Several acoustic techniques have been used to determine elastic and damping properties of trees, logs and beams. Time of flight (TOF) measurements in the outerwood of 14-year-old Pinus radiata trees showed that pruning operations increased the outerwood stiffness by up to 25% compared with unpruned trees. However, at the most 5% to 10% of the increased stiffness can be explained by the fact that the outerwood of the pruned trees is free of knots, as TOF measurements are little affected by knots. Thus, it is not known what causes the increase of outerwood stiffness in the pruned trees. One possible explanation could be a smaller microfibril angle (MFA) in the S2 layer of the outerwood cells, which would cause a significant increase in stiffness. Thinning operations decreased the outerwood stiffness by up to 8%. In small Eucalyptus nitens and Pinus radiata logs, which had branch nodes and nodal whorls at specific locations, MOE calculations (using the resonance technique) based on different harmonics gave different results. This indicates that defects do interact with acoustic waves. Acoustic tests on laminated beams with artificial defects (holes filled with dowels) at specific locations also had a significant impact on the MOE. Moreover, it was evident that the damping ratio (evaluated from the Q- factor) of the beams increased with increasing diameter of the holes. However, it was found that holes in laminated beams decreased stiffness while branch nodes and nodal whorls increased stiffness. This shows that relatively small defects, occupying a small volume of the beam, have an impact on acoustic measurements. It is not appropriate to base the MOE calculation on a single harmonic, considering that different harmonics investigate different parts of the specimen

Magnetic resonance elastography (MRE) Is capable of non-invasively quantifying the mechanical properties of skeletal muscles in vivo. This information can be clinically useful to understand the effects of pathologies on the mechanical properties of muscle and to quantify the effects of treatment. Advances in inversion algorithms quantify muscle anisotropy in two-dimensional (2D) and three-dimensional (3D) imaging. Databases of the shear stiffness of skeletal muscle have been presented in the relaxed and contracted states in the upper extremity (biceps brachii, flexor digitorum profundus, and upper trapezius), distal leg muscles (tibialis anterior, medial gastrocnemius, lateral gastrocnemius, and trapezius), and proximal leg muscles (vastus lateralis, vastus medialis, and sartorius). MRE measurements have successfully validated a mathematical model of skeletal muscle behavior in the biceps brachii, correlated to electromyographic data in the distal leg muscles and quantified the effects of pathologies on the distal and proximal leg muscles. Future research efforts should be directed toward improving one-dimensional (1D) and 3D MRE data acquisition and image processing, tracking the effects of treatment on pathologic muscle and correlating the shear stiffness with clinical measurements.

The dynamic properties of the elastic coupling are not readily known; therefore testing has to be performed in order to determine these properties. This is the primary objective for this thesis. The dynamic properties in question are the stiffness and damping. An attempt to determine the dynamic properties was also be carried out through the use of finite element analysis. There are two different configurations of couplings. One configuration forms the coupling from several elastic elements, referred to as HRC elements, which are manufactured in three sizes: A, B, and C. The second configuration, referred to as the HEMD coupling, has a single elastic member in the form of a hollow rubber/fabric ring connecting the input to the output. The couplings have cords made of either polyester or nylon. These cords will affect the dynamic properties of the coupling.

In this research, the homogenization relations for elastic properties in isotropic and anisotropic materials are studied by applying two-point statistical functions to composite and polycrystalline materials. The validity of the results is investigated by direct comparison with experimental results. In todays technology, where advanced processing methods can provide materials with a variety of morphologies and features in different scales, a methodology to link property to microstructure is necessary to develop a framework for material design. Statistical distribution functions are commonly used for the representation of microstructures and also for homogenization of materials properties. The use of two-point statistics allows the materials designer to consider morphology and distribution in addition to properties of individual phases and components in the design space. This work is focused on studying the effect of anisotropy on the homogenization technique based on two-point statistics. The contribution of one-point and two-point statistics in the calculation of elastic properties of isotropic and anisotropic composites and textured polycrystalline materials will be investigated. For this purpose, an isotropic and anisotropic composite is simulated and an empirical form of the two-point probability functions are used which allows the construction of a composite Hull. The homogenization technique is also applied to two samples of Al-SiC composite that were fabricated through extrusion with two different particle size ratios (PSR). To validate the applied methodology, the elastic properties of the composites are measured by Ultrasonic methods. This methodology is then extended to completely random and textured polycrystalline materials with hexagonal crystal symmetry and the effect of cold rolling on the annealing texture of near- Titanium alloy are presented.

