I. Felde

6603056879

Publications - 15

On stability of maximal entropy OWA operator weights

István Harmati I. Felde Robert Fullér

Publication Name: Fuzzy Sets and Systems

Publication Date: 2022-11-05

Volume: 448

Issue: Unknown

Page Range: 145-156

Description:

The maximal entropy OWA operator (MEOWA) weights can be obtained by solving a nonlinear programming problem with a linear constraint for the level of orness. Since the exact MEOWA weights are not known for the general case we can only find approximate solutions. We will prove that the nonlinear programming problem for obtaining MEOWA weights is well-posed: it has a unique solution and each MEOWA weight changes continuously with the initial level of orness. Using the implicit function theorem we will show that MEOWA weights are Lipschitz-continuous functions of the orness level. The stability property of the MEOWA weights under small changes of the orness level guarantees that small rounding errors of digital computation and small errors of measurement of the orness level can cause only a small deviation in MEOWA weights, i.e. every successive approximation method can be applied to the computation of the approximation of the exact MEOWA weights.

Open Access: Yes

DOI: 10.1016/j.fss.2022.01.003

Evaluation Of hardening performance of cooling media by using inverse heat conduction methods and property prediction

I. Felde T. Reti

Publication Name: Strojniski Vestnik Journal of Mechanical Engineering

Publication Date: 2010-04-28

Volume: 56

Issue: 2

Page Range: 77-83

Description:

A sequential numerical method for characterization of hardening performance of quenchants applied for steel quenching is outlined here. This novel method is based on the specific processing of measured time-temperature samples performed as a result of cooling curve tests. As a function of surface temperature the heat transfer coefficient, characterises the heat transfer during cooling and is calculated using an iterative inverse algorithm. The heat transfer coefficient is used for the calculation of the microstructural constituents and the hardness profile of cylindrical samples of arbitrary diameters. The hardening performance of the media is evaluated by the estimated hardness of the specimen obtained by heat treatment. © 2010 Journal of Mechanical Engineering. All rights reserved.

Open Access: Yes

DOI: DOI not available

Extension of isothermal time-temperature parameters to non-isothermal conditions: Application to the simulation of rapid tempering

Janez Grum G. Sarmiento A. M. Deus I. Felde T. Reti R. Colas

Publication Name: Strojniski Vestnik Journal of Mechanical Engineering

Publication Date: 2010-04-28

Volume: 56

Issue: 2

Page Range: 84-92

Description:

A phenomenological method for constructing non-isothermal, generalized time-temperature parameters (GTT parameters) is presented. An analysis of the relationship between the various traditional isothermal time-temperature parameters has verified that the generalized Dorn-parameter is regarded to be the sole non-isothermal complex parameter to which a rigorous, physically well-founded interpretation is attributed. Possible applications of GTT parameters are illustrated by examples concerning the prediction of hardness change in quenched steels during rapid tempering treatments. © 2010 Journal of Mechanical Engineering. All rights reserved.

Open Access: Yes

DOI: DOI not available

Evaluation of cooling characteristics of quenchants by using inverse heat conduction methods and property prediction

I. Felde T. Reti

Publication Name: Materials Science Forum

Publication Date: 2010-01-01

Volume: 659

Issue: Unknown

Page Range: 153-158

Description:

A sequential numerical method for characterization of hardening performance of quenchants applied for steel quenching is outlined here. This novel method is based on the specific processing of measured time-temperature samples performed as a result of cooling curve tests. The heat transfer coefficient, as a function of surface temperature, characterises the heat transfer during cooling and is calculated using an iterative inverse algorithm. The heat transfer coefficient is used for calculation of the microstructural constituents and the hardness profile of cylindrical samples of arbitrary diameters. The hardening performance of the media is evaluated by the estimated hardness of the specimen obtained by heat treatment. © (2010) Trans Tech Publications.

Open Access: Yes

DOI: 10.4028/www.scientific.net/MSF.659.153

Diffusion in electrodes used for resistance spot welding of galvannealed steel

Martha P. Guerrero-Mata Patricia Zambrano I. Felde Mihaly Réger Maribel De La Garza T. Reti R. Colas

Publication Name: Defect and Diffusion Forum

Publication Date: 2010-01-01

Volume: 297-301

Issue: Unknown

Page Range: 300-307

Description:

A study was carried out on Zr-Cr bearing copper electrodes used for resistance spot welding of galvannealed steel strips. One electrode exhibited a series of well-defined layers in which Zn diffused to form β- and γ-brasses; an external layer containing iron was detected in this electrode. Another electrode that exhibited a high degree of damage did not exhibited continuous Zn-diffusion layers in all places, moreover, the Fe-containing layer was either removed, or had it grown to a high extent in some places; the occurrence of Cu-rich particles embedded within the Fe containing layer was observed. Multiple cracks were observed within the γ brass layer in both electrodes. The difference in the observed behaviour of the electrodes can be attributed to a difference in the characteristics of the galvannealed coating of the strips, as the first electrode was used to weld strips in which the layer corresponding to the γ phase was well developed, whereas the second electrode was used to weld strips with only an incipient layer. It can be concluded that growth of the γ phase changes the thermophysical properties of the zinc coating, affecting the temperature profile during spot welding. © (2010) Trans Tech Publications.

