This research aims to investigate the influence of 3D through-thickness stitching on the gas permeability and transverse microcracking of cryogenically cycled carbon/epoxy composites. 3D through-thickness stitching can be used to improve the interlaminar properties of polymer matrix composites (PMCs) and produce lightweight, unitized structures for cryogenic storage tanks. To fully utilize stitched composite structures for these applications, their inherent gas permeability challenges must be understood. Therefore, in this study, the stitched composites' damage evolution and gas permeability was experimentally characterized under a) pure thermal stress, b) thermal and uniaxial mechanical stress, and c) thermal and biaxial mechanical stress. Helium gas permeability was measured for each specimen at room or cryogenic temperatures under a mechanically strained state following the thermo-mechanical cycles. Optical microscopy was used to measure microcrack densities and monitor their evolution through the thickness of the composite specimens. Thin plies, graphene nanoplatelets (GNP) modified resin, and a hybrid barrier layer comprising of both were incorporated in the stitched specimens as barrier layers to reduce their gas permeability. The dependence of gas permeability of stitched composites on the mechanical strain, test temperature, and load history was evaluated and correlated to microcrack density. A significant reduction in permeability and damage evolution (transverse microcracks and delaminations) was obtained for all thermo-mechanical cases using the hybrid barrier layer laminate. Additionally, the permeability was several orders of magnitude lower than the allowable. Overall, the hybrid barrier layer shows tremendous promise as a viable barrier layer for stitched/unstitched composites undergoing thermo-mechanical fatigue involving a cryogenic environment.

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BACKGROUND: Polymer-infiltrated zirconia ceramic, benefiting from the synergistic effect of the ceramic matrix providing strength and the polymer enhancing toughness, has the potential to mimic the structure of natural teeth in its optical and mechanical properties. OBJECTIVE: To determine the effect of additives and various sintering temperatures on the optical and mechanical properties of zirconia ceramic matrix composites. MATERIALS AND METHODS: Groups consisted of unmodified zirconia powder, and zirconia modified with porcelain and porogens to form the porous ceramic matrix. Three types of Tosoh zirconia powder, TZ-3YSB-E, Zpex, and Zpex Smile, were used to fabricate porous blocks. Zirconia powder and porcelain powder were ball-milled separately. Zirconia powder was dry pressed and then cold isostatic pressed. The blocks were sintered at 1000 and 1150 ºC and sectioned into discs (n=10). For zirconia with additives groups, 10% of Titankeramik and 5% of PEG8000 were mixed to zirconia powder using a high-speed mixer. The zirconia blocks were pressed and sintered at 1000, 1150, 1200 and 1300 ℃, and sectioned into discs (n=10). Porous discs were treated with a 10% wt solution of 10-MDP for 4 hours and then dried in a vacuum oven for 24 hours. TEGDMA-UDMA resin monomers were infiltrated into discs and cured at 90°C under pressure. Polymer-infiltrated ceramics specimens were polished to 1.5 mm in thickness. Optical properties were determined with an X-rite spectrophotometer. Biaxial flexural strength and Vickers indentation tests were performed using an Instron universal mechanical tester. Vickers hardness and indentation fracture toughness values were calculated by measuring the indent dimensions under FESEM, in addition to microstructure assessment. Statistical analyses were performed using computer software, Microsoft Excel 2016 and JMP Pro 15. RESULTS: This study revealed that the type of zirconia powder utilized for the fabrication of porous ceramics for polymer-infiltration structures did not significantly influence their optical properties. Mean values of fully sintered zirconia showed significantly higher biaxial flexural strength (628.5-1277.4 MPa) than polymer-infiltrated groups (105.4-433.6 MPa), with P-3Y1150 achieving the highest value. Higher pre-sintering temperature from 1000 ℃ to 1150 ℃ led to enhanced biaxial flexural strength for polymer-infiltrated pure zirconia specimens, with values rising from 126.5-158.2 MPa to 243.4-433.6 MPa. Adding porcelain and porogens did not significantly affect the optical or specific mechanical properties, such as biaxial flexural strength and Vickers hardness, despite increasing the sintering temperature to 1300 ℃. Nevertheless, a significant increase in indentation fracture toughness was noted with ZPTKPEG1200 (7.65±0.55 MPa·m1/2) and ZPTKPEG1300 (7.09±0.61 MPa·m1/2), values that were markedly higher than those in all control groups of fully sintered zirconia (p<0.001). Sintering temperature was found to be a key determinant in influencing the ceramic matrix's microstructure, porosity, and density, as