Procjena zamora u vremenskoj i frekvencijskoj domeni za bimodalni spektar naprezanja

undergraduate thesis

• Title (english): Estimation of fatigue in the time and frequency domains for the bimodal stress spectrum
• Author: Sara Večerić
• Mentor: Zvonimir Tomičević (mentor)
• Mentor: Damjan Čakmak (komentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2021-09-30, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering; General Mechanical Engineering (Construction)

Abstract

Ovaj rad bavi se temom zamora materijala uzrokovanog stohastičkim vibracijama. U ovom radu detaljno je opisana Rainflow metoda brojanja ciklusa (metoda „toka kiše“) za ponavljajuću povijest naprezanja. Rainflow metoda za ponavljajuću povijest naprezanja je metoda kojom se pojednostavljuju složene povijesti naprezanja promjenjivih amplituda u niz jednostavnih ciklusa naprezanja konstantnih amplituda što omogućuje proračun zamora. Za duge povijesti naprezanja, proračun visokocikličkog zamora Rainflow metodom u vremenskoj domeni postaje računalno dugotrajan. U svrhu pojednostavljenja, u ovom radu opisane su i korištene spektralne teorije u frekvencijskoj domeni. Na početku rada opisan je fenomen zamornog loma, širenje pukotine u materijalu, Wöhlerova krivulja te S-N metoda proračuna zamora. U drugom dijelu rada detaljno je opisan način brojanja ciklusa nepravilnih amplituda Rainflow metodom za ponavljajuću povijest naprezanja prema ASTM E1049-85 normi. Nadalje, opisane su sve formulacije potrebne za procjenu visokocikličkog zamora u vremenskoj i frekvencijskoj domeni. Detaljno su opisane približne spektralne teorije: Bendat, Dirik, Tovo-Benasciutti i Jiao-Moan. U zadnjem dijelu provedena je analiza rezultata spektralnih teorija s obzirom na dobivene rezultate u vremenskoj domeni. Analiza je provedena pomoću algoritma napisanog u programskom paketu MATLab R2017b.

Abstract (english)

This thesis deals with the topic of material fatigue caused stochastic vibrations. This thesis describes the Rainflow method of cycle counting for repeating stress history. Rainflow method for repeating stress history is a method used to simplify complex variable amplitude stress histories into a series of simple constant amplitude stress cycles that allows fatigue calculation. For long stress histories, the calculation of high-cycle fatigue by the Rainflow method in the time domain becomes computationally time-consuming. For the purpose of simplicity, spectral theories in the frequency domain are also explained and used. At the beginning, the phenomenon of fatigue fracture, crack propagation in the material, Wöhler curve and S-N method of fatigue calculation are described. The second part of the thesis describes the method of counting cycles of irregular amplitudes by the Rainflow method for the repeating stress history according to the ASTM E1049-85 standard. Furthermore, the formulations required to estimate high-cycle fatigue in the time and frequency domains are described. Spectral theories: Bendat, Dirlik, Tovo-Benasciutti and Jiao Moan are also described. The last part analyses and compares the results of spectral theories with the results obtained in the time domain. The analysis was performed using the algorithm written in the software package MATLab R2017b.

• Keywords: zamorni lom; Rainflow metoda; povijest naprezanja; kumulirano oštećenje; broj ciklusa; spektralne teorije; frekvencijska domena
• Keywords (english): fatigue fracture; Rainflow method; stress history; cumulative damage; number of cycles; spectral theories; frequency domain
• Language: croatian
• URN:NBN: urn:nbn:hr:235:159636
• 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; Course: Design; Study programme type: university; Study level: undergraduate; Academic / professional title: sveučilišni/a prvostupnik/ prvostupnica (baccalaureus/baccalaurea) inženjer/inženjerka strojarstva (sveučilišni/a prvostupnik/ prvostupnica (baccalaureus/baccalaurea) inženjer/inženjerka strojarstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access; Embargo expiration date: 2023-09-23
• Created on: 2021-09-22 20:20:16