Određivanje preraspodjele zaostalih naprezanja kod zavarivanja u dva prolaza

master's thesis

• Title (english): Determination of residual stress state redistribution in two-passing ew
• Author: Avelin Bingula
• Mentor: Tomislav Lesičar (mentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2023-07-21, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering; General Mechanical Engineering (Construction)

Abstract

Zavarivanje je jedan od najzastupljenijih metoda spajanja metalnih konstrukcija. Zbog svoje jednostavnosti i brzine zastupljena je u gotovo svim industrijama. Unatoč tome postoje i negativne strane, a to su zaostala naprezanja i deformacije u konstrukciji zbog velikog unosa topline u kratkom vremenu na malom prostoru. Za određivanje zaostalih naprezanja i deformacija stvarnih konstrukcijskih rješenja ne postoji analitičko rješenje, a eksperimentalna ispitivanja najčešće su dugotrajna i skupa. Numeričko modeliranje procesa zavarivanja i numeričke simulacije su se pokazale vrlo učinkovitima u realnim problemima zavarivanja. Prednosti numeričkih simulacija su brzina, paralelno rješavanje više problema i točnost rezultata. U ovom radu je prikazan utjecaj zaostalih naprezanja i deformacija kod zavarivanja u dva prolaza te izrezivanja zavarenih ploča.
Za poznavanje procesa zavarivanja potrebno je poznavati izraze i jednadžbe iz područja termodinamike i elastoplastičnog ponašanja materijala. Iznesene su teorijske osnove toplinsko – mehaničkih jednadžbi kod izmjene topline prilikom procesa zavarivanja i konstitutivne jednadžbe ponašanja elastoplastičnog materijala zbog nelinearne prirode procesa zavarivanja. Numeričke simulacije uglavnom koriste metodu konačnih elemenata te su iste jednadžbe pokazane na konačnim elementima i kako se zaostala naprezanja i deformacije određuju inkrementalno – iterativno.
Sučeono zavarivanje dvaju ploča zavarom u dva prolaza modelirano je dodatkom programskom paketu Abaqus [4] za lakše i brže izrađivanje modela zavara zvan Abaqus Welding Interface (AWI) [19]. AWI sučelje omogućava istovremeno stvaranje dva modela za spregnuto toplinsku – mehaničku analizu. Zbog simetrične karakteristike problema modelirana je samo jedna ploča u procesu zavarivanja. Modeli ploča su diskretizirani osnovnim trodimenzijskim prizmatičnim konačnim elementima, DC3D8 za toplinsku i C3D8 za mehaničku analizu [19]. Rezultati analize su uspoređeni s rezultatima članka Sepe i ostalih [21].
Eksperimentalna istraživanja uzroka i posljedica zaostalih naprezanja i deformacija se provodi na standardiziranim epruvetama za testiranje. Iz numeričkog modela toplinsko – mehaničke analize sučeono zavarene dvije ploče izrezane su dvije epruvete u longitudinalnom i transverzalnom smjeru u odnosu na zavar i promatrani utjecaji zaostalih naprezanja i deformacija nakon izrezivanja iz jednog i dva poteza. Izrezane su SENB plosnata epruveta bez zareza i plosnata epruveta prema HRN EN ISO 6892-1:2019 normi. Presjecima na srednjoj plohi prikazani su rezultati u dijagramima.

Abstract (english)

Welding is one of the most common methods for joining metal structures. Due to its simplicity and speed, it is widely used in almost every industry. However, there are also drawbacks, such as residual stresses and deformations in the structure caused by the high heat input in a short time and a small area. Analytical solutions for determining residual stresses and deformations in actual structural designs are not available, and experimental tests are often time-consuming and expensive. Numerical modelling of the welding process and simulations have proven to be highly effective in addressing real-world welding problems. The advantages of numerical simulations include speed, parallel solving of multiple problems, and result accuracy.
This study examines the influence of residual stresses and deformations in two-pass welding and the cutting of welded plates. Understanding the welding process requires knowledge of expressions and equations from the field of thermodynamics and the elastoplastic behaviour of materials. The theoretical foundations of thermal-mechanical equations for heat transfer in welding processes and the constitutive equations for the behaviour of elastoplastic materials are presented. Numerical simulations primarily employ the finite element method, and the same equations are demonstrated on finite elements to determine residual stresses and deformations incrementally and iteratively.
The butt welding of two plates in two passes is modelled using the Abaqus software package [4] with the assistance of the Abaqus Welding Interface (AWI) [19] for easier and faster weld model creation. The AWI interface enables the simultaneous creation of two models for coupled thermal-mechanical analysis. Due to the symmetric characteristics of the problem, only one plate is modelled in the welding process. The plate models are discretized using basic three-dimensional prismatic finite elements, DC3D8 for thermal analysis and C3D8 for mechanical analysis [19]. The analysis results are compared with the findings of the study by Sepe et al. [21].
Experimental investigations into the causes and consequences of residual stresses and deformations are conducted using standardized test specimens. From the numerical model of the coupled thermal-mechanical analysis, two specimens were cut in the longitudinal and transverse directions relative to the weld, and the effects of residual stresses and deformations after cutting from one and two passes were observed. SENB (Single-Edge Notched Bend) specimen and flat specimen according to the HRN EN ISO 6892-1:2019 standard were cut out of the plate. Presented results in the diagrams are from cross-sections on the middle plane.
By conducting these analyses and experiments, valuable insights into the behaviour of welded joints can be obtained. The obtained results contribute to the understanding of residual stresses and deformations in welded structures, and they can be used to improve welding techniques and optimize welding processes in various industries. Further research and development in this field will lead to safer and more efficient welded structures.

• Keywords: zavarivanje; zaostala naprezanja; zaostale deformacije; elastoplastičan materijal; Abaqus; Abaqus Welding Interface; numerička analiza; metoda konačnih elemenata
• Keywords (english): welding; residual stress; residual strain; elastoplastic material; Abaqus; Abaqus Welding Interface; numerical analysis; finite element method
• Language: croatian
• URN:NBN: urn:nbn:hr:235:349668
• 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: 2023-07-12 17:17:59