Aim of this thesis is to study the mechanical behavior of undamaged and delaminated GFRP specimens to evaluate the effect of defects in a quantitative way. With this aim, experimental tests will be carried out on specimens containing a pre-delaminated region obtained by placing a Teflon layer during manufacturing, to avoid complete resin adhesion. In this way, an artificial controlled delamination is created, similar in all the specimens. The mechanical parameter that has been determined is the stress of damage initiation. This stress is obtained by means of stepwise fatigue load tests monitored by thermal camera. The damage stress of a glass/epoxy composite, as well as the identification of crack initiation and evolution, are evaluated through different thermographic techniques, i.e. by analyzing the surface temperature of the specimen. These techniques are based on the analysis of the temperature amplitude and phase. In order to further investigate the damage evolution into the material, in parallel to experimental tests, simulations of the delaminated specimens are run with the finite element software Abaqus. The implementation of a delamination requires the application of the cohesive elements, that are particular finite elements with the possibility of offering a local variation in stiffness. The models will be calibrated based on the results of the experimental tests. These models can be used to extrapolate the mechanical characteristics of the composite, as well as they can be used for the structural design of composite structures.
Meccanica del comportamento di campioni GFRP non danneggiati e delaminati per valutare l'effetto dei difetti in modo quantitativo. A tal fine, verranno effettuati test sperimentali su campioni contenenti una regione pre-delaminata ottenuta dallo strato di Teflon durante la produzione, per evitare l'adesione completa della resina. In questo modo, viene creata una delaminazione controllata artificialmente, simile in tutti i campioni. Il parametro meccanico che è stato determinato è lo stress dell'iniziazione del danno. Questo stress si ottiene per affaticamento graduale. Lo stress da danno di un composito vetroso / epossidico, così come l'identificazione dell'inizio e dell'evoluzione della cricca, sono valutati attraverso diverse tecniche termografiche, cioè analizzando la temperatura superficiale del campione. Queste tecniche si basano sull'analisi dell'ampiezza e della fase della temperatura. Per studiare ulteriormente l'evoluzione del danno nel materiale, le simulazioni dei campioni delaminati vengono eseguite con il software degli elementi finiti Abaqus. L'implementazione degli elementi coerenti, che sono particolari elementi finiti con la possibilità di una variazione locale di rigidità. I modelli saranno calibrati sulla base dei risultati dei test sperimentali. Questi modelli possono essere utilizzati per estrapolare le caratteristiche meccaniche del composito e possono essere utilizzati per la progettazione strutturale di strutture composite.
Thermographic monitoring and numerical analyses of GFRP delaminated specimen
BHUJANGRAO, DHAWALE TRUNAL
2017/2018
Abstract
Aim of this thesis is to study the mechanical behavior of undamaged and delaminated GFRP specimens to evaluate the effect of defects in a quantitative way. With this aim, experimental tests will be carried out on specimens containing a pre-delaminated region obtained by placing a Teflon layer during manufacturing, to avoid complete resin adhesion. In this way, an artificial controlled delamination is created, similar in all the specimens. The mechanical parameter that has been determined is the stress of damage initiation. This stress is obtained by means of stepwise fatigue load tests monitored by thermal camera. The damage stress of a glass/epoxy composite, as well as the identification of crack initiation and evolution, are evaluated through different thermographic techniques, i.e. by analyzing the surface temperature of the specimen. These techniques are based on the analysis of the temperature amplitude and phase. In order to further investigate the damage evolution into the material, in parallel to experimental tests, simulations of the delaminated specimens are run with the finite element software Abaqus. The implementation of a delamination requires the application of the cohesive elements, that are particular finite elements with the possibility of offering a local variation in stiffness. The models will be calibrated based on the results of the experimental tests. These models can be used to extrapolate the mechanical characteristics of the composite, as well as they can be used for the structural design of composite structures.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/140006