3D failure analysis of UD fibre reinforced composites [Elektronische Ressource] : Puck's theory within FEA / by H. Matthias Deuschle

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• Publié par: universitat_stuttgart
• Publié le: 01 janvier 2010
• Nombre de lectures: 46
• Langue: Deutsch
• Poids de l'ouvrage: 9 Mo

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3D Failure Analysis of
UD Fibre Reinforced Composites:
Puck’s Theory within FEA
H. Matthias Deuschle
INSTITUT FÜR
STATIK UND DYNAMIK
DER LUFT- UND
RAUMFAHRTKONSTRUKTIONEN
UNIVERSITÄT STUTTGART
Bericht aus dem Institut
57-20103DFailureAnalysisof
UDFibreReinforcedComposites:
Puck’sTheorywithinFEA
AthesisacceptedbytheFacultyofAerospaceEngineeringandGeodesy
oftheUniversitat¨ Stuttgartinpartialfulfilmentoftherequirements
forthedegreeofDoctorofEngineeringSciences(Dr.-Ing.)
by
Dipl.-Ing. H.MatthiasDeuschle
borninKarlsruhe
Mainreferee: Prof. Dr.-Ing. habil. Bernd-HelmutKroplin¨
Co-referee: Prof. Dr. rer. nat. SiegfriedSchmauder
Dateofdefence: September6,2010
InstituteofStaticsandDynamicsofAerospaceStructures
Universitat¨ Stuttgart
2010Herausgeber: Prof. Dr.-Ing. BerndKroplin¨
D93
ISBN3-930683-99-7
¨Dieses Werk ist urheberrechtlich geschutzt.¨ Die dadurch begrundeten¨ Rechte, insbesondere die der Uber-
setzung, des Nachdrucks, des Vortrags, der Entnahme von Abbildungen und Tabellen, der Funksendung,
der Mikroverfilmung oder der Vervielfaltigung¨ auf anderen Wegen und der Speicherung in Datenverar-
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dieses Werkes oder von Teilen dieses Werkes ist auch im Einzelfall nur in den Grenzen der gesetzlichen
Bestimmungen des Urheberrechtsgesetzes der Bundesrepublik Deutschland vom 9. September 1965 in der
jeweils geltenden Fassung zulassig.¨ Sie ist grundsatzlich¨ vergutungspflichtig.¨ Zuwiderhandlungen unter-
liegendenStrafbestimmungendesUrheberrechtsgesetzes.
⃝c Institutfur¨ StatikundDynamikderLuft-undRaumfahrtkonstruktionen,
¨UniversitatStuttgart,Stuttgart,2010
Dieser Bericht kann uber¨ das Institut fur¨ Statik und Dynamik der Luft- und Raumfahrtkonstruktio-
nen, Universitat¨ Stuttgart, Pfaffenwaldring 27, 70569 Stuttgart, Telefon: [phone], Fax:
(0711)6856-63706,bezogenwerden.Preface
ThepresentworkistheachievementofmyactivityasaresearchassociatewiththeInstitut
fur¨ Statik und Dynamik der Luft- und Raumfahrtkonstruktionen (ISD) at the Universitat¨
Stuttgart. The completion of this dissertation has been possible thanks to the support of
manypeopleIwouldliketoacknowledge:
Neither the participation in the WWFE-II nor the present thesis could have been realised
without the continuous support of Professor Alfred Puck. The phase-wise daily coopera-
tionhasbeenofinestimablevalueforboth,mepersonallyandfortheproject. Thankyou
for your tireless effort to promote, generously share and impartially discuss your ideas.
Yourintellectualandliteralhospitalitywillbeashiningexampletome.
I am deeply indebted to Professor Bernd-H. Kroplin¨ who created and preserved an at-
mosphere of free thinking, mutual trust, independence and personal responsibility at his
institute. These values have turned out to be precious in times of an increasing economi-
sation and schoolification of the academic landscape. I am extremely grateful for the
opportunity to benefit from as well as to contribute to the character of his outstanding
institute.
SpecialthankstoGunther¨ LutzandtheInstituteofPlasticsProcessingatRWTHAachen
University who generously provided the opportunity to introduce myself to the ”Puck
community” in 2008. The daily backing of my ISD colleagues has however been just as
important. I am particularly grateful to Dr. Thomas Wallmersperger and Manfred Hahn
whohaverepeatedlydelveddeeplyintomynumericalandfracturemechanicalproblems.
Thankstothecolleagueswhomadetheefforttoinfluencemywayofthinkingandformed
the particular spirit of the ISD and to all undergraduate students who worked on relevant
subjectswithintheirtheses.
