No description available.

No description available.

No description available.

Transverse anisotropy is an important phenomenon of practical and scientific interest. Although the presence of ray tissue explains the high radial modulus in many hardwoods, experimental data in the literature shows that this is not the case for pine. It is possible that anisotropy in softwoods may be explained by the cellular structure and associated deformation mechanisms. An experimental approach was developed by which local radial modulus in spruce was determined at sub-annual ring scale. Digital speckle photography (DSP) was used, and the density distribution was carefully characterized using x-ray densitometry and the SilviScan apparatus. A unique set of data was generated for radial modulus versus a wide range of densities. This was possible since earlywood density shows large density variations in spruce. Qualitative comparison was made between data and predictions from stretching and bending honeycomb models. The hypothesis for presence of cell wall stretching was supported by data. A model for wood was therefore developed where both cell wall bending and stretching are included. The purpose was a model for predictions of softwood moduli over a wide range of densities. The relative importance of the deformation mechanisms was investigated in a parametric study. A two-phase model was developed and radial and tangential moduli were predicted. Comparison with experimental data showed good agreement considering the nature of the model (density is the only input parameter). Agreement is much better than for a regular honeycomb model. According to the model, cell wall bending dominates at both low and high densities during tangential loading. In radial loading, cell wall stretching dominates at higher densities. / QC 20101119

The Vasa ship is not adequately supported. Measurements of the hull show that the ship deforms and rotate towards the port side. In addition, damages on the hull at support areas have been observed. The damages are due to high compressive loads. At damaged zones the support has been removed and the loads are thus transferred to adjacent support stanchions. In order to design an improved support, knowledge of the mechanical behaviour of the material is needed. In particular, radial modulus, strength and deformation mechanisms are of interest. In the present study, the mechanical behaviour of recent oak and oak from Vasa is studied. Furthermore, effects of PEG content, degradation and moisture on the properties of Vasa oak are investigated. Oak is characterized by a very abrupt change from earlywood to latewood, where the latewood is much denser than earlywood. Also present in oak are large rays in the radial direction of the wood. Small specimens were tested in compression using Digital Speckle Photography (DSP) in order to obtain strain fields of the whole specimen surface. This technique also provided data on failure mechanisms. Dynamic mechanical thermal analysis (DMTA) was performed to establish differences in moisture softening. In radial compression, modulus and strength of Vasa oak are reduced by 50% compared with recent oak. A significant change of failure mechanism is observed for Vasa oak. In recent oak, failure in radial compression is by continuous folds of rays in the earlywood followed by continued plastic collapse of the earlywood layer. In Vasa oak rays show a more brittle fracture in each earlywood region. DMTA results indicate no effect on moisture softening of Vasa oak from presence of PEG although more work is needed to confirm this. Moisture adsorption for PEG-extracted Vasa oak is not significantly higher than for recent oak below 60% RH, suggesting that the extent of degradation of Vasa oak is limited. Vasa oak containing PEG is much more hygroscopic than PEG-extracted Vasa oak already at 50%. This difference is increasing with increasing relative humidity. / QC 20101118

<p> Various areas of studies on the natural and the prosthetic aortic valves are reviewed. </p> <p> A microtensile technique devised to investigate the inhomogeneous and anisotropic material properties of a porcine aortic valve's leaflets is described. Also, the theory and apparatus of a new stereophotogrammetric technique to define points in space by their Cartesian coordinates is introduced. The technique is used to investigate the local surface strains and curvatures of a porcine aortic valve's leaflets from 0 to 120 mm. Hg. in-vitro. </p> <p> It is found that the valve leaflets display marked inhomogeneity and anisotropy (orthotropy is assumed) in the elastic moduli and transition strains. For the non-coronary leaflet, the radial post-transition moduli vary from 42 to 215 gm/mm² with a mean of 111 gm/mm² (s.d. = 43 gm/mm²); and the radial transition strains vary from 30% to 70% with a mean of 58% (s.d. = 7%). Areas nearer the leaflet's coaptation edge tend to exhibit lower radial transition strains than the annulus edge. The central region of the leaflet is found to be the stiffest. For the same non-coronary leaflet, the circumferential post-transition moduli vary from 220 to 590 gm/mm² with a mean of 342 gm/mm² (s.d. = 118 gm/mm²); and the circumferential transition strains vary from 22% to 47% with a mean of 33% (s.d. = 3%). </p> <p> Inhomogeneity between leaflets is also observed; preliminary results seem to suggest that the non-coronary leaflet is the stiffest in the radial direction and the least stiff in the circumferential direction. In comparison, the right coronary leaflet exhibits the largest radial transition strains (~80% ) and the smallest circumferential transition strains (~25%). </p> <p> For the diastolic valve in-vitro, the circumferential strains are less than 10% at all pressures; therefore , this suggests pre-transition behaviour during diastole which is contrary to the general belief. Radial strains at diastole vary from 10% to well over 100% and show a definite tendency to increase from the sinus-annulus edge to the coaptation edge. The non-coronary leaflet is the least strained of the leaflets (10% to 60% at diastole). </p> <p> The determination of pre-or post-transition state at diastole is discussed and the implications of the results on stress analyses and trileaflet valve designs are noted. </p> / Thesis / Master of Engineering (ME)

