Analyzing micro-macro transitional length scale in unidirectional composites

Understanding the hierarchy in the mechanical behavior of heterogeneous materials requires a systematic characterization of the material response at different length scales, as well as the nature and characteristics of the transitional scales. Characterization of such transitional length scales has been carried out in the past by analytical models that calculate and compare stiffness values at micro and macro scales. The convergence of the material stiffness at the two scales has been used as the criterion for quantification of the so-called transitional length scales. These stiffness calculation approaches are based on the idea of local strain and stress distributions obtained from complex finite element models. Recent advancements in full-field experimental strain measurements have made it possible to identify the transitional length scales in fiber composites based on pure experimental measurements without the requirement of local stress analysis. In this work, we study the validity of such ‘strain-based’ approaches that are used to identify the RVE size in unidirectional fiber composites. Our modeling platform replicates the realistic conditions present in experimental measurements through the randomization of fiber locations and volume fraction within an epoxy matrix.