330, SI 46
DOI:10.5545/sv-jme.2016.3843

 

pdfThe Calculation of Meshing Efficiency of a New Type of Conical Involute Gear (.pdf 1.4MB)




Machine-Vision-Based Human-Oriented Mobile Robots: A Review

Authors - Miha Finžgar* – Primož Podržaj

Abstract

In this paper we present a study of vision-based, human-recognition solutions in human-oriented, mobile-robot applications. Human recognition is composed of detection, tracking and identification. Here, we provide an analysis of each step. The applied vision systems can be conventional 2D, stereo or omnidirectional. The camera sensor can be designed to detect light in the visible or infrared parts of the electromagnetic spectrum. Regardless of the method or the type of sensor chosen, the best results in human recognition can be obtained by using a multimodal solution. In this case, the vision system is enhanced with other forms of sensory information. The most common sensors are laser range finders, microphones and sonars. As medicine is expected to be one of the main fields of application for mobile robots, we give it special emphasis. An overview of current applications and proposal of potential future applications are given. Without doubt, properly controlled mobile robots will play an ever-increasing role in the future of medicine.

Keywords - mobile robot, machine vision, human recognition, image-processing algorithms, medical applications, review, overview

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 63(2017)5, 331-348, SI 47
DOI:10.5545/sv-jme.2017.4324

 

pdfMachine-Vision-Based Human-Oriented Mobile Robots: A Review (.pdf 428KB)



 


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Journal of Mechanical Engineering

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SV-JME-7-8-2017


SV-JME-6-2017


SV-JME-5-2017


SV-JME-4-2017

 

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