Measurement of constitutive properties of additively manufactured epoxy composites for application to sandwich structures

Additive manufacturing technologies are beginning to find a foothold in industrial applications which call for complex geometries and low production volumes. In particular, the aerospace industry is targeting additive manufacturing to enable increased design freedom to reduce weight without sacrificing performance. Most industrial applications use either photopolymers or thermoplastics which can be filled with discontinuous reinforcement. Thermosetting polymers which are preferred by aerospace are not widely used for additive manufacturing on an industrial scale because there is a lack of available material systems and material models for design and prediction of part performance. To address these needs, an epoxy ink loaded with 5.5 vol% chopped carbon fiber is printed and select mechanical properties are measured. Mechanical tests include: tension, flexure, compression, and in-plane shear. Properties generated here are being used to populate a material model for predicting performance of hybrid sandwich composites with composite face sheets and printed cores. A comparison is made between two printed sandwich core geometries, rectangular and honeycomb, with rectangular cores achieving at least 2.6x greater load at break.