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    Dynamic behavior of hemp based composite structures
    (Adana Alparslan Türkeş Bilim ve Teknoloji Üniversitesi, 2025) Çetin, Aykut; Kurtaran, Hasan
    This study investigated the free vibration behavior of hemp-based laminated composite structures through both numerical modeling and experimental investigation. The study includes two primary structural forms: curved composite beams and laminated rectangular plates. The main objective of the study was to assess the dynamic performance of pure and hybrid hemp fiber-reinforced composites and to evaluate the viability of hemp fibers as a sustainable alternative to conventional synthetic reinforcements, particularly glass fiber. The governing equations for the free vibration of curved beams and laminated plates were derived using the principle of virtual work within the framework of First-Order Shear Deformation Theory (FSDT). For laminated plates exhibiting large-amplitude vibrations, the equations were formulated based on nonlinear Green-Lagrange strain measures. Spatial derivatives in the vibration equations were computed using the Generalized Differential Quadrature (GDQ) method. To determine the mechanical properties, tensile tests were conducted on laminates reinforced with hemp, carbon, and glass fibers. Tensile and vibration test specimens were manufactured using the Vacuum-Assisted Resin Transfer Molding (VARTM) technique. First-mode natural frequencies and damping ratios were measured experimentally using a vibration test setup for nine different composite beams. The developed numerical models were validated through experimental testing and comparison with existing literature, showing a high degree of agreement and confirming the models' accuracy and reliability. After validation, a series of parametric studies was conducted to investigate the influence of curvature ratio, aspect ratio, stacking sequence, boundary conditions, and hybrid fiber configurations on the natural frequencies. The experimental and numerical findings revealed that, in terms of natural frequency performance, the pure carbon composite indicated the highest value. After pure carbon composites, a certain configuration of the carbon/hemp hybrid composites exhibited the highest natural frequency values, higher than the carbon/glass counterpart. CHHHC (C: carbon, H: hemp) and CHCHC stacking sequences consistently indicated higher frequency values than carbon/glass hybrid composites in various configurations, regardless of the boundary conditions. Overall, the results confirm that carefully configured hemp-based hybrid laminates offer promising frequency values for structural applications.