Modeliranje zamornog ponašanja sinteriranog čelika pri visokocikličkom zamoru uz razmatranje utjecaja mikrostrukture

master's thesis

• Title (english): Modelling of high cyclic fatigue behaviour of sinter steel by considering microstructural effects
• Author: Dario Stuhne
• Mentor: Tomislav Lesičar (mentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2020-12, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering

Abstract

Tehnologija metalurgije praha ima brojne prednosti nad klasičnom metalurgijom. No, kod proizvodnje dijelova tehnologijom metalurgije praha zbog postupka koji se sastoji od tlačenja praškastog materijala u kalupu koji se nakon toga zagrijava na odgovarajuću temperaturu u nekom vremenskom intervalu, u gotovom proizvodu dolazi do pojave zaostale poroznosti. Stoga je ovom diplomskom radu razmatran utjecaj mikrostrukture sinteriranog čelika na njegovo zamorno ponašanje u uvjetima visokocikličkog zamora. U radu je razmatran sinterirani čelik Astaloy Mo+0,2C. Detaljno je objašnjena metodologija numeričkog modeliranja zamora materijala i konstitutivnog ponašanja heterogenih materijala. Na temelju metalografskih ispitivanja je određen reprezentativni volumenski element (RVE) koji statistički predstavlja ponašanje mikrostrukture heterogenog materijala. Nadalje, određene su linearno-elastične karakteristike feritne matrice sinteriranog čelika primjenom homogenizacije na prethodno definiranom RVEu, koje su poslužile kao temelj prilikom procjene visokocikličkog zamora. Numeričke simulacije su provedene u programsku paketu Abaqus. Nakon određivanja linearno elastičnog ponašanja, određene su zamorne karakteristike feritne matrice Astaloya Mo+0,2C uz eksplicitno razmatranje mikrostrukture materijala. Kod određivanja zamornih karakteristika feritne matrice u uvjetima visokocikličkog zamora, razmatrana su dva slučaja: bez razmatranja utjecaja srednjeg naprezanja i s razmatranjem utjecaja srednjeg naprezanja prema Goodmanu. Numeričke simulacije zamornog ponašanja provedene su u programskom paketu fe-safe. Nažalost, eksperimentalna ispitivanja mehaničkih karakteristika Astaloya Mo+0,2C nisu u potpunosti provedena zbog posljedica uzrokovanih pandemijom koronavirusa Covid-19. Zbog toga nije bila moguća validacija rezultata numeričkih simulacija, a materijalne karakteristike materijala nužne za provedbu numeričkih analiza su preuzete iz literature.

Abstract (english)

Powder metallurgy technology has numerous advantages over classical metallurgy. However, in the production of parts by powder metallurgy technology due to a process consisting of pressing the powdered material in a mold which is then heated to the appropriate temperature in a certain time interval, residual porosity occurs in the finished product. Therefore, this master's thesis discusses the influence of the microstructure of sintered steel on its fatigue behavior under conditions of high-cyclic fatigue. The material considered is sintered steel Astaloy Mo+0.2C. The methodology of numerical modeling of material fatigue and the constitutive behavior of heterogeneous materials is explained in detail. Based on the metallographic testing, a representative volume element (RVE) was determined, which statistically represents the microstructural behavior of the heterogeneous material. Furthermore, the linear-elastic characteristics of the sintered steel ferrite matrix were determined using homogenization on a predefined RVE, which served as a basis in the assessment of high-cyclic fatigue. Numerical simulations were performed in the software package Abaqus. After determining the linear elastic behavior, the fatigue characteristics of the Astaloy Mo+0.2C ferrite matrix were determined by explicit consideration of the material microstructure. During determination the fatigue characteristics of the ferrite matrix under conditions of high-cyclic fatigue, two cases were considered: without the influence of medium stress and with consideration of the influence of medium stress according to Goodman. Numerical simulations of fatigue behavior were performed in the software package fe-safe. Unfortunately, experimental study of the mechanical properties of Astaloy Mo+0.2C has not been fully performed due to the consequences caused by the Covid-19 coronavirus pandemic. Therefore, it was not possible to validate the results of numerical simulations, while the material characteristics necessary for the conduction of numerical analyzes were taken from the literature.

• Keywords: metalurgija praha; sinterirani čelik Astaloy Mo; reprezentativni volumenski element; visokociklički zamor; modeliranje heterogenih materijala
• Keywords (english): powder metallurgy; sintered steel Astaloy Mo; representative volume element; high-cyclic fatigue; modeling of heterogeneous materials
• Language: croatian
• URN:NBN: urn:nbn:hr:235:769207
• Study programme: Title: Mechanical Engineering; 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: 2020-11-25 20:36:46