PERFORMANCE OF ADDITIVELY MANUFACTURED CHOPPED FIBER COMPOSITES AS A FUNCTION OF POROSITY

Abstract

Additive manufacturing (AM) of short-fiber reinforced composites are actively being considered for construction of low-cost, weight reducing alternatives to non-structural metal components. In addition AM parts are being used for rapid manufacturing of composite tooling. AM is notorious for generating parts with higher porosity than more traditional manufacturing technologies. Due to the aerospace industry’s low risk tolerance, novel material systems require comprehensive characterization of their associated manufacturing defects and the impact of defects on performance in order to receive certification. AM short fiber composites still require this analysis. Although traditional composite manufacturing methods, such as an autoclave or VARTM can produce porosity, the origin and transport of porosity has been thoroughly studied and acceptable limits for part qualification have been established to minimize the effect on performance. In AM components studies establishing the origination of porosity origin and processing defect related minimization strategies are lacking. A preliminary study on the impacts of porosity caused by print parameters such print speed, layer height, first layer height, and step-over distance has been undertaken. Direct Ink Writing (DIW) was selected for this study using an epoxy-based ink filled with clay and chopped carbon fiber. To understand performance, fracture and shear specimens were fabricated with different test parameters based on the assumed levels of porosity from screening tests. Samples were then mechanically tested using a novel in-plane shear test method and a single edge notch tension test. This study explores the processing parameter’s contribution to porosity and establishes general trends to understand the influence of porosity on performance for additively manufactured chopped fiber composites.