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Editorial Office

University of Ljubljana
Faculty of Mechanical Engineering
Journal of Mechanical Engineering

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SI-1000 Ljubljana
Slovenia

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E: info@sv-jme.eu



The journal is subsidized by Slovenian Research Agency.

 
ISSN: 0039-2480

Journal of Mechanical Engineering 63 (2017) 6

 

 

 


 

In-situ Observations of a Multi-Asperity Real Contact Area on a Submicron Scale

Authors - Blaž Brodnik Žugelj – Mitjan Kalin*


Abstract

We present apparatus that allows in-situ optical measurements of the evolving real contact area between a rigid glass and a deformable Al6026 surface with 700 nm of lateral and 20 nm of vertical resolution. In previous experimental studies of multi-asperity real contact area this was investigated either with much less accuracy or did not include the full (loaded) nominal contact area, which can hinder the relevant sub-micron deformation phenomena. During experiments involving the real contact area, the contact load and asperity deformations are simultaneously measured. To show the relevance of the developed experimental procedure measurements are compared to the results calculated with the Greenwood-Williamson (GW) and a modified Abbott-Firestone (AF(H)) models, which represent the two extreme deformation-regime models. The AF(H) model shows relatively good agreement between the real contact area and the asperity deformations (< 60 %), while the GW model deviates by up to 10 times, depending on the deformation value. In contrast, the GW model shows better agreement for the relationship between the contact load and the asperity deformation (< 20 %), while the AF(H) deviates by more, approximately 30 %. The results also indicate that the real contact area is a non-linear function of the contact load, while theoretical models predict their linearity. Finally, it is demonstrated that the real contact area reaches only up to 9 % of the nominal value in the loading range up to the material yield strength, as calculated for the nominal contact parameters

Keywords - test rig, in-situ experiment, optical technique, asperities, real contact area

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 63(2017)6, 351-362, SI 51
DOI:10.5545/sv-jme.2017.4366

 

pdfIn-situ Observations of a Multi-Asperity Real Contact Area on a Submicron Scale (.pdf 1.6MB)

 


  

Analysis of the Influence of Laser Power on the Microstructure and Properties of a Titanium Alloy-Reinforced Boron Carbide Matrix Composite (Ti6Al4V-B4C)

Authors - Musibau O. Ogunlana* – Esther T. Akinlabi – Mutiu F. Erinosho


Abstract

Laser Metal Deposition (LMD) process is a means of producing metal composites with the aid of a laser beam, ejected onto the substrate with the participating powder and fused together after solidification. In this research work, Ti6Al4V alloy is fused with 20 wt % of B4C in order to form metal matrix composites (MMCs). Using the Ytterbium Fibre Laser System powdered at 3000 W, the laser powers were varied between 800 W and 2400 W while all other supporting process parameters were kept constant. The deposited Ti6Al4V-B4C composites were characterized through the surfacing microstructure, microhardness and dry sliding wear. The microstructural properties of the deposited samples were profound, with a Widmanstätten structure of α-Ti, β-Ti and (α+β) Ti phases. The microhardness tests revealed that the composites deposited with a laser power of 2000 W exhibited the highest hardness value and standard deviation of HV 445 ± 61. Furthermore, characterisation revealed that the sample produced with the laser power of 800 W had the lowest wear loss and wear rate of 35.2 × 103 mm3 and 6.42 × 10-4 mm3/Nm. However, the motivation for this work is to improve the material properties of the Ti6Al4V alloy for surface engineering applications.

Keywords - Dry sliding wear, LMD, microhardness, microstructure, Ti6Al4V-B4C composites, X-Ray Diffraction

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 63(2017)6, 363-373, SI 52
DOI:10.5545/sv-jme.2016.4159

 

pdfAnalysis of the Influence of Laser Power on the Microstructure and Properties of a Titanium Alloy-Reinforced Boron Carbide Matrix Composite (Ti6Al4V-B4C) (.pdf 1.6MB)

 


 

Control-Oriented Modelling with Experimental Verification and Design of the Appropriate Gains of a PI Speed Ratio Controller of Chain CVTs

Authors - Ahmet Yildiz* – Osman Kopmaz


Abstract

The continuously variable transmission (CVT) system represents one of the best solutions to minimize the fuel consumption for vehicles that are driven by an internal combustion engine or an electrical motor. Hence, the theoretical analysis of a chain CVT is crucial in the optimization of the design and control strategy. This paper is concerned with the transient dynamics of a chain CVT with a speed ratio controller adopted from the Carbone-Mangialardi-Mantriota model and its experimental verification. To this end, a theoretical model is developed with a PI speed ratio controller, considering the momentary solution of a first order differential equation governing the shifting speed, which represents the whole dynamics of the CVT. To verify the developed model, the experiments are carried out on a chain CVT test rig. It is observed that the numerical and experimental results are in good agreement, which implies that the developed model embedded in a speed ratio controller is appropriate to predict the shifting dynamics of the chain CVT. Afterwards, the developed model is used to design the appropriate PI gains by numerical experiments in order to obtain the same slope of the time response of speed ratio for different input angular velocities. Therefore, the same shifting speed can be secured for the different working conditions in this manner. This paper contains very important results for manufacturers about the control parameter and gain effect on the shifting dynamics of chain CVT, and the developed model can be used for different control algorithms in automotive applications.

