| dc.description.abstract | Throughout the aerospace industry, carbon fiber reinforced polymer (CFRP) laminated composites are used extensively in spacecraft and aircraft vehicles due to their high specific strength and stiffness and other properties. Processing these advanced structural CFRP composites, especially in prepreg form, is often completed via autoclaves where elevated temperatures and pressures of typically 180 ◦C (350 ◦F) and 0.7 MPa (7 bars), respectively, are applied to cure the polymer matrix and compress the constituent laminae together. However, autoclaves are energy intensive, expensive, and impose geometrical constraints on components due to thermal gradients within the chamber. Thus, there exists a need to find alternative manufacturing techniques. Throughout this thesis, an alternative method to autoclave processing is presented using vacuum-bag only (VBO) techniques with nanoporous networks (NPNs) in the interlaminar regions in autoclave-required epoxy prepreg CFRP composites. Nanoporous materials are defined as materials containing pores in the mid nanometer to low micrometer range. Once placed in the interlaminar region of the laminate, voids are reduced by the induced capillary pressures of the NPNs, and trapped gas evacuates through the NPN. By utilizing capillary flow porometry, capillary pressure and through-thickness permeability are quantified for various NPNs, along with other porous materials. Capillary pressure and permeability exhibit an inversely proportional relationship for all tested materials with CNT-based and polymer aerogel NPNs providing capillary pressures higher than an autoclave pressure of 0.7 MPa. Accordingly, an Ashby-type plot is presented as an aid for NPN selection for composites manufacturing. Previous studies of unidirectional glass fiber reinforced polymer (GFRP) composites and unidirectional CFRP composites show success with NPN-enabled VBO-manufacturing using aligned carbon nanotubes (A-CNTs) and electrospun polymer nanofiber (EPN) mats. However, success with woven prepreg has not been consistently achieved before this thesis. Autoclave woven epoxy CFRP laminates of IM7/8552 are manufactured using EPN and polymer aerogel NPNs with a VBO procedure. Once manufactured, these laminates were characterized for quality through void content analysis. 0.11 void vol% was achieved which is well within the 1 vol% of void requirement for aerospace-grade composite components. To aid the in the understanding of NPNs, in situ experiments utilizing microcomputed tomography are developed to investigate the (presumed Newtonian) flow of resin throughout the NPN as a function of temperature, which varies throughout a typical manufacturer recommended cure cycle (MRCC), along with the void evolution throughout the cure cycle. Based on this new in situ understanding, a manufacturing process modification is devised to produce void-free woven laminates at the 152.4 mm laminate scale. Through manufacturing, material characterization, and designed in situ experiments, this thesis demonstrates the use of NPNs for VBO-manufacturing of low-void content aerospace-grade CFRP composites to replace autoclaves for energy and cost savings. | |
