Influence of intralaminar discontinuity distribution on mechanical properties and damage evolution of unidirectional CFRP laminates

Intralaminar fiber discontinuities in unidirectional carbon fiber reinforced plastic (CFRP) laminates form resin-rich pockets that affect tensile response and damage evolution. This study examines how the distribution of these discontinuities influences the tensile behavior of laminates containing multiple resin pockets. Two configurations were investigated: Pattern I and Pattern II. Pattern I laminates featured both surface and internal resin pockets, with variations in the total number of plies and pocket spacing. In contrast, Pattern II laminates maintained a constant thickness while redistributing resin pocket plies throughout the laminate thickness. Tensile tests, combined with in situ edge optical observations, were conducted to characterize stiffness, maximum load, and damage progression. In Pattern I, increasing laminate thickness enhanced the maximum load but led to localized delamination and abrupt failure, which were associated with two dominant delamination surfaces. In Pattern II, redistributing resin pockets through the thickness altered delamination development, generally resulting in more distributed damage evolution, although localized failure occurred for specific configurations. Increasing resin pocket spacing improved the load-carrying capacity in both patterns. The results demonstrate that tensile performance and damage evolution are primarily governed by the through-thickness distribution and spacing of intralaminar discontinuities, rather than laminate thickness alone.