Comparative study of the tensile properties of 2D and UD over-braided multilayer composites

Abstract In over-braided multilayer composites, the braid angle gradually increases from the first layer (the innermost layer) to the last one (the outermost layer). A two-dimensional (2D) braided structure is the most commonly used architecture for over-braiding. A unidirectional (UD) braided structure was developed to decrease the out-of-plane crimp in the 2D braided structure. To broaden the application of the 2D over-braided multilayer composite (2DMLC) and UD over-braided multilayer composite (UDMLC), their tensile properties and failure mechanisms must be studied. This research revealed that a slight range variation (2°–7°) in the braid angle has a significant effect on the tensile properties of these two composites, and the modulus and strength of the UDMLC were 8.63% and 10.90% higher than those of the 2DMLC, respectively. During tensile failure, the generation and propagation of matrix cracks were affected by the braided structure. As the braid angle gradually increased from the first to the last layer, the damage decreased. Moreover, after the tensile test, both the 2DMLC and UDMLC were concave toward the first layer in the transverse direction of the samples, and only the 2DMLC bent to the last layer in the longitudinal direction of the sample.