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

• Published in: Engineering fracture mechanics 2010-11, Vol.77 (16), p.3227-3245
• Main Authors: Kheng, E., Iyer, H.R., Podsiadlo, P., Kaushik, A.K., Kotov, N.A., Arruda, E.M., Waas, A.M.
• Format: Article
• Language: English
• Subjects: Exact sciences and technology; Finite elements; Finite strain; Fracture mechanics (crack, fatigue, damage...); Fracture toughness; Fundamental areas of phenomenology (including applications); Inelasticity (thermoplasticity, viscoplasticity...); Nanocomposite; Physics; Solid mechanics; Structural and continuum mechanics; Thin film
• ISSN: 0013-7944; 1873-7315
• DOI: 10.1016/j.engfracmech.2010.08.006

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.