Low-velocity impact damage in fibre metal laminates - a study of the impact resistance and metal-composite debonding

Tuomas Pärnänen

Lujitemuovi-metalli-yhdistelmälaminaattien iskuvaurioituminen – tutkimus iskunkestävyydestä ja kerrostenvälisestä murtumisesta

Tuomas Pärnänen

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Lujitemuovi-metalli-yhdistelmälaminaatit (jatkossa laminaatit) ovat rakenteita, jotka muodostuvat ohuista metalli- ja lujitemuovikerroksista. Tässä väitöskirjassa tutkitaan laminaattien vaurioitumista hitaiden törmäystyyppisten iskujen vaikutuksesta. Iskuvaurioitumista tutkitaan pudotus- ja painamiskokein sekä elementtimenetelmään perustuvilla simulaatioilla. Työn ensimmäisessä osassa tutkitaan erityisesti AZ31B-H24 magnesiumkerroksia sisältävien laminaattien iskunkestävyyttä. Tulosten mukaan laminaatin iskunkestävyys on 2024-T3 alumiinikerroksia sisältävää Glare 5 -laminaattia heikompi. Iskunkestävyyden lisäksi ensimmäisessä osassa tutkitaan iskuvaurioiden kehittymistä tarkastelemalla eri iskuenergioilla kuormitettujen koekappaleiden vaurioita. Lopuksi laminaattien iskukuormittumista tutkitaan elementtimenetelmään perustuvilla simulaatioilla. Työn toisessa osassa keskitytään kerrostenväliseen murtumiseen, joka tapahtuu metallien ja lujitemuovien rajapinnassa. Työn tulokset osoittavat, että murtuminen laminaatin alimmaisessa rajapinnassa tapahtuu iskun aikana kahdessa eri vaiheessa. Iskun alkuvaiheessa murtuma muodostuu laminaatin normaalin suuntaisten leikkausvoimien seurauksena. Iskun paluuvaiheen aikana lujitemuovikerrokset pyrkivät suoristumaan plastisesti muovautuneita metallikerroksia enemmän. Ero materiaalivasteessa johtaa repivään kuormitukseen ja murtumiseen. Rajapinnan murtumista ei tyypillisesti ole otettu huomioon iskumalleissa ja toisinaan ainoastaan leikkausvoimista aiheutuva murtuminen on huomioitu. Väitöskirjan tulokset osoittavat, että kaksivaiheinen murtuminen vaikuttaa merkittävästi laminaatin muodonmuutoksiin ja iskunjälkeiseen venymätilaan. Realistinen vauriotilan määrittäminen on erityisen tärkeää iskunjälkeistä lujuutta tarkasteltaessa. Tämän vuoksi jatkossa on suositeltavaa ottaa huomioon kaksivaiheinen murtuminen laminaattien iskukuormitusta mallinnettaessa.

Julkaisun otsikon käännös	Lujitemuovi-metalli-yhdistelmälaminaattien iskuvaurioituminen – tutkimus iskunkestävyydestä ja kerrostenvälisestä murtumisesta
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Saarela, Olli, Vastuuprofessori Kanerva, Mikko, Ohjaaja
Kustantaja	Aalto University
Painoksen ISBN	978-952-60-7189-3
Sähköinen ISBN	978-952-60-7188-6
Tila	Julkaistu - 2016
OKM-julkaisutyyppi	G5 Tohtorinväitöskirja (artikkeli)

Tutkimusalat

yhdistelmälaminaatit
iskunkestävyys
kerrostenvälinen murtuminen

Pääsy asiakirjaan

http://urn.fi/URN:ISBN:978-952-60-7188-6Lisenssi: Määrittelemätön

Sormenjälki Sukella tutkimusaiheisiin 'Lujitemuovi-metalli-yhdistelmälaminaattien iskuvaurioituminen – tutkimus iskunkestävyydestä ja kerrostenvälisestä murtumisesta'. Ne muodostavat yhdessä ainutlaatuisen sormenjäljen.

Siteeraa tätä

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title = "Low-velocity impact damage in fibre metal laminates - a study of the impact resistance and metal-composite debonding",

abstract = "Fibre metal laminates (FMLs) refer to a hybrid material concept that combines layers of thin metal sheets and fibre-reinforced plastics. This thesis concentrates on the damage characteristics of FMLs subjected to collision-type low-velocity impacts. The damage characteristics are studied by drop-weight impact and quasi-static indentation experiments and using finite element simulations. The work is divided into two parts. In Part I, specific interest is laid on the impact resistance of AZ31B-H24 magnesium alloy-based FMLs. The results indicate a disadvantage for the magnesium alloy, as the impact energy limits for metal cracking are significantly lower when compared to the state-of-the-art FML structure Glare 5 with 2024-T3 aluminium alloy layers. The main reason for the difference in cracking energies is concluded to result from the metal tensile response over the plastic region. The lower rate of strain hardening for the magnesium alloy enhances the local strain accumulation over the impact point, which leads to premature cracking. In addition, the impact damage process is experimentally studied in Part I by using a wide range of impact energies. The purpose of the damage process study is to gain an overall view of the impact damage evolution in FMLs. Finally, impacts on FMLs are studied via finite element simulations.Part II focuses on the debonding occurring in FMLs during impact loading, i.e. on the damage process along the metal-composite interface. The study reveals that the debond at the lowermost metal-composite interface forms in two stages. During the impactor loading phase, a debond tends to form as a fracture mode II cracking caused by out-of-plane shear forces. As the impactor rebound phase follows, the linear-elastic composite layers force the FML to straighten. On the contrary, the lowermost metal sheet has deformed plastically and tends to maintain its deformed shape. The discrepancy in the material response leads to peeling forces and consequently to fracture mode I dominated debonding. In the current literature, the debonding along the metal-composite interface is not commonly taken into account in the impact damage modelling of FMLs, and at times the debonding by shear forces is only considered. The energy absorption by the debonding may not be significant in the impact process, but the results of this thesis indicate that the debonding substantially affects deformations and the post-impact strain state. A realistic prediction of the post-impact damage state is especially important for successful investigations of damage tolerance. Therefore, a modelling methodology that takes into account the debonding with the described two-stage formation process defined in this thesis is suggested for future models.",

