Mikrostrukturno modeliranje elastoplastičnog ponašanja nodularnog lijeva primjenom homogenizacije s reduciranim brojem stupnjeva slobode

master's thesis

• Title (english): Microstructural modelling of elastoplastic behaviour of nodular cast iron by reduced homogenization method
• Author: Luka Plavšić
• Mentor: Tomislav Lesičar (mentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2023-01-25, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering

Abstract

Većina materijala je heterogena, ovisno na kojoj se skali promatraju. Prema tome, može se reći
da su i mehanička svojstva materijala uvelike ovisna o heterogenoj mikrostrukturi, odnosno
međusobnom interakcijom različitih konstituenata na mikrostrukturnoj razini. U novije vrijeme
dolazi do ubrzanog razvoja naprednih višerazinskih numeričkih algoritama uz pomoć kojih je
moguće definirati direktnu vezu između mikrostrukture i konstitutivnog ponašanja materijala
na makrorazini. Na taj je način moguće razviti materijal optimalnih svojstava manipulirajući
raspodjelom, volumenskim udjelom i svojstvima mikrokonstituenata.
U ovom radu razmatran je nodularni lijev oznake EN-GJS-400-18-LT proizveden tehnikama
lijevanja Tundish i Inmould. Provedena je analiza postojećih mikrostruktura uz pomoć opisanih
razdioba prema promjeru nodula grafita te njihove međusobne udaljenosti. Određena je
najtočnija razdioba za obje varijable te je generirana mikrostruktura nodularnog lijeva za oba
načina lijevanja. Metodom homogenizacije s reduciranim brojem stupnjeva slobode izračunate
su vrijednosti materijalnih parametara feritne matrice nodularnog lijeva. Uz pomoć k-means
algoritma klasteriranja koji se temelji na strojnom učenju, materijalne točke mikrostrukture su
grupirane u elemente sa sličnim svojstvima, u kojima je vrijednost naprezanja i deformacija
jednaka. Sve navedeno omogućuje metodi da proračunski model diskretizira s razmjerno malim
brojem klastera što omogućuje značajnu uštedu vremena računanja. Nakon provedenog
klasteriranja inkrementalno se rješavaju Lippmann-Schwingerova jednadžba. Na temelju
numeričkih simulacija, određeni su koeficijenti potpunih polinoma drugog i trećeg reda koji
definiraju elastoplastična svojstva feritne matrice prema Swiftovom zakonu očvršćenja,
pomoću kojih su određene stvarne vrijednosti materijalnih parametara feritne matrice. Točnost
same metode je demonstrirana usporedbom parametara izračunatih numeričkim simulacijama
sa stvarnim vrijednostima preuzetima iz literature.

Abstract (english)

Most materials are heterogeneous, depending on the scale at which they are observed.
Therefore, it can be said that the mechanical properties of the material are largely dependent on
the heterogeneous microstructure, i.e., on the mutual interaction of different constituents at the
microstructural level. In recent times, there has been an accelerated development of advanced
multilevel numerical algorithms with the help of which is possible to define a direct connection
between the microstructure and the constitutive behavior of the material at the macrolevel. In
this way, it is possible to develop a material with optimal properties by manipulating the
distribution, volume fraction and properties of microconstituents.
In this paper, nodular cast EN-GJS-400-18-LT produced by Tundish and Inmould casting
techniques was considered. An analysis of the existing microstructures was carried out with the
help of the described distributions according to the diameter of the graphite nodules and their
mutual distance. The most accurate distribution for both variables was determined and the
microstructure of ductile iron was generated for both methods of casting. The values of the
material parameters of the ferrite matrix of nodular cast iron were calculated using the reduced
homogenization method. With the help of the k-means clustering algorithm based on machine
learning, the material points of the microstructure are grouped into elements with similar
properties, in which the stress and strain values are equal. All of the above allows the method
to discretize the computational model with a relatively small number of clusters, which enables
a significant saving of computation time. After clustering, the Lippmann-Schwinger equation
is solved incrementally. On the basis of numerical simulations, the coefficients of complete
polynomials of the second and third order that define the elastoplastic properties of the ferrite
matrix according to Swift's law of hardening were determined, by means of which the actual
values of the material parameters of the ferrite matrix were determined. The accuracy of the
method itself was demonstrated by comparing parameters calculated by numerical simulations
with real values taken from the literature.

• Keywords: Heterogeni materijal; homogenizacija s reduciranim brojem stupnjeva slobode; k-means klasteriranje; Lippman-Schwingerova jednadžba; nodularni lijev; Inmould; Tundish
• Keywords (english): Heterogeneous material; reduced homogenization method; k-means clustering; LippmanSchwinger equation; nodular casting (ductile iron); Inmould; Tundish
• Language: croatian
• URN:NBN: urn:nbn:hr:235:674885
• Study programme: Title: Mechanical Engineering; specializations in: Design, Process and Energy Engineering, Production Engineering, Engineering Modelling and Computer Simulation, Marine Engineering, Industrial Engineering and Management, Materials Engineering, Mechatronics and Robotics, Autonomous Systems; Course: Engineering Modelling and Computer Simulation; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra inženjer/inženjerka strojarstva (magistar/magistra inženjer/inženjerka strojarstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2023-01-19 20:03:48