Preliminary Experimental/Analytical Correlations of the Forming of Stretch Broken Carbon Fiber Tows and Laminates

Abstract

Stretch broken carbon fiber (SBCF) is generated by breaking individual filaments in carbon fiber tows at inherent flaws in tension in a continuous process. This process results in randomly broken, collimated fiber fragments. The shorter fiber length improves forming properties while retaining mechanical strength through shear load transfer. SBCF has the potential to take advantage of low-cost manufacturing processes like those used in sheet metal forming, resulting in ordersof- magnitude cost savings and enabling conversion to composite structures across the industry. Because uncured continuous carbon fiber composites do not exhibit significant plastic deformation, they cannot be readily adapted to many common sheet metal forming techniques. SBCF composites exhibit pseudo-plastic deformation, but this deformation is due to different mechanisms. To adapt the manufacturing processes for large and complex parts, new materials testing techniques are needed to quantify the forming behavior of SBCF at the meso-scale (tow and ply). This work’s primary objective is to develop predictive models for complex shape forming and large component characterization. Tests have been developed to characterize the behavior of SBCF tows under various forming conditions. Tow forming and laminate bulge testing allowed for experimental characterization of the SBCF response. Respectively, these tests focus on developing the load-displacement material response along with variation of the strain distribution. Using design of experiment (DOE) technique, the forming response to materials properties such as resin viscosity and mean fiber length have been related. For each test, a correlated Finite Element Analysis (FEA) model was developed, allowing for progression toward understanding a wider array of properties than experimentally.