Compressive buckling of variable stiffness laminated beams with delamination defects

Abstract Fiber reinforced polymer (FRP) structures in practical applications inevitably contain some micro‐defects, which are susceptible to result in the degradation of the mechanical properties, and even lead to structural instability. A series of variable stiffness (VS) specimens are prepared and applied to 4‐point bending (4P‐bending) experiments and uniaxial compressive (UC‐buckling) experiments to investigate the influence of curvilinear paths of towpregs on the buckling performance of laminated beams. By calculating the equivalent flexural stiffness (EFS) analysis of VS laminated beams, an analytical method is proposed to study the effects of the design parameters on the bending and buckling performances of laminated beams with or without delamination. A variable, the loss rate of the stiffness, is introduced and formulated to quantitatively analyze the degradation process of each VS specimen in terms of flexural stiffness. With buckling shape images obtained from UC‐buckling tests, the changes from unilateral buckling to bilateral buckling that occurred on VS specimens were captured and compared. The results show that the advantages of VS design on improving the damage tolerance capability of laminated structures. Compared with the traditional constant stiffness (CS) specimens, the specially designed VS specimens have increased their bending stiffness and structural stability by 21.8% and 24.36%, respectively. Highlights A method is proposed to analyze the flexural stiffness distribution. The concept of equivalent flexural stiffness is introduced and formulated. The evolution of buckling behaviors occurred on VS beams are characterized. Most VS specimens have a better tolerance to delamination damages.