Investigation on delamination behavior of additively manufactured Kevlar and carbon composites subjected to Mode‐II loading conditions

Abstract With increased design and manufacturing complexity of required components in various industries, additive manufacturing of composites shows great potential in the production of next‐generation lightweight structures. Fused filament fabrication (FFF) is one such method of composite fabrication where components are 3D printed by heating a filament material above its gel temperature and depositing it on previously printed layers. The composite components fabricated by FFF are known to be susceptible to delamination owing to weak interlayer adhesion. This experimental study is an attempt to understand the underlying interlaminar delamination phenomenon of FFF‐printed end‐notched flexure (ENF) composite specimens subjected to mode‐II loading conditions. The composite specimens are 3D printed by an industrial FFF printer utilizing micro carbon fiber infused Nylon aka Onyx as the base specimen material. Either Onyx, continuous carbon fibers, or continuous Kevlar fibers are used as interfacial materials for the current study. In addition, the ENF composite specimen arms are optimally reinforced with continuous carbon fibers in pre‐selected layers of the specimen. The first category of specimens comprising three different interface material configurations aims to understand the delamination behavior of Onyx layers with other Onyx layers or continuous fiber reinforced layers (Onyx//Onyx, Onyx//Kevlar, and Onyx//carbon). On the other hand, the second category comprising three other different interface material configurations aims to understand the delamination behavior of continuous fiber reinforced layers in the composite specimens (Kevlar//Kevlar, carbon//carbon, and Kevlar//carbon). In addition, the relative orientation of interfacial layers is also varied to investigate the effect of print orientation on the delamination behavior of ENF specimens. Digital image correlation (DIC) is employed to accurately quantify the extent of crack propagation by accessing full‐field shear strain distribution of the front face of specimens generated during a three‐point bend loading event under quasi‐static loading conditions. The resistance to crack initiation and propagation is observed to be highly dependent on interfacial layer materials and their relative orientation. Highlights Interlaminar fracture of additively manufactured composites under mode‐II loading. DIC technique is used for quantifying crack advancement during loading events. Twelve different interfaces of additively manufactured composites are analyzed. Effects of print orientation and interface material type are investigated. Delaminated surfaces are examined to correlate underlying fracture mechanisms.