Solid oxide fuel cells represent a potentially important application for ceramic materials. There are, however, some significant issues which can affect the reliability and durability of the cell. Mechanical failure owing to stress is one of the critical factors which can affect the stability and working life of the fuel cell stacks. These stresses generate in Solid Oxide Fuel Cells (SOFCs) owing to mechanical forces and change in temperature during fabrication, assembly and operating conditions. There can be chances of cell delamination and micro-cracks in cell electrodes if these stresses are too high. The elastic properties and thermal expansion coefficient play a vital role to improve cell stability and performance. These properties depend on the types of materials and geometries of the composites. In this research, a numerical framework to predict the effective elastic properties and the effective thermal expansion coefficient for porous Yttria-Stabilized Zirconia (YSZ) electrode microstructures in a Solid Oxide Fuel Cell is presented. The electrodes of Solid Oxide Fuel Cells are discretized as porous microstructures that are formed by randomly distributed and overlapping spheres with particle size distributions that match those of actual ceramic powder. Three-dimensional (3D) microstructures of YSZ-pore are formed with a porosity ranging from 25% to 40%. The technique involves the construction of the YSZ-pores microstructures based on measurable starting parameters and subsequent numerical prediction of effective elastic properties and effective thermal expansion coefficient. Three domain sizes are considered for the generation of YSZ-pore microstructures. The method of prediction of effective Young’s modulus (Eeff), effective Poisson’s ratio , effective bulk modulus effective shear modulus , and effective thermal expansion coefficients for various porosities (P) of Yttria-Stabilized Zirconia (YSZ) electrode material in Solid Oxide Fuel Cells is based on the Finite Volume analysis which in turn is based on the solution of the linear elastic stress analysis problem. The predicted results are compared with some theoretical correlations of two-phase composites for effective elastic properties and effective thermal expansion coefficient. It has been found that predicted results are falling inside of the upper and lower bounds. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2013-10-01 17:01:05.068

Negative Poisson’s ratio, or auxetic, materials present the possibility of designing structures and components with tailored or enhanced mechanical properties. This thesis explores the phenomenon of auxetic behaviour in cubic crystals using classical and quantum modelling techniques and assesses the validity of these techniques when predicting auxetic behaviour in cubic elemental metals. These techniques are then used to explore the mechanism of this behaviour. The findings of the atomistic modelling are then used as a template to create networks of bending beams with tailored Poisson’s ratio behaviour.

Structural and mechanical properties of nucleic acids play a key role in a wide range of biological processes, as well as in the field of nucleic acid nanotechnology. The thesis presents results of several studies focused on modelling these properties. Extensive unrestrained atomic-resolution molecular dynamics (MD) simulations are used to investigate structural dynamics of nucleic acids, and to parametrize their mechanical models. The deformation energy is assumed to be a general quadratic function of suitably chosen internal coordinates. Two types of models are employed which differ in the level of coarse- graining. The first one is based on the description of conformation at the level of individual bases and the second, coarser one is used to study global bending and twisting flexibility. The models are applied to explain mechanical properties of A-tracts in the context of DNA looping and nucleosome positioning, to characterize twist-stretch cou- pled deformations in DNA and RNA, and to predict changes in the properties of damaged DNA that are likely to be relevant for damage recognition and repair. Besides that, we propose a general model of DNA allostery, applied to study the effect of minor groove binding of small ligands and the allosteric coupling between proteins mediated by the DNA. A careful...

Thesis (M.Sc. (Physics)) --University of Limpopo, 2005 / Self-consistent electronic structure calculations have been performed on ordered cubic-based magnesium-lithium (Mgx-Li1−x) alloys spanning the concentration range 0 ≤ x ≤ 1, using an ab initio plane wave pseudopotential (PWP) method. The first principle pseudopotential planewave approach is used within the local density approximation (LDA) and generalized-gradient approximation (GGA)of the density functional theory (DFT) framework. We have calculated the binding energy curves and the systematic trends in various cohesive and elastic properties at zero temperature, as a function of Li concentration. The calculated equilibrium lattice parameters show a large deviation from Vegard’s rule in the Li-rich region whilst the bulk moduli decrease monotonically with increase in Li concentration. The heats of formation for different ground state superstructures predict that the DO3, B2 and DO22 structures would be the most stable at absolute zero amongst various phases having the Mg3Li, MgLi and MgLi3 compositions, respectively. This stability is reflected in the electronic density of states (DOS). Because of the special significance of the isotropic bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio for technological and engineering applications, we have also calculated these quantities from the elastic constants. The elastic constants indicate the softness of the material as more Li is added with the bcc-based phases becoming mechanically less stable for Li concentration less than 50%. Our results show good agreement within the estimated uncertainty with both experimental and previous theoretical results. / The National Research Foundation (NRF), South Africa-Royal Society (RS), Great Britain collaboration and Council for the Scientific and Industrial Research (CSIR)

