Journal of Mechanical Engineering 54 (2008)12

Cover plate

Some results of the numerical simulation of deep drawing of oval rings, which provide a closed file position of self-standing files, are shown in the title page. Rings are stamped from a thin steel strip in the progressive drawing tool. The simulation is performed in order to analyse the strain-stress state evolution of the manufacture process. For three characteristic process stages the figure displays the corresponding shape formation and equivalent plastic strain distribution in the drawn part. A local large strain area which indicates possible fracture is clearly seen.

 

 

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Usage of the Yield Curve in Numerical Simulations

Corresponding author - Pino Koc

Authors - Boris Štok

Abstract

A comparison of two approaches used in the yield curve characterization of the same material is given in the paper. The first approach is commonly used Ludwig’s law with the extension over large strains based on the pre-necking response of a tensile test specimen, whereas the second approach is inverse identification which is based on the post-necking behaviour of the same tensile test specimen.   Features of both approaches are examined in the tensile test and deep drawing simulations. In the tensile test simulation the inverse identification method proved to be superior over Ludwig’s law. The deep drawing simulation demonstrates how inappropriate yield curve usage leads to wrong predictions.  

Keywords - tensile testing, yield curve, inverse identification metod, deep drawing

Paper's information

Strojniški vestnik - Journal of Mechanical Engineering 54(2008)12, 821-829
UDC 621.7.01

 Usage of the Yield Curve in Numerical Simulations (pdf)

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Multiple Parametric Models of Heat Transfer in Lightweight Building Elements with Ventilated Cavities

Corresponding author - Uroš Leskovšek

Authors - Ciril Arkar - Boštjan Černe - Sašo Medved

Abstract

Lightweight building elements (LBEs) with one or two ventilated cavities are multifunctional building-envelope elements that lower the heat transfer to the ambient and enable solar heating. In the case of two ventilated cavities they operate as recuperative heat exchangers in the building’s ventilation system. This paper presents the development of a calculation procedure for the characterisation of such innovative building-envelope elements. Using a commercial numerical tool, a wide range of influential parameters was studied. Based on the numerical results, multiple parametrical models (MPMs) for determining an effective U-value and the heat gains on the supply of ventilation air were developed for the case of an LBE with one ventilated cavity, meanwhile MPMs for calculating the effective U-value and the heat-recovery rate were developed for an LBE with two ventilated cavities. Such MPMs can be integrated into well-known computer tools for buildings’ energy-efficiency simulations, for example, TRNSYS. The accuracy of the models was verified with field experiments. 

Keywords - lightweight building elements, heat transfer, solar heating, multiple regression

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 54(2008)12, 830-840
UDC 536.24:699.86

 Multiple Parametric Models of Heat Transfer in Lightweight Building Elements with Ventilated Cavities (pdf)

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Advances in Water Power-Control Hydraulics Experimental Research

Corresponding author - Franc Majdič
Authors - Jožef Pezdirnik

 

Abstract

Environmental protection regulations are becoming increasingly strict. By using water instead of a hydraulic mineral oil in power-control hydraulic systems we can make a very positive step in complying with these regulations. However, introducing the water instead of oil in power control hydraulics is rather novel and difficult task. Moreover, due to several specifics of water that are also discussed in this paper, several requirements need to be fulfilled in every test rig and test specimen. In this paper we present a newly developed hydraulic test rig that is designed for these specific requirements of water as the hydraulic fluid in power control hydraulics. For direct comparison with oil system, the test rig is designed as a twin system with two equivalent circuits: one for water and one for oil tests. Some interesting results on dynamic response of both systems are presented. They show significant differences between the water and oil hydraulics. With these experiments, the test rig proved the suitability for the research in this new area and showed a good control of the parameters measured.

Keywords - water, mineral hydraulic oil, power-control hydraulics, proportional valve

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 54(2008)12, 841-849
UDC 621.22

 Advances in Water Power-Control Hydraulics Experimental Research (pdf)

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Comparative Analyses for Different Modeling Methods in High Speed Turning Operations for Hardened Steel

Corresponding author - Usama Umer

Authors - Shahid Ikramullah Butt, Syed Jawid Askari, Syed Noman Danish, Lijing Xie

Abstract

The modeling of metal cutting process has been a challenging research topic due to the difficulty in accurate modeling of the contact and work material deformation with large plastic strain and friction, high temperature and strain rate, and their coupling effect. Among different modeling methods, finite element method (FEM) has proven to be a robust tool in predicting process parameters and optimizing cutting tool geometry. However successful implementation of a modeling method depends mainly on numerical formulation technique adopted for chip formation. The two formulation techniques namely the Lagrangian and the Eulerian have been used in the past by many researchers. Due to the various limitations of the two approaches, a new arbitrary Lagrangian Eulerian (ALE) method has been adopted for the orthogonal high speed turning operations for AISI H13 hardened steel. This approach does not need any chip separation criterion.  For comparative analysis with other techniques, two Lagrangian models with element deletion and node splitting methods were also simulated and compared with experimental data. It has been found that ALE model results are in good agreement with the experimental ones as compared to the Lagrangian models.