well as the biaxial flexural strength, Vickers hardness, and indentation fracture toughness of polymer-infiltrated zirconia. While changes in temperature did not affect optical properties, and polymer infiltration did not enhance all attributes, it did substantially elevate the indentation fracture toughness in mixed zirconia samples with additives, offering a potential area for further research. CONCLUSION: The mechanical properties of polymer-infiltrated ceramics responded significantly to the sintering temperature and the type of zirconia powder utilized, most notably in the 3Y-TZSB-E group. A notable increased indentation fracture toughness was discernible when Zpex powder, mixed with additives, was subject to polymer infiltration and sintered at temperatures between 1200-1300 °C. Even though polymer infiltration and additive incorporation did not uniformly enhance all properties, a noticeable improvement in fracture toughness was observed. These findings open the door to future research, especially in potential applications of dental restorative materials that demand superior fracture toughness.

Transverse ply cracking often leads to the loss of stiffness and reduction in thermal expansion coefficients. This paper presents the thermoelastic degradation of general cross-ply laminates, containing transverse ply cracks, subjected to biaxial extension, bending and thermal loading. The stress and displacement fields are calculated by using the state space equation method [Zhang D, Ye JQ, Sheng HY. Free-edge and ply cracking effect in cross-ply laminated composites under uniform extension and thermal loading. Compos Struct [in press].]. By this approach, a laminated plate may be composed of an arbitrary number of orthotropic layers, each of which may have different material properties and thickness. The method takes into account all independent material constants and guarantees continuous fields of all interlaminar stresses across interfaces between material layers. After introducing the concept of the effective thermoelastic properties of a laminate, the degradations of axial elastic moduli, Poisson's ratios, thermal expansion coefficients and flexural moduli are predicted and compared with numerical results from other methods or available test results. It is found that the theory provides good predictions of the stiffness degradation in both symmetric and antisymmetric cross-ply laminates. The predictions of stiffness reduction in nonsymmetric cross-ply laminates can be used as benchmark test for other methods.

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Thermomechanically bonded spunbond nonwoven fabrics contain discrete bonds that are formed by melted and fused fibers. Through equi-biaxial tensile testing and simultaneous image capture, the mechanical response of individual bonds was studied through loading in the preferential fiber direction, the machine direction, and in the direction that is perpendicular, the cross direction, of the fabric web. Independent biaxial force and displacement data were collected and analyzed, and the maximum force and stiffness of the bonds in the machine and cross directions were found to be statistically different. After scaling the maximum force and stiffness by a relative basis weight parameter, a fiber orientation parameter, and the width of the bond itself, the peak force and stiffness in the machine and cross directions were found to no longer be statistically different. This indicates that basis weight, fiber orientation, and bond size dictate the biaxial mechanical behavior of the bonds. Furthermore, significant fiber debonding was observed in all the bonds tested, effectively suggesting bond disintegration into the individual component fibers during testing. Digital image correlation, using the captured images, was utilized to calculate local and average Eulerian strains of the bond during the initial stages of the test. The strain experienced by the bonds in the machine direction was always positive and increasing as the biaxial load increased. The strain in the cross direction, however, experienced increasing and decreasing strain. Local strain maps revealed the highly inhomogeneous strain response of the bonds under biaxial loading. / Master of Science

The uterosacral ligaments (USLs) are important anatomical structures that support the uterus and apical vagina within the pelvis. As these structures are over-stretched, become weak, and exhibit laxity, pelvic floor disorders such as pelvic organ prolapse occur. Although several surgical procedures to treat pelvic floor disorders are directed toward the USLs, there is still a lot that is unknown about their function. These surgeries often result in poor outcomes, demonstrating the need for new surgical approaches and biomaterials. The first chapter of this dissertation presents a review of the current knowledge on the mechanical properties of the USLs. The anatomy, microstructure, and clinical significance of the USLs are first reviewed. Then, the