I wish to express particular gratitude to my parents for providing a loving and respectful
parental home. They have constantly striven to open new worlds of experience to me be-
sidesreliablyfundingmyeducation. Eventuallytheyhavehandedmeovertomypersonal
materialsscienceconsultant,mybelovedwifewhopatientlytakesexcellentcareofmein
allaspects.
Stuttgart,September2010
H.MatthiasDeuschleAbstract
Unidirectionally fibre reinforced composites (UD FRCs) are an aspiring material where
high strength, adjustable stiffness, extraordinary durability and low weight is required.
Theirlayer-wiseprocessing intolaminates enablestherealisationof complexgeometries
with locally strongly differing properties. The design concept of integral construction
makes use of this feature and combines different tasks in just one component. The in-
creasing proportion of integral components brings significant savings in terms of struc-
tural weight and maintenance cost of the overall system. This development is currently
opposed by an enormous experimental effort which comes along with the application of
FRCs. The dimensioning of FRC laminates in terms of stiffness and strength has only
hesitantly been included into efficient, computer-aided design processes. For the three-
dimensional prediction of failure and post-failure behaviour there is currently no failure
theory available, which would have been implemented into a powerful design tool like
FiniteElementAnalysis(FEA)uptoapplicationmaturity.
WithPuck’sfracturecriteriaforunidirectionallyfibrereinforcespolymercomposites(UD
FRPCs),however,thereisapersethree-dimensionalfailurehypothesis,whichhasproven
itscapabilityinthecaseofplanestatesofstressandwhichissuccessfullyappliedwithin
theaccordingrestrictions. Thepresentworkaimsontheverificationofthisfailuremodel
for a general three-dimensional load case, its appropriate extension and the combination
with the capabilities of a commercial FE software package. The result is an implementa-
tion which coversthe layer-wisefailure of a lamina and the successive damage evolution
within the laminate. Together with the interlaminar damage analysis which is already
comprised in such software packages, a comprehensive prediction tool for the damage
processinUDFRCcompositesisgenerated.
Thepresentworkcontainsproblemsandapproacheswhicharerelatedtotheachievement
of the above mentioned goal. Starting with the representation of the nonlinear consti-
tutive behaviour of an isolated lamina there occur specific three-dimensional problems.
For example the material bears much more shear load under hydrostatic pressure, than
comprisedintheuniaxiallydeterminedexperimentalstress-strainrelation. Suchcasesare
treated by the self-similar scaling of the e curves. Being a stress-based crite-
rion Puck’s Theory requires the full spacial stress tensor, as soon as a three-dimensional
prediction is striven for. It is shown that only few of the commercially implemented fi-
nite element formulations are capable of providing these results in the case of shell-likeviii
structures. The quality of the results is evaluated by means of the analytical solution
following Pagano. Puck’s criteria for fibre and inter-fibre fracture (IFF) include some
extensions which gain importance particularly in the three-dimensional stress case. The
influences of fibre-parallel stress on the inter-fibre fracture and vice versa are presented
in the present work and their fracture-mechanical basis is demonstrated. In particular the
influence of stresses, which are not acting on the fracture plane, strongly increases in the
three-dimensional case. The versatility of Puck’s inter-fibre fracture criterion is proved
byitsadjustmenttotheapplicationtoisotropicandnotintrinsicallybrittlematerials. Re-
garding the successive three-dimensional damage after the occurrence of an inter-fibre
fracture the existing degradation methods have been identified as insufficient. A fracture
angle-dependent approach is developed, which homogenises the effect of the fractures
and defines the impact on the several stiffnesses. Virtual material tests on representative
laminate sections which contain discrete cracks prove the applicability of the developed
relations. The described failure and post-failure degradation models are prepared for the
application within an implicit Finite Element Analysis. Their implementation into the
commercial software package ABAQUS is modular whereas the post-processing of con-
ventionallyderivedorexistingstressfieldsissufficientforapurefailureprediction. Only
if the post-failure degradation process is to be analysed, deeper manipulations of the FE
analysis in form of a user-defined material subroutine are necessary. The applicability
of the generated implementation is proved by the analysis of twelve test cases which are
provided by the second World Wide Failure Exercise (WWFE-II). The given test cases
comprisethefailureandpost-failureanalysisofpurematrixmaterial,ofisolatedlaminae
and of laminates subjected to three-dimensional load. All the test cases are treated with
an identical subroutine, hence with a single, consistent failure theory and the results are
interpreted regarding the actual material behaviour and the underlying failure prediction
approaches. It is shown that the application of Puck’s fracture hypotheses within a Fi-
nite Element Analysis is a versatile and efficient tool for the three-dimensional failure
predictioninUDFRClaminates.Zusammenfassung
Unidirektionalfaserverstarkte¨ Verbundwerkstoffesinduberall¨ dorteinzukunftstrachtiges¨
Material,wohoheFestigkeit,varia