<p> The spectra of depolarized light scattered from Isotropic and anisotropic liquids were Investigated In order to obtain information on both the reorientational and collisional motions of the liquid molecules. </p> <p> The liquid spectra taken at 22°C on a Coderg spectrometer (1 cm. ^-1 slits) were decomposed into relaxational and collisional components using least squares fitting techniques. Integrated Intensities and depolarization ratios in the zero em -1 (1 cm ^-1= 3 x 10^10 hz.) frequency sjift region as well as in the less than 5 cm^-1 region are reported. </p> <p> The Isotropic liquid spectra from 5 cm ^-1 consisted of a narrow Lorentz and a broader coliisional component which was exponential at shifts > 10 cm^-1. The anisotropic spectra also consisted of relaxational and collisional components; however, the Integrated Intensity of the relaxational and the collisional components Increased by a factor of 20 and 10 respectively from the isotropic liquids. </p> <p> A simple model based on frame distortion Induced anisotropy was constructed to predict the relative Intensity ratios of the collisional component for both Isotropic and anisotropic liquids. </p> <p> The relaxation time of the Lorentz component was Interpreted for both isotropic and anisotropic liquids as being the average time between collisions. It was, found to vary as μ^((3/4)/p), where μ is the reduced mass of two colliding molecules and p the liquid density.</p> <p> The line width parameter 1/vo for all the collisional components was interpreted as being a measure of the duration of a collision and was found to vary as μ^1/2 independent of the density P. </p> / Thesis / Master of Science (MSc)

Mechanical strength of polylactic acid (PLA) is increasingly relevant with time because of its attractive mechanical properties and 3D printability. Additive manufacturing (AM) methods, such as fused deposition modeling (FDM), stereolithography (SLA), and selective laser sintering (SLS), serve a vital role in assisting designers with cheap and efficient generation of the desired components. This document presents research to investigate the anisotropic response of multi-oriented PLA subjected to multiple monotonic loading conditions. Although empirical data has previously been captured for multi-oriented PLA under tensile and compressive loading conditions, the data has yet to be applied with regard to a representative component geometry. The tensile and compressive empirical data were ultimately used to develop elastic and yield constitutive models which aided in the characterization of PLA under torsion and bending. This representative component geometry is expected to experience a combined torsion and bending load condition in an effort to address this integral gap in the mechanical properties of multi-oriented PLA. In addition to the acquired empirical data, finite element analysis (FEA) and analytical modeling are employed to supplement the accurate modeling of future component analysis. As a result of the proposed array of experiments, the torsional and bending capabilities of PLA are forecasted to vary based on the print orientation. Lastly, the broader impact of this work is dedicated to addressing the material's capability to operate in environments which possess significant torsion and bending such as model aircraft wings and shafts for remote controlled cars.

For the characterization of crack advance in mechanical components and specimens under monotonic and fatigue loading, many engineering approaches use the assumption that the plastic deformation at the crack tip is isotropic. There are situations when this assumption is not correct, and the modeling efforts require additional correction factors that account for this simplification. The goal of this work is to study two cases where the plastic anisotropy at the crack tip is predominant and influences the magnitude crack-tip parameters, which in turn determine the amount of crack advance under applied loading. At the microstructural level, the small crack issue it is a long-standing problem in the fatigue community. Most of the small crack models consider that the plastic deformation at the crack tip is isotropic. The proposed approached for analyzing small crack growth is to perform finite element simulation of small cracks growing in a material that is assigned single crystal plastic properties. The nature of the plastic deformation of the material at the crack tip in the intra-granular regions could be accurately described and used for modeling small crack growth. By employing finite element analyses for stationary and growing cracks, the main characteristics of the plastic deformation at the crack tip, such as plastic zone sizes and shapes, crack-tip opening displacements, crack-tip opening stresses, are quantified and crack growth rates are determined. Ultimately, by using this crystal plasticity model calibrated for different microstructures, important time and financial resources for real experiments for the study of small cracks can be spared by employing finite element simulations. At macroscale, it is widely known that the manufacturing processes for aluminum alloys results in highly anisotropic microstructures, known as textures. The plastic behavior of these types of materials is far from isotropic and even the use of classical anisotropic yield criteria, such as that on Hill (Hill, 1950), is far from producing accurate results for describing the plastic deformation. Two of these anisotropic yield functions are implemented into finite element code ANSYS and stationary cracks are studied in a wide variety of textures. Significant variations of the plastic deformation at the crack due to the anisotropy are revealed.

No description available.