Low-velocity impact size effect of carbon fiber composite laminates: Experimental and mechanism research

• The size effect has a significant influence on the LVI response of laminates. • In-plane size increases, characteristic curves growth slowly at impact initial stage. • Large in-plane size makes LVI energy consumed by elastic deformation, reduce damage. • Greater thickness causes matrix damage and delamination damage expansion with impact. The low-velocity impact (LVI) response characteristics of carbon fiber composite laminates under the influence of the size effect was investigated. Firstly, LVI experiments were conducted on composite laminates with varying in-plane dimensions and thicknesses under different impact energies to analyze their LVI response patterns. Secondly, non-destructive testing methods were utilized to examine the surface and internal damage conditions of the laminates, elucidating the LVI damage response characteristics influenced by the size effect. Finally, high-speed imaging and scanning electron microscopy (SEM) techniques were employed in conjunction to reveal the underlying mechanisms of the size effect during LVI on composite laminates. The findings indicate that under identical impact energy conditions, as the in-plane dimension of the laminate increases (with constant thickness), the peak force and absorbed energy progressively decrease, while the maximum displacement increases. Additionally, the degree of surface damage diminishes, and the projected area of internal damage reduces and becomes more concentrated near the impact surface in the depth direction. As the thickness of the laminate increases (with constant in-plane dimension), the peak force and the slope K value of the Displacement-Time curve increase, whereas the absorbed energy initially decreases and then slightly rises, the maximum displacement decreases, the degree of surface damage weakens, and the projected area of internal damage expands. An increase in the in-plane dimension of the laminate facilitates the absorption and dissipation of impact energy through elastic deformation, thereby reducing the extent of internal damage. Meanwhile, an increase in laminate thickness enhances the likelihood of matrix damage and delamination damage propagation. The initiation and propagation of damage across multiple layers of the matrix absorb a significant portion of the impact energy, consequently mitigating fiber fracture damage.