Open Access: Yes

DOI: 10.4028/www.scientific.net/DDF.297-301.300

Characterisation of hardening performance of quenchants by integrated numerical method

I. Felde T. Reti

Publication Name: International Heat Treatment and Surface Engineering

Publication Date: 2008-06-01

Volume: 2

Issue: 2

Page Range: 55-59

Description:

An integrated numerical technique for evaluation of hardening performance of cooling media applied for steel quenching is outlined. The newly developed method is based on the specific processing of measured time-temperature samples performed as a result of cooling curve tests. The heat transfer coefficient as a function of surface temperature characterises the heat transfer during cooling and is calculated using an iterative inverse algorithm. The heat transfer coefficient is used for calculation of the microstructural constituents and the hardness profile of cylindrical samples of arbitrary diameter. The hardening performance of media is evaluated by the estimated hardness of specimens obtained by heat treatment. © 2008 IHTSE Partnership.

Open Access: Yes

DOI: 10.1179/174951508X318404

Selection of tool materials for cold forming operations using a computerized decision support system

J. Gram I. Czinege I. Felde T. Reti D. Y. Ju

Publication Name: Proceedings of the 17th Ifhtse Congress

Publication Date: 2008-01-01

Volume: 2

Issue: Unknown

Page Range: 773-775

Description:

A computerized decision support system (DSS) is outlined which is designated primarily to selcct the proper tool steel grades for various cold forming operations. This computerized system contains four data base: data base of cold forming operations and tools, of work materials, of cold forming tool materials and of wear resistant PVD coatings. The decision strategy makes it possible to select appropriate tool materials taking into consideration their most important material properties (wear resistance, toughness, compressive yield strength, tempering resistance, dimensional stability, machinability, and material price). The practical advantages of the developed decision support system are demonstrated on example.

Open Access: Yes

DOI: DOI not available

Analysis of a numerical method developed for estimation of the heat transfer coefficient obtained during quenching

G. Sarmiento A. M. Deus B. Smoljan I. Felde T. Reti

Publication Name: Proceedings of the 17th Ifhtse Congress

Publication Date: 2008-01-01

Volume: 2

Issue: Unknown

Page Range: 816-819

Description:

A numerical method for prediction of the Heat Transfer Coefficient (HTC) obtained during quenching is described in this paper. An iterative regularization algorithm is used to solve the inverse problem under study. The unknown HTC function is approximated by polynomial functions of surface temperature. The numerical method developed is verified by using the temperature data measured with a JIS silver probe.

Open Access: Yes

DOI: DOI not available

On the topological characterization of 3-D polyhedral microstructures

Ágnes Csizmazia I. Felde T. Reti

Publication Name: Materials Science Forum

Publication Date: 2007-01-01

Volume: 537-538

Issue: Unknown

Page Range: 563-570

Description:

To characterize topologically the polycrystalline microstructure of single-phase alloys computer simulations are performed on 3-dimensional cellular models. These infinite periodic cellular systems are constructed from a finite set of space filling convex polyhedra (grains). It is shown that the appropriately selected topological shape factors can be successfully used for the quantitative characterization of computer-simulated microstructures of various types.

Open Access: Yes

DOI: 10.4028/0-87849-426-x.563

On the temperature rate dependent transformation processes

L. Costa I. Czinege I. Felde T. Reti R. Colas

Publication Name: Materials Science Forum

Publication Date: 2007-01-01

Volume: 537-538

Issue: Unknown

Page Range: 571-578

Description:

Kinetic models of new types are suggested which are designated primarily to predict the progress of non-isothermal transformations occurring during rapid heating and cooling in alloys. A common feature of each model outlined is that it takes into account not only the varying temperature but also the rate of temperature change on the transformation rate of the process. The two models represented by differential equations are generated by using the concept of virtual kinetic parameters, which can be determined from non-isothermal experiments only. A key property of the virtual parameter "p" involved in the transformation rate equations is that it quantitatively characterizes the temperature rate dependence of the non-isothermal reaction.

