Mechanical Engineering Graduate Seminar

Thursday, March 30 at 3:30 pm to 4:20 pm
Seamans Center, 3505 SC
103 South Capitol Street, Iowa City, Iowa

"Toward a description of injection-initiated fracture in soft solids" presented by Shelby Hutchens, Assistant Professor, Mechanical Science & Engineering, University of Illinois, Urbana-Champaign. Abstract: Rapid, 3-D mechanical characterization of soft solids enables understanding of health-related mechanisms, e.g., tissue property changes at the onset of disease and biomaterial structure-function relationships. A recently explored technique known as cavitation rheology (CR) provides a promising avenue for quickly and inexpensively characterizing the nonlinear behavior of soft materials as it contributes to failure. Briefly, a cavitation rheology experiment is performed by syringe-mediated pressurization of fluid within a needle that is embedded within a material. As the pressure increases, a void or bubble forms at the tip of the needle and grows stably. At a critical, maximum pressure value, Pc, the void suddenly and rapidly grows, resulting in a pressure drop. The injecting fluid used in this technique leads to localized, hydrostatic loading, a primary injury mechanism in blast and blunt force trauma. Thus, in addition to its use as a metrology tool, CR enables ready initiation and characterization of tissue-relevant failure modes. Past CR measurements in synthetic, polymeric materials at length scales from mm’s to μm’s have been found to correlate with both elastic modulus and fracture energy. Recently, we have developed a preliminary model that accurately captures which mechanism, elasticity or fracture, governs the experimentally measured ‘cavitation’ event. While demonstrating qualitative prediction of the observed behavior, this model relies upon an oversimplification of the crack geometry. In an effort to better understand injection initiated fracture geometry, we characterize the systematic evolution of crack morphology as a function of cross-link density in a soft elastomer (< 1 MPa). Crack shape is quantified using micro-computed tomography and shown to transition from being roughly penny-shaped, to multi-lobed (predominately three), to spherical with decreasing crosslinking. Individuals with disabilities are encouraged to attend all University of Iowa sponsored events. If you have a disability that requires an accommodation in order to participate in this program, please call the department  in advance, at 335-5939.

Contact Info: MIE Office,, 319.335.5939