keywords = "fibre metal laminates, hybrids, impact, impact resistance, debonding, yhdistelm{\"a}laminaatit, iskunkest{\"a}vyys, kerrostenv{\"a}linen murtuminen, fibre metal laminates, hybrids, impact, impact resistance, debonding",

author = "Tuomas P{\"a}rn{\"a}nen",

year = "2016",

language = "English",

isbn = "978-952-60-7189-3",

series = "Aalto University publication series DOCTORAL DISSERTATIONS",

publisher = "Aalto University",

number = "262",

school = "Aalto University",

}

TY - THES

T1 - Low-velocity impact damage in fibre metal laminates - a study of the impact resistance and metal-composite debonding

AU - Pärnänen, Tuomas

PY - 2016

Y1 - 2016

N2 - Fibre metal laminates (FMLs) refer to a hybrid material concept that combines layers of thin metal sheets and fibre-reinforced plastics. This thesis concentrates on the damage characteristics of FMLs subjected to collision-type low-velocity impacts. The damage characteristics are studied by drop-weight impact and quasi-static indentation experiments and using finite element simulations. The work is divided into two parts. In Part I, specific interest is laid on the impact resistance of AZ31B-H24 magnesium alloy-based FMLs. The results indicate a disadvantage for the magnesium alloy, as the impact energy limits for metal cracking are significantly lower when compared to the state-of-the-art FML structure Glare 5 with 2024-T3 aluminium alloy layers. The main reason for the difference in cracking energies is concluded to result from the metal tensile response over the plastic region. The lower rate of strain hardening for the magnesium alloy enhances the local strain accumulation over the impact point, which leads to premature cracking. In addition, the impact damage process is experimentally studied in Part I by using a wide range of impact energies. The purpose of the damage process study is to gain an overall view of the impact damage evolution in FMLs. Finally, impacts on FMLs are studied via finite element simulations.Part II focuses on the debonding occurring in FMLs during impact loading, i.e. on the damage process along the metal-composite interface. The study reveals that the debond at the lowermost metal-composite interface forms in two stages. During the impactor loading phase, a debond tends to form as a fracture mode II cracking caused by out-of-plane shear forces. As the impactor rebound phase follows, the linear-elastic composite layers force the FML to straighten. On the contrary, the lowermost metal sheet has deformed plastically and tends to maintain its deformed shape. The discrepancy in the material response leads to peeling forces and consequently to fracture mode I dominated debonding. In the current literature, the debonding along the metal-composite interface is not commonly taken into account in the impact damage modelling of FMLs, and at times the debonding by shear forces is only considered. The energy absorption by the debonding may not be significant in the impact process, but the results of this thesis indicate that the debonding substantially affects deformations and the post-impact strain state. A realistic prediction of the post-impact damage state is especially important for successful investigations of damage tolerance. Therefore, a modelling methodology that takes into account the debonding with the described two-stage formation process defined in this thesis is suggested for future models.

AB - Fibre metal laminates (FMLs) refer to a hybrid material concept that combines layers of thin metal sheets and fibre-reinforced plastics. This thesis concentrates on the damage characteristics of FMLs subjected to collision-type low-velocity impacts. The damage characteristics are studied by drop-weight impact and quasi-static indentation experiments and using finite element simulations. The work is divided into two parts. In Part I, specific interest is laid on the impact resistance of AZ31B-H24 magnesium alloy-based FMLs. The results indicate a disadvantage for the magnesium alloy, as the impact energy limits for metal cracking are significantly lower when compared to the state-of-the-art FML structure Glare 5 with 2024-T3 aluminium alloy layers. The main reason for the difference in cracking energies is concluded to result from the metal tensile response over the plastic region. The lower rate of strain hardening for the magnesium alloy enhances the local strain accumulation over the impact point, which leads to premature cracking. In addition, the impact damage process is experimentally studied in Part I by using a wide range of impact energies. The purpose of the damage process study is to gain an overall view of the impact damage evolution in FMLs. Finally, impacts on FMLs are studied via finite element simulations.Part II focuses on the debonding occurring in FMLs during impact loading, i.e. on the damage process along the metal-composite interface. The study reveals that the debond at the lowermost metal-composite interface forms in two stages. During the impactor loading phase, a debond tends to form as a fracture mode II cracking caused by out-of-plane shear forces. As the impactor rebound phase follows, the linear-elastic composite layers force the FML to straighten. On the contrary, the lowermost metal sheet has deformed plastically and tends to maintain its deformed shape. The discrepancy in the material response leads to peeling forces and consequently to fracture mode I dominated debonding. In the current literature, the debonding along the metal-composite interface is not commonly taken into account in the impact damage modelling of FMLs, and at times the debonding by shear forces is only considered. The energy absorption by the debonding may not be significant in the impact process, but the results of this thesis indicate that the debonding substantially affects deformations and the post-impact strain state. A realistic prediction of the post-impact damage state is especially important for successful investigations of damage tolerance. Therefore, a modelling methodology that takes into account the debonding with the described two-stage formation process defined in this thesis is suggested for future models.

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KW - hybrids

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KW - iskunkestävyys

KW - kerrostenvälinen murtuminen

KW - fibre metal laminates

KW - hybrids

KW - impact

KW - impact resistance

KW - debonding

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