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Ballistic impact performance of 3D woven aerospace composites was evaluated in a collaboration between Southwest Research Institute (SwRI) and Albany Engineered Composites (AEC). 3D woven preforms were manufactured with IM7 carbon fiber and injected with PR520 epoxy resin using a resin transfer molding (RTM) process. For comparison, a 2D laminated composite was manufactured from non-crimp fabric (NCF) using the same epoxy and injection processes. 7.62 mm (.30 caliber) fragment simulating projectiles (FSPs) were used to determine both the ballistic limits of the composites as well as the performance during secondary (repeated) impacts near the initial impact. Composites with 3D woven fiber reinforcement inherently do not experience any delamination and exhibit different failure behavior during impact events when compared to traditional 2D composites. This is due to the through-the-thickness fiber interlocking in the 3D woven preform and lack of distinct resin layers (lamina). Damage areas surrounding impact regions for both 3D and 2D composites were examined using microcomputed tomography. Measurements from targets after ballistic impact testing have shown that the 3D woven composite target resulted in nearly 70 % smaller damage area after both initial impact and secondary impacts when compared with a 2D laminated baseline composite. [ABSTRACT FROM AUTHOR]

Due the presence of through-thickness reinforcement which eliminates delamination, 3D woven composites have superior fracture toughness, fatigue life, and damage tolerance compared to laminated composites. Unlike 2D laminated composites which exhibit catastrophic failure typically through delamination, 3D woven composites exhibit a progressive damage behavior that leads to high specific energy absorption (SEA). Thus, enabling the manufacture of reduced weight structural components for energy absorption compared to traditional materials such as laminated composites or high strength metals. This is of particular importance for automotive applications, where weight reduction is sought through material change in vehicle components that play a critical role in crashworthiness. The rate dependent nature of these materials, however, is not well understood. The goal of this study was to experimentally compare the SEA of various 3D woven and 2D laminated composites manufactured with identical carbon fiber and resin that were tested under quasi-static and various dynamic crushing loads. In general, 3D woven composites were found to have higher SEA measures than 2D laminates, and orthogonal fiber topologies were found to have higher values than ply-to-ply interlocking configurations. All specimens tested displayed substantially reduced SEA for higher velocity impacts. Microcomputed tomography scans of tested samples were used to gain insight into energy absorption mechanisms in 3D woven composites. Finally, resin toughening was found to have a significant impact on SEA performance. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate the bearing/bypass interaction of a carbon fiber reinforced three-dimensional woven ply to ply composite. The composite was reinforced with a three-dimensional woven ply to ply preform and injected with PR520 epoxy resin using a resin transfer molding (RTM) process. The preform was woven with 24K IM7 carbon fiber tows in the warp and weft directions. Results of filled-hole tension and compression, single-fastener bearing, and double-fastener bearing are presented and discussed. All bearing experiments are single-shear and include supported single-fastener tensile and compressive loading, and supported double-fastener tensile and compressive loading. A 6.35 mm nominal diameter Hi-Lok steel alloy pin with an aluminum alloy collar was used for filled-hole tension and compression, as well as for all bearing experiments. The experimental study presented in this paper demonstrates that a practical bearing/bypass interaction diagram can be constructed for a three-dimensional woven composite using the same procedures and standardized test methods recommended in the literature for two-dimensional laminated composites. Representative stress-strain curves for filled-hole tension and compression are presented, as well as for single-fastener bearing and double-fastener bearing under tensile and compressive loading. Findings and practical recommendations on the bearing/bypass performance of the three-dimensional woven composite are also discussed. [ABSTRACT FROM AUTHOR]