results of published experimental studies on the {emph{in vivo}} and {emph{ex vivo}}, uniaxial and biaxial tensile tests are compiled. Based on the existing findings, research gaps are identified and future research directions are discussed. The second chapter proposes the use of planar biaxial testing, digital image correlation (DIC), and optical coherence tomography (OCT) to quantify the deformations of the USLs, both in-plane and out-of-plane. Using virgin swine as an animal model, the USLs were found to deform significantly less in their main direction (MD) of {emph{in vivo}} loading than in the direction perpendicular to it (PD) at increasing equibiaxial stresses. Under constant equibiaxial loading, the USLs deformed over time equally, at comparable rates in both the MD and PD. The thickness of the USLs decreased as the equibiaxial loading increased but, under constant equibiaxial loading, the thickness increased in some specimens and decreased in others. The third chapter presents new experimental methods for testing the {emph{ex vivo}} tensile properties of the uterosacral ligaments (USLs) in rats. USL specimens were carefully dissected to preserve their anatomical attachments, and they were loaded along their main {emph{in vivo}} loading direction (MD) using a custom-built uniaxial tensile testing device. This chapter reports the first mechanical data on the rat USLs in isolation from surrounding organs. It is also the first experimental study to provide measurements of the inhomogeneous deformations of the USLs during loading along their main textit{in vivo} loading direction, revealing that the USLs may behave as auxetic structures. The fourth and final chapter presents preliminary findings on novel imaging applications to characterize the evolving structure of the USLs before, during, and after tensile pulling along the ligaments' main textit{in vivo} axis of loading. Rat USLs were excised using the proposed novel dissection method and pulled uniaxially as was performed in the previous chapter. Before and after mechanical testing, second harmonic generation (SHG) was used to image collagen and muscle within the three anatomical regions of the USLs. During mechanical testing, OCT was used to collect out-of-plane images of the cervical/intermediate regions of the USL specimens, resulting in 3D volume scans of the regions. SHG images showed the USLs to have complex microstructures with significant wavy collagen bundles interwoven with muscle bundles. Preliminary observation of the microstructure during testing revealed interwoven sections of tissue with collagenous fibers that reoriented in all directions illustrating how the USLs may expand laterally during uniaxial loading, causing the auxetic properties documented in the previous chapter. Though more quantitative work remains to be done, the findings presented in this dissertation improve our understanding of how the USLs deform with increasing load, such as what occurs during pregnancy. Together, these studies serve as a springboard for future investigations on the supportive function of the USLs in animal models by offering guidelines on testing methods that capture their complex mechanical behavior. / Doctor of Philosophy / The uterosacral ligaments (USLs) are important anatomical structures that support the uterus and vagina and are often used to restore the support of pelvic organs during surgeries for pelvic organ prolapse. These surgeries often result in poor outcomes, demonstrating the need for new surgical approaches and graft materials. Due to their supportive role, the mechanical properties of the USLs are important for their physiological function, and they must be investigated to improve current treatment strategies for pelvic organ prolapse. To this end, we designed new equipment, dissection, and testing methods to characterize the mechanical behavior of the USLs using swine and rats as animal models. We provided the first three-dimensional characterization of time-dependent deformations of swine USLs as they were pulled along their two physiological loading directions using advanced imaging methods, including digital image correlation and optical coherence tomography. We isolated the USLs from rats with their anatomical attachments and mechanically tested them along their main physiological loading direction, reporting the first mechanical data on the rat USLs in isolation from surrounding organs. Finally, we used the advanced imaging techniques optical second harmonic generation microscopy and optical coherence tomography to determine how the microstructure (e.g., collagen and muscle) of the rat USLs evolves before, during, and after mechanical testing. These findings advance our understanding of the three-dimensional, nonlinear, heterogeneous, elastic, and viscoelastic deformations of the USLs. Our work may serve as a springboard for future investigations on the supportive function of the USLs by offering guidelines on testing methods that capture their complex mechanical behavior.

