In this study, Thermomechanical properties of Ti-50.8 and 50.7 at% Ni alloy severely deformed using Equal Channel Angular Extrusion (ECAE) are investigated. The aim of this study is to reveal the effects of severe plastic deformation on shape memory, pseudelasticity, interplay between plastic deformation via dislocation slip and twinning, and forward and reverse martensitic transformation. The samples are processed at room temperature, i.e. slightly above the austenite finish temperature, and at 450 °C, i.e. well-above the austenite finish temperature. Transformation temperatures, microstructural evolution, and thermomechanical properties of ECAE processed samples are studied before and after low temperature annealing heat treatment and compared with conventional cold drawn and precipitation hardened material. The unique findings are: 1) the observation of a mixture of heavily deformed B2 (austenite) and B19’ (martensite) phases in the samples processed at room temperature although martensite stabilization was expected, 2) the observation of highly organized, twin-related nanograins in B2 phase of the samples deformed at room temperature which was attributed to B2 to B19' via SIM, and B19' to B2 via SPD (SIM: Stress Induced Martensitic transformation, SPD: Severe Plastic Deformation) transformation sequence, 3) simultaneous observation of B2 austenite and strain induced B19’ martensite in the samples deformed at 450 °C, and 4) perfect pseudoelasticity, small pseudoelastic stress hysteresis and excellent cyclic response with no irrecoverable strain up to 1000 cycles for ECAE at 450 °C processed sample. Strain induced martensite in NiTi alloys was reported for the first time. The formation of well-organized twin-related nanograins via severe plastic deformation opens a new opportunity for twinning induced grain boundary engineering in NiTi alloys which significantly improves the matrix strength and the cyclic response against degradation of shape memory and pseudoelasticity.

No description available.

<p>This thesis deals with glued laminated beams with holes. Different hole geometries, circular and quadratic,  and reinforcement methods were investigated. A total of 24 tests were performed using two types of reinforcements (glass fiber and plywood) and testing unreinforced beam. During testing of the beams without reinforcement a contact free deformation measurement system was used to capture the deformation pattern. A commercial finite element software package was used to perform numerical calculations of the response of the beams. The FE-analyses were also compared with the experimental results. The test results showed that the reinforcement with plywood was more efficient than the reinforcement with glass fiber. In addition, the two hole geometries showed different failure behaviors. The beams with quadratic holes showed a less brittle behavior, although at a lower load level than the beams with circular holes.</p> / <p> </p><p>Denna rapport behandlar limträbalkar med hål. Olika hålgeometrier, cirkulära och kvadratiska hål, och olika metoder att förstärka balkarna vid hålet undersöktes. Totalt 24 enskilda provningar genomfördes med två olika förstärkningsmetoder (glasfiber och plywood) samt med balkar utan förstärkning. Vid provning av de oförstärkta balkarna användes ett system för beröringsfri deformationsmätning för att få en bild av deformationsmönstret. Ett kommersiellt finita elementprogram användes också för att analysera balkarnas respons och för att jämföra med provningsresultaten. Provningarna visade att förstärkningen med plywood var effektivare än förstärkningen med glasfiber. Vidare uppvisade de olika hålgeometrierna olika brottbeteenden, där de kvadratiska hålen gav mindre spröda brott, dock vid en i genomsnitt lägre brottlast än de cirkulära hålen.</p>

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 93-95). Also available in electronic version. Access restricted to campus users.

