Carbon Fiber Composite Cellular Structures

Abstract

Ultralight sandwich panel structures which utilize light, stiff, and strong face sheets, and stiff, strong, compressible cellular cores have attracted significant research interest for use in aerospace and energy absorption applications. The cores of these sandwich structures are typically fabricated using high strength cellular materials, such as aluminum and titanium alloys, or polymer foams and honeycombs. However, for weight sensitive, ambient temperature applications, carbon fiber composites have emerged as a promising material due to its high specific strength and low density. Carbon fiber reinforced polymer (CFRP) composite cellular materials, when combined with structurally efficient sandwich panel designs, offer new opportunities for fabricating ultralight structures. This dissertation explores carbon fiber and carbon fiber hybrid sandwich panel design concepts, details the novel fabrication methods which have been developed for these structures, investigates the mechanical performance of the structures made using these approaches, and develops micromechanical models which predict the relationships between the mechanical properties of these structures and parent material properties, unit cell topology, and core density.The dissertation develops four fabrication approaches for making carbon fiber and carbon fiber hybrid sandwich structures. These include a mechanical snap fitting and adhesive bonding method, a braided carbon fiber net method, a simplified linear braid approach, and a pultruded rod/linear tow technique. CFRP lattice structures made from carbon fiber laminates using a mechanical snap-fitting and adhesive bonding technique have been found to have high strength in through-thickness compression and in-plane iii shear. However, under compression or shear loading, these structures typically fail abruptly, exhibiting little ability to support load after initial strut failure. The trusses are also brittle, and absorb little energy during impact. The braided net fabrication approach utilizes a braided carbon fiber net within polymer and syntactic foams to form the core, woven carbon fiber face sheets, polymer and syntactic foam molds, and Kevlar stitching of core to the face sheets, followed by vacuum assisted resin transfer molding. This approach has facilitated the fabrication of empty lattice (truss and face sheet only) and hybrid core specimens ranging in density from 35 -478 kg/m 3 , and the mechanical performance of these structures characterized. The cellular structures made using this approach have been shown to have high compressive and shear strengths, as well as excellent energy absorption capacity. The linear braid method represents a simplified fabrication approach which utilizes linear braids to form the trusses within a hybrid cellular material. This method has facilitated the manufacture of hybrid cellular materials with a truss volume fraction ranging from 1.5 -17.5% of the core. The fraction of the truss contained in the nodes is found to lead to saturation in core streng...

Experimental Investigation and Simulation of 3d-Printed Lattice Structures

“…Cellular structures are classified by their inner topology and are thus considered either as stochastic or as ordered. They can be further differentiated in open or closed cell types [1]. Ordered materials generally have better mechanical properties, high surface area densities and lower pressure drops when compared to stochastic structures.…”

“…Lattices have a trusslike structure with interconnected struts and nodes in a threedimensional space [3]. They consist of repeating unit cells, which have periodicity in three dimensions [1]. The differences in performance come from a different deformation behaviour.…”

Investigating the low-velocity impact behaviour of sandwich composite structures with 3D-printed hexagonal honeycomb core—a review

“…Energy absorption can be achieved in sandwich panel structures using light, rigid, resilient face sheets, and strong compressible cell cores [33]. The mechanism demonstrates that the ability to absorb energy originates from the continuous deformation (plastic strain, collapse, and fracture) of cell walls under impact [60].…”

Overview and comparison of modelling methods for foams

“…In general, cellular materials can be divided according to their microstructure in irregular and regular structures (Figure 2). 27 Cellular materials with an irregular structure are called foams. They exhibit a stochastic/random architecture.…”