Numeričko modeliranje procesa zavarivanja

master's thesis

• Title (english): Numerical modelling of welding process
• Author: Jurica Galović
• Mentor: Ivica Skozrit (mentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2017-01-26, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering

Abstract

Tema ovog rada je problem numeričkog određivanja temperaturnog polja, te zaostalih naprezanja i deformacija koje su posljedica procesa zavarivanja. Potrebno je odrediti optimalan numerički model koji daje odgovarajuće rezultate uz najkraće vrijeme računanja i pripreme modela. Analize su provedene metodom konačnih elemenata u komercijalnom programskom paketu Abaqus 6.13-4. Rad je podijeljen u osam cjelina.

U prvom, uvodnom poglavlju prezentiran je cilj ovoga rada i ukratko opisan postupak zavarivanja.

U drugom poglavlju rada dan je pregled zaostalih naprezanja i deformacija te objašnjen njihov nastanak na pojednostavljenom modelu sa tri štapa. Ukratko je pojašnjena problematika do koje dolazi uslijed promjene geometrije konstrukcije nakon provođenja zavarivanja.

U trećem poglavlju izložena su teoretska znanja potrebna za razumijevanje pojava koje se javljaju u procesu zavarivanja. Dan je pregled osnova termodinamike i elasto-plastičnog ponašanja materijala uz analitičke izraze.

Četvrti dio rada ukratko opisuje metodu konačnih elemenata te sekvencijalno i potpuno spregnutu metodu rješavanja nelinearnih toplinsko-mehaničkih problema. Opisana je geometrijska i materijalna nelinearnost te inkrementalno-iterativna metoda kojom se rješavaju nelinearni problemi.

U petom poglavlju prikazana je numerička formulacija i potencijalni numerički problemi konačnih elemenata korištenih u ovom radu te načini kojima se ti problemi izbjegavaju. Također, kroz dva toplinska i dva mehanička problema korišteni konačni elementi su verificirani.

U šestom poglavlju dane su karakteristike materijala i opisan je materijalni model. Prikazan je postupak toplinske i mehaničke simulacije procesa zavarivanja klasičnom metodom te korištena pojednostavljenja poput reducirano opisanog toplinskog toka i smanjenog broja prolaza elektrode. Numerička analiza izvršena je sekvencijalno spregnutom toplinsko-mehaničkom analizom sa potpunim 3D modelom, potpunim ljuskastim i kombiniranim 3D ljuskastim modelom. Prikazani su dobiveni rezultati i definiran je optimalan numerički model.

Sedmo poglavlje ukratko opisuje metodu rađanja elemenata. Prikazani su rezultati 3D i kombiniranog modela dobiveni ovom metodom i dana je usporedba sa klasičnom metodom.

U osmom poglavlju prikazani su rezultati toplinske i mehaničke analize dobiveni različitim geometrijskim modeliranjem ploča.

U zadnjem, devetom poglavlju izveden je zaključak temeljen na dobivenim rezultatima provedenih simulacija. Ukratko je opisan cijeli rad te zapažanja uočena tijekom izrade rada.

Abstract (english)

The subject of this thesis is the problem of numerical determination of temperature field and of stress and strain fields as a consequence of welding process. Optimal numerical model that gives adequate results in minimal calculation and model preparation time is proposed. Analyses were conducted using finite elements method in commercial software package Abaqus 6.13-4. Thesis is divided into nine sections.

In the first, introductory section, the goal of this work is defined and the process of welding is briefly described.

In the second section, residual stresses and strains are presented. Process of their formation is explained on simplified model with three rods. Problems that arise from change in geometry after welding are briefly described.

Third section deals with fundamental theoretical knowledge that is necessary for understanding the phenomena that are present in welding. Basic thermodynamics and elasto-plastic material behaviour are presented together with analytical expressions.

In the fourth section, finite element method, sequentially and fully coupled method for solving nonlinear thermo-mechanical problems are described. Moreover, geometric nonlinearity, material nonlinearity and incremental-iterative method for solving nonlinear problems are presented.

In the fifth section, numerical formulation, potential numerical problems of utilised finite elements and means to solve those problems are presented. Also, finite elements were verified through two thermal and two mechanical problems.

Sixth section presents material characteristics and material model used in this thesis. Process of thermal and mechanical welding simulation with simplifications such as simplified heat flux and reduced number of welding passes using conventional method is described. Numerical analysis is conducted using sequentially coupled thermo-mechanical analysis with complete 3D model, complete shell model and shell-to-solid model. Collected results are presented and optimal numerical model is proposed.

In the seventh section, element birth method and its specifics are briefly explained. Results obtained with complete 3D model and shell-to-solid model using this method are presented and compared to those obtained with conventional method.

Results of thermal and mechanical analyses obtained with different extrusions of welded plates are presented in the eight section.

In the last, ninth section, conclusion was drawn from the results gathered in conducted simulations. The whole thesis and observations are briefly depicted.

• Keywords: metoda konačnih elemenata; numeričko modeliranje procesa zavarivanja; određivanje zaostalih naprezanja i deformacija uslijed zavarivanja; klasična metoda; metoda rađanja
• Keywords (english): finite element analysis; numerical modelling of welding; determination of residual stresses and strains in welding; conventional method; element birth method
• Language: croatian
• URN:NBN: urn:nbn:hr:235:411787
• 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
• Repository: Repository of Faculty of Mechanical Engineering and Naval Architecture University of Zagreb
• Created on: 2019-05-22 18:25:02