Miran Ulbin

Contact problems of gears using Overhauser splines

Abstract This paper presents a new finite element technique which provides more accurate contact stress predictions than other already established methods. A novel contact detection algorithm in the framework of the contact problem analysis with the finite element method using Overhauser splines is presented. Using this approach the contact area is approximated with Overhauser spline interpolation functions over boundary nodes, which results in ‘smooth’ and accurate geometrical descriptions that is crucial to contact stress analysis. The geometry is also completely decoupled from the finite element polynomial shape functions. A single parametric curve is used to model the contacting surface providing the C1 boundary continuity and exact boundary condition definition. In addition, the geometrical description using splines provides the data required for actual contact area determination and exact contact size calculation. Implementation of the proposed approach in the developed finite element code is presented. Benefits and drawbacks of the proposed approach are discussed. The method is successfully used for simulation of contact problems in gears.

Knowledge-Based System for Supporting the Design of a Plate-Press

This paper presents a knowledge-based system capable of giving the designer quality support when making decisions from the aspect of modeling the reinforcement of a plate-press within a position of maximum compressive load, and by choosing suitable material for the plate. Based on the selected combination of reinforcement and material, this system acquaints the user with the size and position of the largest comparative stress, and the greatest nodal displacement in the load-direction. This system operates based on the implemented knowledge of experts in the execution of design, material selection, and numerical analysis based on the finite-element method (FEM), which was written with the help of parameters within the knowledge-base of the CATIA V5 CAD -system. Using this system gives the user an opportunity to reach conclusions that are crucial for designing a plate-press or pressure-loaded die-elements, in general. The results reveal that the system can dramatically shorten design time and improve design quality in comparison to manual design process.

Concurrent computer-aided design system for supporting technological aspect of cutting die design

Designing of stamping dies is a complex procedure where comprehensive knowledge is needed, in order to understand the interactions of various interdependent parameters that are extensively engaged within all development phases of a sheet-metal stamping product. Many important die design decisions are made based on technological knowledge, which is especially closely related to understanding the activities of product design and process planning. Due to the lack of such valuable knowledge within conventional three-dimensional computer-aided design systems, a concurrent system for supporting technological aspect of die design process is proposed within this article. The system that was developed on top of computer-aided three-dimensional interactive application CATIA V5 product lifecycle management software enables die design automation on the basis of constraint solving. Product design and process planning activities are accomplished concurrently by system’s modules. Finally, it extracts relevant technological information and decisions directly to the die design phase. The system also represents unique basis for the development of some modules capable of automatic reasoning, regarding die design and performing actions on this basis. The experimental results showed that the use of this system significantly shortens sheet-metal product development cycle, improves its quality, and enables efficient training of inexperienced designers.

Stress Accuracy Of Parabolic Finite ElementsIn Contact Problems Analysis

The paper presents the stress distribution errors discovered while analysing contact problems with parabolic finite elements. Usage of parabolic instead of linear finite elements in finite element analysis usually results in more accurate stresses. On the other hand usage of parabolic finite elements would result in jagged stress distribution. The jagged stress distribution occurs using either Penalty function method or Lagrange multiplier method. Stress distribution errors were discovered also in analysis where Gauss integration point positions were used for contact analysis. Series of contact problems analyses with special attention to stress accuracy will be presented in the paper. Presented contact problems were analysed with different commercial and non-commercial finite element systems. Obtained results of contact problems analysis with parabolic finite elements will be compared to contact problems analysis with linear finite elements. Results of contact problems analysis using finite elements will then be compared to results obtained with theoretical solution or experimental data. The possible reasons for stress errors will be discussed and some workaround for this problem will be proposed. Transactions on Engineering Sciences vol 24,

Inženirske računalniške simulacije v konstrukterstvu : univerzitetni učbenik

Ucbenik s podrocja inženirskih racunalniskih simulacij je namenjen kot studijski pripomocek pri izvedbi predavanj predmetov Inženirske racunalniske simulacije in Racunalniske simulacije v konstrukterstvu ter posredno pri predmetih Inženirska orodja 2 in Numericna mehanika trdnin. Vsebuje razlago celotne snovi, ki jo morajo studentje pri teh predmetih osvojiti, in je skladen z ucnimi nacrtom omenjenih predmetov.

Computational Analysis of the Explosive Compaction Fabrication Process of Cylindrical Uni-directional Porous Copper

The explosive compaction fabrication process of cylindrical uni-directional porous copper, consisting of an outer pipe completely filled with smaller inner pipes, was investigated by experimental and computational simulations to analyze and optimize the fabrication process conditions. The computational simulations were carried out using a two-dimensional model, mimicking the transverse cross-section of fabricated specimens. The computational simulation results revealed that the velocity of the outer pipe, which cannot be experimentally measured, was insufficient for explosive welding and that the walls of the inner pipes had the potential to fail depending on their initial positioning and thickness.

STUDIES IN NUMERICAL STABILITY OF EXPLICIT CONTACT-IMPACT ALGORITHM TO THE FINITE ELEMENT SOLUTION OF WAVE PROPAGATION PROBLEMS

Abstract. In dynamic transient analysis, recent comprehensive studies have shown that using mass penalty together with standard stiffness penalty, the so-called bipenalty technique, preserves the critical time step in conditionally stable time integration schemes. In this paper, the bipenalty approach is applied in the explicit contact-impact algorithm based on the pre-discretization penalty formulation. The attention is focused on the stability of this algorithm. Specifically, the upper estimation of the stable Courant number on the stiffness and mass penalty is derived based on the simple dynamic system with two degrees-of-freedom. The results are verified by means of the dynamic Signorini problem, which is represented by the motion of a bar that comes into contact with a rigid obstacle.

Fatigue Crack Initiation Along Inclusion Interfaces of Contacting Mechanical Elements

This paper utilises the theory of fatigue crack initiation along inclusion interfaces of contacting mechanical elements. The assumption is warranted by the fact that hard inclusions in form of carbides are often present in high strength steels and have a significant impact on local strength reduction. If the inclusion and the interface are strong enough to withstand breaking during the initial loading, the plastic deformation is accumulated in the grain matrix after some cyclic loading. The motion of dislocations in the matrix is blocked by inclusion. Fig. 1 illustrates the theoretical model with inclusion of radius R residing within the slip band zone (Tanaka and Mura [1]). The slip band zone is elliptic with semi-major axis l 1 and semi-minor axis l 2. The inclusion is assumed to be much smaller than the slip band zone.