Structural design and multifunctional applications of shear-stiffening composites

Recent advancements in the dynamic behavior and structural design of shear-stiffening materials have garnered considerable attention due to their adaptive mechanical properties under varying strain rates. This thesis explores the structural innovations and multifunctional properties of shear-stiffening composites, spotlighting their versatile applications across diverse sectors such as transportation, healthcare, and protective gear. It highlights the innovative gradient designs inspired by natural phenomena, advanced magnetorheological systems, pioneering energy-harvesting technologies and beneficial interactions with the structural integrity of the fibers.

Drawing inspiration from the naturally occurring gradient structure of the squid beak, novel gradient shear-stiffening elastomer have been crafted using direct ink writing techniques. These materials exhibit superior toughness, flexibility, and impact resistance, rendering them ideal for applications that demand efficient energy dissipation under complex loading scenarios. The biomimetic approach to their fabrication marks a significant leap in mechanical performance, particularly enhancing impact protection and the functionality of wearable technologies.

In the realm of transportation, especially in rail vehicle design, shear-stiffening elastomers have been successfully implemented in the form of magnetorheological shear-stiffening elastomer joints. These innovative joints address the challenge of balancing conflicting stiffness demands in train bogies, offering tunable stiffness via external magnetic fields and leveraging inherent frequency-dependent properties. MRSSE joints enhance operational stability on straight tracks while providing necessary flexibility on curves, demonstrating exceptional performance under dynamic conditions through comprehensive MTS testing and dynamic modeling.

Moreover, the fusion of shear-stiffening materials with liquid metal in the domain of triboelectric nanogenerators technology has fostered the creation of multifunctional self-powered devices. These liquid metal-based shear stiffening elastomers integrate electrothermal aluminum foil and shear-stiffening elastomers, crafting devices capable of simultaneous energy harvesting, Joule heating, and enhanced mechanical impact protection. These devices are particularly promising for deployment in intelligent medical plasters, wearable electronics, and personal healthcare systems, offering innovative strategies for designing sensors that boast superior anti-impact properties.

Furthermore, the thesis extends its exploration into Kevlar-reinforced shear stiffening elastomer, adopting advanced viscoelastic shear-stiffening elastomers as the matrix and integrating high-toughness Kevlar aramid fibers. This novel approach leverages the synergistic dynamic interactions between the rate-dependent strengthening behavior of the matrix and the structural integrity of the fibers, markedly enhancing impact resistance across diverse strain rates and loading scenarios. This advancement is particularly applicable in high-end equipment manufacturing, such as Formula racing, where these composites demonstrate substantial improvements in durability and shock absorption, bridging the gap in impact resistance often noted with conventional fiber-reinforced polymers.

Overall, this thesis comprehensively explores the latest advancements in the structural design and dynamic behavior of shear-stiffening materials, and it emphasizes their widespread applications in sectors such as transportation, healthcare, and protective equipment. Additionally, it suggests that future research could offer more possibilities for enhancing the performance, diversifying the structures, and augmenting the functionalities of shear-stiffening composites.