Collaborative Research: Mechanics of Structural Toughening in Sutured Composites

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This grant will investigate the mechanics of how suture geometry influences composite performance. Biological armors and carapaces employ suture joints, which are wavy, compliant interlayers that connect rigid material domains, and these sutures can manifest at length scales ranging from a few nanometers to millimeters in size. It is generally assumed that suture joints amplify the strength and toughness of biological composites in the presence of complex loading conditions, but the underlying mechanisms are not understood. Recent advancements in processing and characterization of material structure at requisite length scales will enable this project to provide the first systematic experimental investigation and theoretical modeling of suture mechanics. This new knowledge could provide the basis for a new additive manufacturing paradigm for printing polymer composites with improved performance. Education and outreach programs will be developed to engage kindergarten to graduate students, exposing them to engaging concepts in mechanics and materials science. Activities include course development, undergraduate student research, outreach lessons, and a Rocky Mountain Mechanics Symposium.The specific goal of the project is to establish structure-property relationships between suture geometry and three key stages of composite failure: crack nucleation, crack trapping, and mechanical interlocking. This project will seek answers to the questions such as: which structural suture parameters promote or inhibit each of the three stages, and how can parameters be balanced to amplify composite strength and toughness, and increase service life? More specifically, the research objectives of this project include: (i) understanding single-suture mechanics in thin films; (ii) understanding suture-suture interactions in thin films, (iii) establishing a two-wavelength additive manufacturing platform to extrapolate knowledge from thin films to 3D architectures where performance in the presence of bending, torsion, and compressive loadings can be studied. In pursuit of these objectives, two-stage reactive polymers will be employed to fabricate composites comprised of sutures with varying wavelength, amplitude, line width, and interlocking angles; atomic force microscopy will be used in fast force mapping mode to characterize variations in suture properties with nanometer resolution; finite element modeling will be leveraged to relate suture geometry to bulk composite performance. Results will offer new insights on structural toughening mechanisms and fracture behavior in hierarchical composites, and will lead to a single-resin, two-wavelength 3D composite printing methodology.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.