Effect of fiber discontinuity on mechanical properties of interlaminar-toughened CFRP laminates

Abstract

In fabricating complicated laminated composite structures by using prepregs, various kinds of fiber discontinuities such as ply drop-off and seams can be formed. Special care must be taken for the fiber discontinuity since they can induce stress concentration, and damage onset and growth originated from them may lead to catastrophic failure of the structure. The present study evaluates mechanical behaviour in unidirectional CFRP laminates that contain centered or dispersed fiber discontinuities fabricated by using interlaminar-toughened CFRP prepregs. Tensile testing has shown that higher onset stress of the interlaminar delamination between continuous and discontinuous plies can be achieved by interlaminar-toughened CFRP with centered fiber discontinuity compared to that for conventional CFRP prepregs. As for the specimen with dispersed fiber discontinuities, fracture stress keeps almost constant with more than 20 mm of interval of the dispersed fiber discontinuities. By applying the onset stress of the delamination that is experimentally obtained using centered discontinuity to an analytical model, critical energy release rate by the delamination onset is calculated. Then it is indicated that one can predict the fracture stress of the specimen with the dispersed fiber discontinuities with more than 20 mm interval of the discontinuities by using the critical energy release rate. This indicates that fracture of the laminate is dominated by the interlaminar delamination between discontinuous plies with more than 20 mm of interval.

Exploration of impact response and damage mechanism of discontinuous CFRP laminates subjected to low velocity impact

“…That is, the discontinuous structure can avoid the specimen bearing a higher load for reducing the damage under a low energy impact. 14,20 According to the mechanical response of the specimen under impact with an energy of 12 J, the specimen with a discontinuous structure shows a greater deformation for reducing the damage under the action of the impactor (Figure 5D). Further, a discontinuous structure also shows a good effect on the restraining crack growth as displayed in Figure 7.…”

“…[16][17][18] The rapid transfer of stress in the direction of the fiber arrangement can be blocked to some extent by interfaces, which suppress the damage among layers and reduce delamination. 14,19,20 Inspired by this, some researchers introduced discontinuous structures to design a structure resembling a nacre material. [21][22][23] Discontinuous structures were introduced into unidirectional continuous fiber reinforced composites, and it exhibited a significant nonlinear response under tensile stress.…”

“…Further, the energy is absorbed by a large number of interfaces when subjected to damage, which continuously decay the destructive force, transforming and absorbing the stress 16–18 . The rapid transfer of stress in the direction of the fiber arrangement can be blocked to some extent by interfaces, which suppress the damage among layers and reduce delamination 14,19,20 . Inspired by this, some researchers introduced discontinuous structures to design a structure resembling a nacre material 21–23 …”

Measurement of microscopic strain distributions of CFRP laminates with fiber discontinuities by sampling moiré method

“…This leads to component failures through delamination and/or failure of resin. Some studies have investigated the mechanical properties and damage behaviors in laminates with fiber discontinuity [10][11][12][13][14][15][16][17]. These works analytically evaluated the strain/stress distributions around the fiber discontinuous area(s) where some of them introduced cracking prediction methods for the composite laminates.…”

“…This was done to investigate the deformation behavior that caused the damage due to fiber discontinuity in these laminates. A UD laminate, with its simpler damage behavior compared to other laminate configurations, was used to acquire a deeper understanding based on previous efforts on material characterization [10][11][12][13].…”