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Description
The presence of inclusions embedded within a polymer matrix significantly influences the macro- and nano-scale properties of the matrix. Characterizing the mechanical properties of such inclusion-embedded matrices is crucial for their diverse applications. Atomic force microscopy (AFM) has the unique ability to nondestructively characterize local modulus and height contours of nanocomposite surfaces. While previous studies have established a strong correlation between nanoparticle dispersion and the mechanical properties of nanocomposites, the combined influence of structural effects and material properties convolutes precise characterization. This study aims to deconvolute the effects of the nanoparticle’s embedment depth and damaged polymer on force-displacement curves using finite element analysis (FEA) to simulate the probe-matrix interactions in AFM. Validation of the FEA models was conducted using the Derjaguin-Muller-Toporov (DMT) and Hertzian contact mechanics models. Indentations were modeled for polymer matrices with inclusions embedded at varying depths and damaged polymer to analyze linear and nonlinear material, geometric, and contact mechanics effects. Nonlinear material behavior was characterized using a bilinear elastoplastic stress-strain curve and yield strength derived from Hertzian contact theory and Tresca’s yield criterion. Results revealed that inclusion depth and damaged polymer have distinct and measurable impacts on force-displacement curves retrace slopes, offering insights to identifiable patterns in mechanical behavior.
ContributorsChurch, Jett (Author) / Wilbur, Joshua (Thesis director) / Yekani Fard, Masoud (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor)
Created2025-05
Description
This study presents a novel approach to 4D printing by employing surface tension-assisted additive manufacturing to fabricate multi-material structures with tunable surface roughness in response to humidity. Poly(ethylene glycol) diacrylate (PEGDA) was selected as the material due to its hygro-responsive and photocurable properties. The photocurable resin was prepared by varying concentrations of PEGDA, deionized (DI) water, and photoinitiator (PI). The optimized curing and drying times on swelling behavior were studied. The optimal material—mixture of 30 wt% DI water and 0.1 wt% PI—demonstrated the highest swelling ratio while maintaining structural integrity. Vat photopolymerization (VPP) printing method was used to create mesh designs and surface tension-assisted manufacturing was utilized to suspend films of hygro-responsive material. Retentiveness testing showed that circular holes with smaller diameters retained the most material due to uniform tension distribution. The structures exhibited increased surface roughness upon swelling which confirmed the feasibility of the manufacturing methodology. This research suggests the potential for adaptive applications such as responsive grippers or movements with different patterned surface roughness. Future work will focus on improving mechanical properties such as adhesion between different materials and structural brittleness and optimizing fabrication processes through the usage of hydrophobic coatings.
ContributorsYoo, Minju (Author) / Li, Cindy (Thesis director) / Tang, Tengteng (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor) / The Design School (Contributor)
Created2025-05
Description
Hats are commonly worn by people in extreme heat conditions, in a variety of colors and styles. In hot environments with high amounts of incident radiation, people often experience significant thermal discomfort, and conventional wisdom leads many of those people to wear hats to alleviate some of their discomfort. Despite this common practice, the effectiveness of different styles and colors of hats relative to each other has not been thoroughly researched. Hats can have varied impacts on the factors which impact thermal discomfort, including incident radiation, convective heat loss, and evaporative heat loss from sweat. The difference between styles and colors of hats can cause them to have different interactions with these methods of heat transfer, which lead to variance in the total impact on thermal discomfort. This research was conducted in order to create an experimentally justified recommendation for hat selection to limit thermal discomfort in hot and sunny areas.
ContributorsLyons, Caitlyn (Author) / Rykaczewski, Konrad (Thesis director) / Joshi, Ankit (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor)
Created2025-05