Keywords - chain CVT, speed ratio control, PID, shifting dynamics

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 63(2017)6, 374-382, SI 53
DOI:10.5545/sv-jme.2016.4184

 

pdfControl-Oriented Modelling with Experimental Verification and Design of the Appropriate Gains of a PI Speed Ratio Controller of Chain CVTs (.pdf 1.3MB)

 


 

Mixed Convection Heat Transfer in a Square Lid-Driven Cavity Filled with Al2O3-Water Nanofluid

Authors - Yazan Taamneh* – Kahled Bataineh


Abstract

This work is focused on the steady laminar mixed convection flow in a lid-driven square cavity filled with Al2O3 water-nanofluid using computational fluid dynamics. The top lid of the cavity was kept at a higher temperature in comparison with the bottom wall and moving at a constant speed while the left and right walls were kept insulated. Simulations were performed using Fluent ver. 6.3 where the water based nanofluid was considered as a single phase. A parametric study was conducted, and the effects of the Richardson number (0.1 ≤Ri ≤10), the volume fraction of the nanoparticle (0 ≤φ ≤0.04) on the fluid flow, and heat transfer inside the cavity were investigated. It was found that when (1 ≤Ri ≤10) the average Nusselt number increases accordingly for the whole range of solid volume fraction of the nanofluid. The simulation results showed that the presence of nanoparticles in the base fluid increases the heat transfer rate. The variations of isotherm and streamline patterns inside the cavity with different volume fractions of nanoparticle and Richardson number were discussed and demonstrated.

Keywords - mixed convection, nanofluid, square cavity, CFD, lid-driven


Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 63(2017)6, 383-393, SI 54
DOI:10.5545/sv-jme.2017.4449

 

pdfMixed Convection Heat Transfer in a Square Lid-Driven Cavity Filled with Al2O3-Water Nanofluid (.pdf 751KB)




A Practical Method to Detect a Transverse Cracked Rotor Using Transient Response

Authors - Xiaofeng Wang – Jun Liu* – Weimin Ge

Abstract

To detect a transverse crack caused by fatigue or creep, most of the research has thus far paid attention only to resonances of steady-state oscillations created by the crack and proposed diagnosis systems utilizing these vibration phenomena. However, from a practical view point, these diagnosis systems have the following flaws: (1) the probability that a resonance occurs due to a crack in the rated rotational speed range is a lower position; (2) It is very dangerous to observe vibration characteristics in resonance ranges. In order to solve these problems, this paper uses a practical detection method utilizing the characteristic changes in a transient oscillation during the start-up, the shutdown, or the variable running speeds of rotating machinery. This method has great advantages, because it can check the occurrence signals of a crack in a wide speed range using a single sweep and avoid the operation in dangerous resonance ranges. Non-stationary characteristics during passages through the main resonance and various kinds of resonances are studied numerically and experimentally.

Keywords - transient response, nonlinear rotor, cracked rotor, crack identification, experiments

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 63(2017)6, 394-404, SI 55
DOI:10.5545/sv-jme.2017.4332

 

pdfA Practical Method to Detect a Transverse Cracked Rotor Using Transient Response (.pdf 2.9MB)




The Influence of Airflow Characteristics and Accumulation Grid Velocity on the Formation of a Stone Wool Primary Layer

Authors - Marko Peternelj* – Benjamin Bizjan – Branko Širok


Abstract

In this paper, the industrial process of stone wool primary layer formation has been investigated. The blow-away airflow, collecting chamber suction pressure, and peripheral velocity of collecting member effects on primary layer area density have been investigated. In total, 27 operating points have been measured by means of primary layer visualization. Computer-aided visualization has been carried out by two digital cameras. Each operating point was monitored at two locations: the first one at the beginning of fibre accumulation, forming the primary layer, and the secondary one at the end of the formation zone. The mass attenuation coefficient was calculated for each operating point and then used to calculate the primary layer area density. It was determined that primary layer bulk density distribution and primary layer texture are significantly influenced by accumulation grid peripheral velocity and blow-away airflow; however, suction pressure has a less pronounced effect on those characteristics. At the highest accumulation grid velocity and blow-away flow rate, the area density was 37 % lower than at the lowest grid velocity and blow-away flow, with a corresponding increase in a standard deviation of 750 %. Multiple regression models suggest very good agreement with the measured data (R2 = 0.94 to 0.98).

Keywords - mineral wool, fibre, primary layer formation, spinner, collecting chamber, pneumatic transport

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 63(2017)6, 405-414, SI 56
DOI:10.5545/sv-jme.2017.4503

 

pdfThe Influence of Airflow Characteristics and Accumulation Grid Velocity on the Formation of a Stone Wool Primary Layer (.pdf 1.0MB)

 



Leaflet SV-JME


 

 

Journal of Mechanical Engineering

in digital form


SV-JME-7-8-2017


SV-JME-6-2017


SV-JME-5-2017


SV-JME-4-2017

 

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