Elastic interfaces in random media and their application to fatigue fracture

Juha Savolainen

Elastic interfaces in random media and their application to fatigue fracture

Julkaisun otsikon käännös: Joustavat rajapinnat ja niiden sovellus väsymismurtumiin

Juha Savolainen

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Tämä väitöskirja käsittelee joustavia rajapintoja rosoisessa väliaineessa sekä niiden sovelluksia murtomekaniikassa ja erityisesti materiaalien väsymisessä. Työhön sisältyy kolme julkaisua, joista yksi on kokeellinen, yksi numeerinen ja yksi analyyttinen. Väsyminen tarkoittaa materiaalien murtumista toistuvasta kuormituksesta. Tässä työssä olemme kiinnostuneita yksittäisen särön etenemisestä kappaleessa sekä erityisesti Parisin-Erdoganin laista, jonka mukaan särön nopeus kasvaa jännitysintensiteettikertoimena tunnetun funktion potenssina. Yhden särön tarkastelu yleensä riittää, sillä kappaleen pisin särö kasvaa tavallisesti nopeiten ja johtaa kappaleen lopulliseen repeämiseen tarpeeksi pitkässä kuormituksessa. Joustavat rajapinnat kuvaavat itsensä kanssa vuorovaikuttavia rajoja kahden järjestelmän välillä. Tässä tapauksessa rajana on se, kuinka pitkälle särö on edennyt, eli raja rikkinäisen ja ehjän aineksen välillä. Materiaalin sisäiset elastiset vuorovaikutukset pyrkivät suoristamaan rosoista särörintamaa. Särön edetessä yhdestä kohtaa on sen tapana vetää muuta murtumaa mukanaan. Numeerinen julkaisu käsittelee vyöryinä tunnettuja ketjureaktioita rajapinnan liikkeessä. Jotta liike saataisiin erotettua esimerkiksi mittalaitteiden kohinasta, on vyöryt tapana määritellä jotain kynnystä isompana liikkeenä. Vyöryjä voi olla kaiken kokoisia riippuen siitä milloin mikäkin liikkeen ketjureaktio päättyi, joten kynnyksen valinta vaikuttaa vyöryihin. Tuloksemme osoittavat miten kynnys vaikuttaa erilaisiin vyöryjen jakaumiin ja siihen näyttäytyvätkö vyöryt toisistaan riippuvaisina. Näytämme myös aikaisemmissa tutkimuksissa havaittujen rajapintojen seismisten ominaisuuksien johtuneen niille käytetyistä määritelmistä. Kokeellinen julkaisu tutkii mikroskooppisia hyppyjä murtuman liikkeessä, ja kuinka ne johtavat Parisin-Erdoganin lakiin. Havaitsimme hyppyjen noudattavan samanlaista kokojakaumaa erilaisilla kuormituksilla, vaikka eri kuormitukset johtivatkin erilaisiin keskimääräisiin nopeuksiin särölle sekä erilaisiin eksponentteihin Parisin-Erdoganin laissa. Jakaumissa oli kuitenkin erona se, että mitä nopeampaa kappaleen murtuminen oli, sitä pidempiin hyppäyksiin jakauma ulottui. Analyyttisessä julkaisussa vertasimme lämmön käynnistämän hitaan rajapintojen liikkeen teoriaa väsymysmurtumiin sekä jaksottaiseen liikkeeseen samankaltaisissa järjestelmissä, kuten magneettisten vyöhykkeiden seinämissä. Havaitsimme magneettisten vyöhykkeiden käytöksen vastaavan paremmin väsymysmurtumia kuin itse tulosten väsymiselle. Tämä viittaa siihen, että aikaisemmissa tutkimuksissa ilmoitetut suureet tasomurtumille eivät päde väsymysmurtumille.

Julkaisun otsikon käännös	Joustavat rajapinnat ja niiden sovellus väsymismurtumiin
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Alava, Mikko, Vastuuprofessori Alava, Mikko, Ohjaaja
Kustantaja	Aalto University
Painoksen ISBN	978-952-64-1363-1
Sähköinen ISBN	978-952-64-1364-8
Tila	Julkaistu - 2023
OKM-julkaisutyyppi	G5 Artikkeliväitöskirja

Tutkimusalat

joustavat rajapinnat
väsymismurtumat
murtomekaniikka
vyöryt

Pääsy asiakirjaan

http://urn.fi/URN:ISBN:978-952-64-1364-8

Science-IT
Hakala, M. (Manager)
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@phdthesis{db30ff3c3921435ab1c89a2733d3d585,

title = "Elastic interfaces in random media and their application to fatigue fracture",

abstract = "This dissertation looks at elastic interfaces in disordered media and their application to fracture mechanics, in particular fatigue fractures. The work goes through three publications, of which one is experimental, one numerical, and one analytical. The fracturing of materials under repetitive stress is called fatigue. We are interested in the propagation of a single crack and the Paris-Erdogan law, which states that the crack's velocity grows as a power of a function known as the stress intensity factor. Often it is enough to look at just the largest crack in a solid, as it is the one that advances the fastest and eventually splits the object under long enough loading. Elastic interfaces describe self-interacting boundaries between two systems. In this case, the boundary is the front of a crack, the deepest part of the crack inside a material. Elastic forces inside the material try to keep the crack front straight even if the material is rough in composition. As one part of the crack front advances, it pulls its neighbors forward. The numerical publication looks at chain reactions of movement called avalanches in the elastic interface model. Avalanches are often defined as signals that are greater than some threshold, for example to separate relevant data from noise. Avalanches are however scale-free in size, so the choice of the threshold alters the results. Our results show how different distributions of avalanches change with the threshold and how a threshold determines whether the avalanches are correlated or not. We also show that previously found seismological behavior in interface movement results from how it has been defined. The experimental publication looks at microscopic jumps in crack movement and how they result in the Paris-Erdogan law. The jumps are found to follow the same distribution for different loading schemes, even though they result in different average speeds and different slopes for the Paris-Erdogan law. The distributions, however, differ in their cutoffs, so faster average movement results from the jump distribution lasting longer. The analytical publication compares slow thermally induced interface movement to the Paris-Erdogan law and to periodic movement in other systems such as magnetic domain walls. We find that the results for magnetic domain walls describe fatigue fractures better than the results intended for fractures. This implies that previously found material parameters for planar cracks might not be correct for fatigue experiments.",