Minimally invasive technique (MIS) revolutionized the field of surgery for its shorter hospitalization time, lower complication rates, and ultimately reduced morbidity and mortality. However, one of the critical challenges that prevent it from reaching the full potentials is the restricted visualization from the traditional monocular camera systems at the presence of tissue deformations. This dissertation aims to design a new approach which can provide the surgeons with real time 3D visualization of complete organ deformations during the MIS operation. This new approach even allows the surgeon to see through the wall of an organ rather than just looking at its surface. The proposed design consists of two stages. The first training stage identified the deformation subspaces from a training data set in the transformed spherical harmonic domain, such that each surface can be sparsely represented in the structured dictionary with low dimensionality. This novel idea is based on our experimental discovery that the spherical harmonic coefficients of any organ surface lie in specific low dimensional subspaces. The second reconstruction stage reconstructs the complete deformations in realtime using surface samples obtained with an optical device from a limited field of view while applying the structured dictionary. The sparse surface representation algorithm is also applied to ultrasound image enhancement and efficient surgical simulation. The former is achieved by fusing ultrasound samples 5 with optical data under proper weighting strategies. The high speed of surgical simulation is obtained by decreasing the computational cost based on the high compactness of the surface representation algorithm. In order to verify the proposed approaches, we first use the computer models to demonstrate that the proposed approach matches the accuracy of complex mathematical modeling techniques. Then ex-vivo experiments are conducted on freshly excised porcine kidneys utilizing a 3D MRI machine, a 3D optical device and an ultrasound machine to further test the feasibility under practical settings. / text

This thesis investigates various rigidity and flexibility phenomena of convex projective structures on hyperbolic manifolds, particularly in dimension 3. Let M[superscipt n] be a finite volume hyperbolic n-manifold where [mathematical equation] and [mathematical symbol] be its fundamental group. Mostow rigidity tells us that there is a unique conjugacy class of discrete faithful representation of [mathematical symbol] into PSO(subscript n, 1). In light of this fact we examine when this representations can be non-trivially deformed into the larger Lie group of PGL[subscript n+1](R) as well as the relationship between these deformations and convex projective structures on M. Specifically, we show that various two-bridge knots do not admit such deformations into PGL[subscript 4](R) satisfying certain boundary conditions. We subsequently use this result to show that certain orbifold surgeries on amphicheiral knot complements do admit deformations. / text

The Åreskutan nappe complex consists of the partly molten rock migmatite, which originates from the subduction formed by the collision of continents Baltica and Laurentia. It is a so-called hot nappe, which has been deeply buried in the subduction zone, based on findings of high-pressure minerals in the migmatitic gneiss. As the nappe returned to shallower depths the rock was partially molten during the subsequent exhumation as the lithostatic pressure decreased. Tectonic forces led to thrusting of the nappe towards the east and the building of mount Åreskutan. It is generally accepted that the shear zone between the migmatite of the Åreskutan Nappe and the underlying Lower Seve Nappe is a mylonitic shear zone, but the question of whether similar shear zones can be found at other sites in the migmatite complex has now been raised. In this project two major shear zones have been identified and shear direction has been determined after detailed geological mapping. Many small shear zones have also been identified, but their sense of shear direction was more difficult to determine. The two major shear zones identified have been labelled the Eastern Major Shear Zone and Western Major Shear Zone. In these shear zones the original migmatite appearing on Åreskutan is deformed and sheared with a top to the east sense of shear. The strongest evidence for determining the shear sense are garnets found mantled by micas in a sigma-type shear microstructures, found during microscope analysis. A grade of mylonitization can be seen in the mineral microstructures, with the most fine-grained matrix in the centre of the shear zones. It indicates that ductile deformation dominates, even though some minerals tend to break in a brittle manner.

Ο θεματικός πυρήνας του κεφαλαίου είναι η δομή της πλαστικής ζώνης διάτμησης του Φελλού στη Βορειοδυτική Άνδρο, η οποία μελετάται μέσα από την ανάλυση τομών. Η μελέτη αυτή είχε ως βασικούς στόχους (α) την κατανόηση της δομής και των κινηματικών χαρακτηριστικών της ζώνης διάτμησης, και (β) την καταγραφή των σταδίων κατασκευής του μυλωνιτικού ιστού. Κύριος σκοπός της μικροτεκτονικής ανάλυσης των μυλωνιτικών δειγμάτων είναι η παρουσίαση του προσανατολισμού του κινηματικού δείκτη σε σχέση με την φορά βύθισης γράμμωσης. / The core theme of the chapter is the structure of the plastic shear zone of Felloy in North Andros, which is studied through the analysis of sections.This study had as main objectives (a) the understanding of the structure and the kinematic characteristics of the shear zone, and (b) the recording of the construction stages of the tissue. The main purpose of the Microtectonics analyzing of the samples is the presentation of the orientation of the kinematic index in hense with the sink lineage.