Keywords - high speed machining, process modelling, finite element methods, AISI H13 steel

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 54(2008)12, 850-854
UDC 621.941

 Comparative Analyses for Different Modeling Methods in High Speed Turning Operations for Hardened Steel (pdf)

 

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Economic Design of Control Charts

Corresponding author - Rok Zupančič

Authors - Alojz Sluga

Abstract

Control charts are widely used in industry for monitoring and controlling manufacturing processes. They should be designed economically in order to achieve minimum quality control costs. In this paper, an economic design of Shewhart control charts for process mean is proposed that takes into account various parameters. Standards for sample size within statistical process control do not exist due to high diversity of modern production. In the proposed economic model process-mean shift is assumed as random variable. This is a better approximation of the real world, than the models that assume process-mean shift as a constant value. Probability density function is used for description of process-mean shift. The optimum sample size is computed on base of loss function, regarding to constraints of particular production process. The comparison of optimum sample sizes assuming process-mean shift as a constant value versus random variable is presented.

Keywords - control charts, quality control, economic design, statistical process control

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 54(2008)12, 855-865 
UDC 658.562

 Economic Design of Control Charts (pdf)

 

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Effects of the Variation of Torque Motor Parameters on Servovalve Performance

Corresponding author - Dušan Gordić

Authors - Milun Babić - Nebojša Jovičić - Dobrica Milovanović

Abstract

An electrohydraulic servovalve is an essential item of fluid power servomechanism where fast response, high power output and working fidelity are necessary. Based on detailed and experimentally verified mathematical model of two-stage spool position mechanical feedback electrohydraulic servovalves sensitivity analysis has been performed. The effects of variation of few torque motor electromagnetic parameters (air-gap length (thickness) at null, residual magnetic flux density (magnetic inductivity) of permanent magnet and number of turns of each coil) on dynamic performance of B.31.210.12.1000.U2V PPT servovalve have been studied. Obtained results are in accordance with servovalve engineering design practice.

Keywords - electrohidraulics, servovalves, torque motors, sensitivity analysis

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 54(2008)12, 866-873
UDC 681.527.34

 Effects of the Variation of Torque Motor Parameters on Servovalve Performance (pdf)

 

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Using of Acoustic Models in Mechanical Diagnostics

Corresponding author - Mateja Ploj Virtič

Authors - Boris Aberšek - Uroš Župerl

Abstract

This paper presents an acoustical model for control and diagnostics of single stage gear wheels. The model is based on various methods and procedures that as a result provide information about the generator’s condition, the gear in particular. The acoustical model is part of a complex system that units’ different models to meet diagnostics of single stage gear wheels as precise as possible. Using the adaptive FIR filter, acoustical model enables the calculation of impulse response for different notch lengths between 0 and ac. The acoustical model consists of digital FIR filter, modified by LMS algorithm, used to calculate impulse responses in non-linear systems, the model for the calculation of any impulse response and the frequency analysis with the use of FFT for the simulation of frequency spectrums. Frequency spectrum of the simulated sound signal enables an analysis of the error that can be used for calculating the remaining service life and/or determining the control cycle of maintenance..

Keywords - mechanical fault diagnostics, acoustic models, impulse response, adaptive algorithm

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 54(2008)12, 874-882
UDC 621.833

 Using of Acoustic Models in Mechanical Diagnostics (pdf)

 

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Characterization of the Vibrations and Structural Noise of a Suction Unit's Cover

Corresponding author - Jurij Žumer

Authors - Miha Boltežar, Andrej Biček

Abstract

In this paper we report on a study of the vibrations of a suction unit's cover and the relation with the generated structural noise. The existing cover of the suction unit was designed, taking into account only the geometrical requirements. Two different methods were used for characterization of the vibration and structural noise of the cover: numerical modal analysis made with the FEM (Finite Element Method) and experimental modal analysis made during the operation of the suction unit. The results of the experimental modal analysis of the cover’s vibrations visually confirmed the results of a numerical modal analysis up to the 1st BPF (Blade Passing Frequency) and characterized the main exciting sources with the prevailing aerodynamic excitation. The vibration modal analysis tries to find a relation with the cover’s structural noise using an experimental local noise modal analysis. A different method of measurement of local structural noise is introduced.

Keywords - suction unit, suction unit’s cover, vibrations, structural noise, numerical modal analysis

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 54(2008)12, 883-891
UDC 534:519.61/.64:621.63

 Characterization of the Vibrations and Structural Noise of a Suction Unit's Cover (pdf)

 

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