Effective Young’s modulus of a unidirectional fiber reinforced composite: a mean Green operator interpretation

Experimental measurements of the effective Young’s modulus of an unidirectional composite obtained by embedding 3D-printed PLA–CF fibers in a cold-curing polyurethane elastomeric matrix are presented. Specimens with a controlled number of aligned fibers were tested in uniaxial compression along the direction of alignment. The force-displacement records were processed with a routine that identifies the linear loading regime, converts it to stress–strain through the specimen geometry, and returns the longitudinal modulus together with a combined uncertainty built from the repeatability of multiple tests and from the scatter of the experimental curve. The measured modulus increases monotonically, on average, with the fiber volume fraction, yet remains several orders of magnitude below the modulus of the fiber material. Finally, the data are interpreted within a mean Green-operator (mGo) based Ponte-Castañeda and Willis homogenization scheme, which provides the full anisotropic effective moduli.