SAMMANFATTNING  Syfte  Syftet med studien var att undersöka huruvida färginfiltrering med effektfärg påverkar böjhållfastheten i flerskiktad zirkonia.  Material och metod Zirkoniamaterialet KATANA™ Zirconia YML, Kuraray Noritake användes i studien. Totalt framställdes 54 stycken provkroppar varav sex stycken utgjorde en pilotstudie för polering. Resterande 48 delades in i sex grupper (n = 8). Tre av grupperna frästes ut från Emalj och Body 1 (E-B1) och de resterande tre grupperna frästes ut från Body 2 och Body 3 (B2-B3). Två grupper, från de olika skikten, infiltrerades med Esthetic Colorant A plus (A), två grupper infiltrerades med Esthetic Colorant Opaque (O) samt två grupper utgjorde kontrollgrupper utan infiltrering (K). Provkropparna infiltrerades och sintrades enligt fabrikantens anvisningar. Därefter polerades de enligt ett poleringsschema och slutligen genomfördes ett biaxialt böjhållfasthetstest. Resultaten från samtliga grupper analyserades med One-way ANOVA, Tukey’s test, med en signifikansnivå på α = 0,05 med hjälp av statistikprogrammet SPSS.  Resultat Resultatet påvisade ingen signifikant skillnad i böjhållfastheten inom grupperna för de två skikten (E-B1A, E-B1O och E-B1K) samt (B2-B3A, B2-B3O och B2-B3K). Grupperna med skikten som inkluderade B2-B3 uppvisade signifikant högre böjhållfasthet oavsett infiltrering/kontroll än grupperna E-B1A, E-B1O och E-B1K.   Slutsats Böjhållfastheten i flerskiktad zirkonia påverkas inte av infiltrering med effektfärg. / ABSTRACT Purpose The purpose of this in vitro study was to investigate whether color infiltration with effect colors affect the biaxial flexural strength of multilayer zirconia.   Material and method The zirconia material KATANA™ Zirconia YML, Kuraray Noritake was used in the study. A total of 54 specimens were produced, of which six were part of a pilot study for polishing. The remaining 48 were divided into six groups (n=8). Three of the groups were milled of Enamel and Body 1 (E-B1) and the remaining three groups were milled of Body 2 and Body 3 (B2-B3). Two groups, from the different layers, were colored with Esthetic Colorant A plus (A), two groups were colored with Esthetic Colorant Opaque (O), while two groups served as control groups (K). The specimens were colored and sintered according to the manufacturer's instructions, polished according to a polishing schedule, and finally a biaxial flexural strength test was performed. The results were analyzed using One-way ANOVA, Tukey's test, with a significance level of α = 0.05 using the statistical software SPSS.   Results The results showed no significant difference in flexural strength within the groups for the two layers (E-B1A, E-B1O, and E-B1K) and (B2-B3A, B2-B3O, and B2-B3K). The groups with layers that included B2-B3 showed significantly higher flexural strength regardless of coloring/control than the groups E-B1A, E-B1O, and E-B1K.  Conclusion The flexural strength of multilayered zirconia is not affected by color infiltration with effect colors.