Pull-Out Performance of 3D Printed Composites with Embedded Fins on the Fiber
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Pull-Out Performance of 3D Printed Composites with Embedded Fins on the Fiber Johannes Liljenhjerte1 and S. Kumar1,2 1
Department of Mechanical and Materials Engineering, Masdar Institute of Science and
Technology, 54224, Abu Dhabi, UAE. 2
Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge,
MA 02139-4307, U.S.A.
ABSTRACT In this study, pull-out capacity of 3D printed composites are experimentally and computationally investigated. Cylindrical multi-material prototypes consist of a fiber embedded in a soft matrix. Embedded fiber has tiny orderly spaced geometrical features (fins) on its circumference over the bond length. Fins are either vertically aligned or inclined to the axis of the fiber (loading direction). Both fiber and fins are made of the same stiffer material, while the matrix is made of soft rubbery polymer. Pull-out performance of the samples were evaluated using tensile testing machine. It was found that orientation of the fins influences both the pull-out capacity and the effective stiffness of the interface. The pull-out capacity and stiffness response were found to increase by ~62 % and ~65.5 %, respectively, for a system with a volume fraction of 2.7 %, compared to a baseline design with no fins. In the later part of study, Finite Element (FE) simulations were performed for all prototypes. FE analyses indicate that the von Mises stresses at the interface between the matrix and fiber can be significantly reduced by the incorporation of fins. This study provides insight into the mechanics of stress transfer through the embedded fins, and the design aspects of the interface of fiber reinforced composites. INTRODUCTION Different modes of failure can occur in fiber reinforced composites. These include failure of inclusions, matrix, interfacial debonding, and a combination thereof. Generally the interphase/interface is structurally the weakest link in fiber reinforced composites, and therefore failure emanates at the locations of stress concentrations and then the damage propagates along the interface until complete debonding. Earlier studies demonstrate that tailoring the material properties of interlayer can significantly influence the interfacial strength and global load carrying capacity of multi-material structural systems [1-6]. The focus of this study is to design a geometrically engineered interphase region with an objective of optimizing the structural performance of fiber reinforced composites, with a particular focus on strength and stiffness. Properties of the interphase are tailored by introducing aligned geometrical features (fins) on the embedded fiber, so as to improve the interfacial stiffness and strength (see Figure 1).
a)
b) Tab for mounting Fiber with embedded fins Soft matrix Tab for mounting
Figure 1. a) Concept of the tailored interphase/interface, and b) Geometric model of a 3D printed specimen.
GEOMETRY AND MATERIALS Four different interphase designs were fabricated using a multi-material 3D printer. Fiber and fins were printed with th
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