Bouleni delaminovanych kompozitnich desek

Buckling and postbuckling of delaminated composite plates

dissertation

en

Buckling and postbuckling behaviour of a composite plate can be significantly influenced by the presence of delaminations, i.e. by regions where connectivity between layers is lost. Therefore, the aim of this work is to extend our knowledge about the buckling of delaminated plates, especially about the behaviour of plates with multiple delaminations and plates with delaminations which have irregular shape, because such damage more closely reflects the true nature of low-velocity impact induced damage in laminated plates. The thesis consists of three main parts. The first part comprises of the summary of analysis techniques used to investigate the behaviour of delaminated plates and presents the main results of the studies on the buckling of delaminated plates. A brief discussion of limits of computational analyses is also included. In the second part of the thesis, the computational model used to analyse the behaviour of delaminated plates is presented. The capability of the model to predict the postbuckling behaviour of delaminated plates is illustrated on several verification studies based on experimental and numerical analyses found in literature. Finally, in the third part, three studies on the buckling of plates with multiple delaminations and one study on the buckling response of plates with a delamination of an arbitrary shape are presented. Effects of several parameters on the buckling response such as ply orientation, number of delaminations, their shape and orientation, out-of-plane and in-plane position are discussed. Some implications of the studies for the design praxis are formulated.

Chování laminátových desek namáhaných na tlak ci na smyk muže být výrazne ovlivneno prítomností delaminací, tedy oblastí, kde je porušena vazba mezi sousedními vrstvami. Cílem této práce je rozšírit znalosti o chování delaminovaných desek, a to predevším o chování desek s vetším poctem delaminací a desek s delaminacemi libovolného tvaru, nebot taková podoba porušení laminátu více odpovídá poškození vznikajícího v dusledku nízkorychlostního dopadu cizího telesa na laminátovou desku. Disertacní práce se skládá ze trí hlavních cástí. V první cásti jsou strucne nastíneny postupy využívané pri analýze boulení delaminovaných desek a jsou diskutována omezení techto analýz. Dále jsou v této cásti shrnuty hlavní poznatky o boulení delaminovaných desek. V druhé cásti práce je popsán výpoctový model použitý v rámci disertacní práce pro analýzu boulení delaminovaných desek. Schopnost modelu predpovedet chování delaminovaných desek je pak dokumentována na nekolika overovacích úlohách. Tretí cást disertacní práce se skládá ze trí samostatných studií chování desek s nekolika delaminacemi eliptického ci kruhového tvaru a jedné studie zabývající se možností náhrady obecného tvaru delaminace kruhem ci elipsou. Je probírán vliv rady parametru na chování delaminovaných desek, konkrétne vliv orientace vrstev laminátu a dále vliv poctu, tvaru, orientace a umístení delaminací. Na základe techto studií jsou pak zformulována doporucení ohledne postupu pri posuzování únosnosti delaminovaných konstrukcí.

Buckling and postbuckling behaviour of a composite plate can be significantly influenced by the presence of delaminations, i.e. by regions where connectivity between layers is lost. Therefore, the aim of this work is to extend our knowledge about the buckling of delaminated plates, especially about the behaviour of plates with multiple delaminations and plates with delaminations which have irregular shape, because such damage more closely reflects the true nature of low-velocity impact induced damage in laminated plates. The thesis consists of three main parts. The first part comprises of the summary of analysis techniques used to investigate the behaviour of delaminated plates and presents the main results of the studies on the buckling of delaminated plates. A brief discussion of limits of computational analyses is also included. In the second part of the thesis, the computational model used to analyse the behaviour of delaminated plates is presented. The capability of the model to predict the postbuckling behaviour of delaminated plates is illustrated on several verification studies based on experimental and numerical analyses found in literature. Finally, in the third part, three studies on the buckling of plates with multiple delaminations and one study on the buckling response of plates with a delamination of an arbitrary shape are presented. Effects of several parameters on the buckling response such as ply orientation, number of delaminations, their shape and orientation, out-of-plane and in-plane position are discussed. Some implications of the studies for the design praxis are formulated.

Lamináty, ztráta stability, boulení, delaminace, výpoctová analýza

Laminates, buckling, postbuckling, delamination, computational analysis

02.11.2010

Brno