Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item Forming evaluation metrics and methods for complex stretch broken and continuous carbon fiber parts(Montana State University - Bozeman, College of Engineering, 2023) Dube, Madison Eve; Chairperson, Graduate Committee: Cecily RyanCarbon fiber composites are an ideal material for aircraft structures due to their light weight and high strength and stiffness. Traditional continuous carbon fiber composites are limited by their ability to form into complex geometric features as they have minimal abilities to stretch into a mold. Stretch broken carbon fiber is discontinuous which allows for the different tows of carbon fiber to slip relative to each other allowing for laminate displacements unattainable to continuous carbon fiber. In order to develop and improve stretch broken carbon fiber manufacturing processes, a method is developed herein to analyze the forming quality of a complex carbon fiber part. This method quantifies common qualitative forming metrics by measuring, evaluating, and scoring carbon fiber defects including: bridging, wrinkling, variation in thickness, forming depth, corner thinning and thickening, resin pooling, and additional texture defects. The scores produced from evaluating the various forming metrics on formed carbon fiber parts are assembled in a weighted matrix to produce an overall forming score. This forming evaluation method is demonstrated on three different geometric mold designs to assess that it is quantitative, repeatable, accounts for many carbon fiber defects, and accounts for discrepancies between the formed part and the designed part. This method was also tested on different carbon fiber prepreg materials: MSU SBCF/Cycom 977-3 resin from Solvay, MSU SBCF/Hexcel 8552, and Hexcel IM7/8552. Through testing, the method is found to have achieved the method design goals as well as ascertaining areas of improvement for MSU SBCF prepreg which is still under development. Results show that stretch broken carbon fiber and traditional continuous carbon fiber achieve similar overarching forming scores, but outperform one another in different category metrics. MSU SBCF has higher scores in corner thickening and resin pooling; continuous carbon fiber has higher scores in wrinkling and bridging. The method forms the foundation to evaluate layup practices and autoclave cure cycles when systematically applied in a process development setting. This method is also extendable to dissimilar geometric part types with modifications in suitable metrics.Item Forming parameters and quantification of continous and stretch broken carbon fibers(Montana State University - Bozeman, College of Engineering, 2021) Janicki, Joseph Charles; Chairperson, Graduate Committee: Dilpreet S. Bajwa; This thesis contains two articles of which Joseph Charles Janicki is not the main author.Continuous carbon fibers are premium reinforcing material for aerospace composites. Carbon fiber reinforced polymers are five times stronger than steel and twice as stiff, making it an ideal candidate for structural aircraft components where weight is an important factor. The challenge with continuous carbon fibers is their difficulty to form deep drawn parts requiring intricate manufacturing techniques that increase manufacturing time, cost, and material waste. An alternative to continuous carbon fibers is stretch broken carbon fiber (SBCF). SBCF is a form of aligned discontinuous fiber, it has been proposed as an alternative to overcome this formability challenge. SBCF provides flexibility to form complex shapes while maintaining comparable strength and stiffness. A variety of testing methods have been developed to study both the ability of SBCF to form over traditional continuous carbon fiber and how different iterations of SBCF perform against each other. These include testing carbon fiber tows in tension on a universal test stand as well as designing and creating a forming tool that tests resin impregnated tows under different geometry conditions and temperatures. Tensile properties of both a continuous tow and a SBCF tow were evaluated at different gauge lengths and temperatures. It shows that SBCF tow maximum load increases as the gauge length decreases as well as elevated temperature has a clear effect on the tensile properties when fiber continuity is considered. Cross-sectional areas of continuous and SBCF tows were calculated using both areal weight and scanning electron microscopy showing that in general continuous fiber tows have a larger cross-section than SBCF. Using a forming fixture to test samples, results were statistically analyzed in order to display the significance of geometry and temperature on the maximum forming load of different fibers. The suite of testing and results indicate that in general SBCF maintains superior formability to that of continuous fibers. Overall lower maximum force is required for SBCF to form into deep drawn shapes. This supports their ability to be used more readily in complex aircraft structure while minimizing the disadvantages posed by traditional carbon composites.