We are developing and applying several novel measurements to study the mechanics, fracture behavior and structure of polymers.
Laser-induced Projectile Impact Testing (LIPIT)
We use LIPIT to study the impact behavior and subsequent penetration of a microparticle onto a film at impact velocities from 50 m/s to 2 km/s. By measuring the kinetic energy loss due to penetration of the particle through the film, we can quantify the fracture energy of the polymer film.
We apply WC to characterize the elasticity and fracture of thin films by applying a uniaxial compressive strain to cause either wrinkle or crack formation. At a critical wrinkling strain, wrinkles appear parallel to the compressive strain direction due to the onset of an elastic instability. At a critical fracture strain, cracks form orthogonal to the compressive strain direction, and we can track the growth of these cracks to quantify the fracture energy.
Cavitation Rheology (CR)
We use CR to study the fracture behavior of elastic materials, such as gels, via nucleation of a bubble. By measuring the critical pressure of this nucleation event as a function of the needle size, we can quantify the fracture energy of the material. We observe the bubble formation in order to discern whether the behavior is an elastic instability or permanent fracture.
Contact Adhesion Testing (CAT)
We use CAT to measure the elasticity and adhesive failure of materials. CAT measures the stress, strain and contact area during the formation and subsequent separation of an interface formed between two materials. By applying linear elastic fracture mechanics, we can quantify the elasticity and adhesion energy of the materials interface.
Poromechanical Relaxation Indentation (PRI)
We use PRI to study the network structure of polymer networks swollen with solvents. PRI is a contact mechanics-based measurement that quantifies the time- and length-scale of the poroelastic relaxation process, due to solvent diffusion, that occurs in fluid-filled porous materials. We can determine the mesh size of a polymer network by mapping these results to Biot’s theory of poroelasticity.
Neutron Scattering (SANS & QENS)
We use small-angle neutron scattering (SANS) and quasi-elastic neutron scattering (QENS) to study the structure and dynamics of materials, respectively. SANS characterizes the structure (i.e. spatial correlations) of the polymer material, such as persistence length or mesh size, that is directly related to elasticity. QENS provides information about the dynamics (i.e. dynamic correlations) within the material, such as segmental motions, that is relevant to its fracture toughness.