Numerical simulation of chopped fiber interlaminar toughening of flax fiber/epoxy composites

Abstract

Flax fiber/epoxy composites have attracted extensive attention in aviation applications due to the advantages of low density，remarkable mechanical properties and environmental friendliness. However，the interface compatibility between hydrophilic flax fiber and hydrophobic epoxy resin matrix is poor, which makes the lamination resistance of the composite insufficient, and affects the bearing capacity and service life of the material. Chopped fiber interlaminar toughening is an effective method to improve the interlaminar fracture toughness of composites. Besides，the numerical simulation based on cohesive zone models has also become an effective tool for analyzing interlaminar toughening in the composites. In this study，three different cohesive zone models，including bilinear，exponential and trilinear cohesive zone laws，are used to simulate the mode Ⅰ interlaminar fracture behavior of chopped aramid fiber interleaved flax fiber/epoxy composites. The numerical results are analyzed and compared with the double cantilever beam（DCB）experimental results and digital image correlation（DIC）observations，summarizing the influence of different cohesive zone laws. The results show that bilinear and exponential cohesive zone models are unsuitable for simulating the interlaminar toughening effect of chopped fiber interleave due to the numerical results with no laddered or fluctuated descent. The trilinear cohesive zone model can effectively present the chopped fiber interlaminar toughening effect and behavior by including the toughening effects of fiber bridging and matrix failure so that fiber bridging failure mode and crack propagation behavior are similar to those observed with the DIC method. This research provides a rational basis for the chopped fiber interlaminar toughening design of flax fiber/epoxy composites.

Keywords

• flax fiber composites
• chopped fiber interleave
• interlaminar toughening
• cohesive zone model
• fiber bridging