Study of the dynamic response of composite laminates for the evaluation of the material elastic constants

The following study investigates the dynamic response and mechanical elastic properties of four different composite materials: flax fiber with epoxy resin, carbon fiber with epoxy resin, and two types of glass fiber composites — one with an inorganic resin and the other with a 30% organic resin component. The primary objective is to characterize the elastic moduli and damping coefficients of these composites at varying temperatures. Utilizing the impulse excitation method, the natural frequencies of the composites were measured and analyzed according to the ASTM E1876-21 standard to evaluate the longitudinal modulus E1 and the shear modulus G12. To enhance the accuracy of these evaluations, the coefficients of thermal expansion (CTEs) in three directions were also evaluated by directly measuring strains of each composite during a typical thermal expansion. This allowed for the separation of the thermal effects on the composite expansions from the mechanical properties, ensuring precise determination of the moduli under thermal variations. Additionally, the study examines the impact of 70 ℃ distilled water aging on the mechanical properties of the composites. Specimens were submerged in distilled water for 7 and 13 days in accordance with the ASTM D570 standard, followed by a reevaluation of their mechanical properties. The study revealed significant insights into the changes in elastic moduli and damping coefficients due to both temperature variations and aging in water. The results of this research provide a comprehensive understanding of the dynamic behavior and durability of these composite materials, contributing to their potential applications in various engineering fields, particularly the automotive one.