Journal of Mechanical Engineering 53 (2007) 12

 

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Analytical Tracing of the Evolution of the Elasto-Plastic State during the Bending of Beams with a Rectangular Cross-Section

Corresponding author - Boris Štok

Authors - Miroslav Halilovič

Abstract

The deflection analysis of beams with rectangular cross-sections is considered under specific loading conditions and assuming elasto-plastic behaviour with no hardening. Within the framework of the small-strain and small-displacement approach, analytical solutions are derived that enable the elasto-plastic analyses of beams to be performed in a closed analytical form. As a consequence, clear tracing of the evolution of the elasto-plastic response with a propagation of the plastic zone through the solid body, i.e., its spreading along the beam's longitudinal axis as well as its penetration through the cross-section, is enabled as loads increase, from the appearance of a first plastic yielding in the structure until its collapse.

Keywords - beams, elastioplastic analysis, analytic functions, beam collapse

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)12, 806-818
UDK 531/534

Analytical Tracing of the Evolution of the Elasto-Plastic State during the Bending of Beams with a Rectangular Cross-Section (pdf)

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A Model for Predicting the Mechanical Properties of Wood-Plastic Composites - A Micro-Mechanical Approach

Corresponding author - Aleš Hančič

Authors - Franc Kosel - A. R. Campos - A. M. Cunha - Gašper Gantar

Abstract

The development of a new composite that is made up of natural fibres and low-price polymers, such as HDPE or PP, began in the 1990s. Because this material is relatively new to the market and due to the random characteristics of the fibres, no attempts have been made to analytically define the mechanical properties of this material. In this paper a micro-mechanical approach, called the generalised method of cells (GMCs), is introduced to describe the properties of injection-moulded wood-plastic composites made up of polypropylene (PP) or polystyrene (PS) and wood or cellulose short fibres. The main problem with an analytical approach is that the natural fibres are not uniform in shape and size, which makes them hard to fit into standard mathematical models. In this paper the average values of the fibre sizes were used. The materials were first scanned with optical and electron microscopes to determine the fibre properties and their scatter. These values were then used to determine the elastic and plastic response of the composite together with the maximum strength and elongation of the composite, where the Tsai-Hill failure-criterion was used. The results were then compared to the experimental data in order to evaluate the practical usefulness of this method. The time-dependent mechanical behaviour of the composite was not considered due to the complex and random properties of the fibre.

Keywords - wood-plastic composites, generalised method of cells (GMC), natural fibres, mechanical properties

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)12, 819-833
UDK 678.017

 A Model for Predicting the Mechanical Properties of Wood-Plastic Composites - A Micro-Mechanical Approach (pdf)

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Prediction of the Nonlinear Creep Deformation of Plastic Products

Corresponding author - Jan Spoormaker

Authors - Ihor Skrypnyk - Anton Heidweiller

Abstract

Based on an example of the non-linear creep deformations of an air inlet, this paper demonstrates modern capabilities in the FEA modeling of complex 3D visco-elastic deformations in relation to the design of plastic products. The importance of such capabilities for designing complex plastic components is discussed. Because commercial FEA packages do not yet render these capabilities "off the shelf", the non-linear visco-elasticity model is incorporated through a user subroutine. The specifics of the constitutive model and its numerical implemen-tation are outlined for the case of implementation in the commercial FEA package MSC.MARC.

Keywords - non-linear creep, stress relaxation, FEA modeling, plastic product design

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)12, 834-843
UDK 620.172.21:678.7

Prediction of the Nonlinear Creep Deformation of Plastic Products (pdf)

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The Development of Advanced Methods for Scheduling Production Processes

Corresponding author - Tadej Tasič

Authors - Borut Buchmeister - Bojan Ačko

Abstract

The planning of dates and capacities belongs to the area of production management. Scheduling represents the allocation of scarce sources to tasks in a definite period of time. So it is about a process of deciding, with the goal of optimization, about one or more criteria. In general it includes rough (long-term), medium-term and detailed (short-term) planning. The last of these has the greatest importance because of a direct connection with operational effectiveness. Some developed scheduling procedures are presented in the paper, i.e., the priority (dispatching) rules, the filtered-beam search, and the constraint-guided heuristic search.  All this is substantiated with described examples.

