Structure-performance relationship in sutured photopolymer composite films with tunable mechanical heterogeneity

Abstract

This dissertation investigates the structure-performance relationships of bioinspired materials using photopolymer films. Nature utilizes mechanical heterogeneity in a variety of design architectures to tune biological materials considering their environmental and loading conditions. Compliant interlayers within stiff matrices, often referred to as sutures, are prevalent in biological structures, offering enhanced mechanical performance often despite their weaker material properties. To mimic nature's architecture in engineering materials, understanding the mechanisms through which biological structures achieve their outstanding properties is necessary. Previous manufacturing processes were unable to replicate the complex designs of biological structures, and literature in this field was bound by this limitation. Advancements in the field of photopolymers have enabled the development of mechanical heterogeneity in a defect-free network, facilitating explorations into bioinspired structures, eliminating many of the challenges associated with previous additive manufacturing techniques. In this work, we employ a two-stage reactive polymer (TSRP) system to investigate the structure performance relationship of bioinspired sutured composites, but first, a thorough understanding of the material system is deemed necessary. Through thickness characterization of the photopolymer system demonstrated complexities in material properties, providing details on our control over the material system. The TSRP system is then used to incorporate compliant sutures into stiff matrices to study the impact of mechanical heterogeneity. First, we investigated composites embedded with a single suture joint of sinusoidal geometries. Variations in geometrical features of the sinusoidal wave were explored with respect to the applied tensile load and empirical relationships were developed to correlate the composite performance to the geometrical features of the embedded suture. Further analysis of the failure of suture composites revealed toughening mechanisms such as crack guiding and crack arrest that significantly enhance the composite toughness. Then, we explored composite films embedded with periodic patterns of stiff and compliant interlayers at various length scales. Additional discussion on the fracture toughness of composite films explained the differences observed for composite performance at different length scales. The findings of this research offer fundamental insights into the complexity of nature's architecture and enable a framework for engineering composites and bio-inspired structures in the future.