Fiber Angle influence and Toughness characterization of bioinspired discontinuous fiber helicoids composite materials produced via additive manufacturing

Abstract

Over millennia nature has produced composite materials with excellent mechanical properties compared to the low properties of their base materials and has managed to obtain a good compatibility between stiffness and toughness; as a result, they are a good source of inspiration for material optimization for applications, such as increasing toughness and damage resistance, something that is difficult in conventional engineering materials. Nowadays eight structural elements are identified in biological materials: fibrous, helicoidal, gradients, layered, tubular, cellular, suture, and overlapping. Helical structures consist of stacks of ordered fibers that form layers that are rotated at a constant angle of inclination. These include plywood and Bouligand structures. Bouligand structures consist of an arrangement of fibrous laminates that completes a 180° turn and provides some biological materials with increased strength and toughness in multiple directions and exceptionally high fracture toughness. The classical composite materials mechanics provides some constitutive model approximations for this type of materials, but they still need to be studied and tested to properly understand their behavior. Injection molding, compression molding, hand layup, resin transfer molding, filament winding, pultrusion, and automated fiber placement are just a few of the traditional methods used to make fiber-reinforced polymer composites (FRPC). However, these traditional manufacturing techniques have a restriction on specific fiber alignment and demand expensive molds, dies, or lithographic masks. Additive manufacturing has the potential to replace many conventional manufacturing processes due to its ability to create complex geometries with customizable material properties and employ several materials simultaneously, among other things. Fused deposition modeling (FDM) is the most widely used manufacturing additive technique for manufacturing FRPC due to its low cost, low energy input, material consumption, and operation simplicity. This work presents three-dimensional models mimicking the Bouligand structures by turning the pitch angle of the layers and a analytical models comparison were made. The specimens were fabricated using the FDM technique. A thermoplastic polyurethane (TPU) was used for the matrix and polylactic acid (PLA) for the fibers. Tensile tests were used to mechanically characterize both the raw materials and the manufactured composites to examine the impact of the helical angle and the contribution of the matrix and fiber materials to the stiffness and toughness of the composite. Experiments and analysis revealed that high rotation angles improve the stiffness, strength, and toughness of the composite.