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This thesis focuses on the use of scaled physical experiments to better understand the development and long-term evolution of fault systems that are otherwise impossible to observe directly. The document is divided into three chapters. The first chapter documents the implementation of an inexpensive stereo vision method for acquiring high resolution three-dimensional strain data for table-top experiments. The second chapter applies the stereo vision method to a tectonic problem—the development of slip partitioning in obliquely loaded crustal systems. Slip partitioned fault systems accommodate oblique convergence with different slip rake on two or more faults and are well documented in the crust. In this chapter, we simulate oblique convergence using blocks with 30° dipping contacts under wet kaolin clay. The experiments reveal three styles of slip partitioning development—contingent upon convergence angle and the presence or absence of a pre-existing vertical fault. Across all experiments, the slip rates along slip-partitioned faults vary temporally suggesting that the faults continuously adjust to conditions produced by the other fault. The lack of steady state in the experiments suggests that slip-partitioned crustal systems may also evolve with oscillating behavior rather than developing a single efficient active fault structure to accommodate oblique convergence. The third chapter documents rheological tests of wet kaolin for applications to crustal deformation experiments. This chapter investigates thixotropy in the clay as well as the role of grain size distribution and water content on its shear strength.

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.

While machine perfusion of explanted kidneys is theoretically superior to standard cold storage, it may damage potential transplants unless machine-associated swelling is controlled. This thesis presents the effects of perfusate tonicity on renal swelling during hypothermic machine perfusion. Phosphate buffered solution (PBS) and PBS supplemented with 5% w/v mannitol were used as isotonic (289 mOsm/kg) and hypertonic (568 mOsm/kg) perfusates, respectively. Porcine kidney pairs were procured then flushed and machine perfused; the right and left kidneys were assigned opposite perfusates. An experimental methodology was developed to image porcine kidneys undergoing hypothermic machine perfusion (5 deg C) for 15 minutes followed by 120 minutes without perfusion to quantify surface displacement (renal swelling) with digital image correlation (DIC). Surface displacement and size (thickness) were compared between the right and left kidneys of each pair. In addition, discharged renal fluids (i.e., filtrate and venous outflow) and biopsies were collected. On average, kidneys perfused with the mannitol solution were smaller in size than the kidneys perfused with PBS (p < 0.05) at the start and end of each experiment; however, there was no significant difference between the renal sizes at the end of the 15 minute perfusion interval (p > 0.05). Thus, hypertonic and isotonic perfusates yielded different renal swelling outcomes (i.e., physical size and surface displacement), which suggests that perfusate tonicity influences renal swelling. These experiments are the first time ex vivo renal surface displacement measurements have been collected during machine perfusion. / Master of Science / There is a chronic shortage of transplantable organs in the United States. As more marginal donor organs are being used to increase the number of transplantable organs, there has been a renewed interest in machine perfusion for organ preservation. While machine perfusion of explanted kidneys is theoretically superior to standard cold storage, it may damage potential transplants unless machine-associated swelling is controlled. This thesis presents the effects of perfusate tonicity on renal swelling during hypothermic machine perfusion. Isotonic and hypertonic solutions were used as perfusates. Porcine kidney pairs were procured then flushed and machine perfused; the right and left kidneys were assigned opposite perfusates. An experimental methodology was developed to image porcine kidneys undergoing hypothermic machine perfusion (5 °C) for 15 minutes followed by 120 minutes without perfusion to quantify surface displacement (renal swelling) with digital image correlation (DIC). DIC is a non-contact technique for measuring shape and displacement in three-dimensions. The results from these experiments show that hypertonic and isotonic fluids yielded different renal swelling outcomes (i.e., physical size and surface displacement), which suggests that tonicity influences renal swelling. This indicates that perfusate tonicity is an important factor for improving renal preservation with machine perfusion, which may increase the number of organs available for transplantation.

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 / For numerous industrial and consumer applications, such as the medical, automotive, packaging, and consumer goods, nonwoven fabrics are often thermomechanically bonded at discrete bond locations in patterns appropriate for the intended use. To produce the nonwoven, fibers are extruded onto a belt and the mat of fibers is passed through a calendar roll to form the thermomechanical bonds. As the fibers move on the belt, there is a preferential fiber direction parallel to the belt. Mechanical biaxial tensile tests were performed on nonwoven sheets in order to gain insight into the response parallel and perpendicular to the preferential fiber direction. Force and displacement data were collected and the maximum force and stiffness response parallel to the preferential fiber direction were found to be significantly higher than perpendicular to the preferential fiber direction. Strain measurements were also performed to examine the local strain of the bonds. Knowledge of the biaxial tensile behavior of bonds in nonwovens allows manufacturers to make informed decisions about the ultimate final application of the nonwoven.

