Fracture toughness of exponential layer-by-layer polyurethane/poly(acrylic acid) nanocomposite films

This paper characterizes the fracture toughness of layer-by-layer (LBL) manufactured thin films with elastic polyurethane, a tough polymer, and poly(acrylic acid) as a stiffening agent. A single-edge-notch tension (SENT) specimen is used to study mode I crack propagation as a function of applied loading. Experimental results for the full-field time histories of the strain maps in the fracturing film have been analyzed to obtain R-curve parameters for the nanocomposite. In particular, by using the strain maps, details of the traction law are measured. A validated finite strain phenomenological visco-plastic constitutive model is used to characterize the nanocomposite film while a discrete cohesive zone model (DCZM) is implemented to model the fracture behavior. The LBL manufactured nanocomposite is found to display a higher fracture toughness than the unstiffened base polymer.