Design and Analysis of Joining Methods for Open Architecture Composite Structures

Abstract

Recent research has shown that ¬Open-Architecture Composite Structures (O-ACS or simply Open Structures) can be utilized to create structures with characteristics that traditional composite structures cannot achieve. The stiffness to weight ratio of O-ACS exceeds comparable metal structures, as well as composite ones. The weight savings, ability to optimize, rapid manufacturability, and aesthetics provided by O-ACS components make them highly applicable to many areas. However, in order for this patented structure to complete the transition from an R&D project to a successful commercial product, a system of connecting these structures must be devised. This thesis details the design and analysis of a family of novel methods of joining O-ACS to form useful assemblies. The joining concepts can be separated at the highest level into those that are readily detachable and those that are permanently affixed. Several methods of fixturing have been examined, including; mechanical fasteners, bonding adhesives, compression fittings, and combinations thereof. A thorough investigation into design, manufacturing methods, and testing of various joining concepts has been performed and design proposals based upon the structures’ constraints are put forth. Five concept joints were proposed and evaluated based on characteristics such as weight, strength, ease of manufacturing, and design utility. The first subset of concepts investigated focuses on a component that is permanently affixed to the end of the O-ACS which allows for the structure to be mechanically fastened. One such concept consisted of a simple secondarily bonded metallic component that features a clevis for mechanical fastening of O-ACS components. This design disregards ultimate weight savings in lieu of simplicity, allowing for efficient manufacturing and reliability. An evolution of this type of connection was developed in order to prioritize weight savings through use of a variety of composite manufacturing methods. Due to certain design criteria, a permanent joint design may be more desirable. As such, a family of coupling joints that utilize secondary bonding were developed to allow for a permanent connection between O-ACS components. Conversely, some situations require a field-deployable joint with limited resources. Therefore, a novel compression joint was designed to allow for such situations where the ability to assemble and break down an O-ACS assembly is required. A thorough evaluation of the manufacturing processes of these joints has been conducted and testing was conducted on a range of test specimens. Test data was collected and performance is evaluated and discussed. A comprehensive design assessment on each joint is presented based on the manufacturing processes, performance, and weight.