Lightweighting demands have been achieved by third generation (3G) Advanced High Strength Steels (AHSSs) by a means of increased strength. The challenge faced in doing so, however, is in ensuring that ductility and crashworthiness is efficiently retained. Key methods in which automotive research has been invested to achieve this strength-ductility balance is by microalloying to promote grain refinement, the introduction of precipitates, and the effective use of plasticity enhancing mechanisms. Specifically, the ability to tailor the stability of retained austenite during deformation has been crucial in manipulating the strength-to-ductility ratio of 3G AHSSs using the Transformation Induced Plasticity (TRIP) effect. On the other hand, dual phase (DP) (i.e: non-TRIP-assisted steels) continue to be most significantly manufactured due to their robust thermomechanical processing but are also compromised by their poor damage tolerance. Hence, considerable reports are available regarding the damage tolerance of DP steels, but the ability for the volume expansion associated with the austenite-to-martensite transformation to suppress damage evolution and enhance a steel’s local formability has not yet been thoroughly investigated. Nonetheless, the damage processes that lead to fracture in 3G AHSSs are complex. A full understanding of the underlying phenomena requires a careful assessment of the strain partitioning amongst phases, how the microstructure evolves with strain and how damage, in the form of voids and micro-cracks, nucleates and grows. This can only be accomplished by applying a range of methodologies, including microscopic Digital Image Correlation (µDIC), X-ray Computed Microtomography (µXCT), Electron Backscattered Diffraction (EBSD) and X-ray Diffraction (XRD), all of which can be tracked as deformation proceeds. This PhD thesis uses a novel post µDIC data processing technique to prove that a reduction in strain gradient, linked to the evolution Geometrically Necessary Dislocations (GNDs), at dissimilar phase interfaces is attainable with vanadium-microalloying and with use of the TRIP effect. A local strain gradient post µDIC data processing technique was developed and first applied on 3G DP steels to show that the microcompatibility between ferrite and martensite directly at the interface is considerably improved with vanadium-microalloying. This in turn microscopically explains this DP steel’s increased local formability/damage tolerance with vanadium micro-additions. Moreover, when applying this novel µDIC technique on two other 3G experimental steels of interest, an ultrahigh strength Quench & Partition (Q&P) steel and a continuous galvanizing line (CGL)-compatible Medium-Mn (med-Mn) steel, an even slower evolution of microstrain gradients at dissimilar phase interfaces was observed. This indicates that, although vanadium-microalloying can improve the damage tolerance of a DP steel, its ability to achieve the ultrahigh strengths is a direct result of the severe inhibition of dislocation motion at dissimilar phase boundaries. Eventually, at high strains, these local strain gradients cannot be maintained and results in premature damage nucleation. By comparison, at such high strains, distinct evidence of damage nucleation was not apparent in the 3G TRIP-assisted steels which is the result of a slow strain gradient evolution delayed by the effective use of TRIP. This finding triggered a further investigation into isolating the impact the rate of TRIP exhaustion has on damage development. By intercritically annealing this prototype med-Mn steel (0.15C-5.8Mn-1.8Al-0.71Si) with a martensitic starting microstructure, within a narrow temperature interval (from 665 to 710°C), it was possible to make significant changes in the steel’s rate of TRIP exhaustion without making considerable changes to its physical microstructure. This steel exhibits the largest true strain at fracture (ɛf = 0.61), meets U.S. Department of Energy (DoE) mechanical targets (28,809 MPa%), and shows sustained monotonic work hardening when intercritically annealed at an intermediate IA temperature of 685°C for 120s. In addition, this IA condition showed optimal damage tolerance properties as an abundance of voids nucleated during its tensile deformation, but their growth was suppressed by prolonging TRIP over a large strain range. There is reason to believe that the heterogeneous distribution of austenite and Mn throughout this 685°C IA condition compared to the other two enabled its suppressed TRIP kinetics and in turn improved damage tolerance. The impact that changes in stress-state, from a stress triaxiality of 0.33-0.89, has on microstrain partitioning, TRIP kinetics and damage evolution was tested on this med-Mn at its 685°C IA condition. With the machining of notches on tensile specimens, it was seen that a high stress triaxiality (0.74-0.89) accelerated the rate of TRIP, whereas the introduction of shear, through a misaligned notched specimen design, delayed TRIP kinetics. The change in mean stress imposed by the notches was deemed to have played an active role in TRIP exhaustion during the material’s tensile deformation. A unique electropolishing micro-speckle patterning technique was applied to show that the amount of strain that can be accommodated by the steel’s the polygonal ferrite-tempered martensitic regions are considerably impacted by external modifications in stress-state. While damages studies using different such notched tensile geometries revealed that once a critical void size is reached in this med-Mn steel, coalescence proceeds at an increasing, exponential rate up to fracture. It continues to remain a challenge to quantify the effects microstrain partitioning, TRIP kinetics and damage evolution separately, opening new avenues for future experimental and modeling investigations. / Thesis / Candidate in Philosophy / A lot of research up to now has been invested in the automotive industry to create steels that are lightweight, strong and show improved crashworthiness. The means by which this has been achieved is with the use of innovative processing routes to manufacture and implement Advanced High Strength Steels (AHSSs) in a vehicle’s body-in-white. Nonetheless, the constant global pressure to reduce greenhouse gas emissions has eventually driven research to a third-generation class of ultrahigh strength, lightweight AHSSs. These steels retain the weight savings of their second-generation counterparts but are more cost-effective to manufacture and can be adapted to current industrial line capabilities. Considerable work has been done to enable the manufacturing of 3G steels, yet the steel characteristics which underpin fracture, thereby affecting the crashworthiness of these steels, continues to be weakly understood. As such, at a microscopic scale, this thesis uses three different promising 3G AHSSs candidates to evaluate the impact their unique steel characteristics has on the ability to resist damage evolution and fracture.