A multiscale experimental approach to characterize micro-to-macro transition length scale in polymer foams

Bridging between micromechanics response and macroscopic behavior is at the core of multiscale investigations in heterogeneous materials. As such, quantitative characterization of the transitional length scales that correlate micro and macroscale behaviors is of great importance. Experimental characterization of the so-called transitional length scales in foams and other cellular structures is extremely scarce. The present work reports on an experimental-statistical approach proposed to quantify the micro-to-macro transition length scale in polymeric foams. The approach proposed in this work uses full-field strain distributions measured by digital image correlation (DIC) at two scales as input. The physical dimensions of the transition length scale are identified by implementing a statistical algorithm based on spatial averaging of the local strain data obtained from DIC. Interestingly, the transition between micro and macroscale deformation is found to be a function of material density but independent of global strain and stresses applied. The present results provide direct validations to representative volume element (RVE) size in cellular solids determined by computational methods.