There is a growing interest for the reused composite oriented strand board (COSB) for stiffness-critical and contoured applications. COSBs are made of rectangular shape prepreg strands that are randomly oriented within the structure. Development of this product form could markedly reduce the scrap generated during aerospace manufacturing processes. COSBs retain high modulus and drapability during processing and manufacturing. However, before any material can be deployed in industrial applications, its various properties must be well understood so that proper design analysis can be performed. Nondestructive testing (NDT) is widely used in research and industry to evaluate the quality of a variety of materials including composite materials and structures. NDT, as the name indicates, has the benefit that it does not alter or destroy the sample like other techniques, such as cross-sectional imaging. In this chapter, two nondestructive techniques, ultrasound and micro-computed tomography (micro-CT), were used to characterize carbon fiber epoxy composites, particularly comparing conventional laminates and reused COSB. The void content and morphology of samples cured using a range of materials and process parameters were determined using NDT and conventional microscopic analysis of cross sections. The mass distribution of fiber and resin within each sample was also determined. The manufacturing and NDT of COSB were introduced, and provided most detailed information on composite microstructure, including void size, void morphology, void distribution, and overall void content. Conventional micro-CT was determined to be ill-suited to scan large samples because of long scan times and large file sizes. To enhance the capabilities of micro-CT for evaluation of composite materials and structures, a micro-CT postprocessing method using stitching computer programming algorithms was developed. The method presented markedly increases the resolution that micro-CT can achieve, as well as the maximum feasible sample size, thus overcoming some of the primary drawbacks to conventional micro-CT. The primary objective of this work was to evaluate the feasibility of NDT methods in the assessment of both conventional composite laminates and the reused COSB fabricated from prepreg scrap. To this end, the advantages and limitations of ultrasound and micro-CT were discussed. The results showed that with stitching up postprocessing, micro-CT can be used to detect global void morphology structure wide, making the technique competitive with ultrasound, yet with greater resolution and equivalent scan size.
Part of the book: Recent Developments in the Field of Carbon Fibers
Sizing of hat-stiffened composite panels is challenging because of the broad design hyperspace in several geometric and material parameters available to the designer. Design tasks can be simplified if parameter sensitivity analysis is performed a priori and design data is made available in terms of a few important parameters. In this chapter, design sensitivity analysis is performed using finite element analysis (FEA) and analytical solution models. Manufacturing and experimental measurements of a hat-stiffened composite structure is performed to validate the FEA and idealized analytical solutions. This is an attempt to initiate a structural architecture methodology to speed the development and qualification of composite aircraft that will reduce design cost, increase the possibility of content reuse, and improve time-to-market. In particular, FEA results were compared with analytical solutions to develop a design methodology that will allow extensive reuse of parametric hat-stiffened panels in the design of composites structural components. This methodology is now widely utilized in developing a library of commonly used, built-in, composite structural elements in design of modern aircrafts. In this chapter, hat stiffened composite panels’ geometric parameter sensitivity analysis work were parametrically investigated using finite element analysis (FEA), analytical solution models and experimental testing on manufactured parts in order to develop structural architectures that speed development and qualification of composite aircraft which has broad benefits in reducing cost, increasing content reuse and improving time-to-market. In particular, FEA results were compared with analytical solutions and a design methodology was developed to allow extensive reuse of parametric elements in structural design of composites and to achieve expedited design, verification, validation, and airworthiness certification and qualification. The goal of this work is to provide the aviation industry with the most up-to-date databases for the application of advanced composite materials incorporated into parametric models to eliminate redundancies in the current process. The work results include a correlated material database, an optimized model component library and a standardized way to design future complex composites structures, e.g. hat stiffened composites panels, with reliable and predictable quality and material weight/cost.
Part of the book: Optimum Composite Structures
In this chapter, we explore a novel type of thermo-hydroforming process conceived to expand the role of sheet metal hydroforming machines from one of just forming sheet metal materials into one of being able to form multiple materials. This work specifically focuses on the use of thermohydroforming to shape and thermal catalyze prepreg composite sheets into rigid parts of complex 3D geometry. Elastomeric Sheet Hydroforming is an excellent low-cost manufacturing method requiring a single tool die on only one side. The mating die is a flexible membrane backed by fluid under high pressure. Various designs configurations exist that allow for significant pressure levels of up to 1400 Bar (20,000 psi), to be contained. The cycle life of the containment vessel components is commonly designed to accommodate up to 1 million cycles of use over 40 years. However, these machines can be expensive ranging in cost from several hundred thousand up to $6 million dollars. Expanding the market scope and potential of the press by enabling them to also form composites will provide benefit to both the machine owners and their customers. The intent of this project is to advance the state of the art in composites forming by demonstrating through FEA modeling that a hydroforming machine can be potentially configured to form thermally catalyzed prepreg composite panels. It is believed that the concept in like manner, will also be applicable to forming metal-composite hybrid panels, stratified metal thermoplastic laminates, thermoplastic synthetic granites and of course sheet metal materials. This concept seeks to benefit the American Manufacturing Industry and create jobs in the U.S. by providing a low-cost method for manufacturers to produce medium to very large sized high-quality sheet composite parts of an advanced nature in construction. This application is for operations requiring volumes less than 30,000 forming cycles per year per machine. Processes currently exist in the industry that utilizes heated air or heated glycol to form sheet materials. However, this process seeks to offer greater benefit by using pure water as a high thermal conductivity working fluid in a scheme that offers vastly elevated pressure during forming and curing cycles.
Part of the book: Characterizations of Some Composite Materials
Hydroforming, in comparison with sheet stamping, is an efficient and economical manufacturing process for complex-shape aerospace composite parts because it does not require the use of a female die. The hydroforming manufacturing method is expected to greatly increase the formability of composite parts by using a controllable heated and pressurized fluid that acts as a support for the composite sheet throughout the forming process. The design of a hydroforming process and a machine to shape complex aerospace composite parts is proposed in this chapter. The design and analysis of a sheet metal hydroforming machine with composite overwrap are presented to sustainably and efficiently produce not only the aerospace composites but also dual-phase and bake hardened steel parts with complex 3D geometry.
Part of the book: Environmental Impact of Aviation and Sustainable Solutions