Comparison of the biaxial strength properties of braided and laminated carbon fiber composites

Abstract This paper presents the results of a series of biaxial tests to measure the strength of 2-D braided carbon/ epoxy specimens, and compares the measured strength with that of laminations constructed with similar materials and fiber orientations. Braided preforms are currently being considered as replacements for laminated structures, because of the potential of cost saving and possible increases in interlaminar strength. However, lower in-plane strengths would be anticipated relative to laminations, particularly in the braid direction, because of the undulation in the braid fiber paths. It was found that in the braid specimen failures controlled by the axial fibers, reasonably similar values of ultimate strength were measured for braids and laminates, with the braid specimens being somewhat lower because of irregularities in the axial fibers that were related to the various braid designs. However, the strength of the braid specimens in failures controlled by the braid direction fibers was much lower than in laminates, corresponding to as much as 60–70% strength loss relative to laminates.