keywords = "elastic interfaces, fatigue fracture, fracture mechanics, avalanches, joustavat rajapinnat, v{\"a}symismurtumat, murtomekaniikka, vy{\"o}ryt, elastic interfaces, fatigue fracture, fracture mechanics, avalanches",

author = "Juha Savolainen",

year = "2023",

language = "English",

isbn = "978-952-64-1363-1",

series = "Aalto University publication series DOCTORAL THESES",

publisher = "Aalto University",

number = "116",

address = "Finland",

school = "Aalto University",

}

TY - BOOK

T1 - Elastic interfaces in random media and their application to fatigue fracture

AU - Savolainen, Juha

PY - 2023

Y1 - 2023

N2 - This dissertation looks at elastic interfaces in disordered media and their application to fracture mechanics, in particular fatigue fractures. The work goes through three publications, of which one is experimental, one numerical, and one analytical. The fracturing of materials under repetitive stress is called fatigue. We are interested in the propagation of a single crack and the Paris-Erdogan law, which states that the crack's velocity grows as a power of a function known as the stress intensity factor. Often it is enough to look at just the largest crack in a solid, as it is the one that advances the fastest and eventually splits the object under long enough loading. Elastic interfaces describe self-interacting boundaries between two systems. In this case, the boundary is the front of a crack, the deepest part of the crack inside a material. Elastic forces inside the material try to keep the crack front straight even if the material is rough in composition. As one part of the crack front advances, it pulls its neighbors forward. The numerical publication looks at chain reactions of movement called avalanches in the elastic interface model. Avalanches are often defined as signals that are greater than some threshold, for example to separate relevant data from noise. Avalanches are however scale-free in size, so the choice of the threshold alters the results. Our results show how different distributions of avalanches change with the threshold and how a threshold determines whether the avalanches are correlated or not. We also show that previously found seismological behavior in interface movement results from how it has been defined. The experimental publication looks at microscopic jumps in crack movement and how they result in the Paris-Erdogan law. The jumps are found to follow the same distribution for different loading schemes, even though they result in different average speeds and different slopes for the Paris-Erdogan law. The distributions, however, differ in their cutoffs, so faster average movement results from the jump distribution lasting longer. The analytical publication compares slow thermally induced interface movement to the Paris-Erdogan law and to periodic movement in other systems such as magnetic domain walls. We find that the results for magnetic domain walls describe fatigue fractures better than the results intended for fractures. This implies that previously found material parameters for planar cracks might not be correct for fatigue experiments.

AB - This dissertation looks at elastic interfaces in disordered media and their application to fracture mechanics, in particular fatigue fractures. The work goes through three publications, of which one is experimental, one numerical, and one analytical. The fracturing of materials under repetitive stress is called fatigue. We are interested in the propagation of a single crack and the Paris-Erdogan law, which states that the crack's velocity grows as a power of a function known as the stress intensity factor. Often it is enough to look at just the largest crack in a solid, as it is the one that advances the fastest and eventually splits the object under long enough loading. Elastic interfaces describe self-interacting boundaries between two systems. In this case, the boundary is the front of a crack, the deepest part of the crack inside a material. Elastic forces inside the material try to keep the crack front straight even if the material is rough in composition. As one part of the crack front advances, it pulls its neighbors forward. The numerical publication looks at chain reactions of movement called avalanches in the elastic interface model. Avalanches are often defined as signals that are greater than some threshold, for example to separate relevant data from noise. Avalanches are however scale-free in size, so the choice of the threshold alters the results. Our results show how different distributions of avalanches change with the threshold and how a threshold determines whether the avalanches are correlated or not. We also show that previously found seismological behavior in interface movement results from how it has been defined. The experimental publication looks at microscopic jumps in crack movement and how they result in the Paris-Erdogan law. The jumps are found to follow the same distribution for different loading schemes, even though they result in different average speeds and different slopes for the Paris-Erdogan law. The distributions, however, differ in their cutoffs, so faster average movement results from the jump distribution lasting longer. The analytical publication compares slow thermally induced interface movement to the Paris-Erdogan law and to periodic movement in other systems such as magnetic domain walls. We find that the results for magnetic domain walls describe fatigue fractures better than the results intended for fractures. This implies that previously found material parameters for planar cracks might not be correct for fatigue experiments.

KW - elastic interfaces

KW - fatigue fracture

KW - fracture mechanics

KW - avalanches

KW - joustavat rajapinnat

KW - väsymismurtumat

KW - murtomekaniikka

KW - vyöryt

KW - elastic interfaces

KW - fatigue fracture

KW - fracture mechanics

KW - avalanches

M3 - Doctoral Thesis

SN - 978-952-64-1363-1

T3 - Aalto University publication series DOCTORAL THESES

PB - Aalto University

ER -

Elastic interfaces in random media and their application to fatigue fracture

Abstrakti

Tutkimusalat

Pääsy asiakirjaan

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Science-IT

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