Effects of automated fiber placement defects on high strain rate compressive response in advanced thermosetting composites

Abstract

The effects of fiber tow gaps, overlaps, and folds on the compressive strength of a fiber-placed composite laminate under dynamic loading conditions are investigated in this work. These layup defects were placed in the 0° fiber direction within a 24-ply quasi-isotropic laminate with a [45/0/–45/90]3S stacking sequence. Different locations of the defect were considered, namely near the bottom (in the 2nd ply), middle (10th ply) and top (23rd ply) of the laminate. High-strain rate compression experiments were conducted on composite that are pristine and with embedded defects using a split Hopkinson pressure bar (SHPB). The results were used to determine the strength knockdown due to the local changes in ply morphology because of fiber bed compaction in the presence of a layup defect. The experimental results revealed the anisotropy of in-plane strength coinciding with the deposited defect orientation. No significant variations in the residual strength were observed regarding the location of the defect (i.e., bottom, middle, or top) within the laminate. A morphological analysis based on microtomography of the cured defects indicates that the sources of the strength knockdown are due to the 0° ply drop-off, fiber misalignment in the adjacent 90° and 45° degree plies and the resin-rich region formed at the corner of the tapered 0° ply, between +45° and –45° laminas. The present study indicates the increased role of local morphological ply variations on the strength of composites under high-strain rate loading conditions, which should be considered during composite design.

Dynamic response of Advanced Placed Ply composites

“…This contrasts with AFP defects e.g. tow overlaps or tow gaps, which have been observed to reduce a composite's strength [47]. While overlaps and gaps are unpredictable features that occur randomly throughout a laminate, the through thickness undulations introduced by the AP-PLY process occur in a structured pattern and, more importantly, can be strategically distributed to improve the local damage tolerance of composite structures subjected to dynamic loads.…”

Effect of Resin Bleed Out on Compaction Behavior of the Fiber Tow Gap Region during Automated Fiber Placement Manufacturing

“…Manufacturing features, such as voids and resin-rich regions, develop when plies neighboring to the gap tow sink into the gap and experience large non-linear deformation caused by the flow of liquid resin into the empty space ( Figure 1 ). Previous reports show that AFP manufacturing defects created during the early stages of cure before resin gelation can significantly affect the mechanical properties of the composites [ 8 , 9 , 10 ]. These regions with irregular morphology can serve as weak points and reduce the strength [ 11 , 12 , 13 ].…”