We are currently working on inverse modeling the fracture toughness of polyurethane and poly-acrylic acid composite films which are built up layer by layer. Classical methods of determining fracture toughness do not work because the films undergo large amounts of plastic deformation during the process of fracture. Thus, a method of analysis and a corresponding experiment needs to be designed to extract the fracture toughness.

Tensile loading of single end notch specimens were carried out on the films, where full-field strain data, forces on the boundaries and displacements at the boundaries are recorded. The experiment is then inversely modeled using the finite element method (via ABAQUS) incorporating a discrete cohesive zone model to back out the fracture toughness of the polymer. The ABAQUS model consists of two separate substrates joined together by discrete cohesive zone elements to match the geometry of the experiment.

In addition to these studies, the impact response of alternatingly stacked laminates of polyurethane and poly-acrylic acid films is also being studied. Square laminated plates, simply supported on all edges and subjected to a perpendicular impact of a 0.5 inch diameter hardened steel ball bearing traveling at speeds of up to 200 m/s are being examined. Experiments have shown that the thin layers of polymer composite in the glass/polymer sandwich show great improvements in impact and piercing resistance over ordinary glass. The experimental setup for the impact test is shown below.