No description available.

The incidence of restenosis has been shown to be correlated with the overstretching of the arterial wall during an angioplasty procedure. It has been proposed that slow balloon inflation results in lower intramural stresses, therefore minimizing vascular injury and restenosis rate. The analysis of the biomechanics of the arterial tissue might contribute to understand which factors trigger restenosis. However, few mechanical data are available on human arteries because of the difficulty of testing artery samples often obtained from autopsy while arteries are still considered "fresh". Various solutions mimicking the physiological environment have been used to preserve artery samples from harvesting to testing. In vitro mechanical testing is usually preferred since it is difficult to test arteries in vivo. Uniaxial and biaxial testing has been used to characterize anisotropic materials such as arteries, although methodological aspects are still debated. Several objectives were formulated and analyzed during the making of this thesis. In one study, the effect of deformation rate on the mechanical behavior of arterial tissue was investigated. The effect of several preservation methods, including cryopreservation, on the mechanical properties of porcine thoracic aortas was also analyzed. Finally, the differences in the mechanical behavior between three different types of sample geometry and boundary conditions were compared under uniaxial and equi-biaxial testing. Thoracic aortas were harvested within the day of death of pigs from a local slaughterhouse. Upon arrival, connective tissue was removed from the external wall of the artery. Then the artery was cut open along its length and cut out in rectangular samples for uniaxial testing, and square and cruciform samples for biaxial testing. Samples belonging to the freezing effect study were preserved for two months at -20°C and -80°C in isotonic saline solution, Krebs-Henseleit solution with 1.8 M dimethylsulfoxide, and dipped in liquid nitrogen. Samples belonging to the deformation rate effect study were tested uniaxially and equi-biaxially at deformation rates from 10 to 200 %/s. The uniaxial and biaxial experiments were simulated with the help of an inverse finite element software. The use of inverse modeling to fit the material properties by taking into account the non-uniform stress distribution was demonstrated. A rate-dependent isotropic hyperelastic constitutive equation, derived from the Mooney-Rivlin model, was fitted to the experimental results (i.e. deformation rate study). In the proposed model, one of the material parameters is a linear function of the deformation rate. Overall, inverse finite element simulations using the proposed constitutive relation accurately predict the mechanical properties of the arterial wall. In this thesis, it was found that easier attachment of samples (rectangular and cruciform) is accomplished using clamps rather than hooks. It was also found that the elastic behavior of arteries is nonlinear and non-isotropic when subjected to large deformations. Characterization of the arterial behavior at large deformations over a higherdeformation range was achieved using cruciform samples. The mechanical properties of arteries did not significantly change after preservation of arteries for two months. Under uniaxial and biaxial testing, loading forces were reduced up to 20% when the deformation rate was increased from 10 to 200 %/s, which is the opposite to the behaviour seen in other biological tissues. The differences observed in the mechanical behavior of fresh and thawed samples were not significant, independently of the storing medium or freezing temperature used. The lack of significant differences observed in the freezing study was likely due to the small number of samples tested per storing group. Further studies are required to clarify the impact of cryopreservation on extracellular matrix architecture to help tailor an optimized approach to preserve the mechanical properties of arteries. From the results obtained in the deformation rate study, it is concluded that the stiffness of arteries decreases with an increase in the deformation rate. In addition, the effect of deformation rate was observed to be higher than the effect of anisotropy. The inverse relationship between stiffness and deformation rate raises doubts on the hypothesized relationship between intramural stress, arterial injury, and restenosis.