Influence of graphene reinforcement distribution on thermomechanical instability and vibration of delaminated structures
Creators: Nikrad, Seyed Farzad
Publisher: name: University of Alberta Library
Year: 2024

<p>Over the last two decades, the realm of nanoscience has experienced exceptional expansion, positioning nanotechnology at the forefront of advancements across various sectors such as computing, sensors, biomedicine, and a plethora of additional applications. Within this landscape, the identification and incorporation of graphene into polymer nanocomposites mark a pivotal advancement in nanoscience. Graphene, characterized by its single layer of carbon atoms arranged in a hexagonal lattice, is renowned for its array of extraordinary attributes.<br>
     Research into functionally graded graphene-reinforced composite (FG-GRC) laminated plates has revealed significant limitations, especially in understanding how interlaminar defects and delamination affect their thermal postbuckling performance and overall instability responses. While the addition of graphene is proven to increase the stiffness and strength of polymeric composite laminates, delamination remains a major obstacle, jeopardizing these improvements. The first two chapters of this thesis thoroughly explores the challenges of graphene distribution within the laminates, highlighting those inconsistencies in the structural integrity and mechanical performance of materials caused by delamination areas and can lead to unexpectable buckling mode shapes under different scenarios.<br>
     In the first chapter, this study conducts a thorough assessment of how diverse distributions of graphene reinforcement can counteract the negative effects of delamination, employing a refined semi-analytical strategy that leverages the third-order shear deformation theory (TSDT) and the Rayleigh-Ritz approximation method. This approach enables to investigate the complex delamination cases, moving from basic shape assumptions in the past to circular and elliptical shapes of delamination. The study provides insights into local and global buckling in composite delaminated plates, focusing on how graphene distribution patterns, delamination configurations, and external conditions impact thermal instability responses. Chapter two delves into how graphene distribution affects the energy release rate (ERR) around delamination edges in graphene-reinforced laminates. It examines multiple delamination scenarios, which partition the laminate into segments with varied graphene reinforcement patterns. This analysis is key to understanding how these patterns influence the laminate&#39;s vulnerability to delamination by studying the ERR across different regions.<br>
     Moreover, this chapter seeks to understand the effect of both symmetrical and asymmetrical graphene distribution patterns, in conjunction with specific delamination configurations, on the fundamental frequencies of FG-GRC plates in both pre- and post-buckled thermal states, highlighting the complex interplay between material distribution, structural imperfections, and their combined effects on the performance of the laminated plate.<br>
     Recent advancements in manufacturing technologies have transformed the fabrication of composite laminates. This innovation offers enhanced design flexibility, customization options, and improved production efficiency. The integration of advanced manufacturing with composite materials has opened up new possibilities for constructing complex and functional engineering structures with unique material characteristics, such as thin-walled composite laminated struts. Nonetheless, it is crucial to consider local buckling as a pivotal design factor for these types of structures, regardless of their cross-sectional shape.<br>
     The final two chapters of this thesis introduce a novel study on the application of graphene sheet reinforcements within composite laminated channel section structures, one of the most practical types of the thin-walled struts. This investigation aims to determine how the integration of graphene, in a variety of symmetric and asymmetric patterns, can enhance the structural performance of channel section struts when subjected to compressive mechanical and thermal loading, while eliminating the need for additional intermediate stiffeners. <br>
     The method used to study the instability and thermally induced vibration of FG-GRC channel section struts employs the von Karman geometrical nonlinearity and relies on the layerwise, third-order shear deformation theory (LW-TSDT). For the purpose of confirming the precision of the outcomes derived from the LW-TSDT and assessing its computational efficiency, a three-dimensional (3D) finite element model is constructed for comparison, utilizing ABAQUS software.<br>
     This thesis delivers pivotal numerical insights for solid mechanic designers, highlighting the critical need to weave these findings into their design simulations for augmented performance and enhanced reliability. Specifically, it was found that the application of the FG-X graphene distribution pattern in channel section struts increases their critical buckling resistance by 30%, whereas the FG-O pattern leads to a reduction of about 26% when compared to a uniform graphene dispersion. These results highlight the critical impact of graphene distribution on the mechanical integrity and buckling resilience of composite materials, stressing the value of optimizing material distribution.</p>