The free vibrations of laminated composite plates: Experimental-numerical investigation

Abstract

Glass fiber-reinforced epoxy (GFRE) laminated composite plates are studied for free vibration to establish precise structural scaling laws under fully clamped-edge conditions. Using an epoxy matrix, 2.8-mm-thick composite plates with glass fibers were fabricated with varied longitudinal orientations. Separating mechanical testing tracks under strict ASTM D3039/D3039M-17(2025) (Tensile Properties) and ASTM D3518/D3518M-18(2025) (Shear Modulus) standards and using non-contact 2D digital image correlation (DIC) full-field strain mapping yielded in-plane orthotropic material constants. Vibration testing employed the natural frequency to assess how vibrations influenced fiber orientation and composite plate length, symmetric [90°/0°/0°/90°] and anti-symmetric [90°/0°/90°/0°], square, and 100, 200, and 300 mm long. A custom MATLAB FEM script using a C 1 -continuous 4-node quadrilateral thin-plate element formulation was created for a quick solution. Mechanical observations and computational estimates converged well, with absolute fundamental frequency variances ranging from 0.002 to 0.074 Hz. Fiber orientation sequences and aspect scaling ratios greatly affect structural natural frequencies. This study is new because it directly, uncoupledly translates full-field optical DIC kinetics into the discrete matrices of an independent, commercial-free structural dynamics algorithm, offering a reliable predictive workflow for initial structural design and resonance tuning.