The elastic properties of a solid are of considerable interest to both science and technology. Not only do they contain fundamental information about the nature of the inter-atomic bonding in the material, but they also determine the mechanical behavior of solids. In the past few years, considerable effort has been devoted to the study of elastic properties of bulk metallic glasses (BMGs), a relatively new class of metallic materials that display a unique combination of mechanical and physical properties. Our research has focused on Zr-based, Cu-based and Ca-based metallic glasses. Zr-based BMGs are known to have superior glass forming ability and high strength, but their ductility is too low for wide-spread practical applications. Cu-based BMGs recently received wide interest because of their low cost and good mechanical properties. Ca-based BMGs have low glass transition temperature Tg, around 390 K, which make them very attractive to be studied near Tg. In this work, resonant ultrasound spectroscopy (RUS) has been applied to study the elastic properties of above mentioned BMGs from 5 K to their glass transition temperature Tg. RUS is a novel technique for determining the elastic moduli of solids, based on the measurement of the resonances of a freely vibrating body. In an RUS experiment, the mechanical resonances of a freely vibrating solid of known shape are measured, and an iteration procedure is used to “match” the measured lines with the calculated spectrum. This allows determination of all elastic constant of the solid from a single frequency scan. Below Tg, the elastic constants of the BMGs under investigation show “normal” behavior, i.e. with increasing temperature, all moduli decrease and Poisson ratio increases. Above Tg changes in the trends occur due to structural relaxation and crystallization. We confirmed the suggested link between ductility and Poisson ratio: BMGs showing good ductility display high Poisson ratio. By increasing palladium content in Zr50Cu40-xAl10Pdx alloys, BMGs with high Poisson ratio and thus good ductility have been obtained. In addition, we developed a simple model to provide fast and good estimate of the temperature dependence of elastic constants of BMGs from room temperature measurements. Keywords: Elastic properties; Bulk metallic glasses (BMGs); Resonant ultrasound spectroscopy (RUS); Internal friction.

The elastic properties of novel transition metal oxides have been investigated, using a powerful technique known as Resonant Ultrasound Spectroscopy (RUS). Two sets of transition metal oxides have been studied. One is the ruthenate Ca2-xSrxRuO4 series with a layered perovskite structure, a Mott transition system that connects the Mott insulator Ca2RuO4 with the unconventional superconductor Sr2RuO4. The other set contains geometrically frustrated materials, including vanadium spinels AV2O4 (A = Zn, Mn and Fe) and titanate pyrochlores A2Ti2O7 (A= Y, Tb, Yb, Ho and Dy). The elastic response of five Ca2-xSrxRuO4 single crystals (x = 2.0, 1.9, 0.5, 0.3 and 0.2) has been measured. For 2.0 ≥ x ≥ 0.5, a dramatic softening over a wide temperature range is observed upon cooling, caused by the rotational instability of RuO6 octahedra (for x = 2.0 and 1.9) or the static rotation of the octahedra (for x = 0.5). For the Ca-rich samples (x = 0.3 and 0.2), the softening occurs in a very narrow temperature range, corresponding to the structural phase transition from high-temperature-tetragonal to low-temperature-orthorhombic symmetry. Elastic softening in ZnV2O4 is observed near the cubic-to-tetragonal structural phase transition at 50 K. The elastic response of MnV2O4 is quite unusual, displaying a softening over a wide temperature range with decreasing temperature. Upon cooling, C’ of FeV2O4 becomes so soft that it drops to almost zero around 140 K, where the cubic-to-tetragonal structural transition occurs. For Y2Ti2O7, all three elastic constants show normal “Varshni” behavior. For spin liquid Tb2Ti2O7, all three elastic constants show a pronounced softening below 50 K, indicative of a possible Jahn-Teller, cubic-to-tetragonal transition at very low temperatures. It is also found that the application of a magnetic field suppresses the elastic softening in this compound. Another spin liquid Yb2Ti2O7 shows no elastic softening. The elastic moduli of the spin-ice compounds, Ho2Ti2O7 and Dy2Ti2O7, show a broad “dip” around 100 K, which is believed to be caused by the strong crystal field effect in those two compounds.