Modelling, Additive Manufacturing, and Testing of Knitted Materials

Abstract

Knitting is a centuries-old textile fabrication technique utilizing a method of “interlooping,” where loops are pulled through each other until the final product is created. Certain patterns curl in on themselves, which can allow for unique self-actuating properties. Though this property may be a nuisance for someone creating a textile that is intended to be flat, it can be manipulated by engineers to create self-supporting structures. While this manipulation has been proven with fabric samples, it has not been applied to more rigid materials, such as thermoplastics commonly used in 3D printing. This research will further explore fabricating knit specimens with 3D printing. The geometry of a knit stitch was established, then used to create a 3D model that can be duplicated to form a specimen of a stockinette pattern. This specimen was 3D printed without the need for support material. Several baseline specimens were fabricated using PLA with a consumer-grade 3D printer. Additionally, several specimens with altered parameters were fabricated to further characterize the behavior of an additively manufactured knit specimen. Additional parametric variation was provided by altering boundary conditions to allow or disallow contraction. The printed specimens were then tested in tensile extension or cyclic patterns with a universal testing machine. The results are presented and compared with load-extension graphs. The load-extension graphs of each specimen were compared, and it was noted that specimens exhibited energy dissipation and had anisotropic behavior.