Keywords - aproduction process planning, deterministic sequencing, scheduling, priority rules

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)12, 844-857
UDK 658.51

The Development of Advanced Methods for Scheduling Production Processes (pdf)

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Computer and Machine Vision in Robot-based Assembly

Corresponding author - Niko Herakovič

Abstract

Against the background of an increasingly demanding world market, robotic assembly systems offer good prospects for the rationalisation and flexibilisation of assembly processes. In modern assembly there is a strong need for advanced robot grasping and for the capability to perform assembly operations in non-structured environments with randomly positioned objects. Vision-based robotic assembly systems, which has been the topic of continuous research interest for almost four decades, have now matured to the point where they can be effectively applied to advanced robot-based assembly tasks. This paper gives an overview of the research work related to the field of automated vision systems for assembly.

Keywords - robotiuc assembly, machine vision, robot vision, object recognition

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)12, 858-873
UDK 681.5

Production Scheduling Model in Aluminium Foundry (pdf)

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An Alternative Strategy for Microtooling for Replication Processes

Corresponding author - Boštjan Juriševič

Authors - Jožko Valentinčič - Oki Blatnik - Davorin Kramar - Henri Orbanić - C. Masclet - Matthieu Museau - H. Paris - Mihael Junkar

Abstract

Microproduction is one of the fastest-growing fields in industry, with new demands from the market increasing every day. This work presents an alternative microtooling strategy, which was applied to a microfluidic device case study. This original strategy for a replication process, like hot embossing or injection molding, is based on the combination of the micro-electro-discharge machining (MEDM) process and an electrode machined with water-jet technology (WJ). The final tool was tested with a hot-embossing process by making some test parts in polymers. The process is considered in its global perspective, starting with the fabrication of the tool electrode that will be used to produce the mold involved in the final cast of the microproduct. The addressed issue consists of identifying the capability of each process and then choosing the machining process parameters that will allow the best process combination to obtain the final microproduct. During this investigation several ideas emerge. They should help to identify the most advantageous characteristics of the involved processes in order to develop a reliable and cost-effective tooling strategy, which are discussed in this contribution. Additionally, an insight is given into similar research activities at the University of Ljubljana.

Keywords -microtooling, water jet cutting, micro die sinking EDM, process chains

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)12, 874-884
UDK 621.9.048

An Alternative Strategy for Microtooling for Replication Processes (pdf)

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The Design and Manufacture of Burnishing Equipment and the Burnishing Process with Al 7075 T6 Material

Corresponding author - Hüdayim Başak

Abstract

The burnishing process is a final process that can also be described as a chipless process. In this paper, burnishing equipment that is designed and manufactured for the burnishing of prismatic parts is introduced.  This burnishing equipment was then used to burnish prismatically manufactured Al 7075 T6 samples using different burnishing parameters. The burnished surfaces were characterized in terms of roughness and hardness.

Keywords - burnishing, prismatic parts, surface roughness, surface hardness

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)12, 885-897
UDK 621.923.7

The Design and Manufacture of Burnishing Equipment and the Burnishing Process with Al 7075 T6 Material (pdf)

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Improving the Dynamic Characteristics of a Rotor System using an Evolutionary Algorithm

Corresponding author - Hamit Saruhan

Abstract

In this paper the optimum design for improving the dynamic characteristics of a flexible, overhung rotor system is studied. The design of a flexible rotor system is a complicated process due to the large number of geometrical parameters of hydrodynamic bearings, which play an important role in the prediction of the dynamic behavior of the rotor system. There are a number of design requirements added to the rotor-system configuration that improve the dynamic characteristics within the rotor's speed range. To improve the dynamic characteristics of the rotor system, a genetic algorithm was employed and the modeling of the components of the rotor system was made with the finite-element method. Also, the method of feasible directions was used in order to validate the efficiency and applicability of the proposed method, and it proved that the proposed method in the rotor-system design is very efficient and useful for improving the dynamic characteristics of the rotor system.

Keywords - rotor systems, optimization, genetic algorithm, finite element methods

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 3(2007)12, 898-912
UDK 62-25

Improving the Dynamic Characteristics of a Rotor System using an Evolutionary Algorithm (pdf)

   

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