Mode-I interlaminar fracture behavior of additively manufactured continuous carbon and Kevlar reinforced composites

Additive manufacturing aka 3D printing of components utilizing continuous fiber reinforcement is gaining widespread popularity owing to their superior performance, weight saving, low labor and equipment costs, and producing complex shaped objects. However, 3D-printed composites are known to be susceptible to weak interlayer adhesion and layer delamination. Therefore, it is imperative to comprehend the delamination behavior of 3D-printed composite specimens to address the broader applications of additive manufacturing. This article is aimed at experimentally investigating the mode-I interlaminar delamination behavior of 3D printed composite materials having different interface (I/F) materials and orientations. Chopped micro carbon fiber infused Nylon (R) (aka Onyx) is taken as base specimen material. Additionally, specimen arms of the Double cantilever beam (DCB) composite specimens are 3D printed by utilizing an industrial fused deposition modeling (FDM) printer and their arms are optimally reinforced by continuous carbon fiber layers In addition, continuous Kevlar and carbon fibers are utilized as I/F layer materials. This study attempts to investigate a total of six different I/F material configurations by systematically subcategorizing them in two sections. The three specimens considered in first category are dedicated to investigating the interlayer adhesion and delamination behavior of Onyx layer with adjacent Onyx layer of continuous fiber reinforced layer (Onyx//Onyx, Onyx//Kevlar, and Onyx//carbon). Whereas the remaining three specimen types of second category are dedicated to investigate interlayer adhesion and delamination behavior of continuous fiber reinforced layers only (Kevlar//Kevlar, carbon//carbon, and Kevlar//carbon). Additionally, the print orientation of the I/F layers is also varied to understand the change in delamination behavior of longitudinally and transversely printed I/F layers. The fracture toughness of the specimens is evaluated in terms of strain energy release rate by utilizing the modified beam theory (MBT). Pure Onyx I/F layers are observed to resist crack propagation with maximum resistance owing to excellent interlayer adhesion. The introduction of continuous fibrous layers is observed to reduce the resistance to crack propagation marginally. Additionally, the resistance to crack propagation is observed to be marginally better for transversely printed I/F layers than the longitudinally printed layers.