Open Access: Yes

DOI: 10.4028/0-87849-426-x.571

Evaluation of steel hardenability by JM®-test

D. Iljkic N. Tomasic G. E. Totten B. Smoljan I. Felde T. Reti

Publication Name: Materials Science Forum

Publication Date: 2007-01-01

Volume: 537-538

Issue: Unknown

Page Range: 607-614

Description:

The modified Jominy-test was designed for prediction of hardenability of high-hardenability tool steels and possibility of application of modified Jominy-test in computer simulation of quenching of high-hardenability tool steels has been investigated. Because of high hardenability there are limits in application of original Jominy-specimen in simulation of quenching of steels. The performance of investigated modified Jominy-test in simulation of quenching of high-hardenability tool steels was estimated by comparison of cooling curves of modified Jominy-specimen (JM®-specimen) and cylindrical specimen. The influence of dimension of JM®-specimen on cooling curves has been investigated. The time of cooling, t8/5 relevant for results of quenching was predicted. Modified Jominy-test can be applied in simulation of quenching of steel with higher hardenability rather than original Jominy-test.

Open Access: Yes

DOI: 10.4028/0-87849-426-x.607

A novel approach of quenchant evaluation by applying quality functions

I. Czinege B. Smoljan I. Felde R. Colas

Publication Name: Materials Science Forum

Publication Date: 2007-01-01

Volume: 537-538

Issue: Unknown

Page Range: 513-518

Description:

A novel numerical approach for testing and evaluation of quenching media and quenching systems is outlined. The technique proposed is based on determination of heat transfer coefficient from temperature signals recorded and applying it as input for simulation of quenching process. The evaluation method is based on the calculated microstructural and mechanical properties of cylindrical samples.

Open Access: Yes

DOI: 10.4028/0-87849-426-x.513

Simulation of phase transformations in steel parts produced by laser powder deposition

L. Costa A. M. Deus I. Felde R. Colaço T. Reti R. Vilar

Publication Name: Materials Science Forum

Publication Date: 2005-01-01

Volume: 473-474

Issue: Unknown

Page Range: 315-320

Description:

Multilayer laser powder deposition is being used for the rapid manufacturing of fully dense near net shape components in a wide variety of materials. In this process parts are built by overlapping consecutive layers of a laser melted material. As a result of this overlapping, the material in each layer will undergo successive thermal cycles as new layers are deposited. Despite their short duration, these thermal cycles can activate solid-state transformations that lead to progressive modification of the microstructure and properties of the material. Since the thermal history of the material in the deposited part will differ from point to point, the part will present a complex and heterogeneous microstructure, and properties that differ from point to point. Given that the microstructure and property distribution in steel parts produced by laser powder deposition can only be predicted by modelling, a three-dimensional thermo-kinetic finite element model of laser powder deposition of tool steels was developed, In the present work this model was applied to the study of the influence of substrate size on the microstructure and properties of a six-layer wall of AISI 420 tool steel. The results show that the temperature field depends significantly on the size of the substrate, leading to distinct microstructures and properties in the final part. © 2005 Trans Tech Publications, Switzerland.

Open Access: Yes

DOI: 10.4028/0-87849-957-1.315

Numerical methods for safeguarding the performance of the quenching process

S. Sarmiente I. Felde S. Segerberg T. Reti J. Bodin

Publication Name: Materials Science Forum

Publication Date: 2005-01-01

Volume: 473-474

Issue: Unknown

Page Range: 335-340

Description:

ivf SmartQuench™ - a new system for testing and evaluation of quenching media and quenching systems - has recently been introduced by IVF. One of the system main features is an advanced computer software, which provides flexible evaluation of quenchants in many respects. The abilities of the computer program is underlined. © 2005 Trans Tech Publications, Switzerland.

Open Access: Yes

DOI: 10.4028/0-87849-957-1.335

A simple technique to estimate the processing window for laser clad coatings

K. Zoltan L. Costa B. Verö I. Felde R. Colaço T. Reti R. Vilar

Publication Name: International Surface Engineering Congress Proceedings of the 1st Congress

Publication Date: 2003-12-01

Volume: Unknown

Issue: Unknown

Page Range: 237-242

Description:

A semi-empirical method for selecting the processing parameters of laser cladding is proposed. This phenomenological approach uses simple mathematical formulae, derived from a statistical analysis of measured data, to relate the laser cladding parameters with the geometric features of the clad track. Given the required clad height and available laser beam power, the proposed method allows one to calculate values of the scanning speed and powder feed rate which are used to obtain low dilution, pore free coatings, fusion bonded to the substrate. To illustrate the application of this method, variable powder feed rate laser cladding experiments were carried out with Stellite 6 powder on mild steel substrates. In this technique the laser beam power and radius and the processing speed are kept constant, while the powder feed rate is varied along a single track length according to a specified linear function. The expressions derived from the model were used to plot the experimental data in a coherent manner, revealing the combined role of the different processing parameters.

Open Access: Yes

DOI: DOI not available