Numeričko modeliranje zaostalih naprezanja pri zavarivanju

master's thesis

• Title (english): Numerical modelling of welding residual stresses
• Author: Bruno Franin
• Mentor: Ivica Skozrit (mentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2016-05-20, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering

Abstract

U ovom diplomskom radu razmatra se problem numeričkog određivanja zaostalih naprezanja i deformacija pri procesu zavarivanja. Numeričke analize rađene su metodom konačnih elemenata sekvencijalno spregnutom toplinsko – mehaničkom analizom. Navedeni postupak je računalno vrlo skup, stoga se provodi uz odgovarajuća pojednostavljenja u svrhu reduciranja korisničkog vremena za pripremu modela i vremena računanja, uz zahtijevanu točnost rezultata simulacije. Radi lakšeg razumijevanja, nastajanje zaostalih naprezanja i deformacija objašnjeno je na pojednostavljenom modelu s tri štapa. Teorijska osnovna izmjene topline i elastoplastičnog ponašanja materijala nužna je za razumijevanje numeričkog modeliranja procesa zavarivanja, stoga su uz numeričke izraze navedeni i analitički. Numeričko modeliranje opisano je izrazima za nelinearnu toplinsku i mehaničku analizu, a također su prikazane osnove rješavanja nelinearnih problema inkrementalno – iterativnom metodom te korišteni konačni elementi. Modeliranje procesa zavarivanja verificirano je na procesu zavarivanja dviju sučeono zavarenih ploča. Za korištenu klasičnu metodu i metodu rađanja elemenata analizirani su ljuskasti modeli, potpuni 3D model i kombinirani 3D/ljuskasti model, te je dana usporedba dviju metoda. Pojednostavljenje modela odnosi se na reducirano opisan toplinski tok, reduciranje trodimenzijskog problema na dvodimenzijski, reducirano opisivanje temperaturne ovisnosti materijala, i pojednostavljenje u vidu prolaza elektrode. Primjenom navedenih pojednostavljenja nastojalo se doći do optimalnog numeričkog modela u slučaju modeliranja navedenim metodama. Analiziranjem rezultata i danim zaključcima pri analizi dviju sučeono zavarenih ploča pristupilo se modeliranju procesa zavarivanja poklopca rebra linera pri montaži na konstrukciju ispušnog kućišta plinske turbine tvrtke Alstom.

Abstract (english)

This master thesis considers the problem of numerical determination of residual stresses and strains during the welding process. Numerical simulations were conducted using finite element method with sequentially coupled thermal - stress analysis. This procedure is computationally very expensive, therefore we are using appropriate simplifications in order to reduce user time to prepare model and computation time, with the required accuracy of the simulation results. For ease of understanding, the formation of residual stresses and strains is explained on simplified model with three roods. Theoretical basic of heat transfer and elastic plastic material behavior is necessary for the understanding of numerical modeling of welding processes, so the are numerical and analytical terms also specified in this thesis. Numerical modeling in terms of a nonlinear thermal and stress analysis solving with incremental – iterative method, and types of used finite elements are also described. Process for numerical modeling of welding is verified on two butt – welded plates, and it was modelled using standard method and element birth and death method. Models are discretized with shell elements, 3D elements, and combined 3D/shell elements using shell to solid coupling method. Simplification of the model refers to the reduced heat flux, reduced temperature dependence of material, and simplification with just one pass through the weld. Applying the above simplifications, we attempted to find the optimal numerical model. By the results and conclusions in the analysis of two butt – welded plates, we apply the optimal process for modelling welding of cover rib on liner during assembly of the gas turbine exhaust housing from the company Alstom.

• Keywords: metoda konačnih elemenata; zaostala naprezanja; klasična metoda; metoda rađanja
• Keywords (english): finite element method; residual stresses; conventional method; element birth and death method
• Language: croatian
• URN:NBN: urn:nbn:hr:235:722613
• 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: 2019-05-22 16:40:17