Mechanical Response Tissue Analysis (MRTA) is an emerging technology for assessing maximal bending stiffness (EI) of human long bones in vivo. The MRTA variable, EI, is the product of Young's modulus of elasticity (E) and cross-sectional moment of inertia (I). EI quantifies material and architectural/geometric properties of bone. Published human research using MRTA to measure EI has been limited to the ulna; however, the tibia requires further investigation due to its central involvement in many human activities and exercise-related clinical problems, e.g. stress fracture of the lower leg. To evaluate the inter- and intra-reliability of tibial EI, 22 healthy women (X + SD: 20.8 + 1.8 yr) were assessed twice daily for three non-consecutive days. Each daily session consisted of five repeated trials. The ulnar EI protocol of McCabe et al. [J Bone and Mineral Res. 1991;6(1):53-59] was adapted to assess tibial EI via MRTA. A significant difference was not found in scores for five repeated trials taken consecutively on the same day. Mean scores for EI were higher on day 1 (59.1 &#177; 35.5 N&#183;m², p < 0.05), compared to day 2 (46.9 &#177; 22.3) and day 3 (49.9 &#177; 18.3). Individual trial mean scores for EI on each day (mean of 5 trials) were highly correlated, R² = 0.84, 0.62, and 0.79 (set 1 vs. 2, for day 1,2,3, respectively) and the average percent change between sets 1 and 2 on each day was 5.3. The inter-test (between day) reproducibility was found to be low and unacceptable, 11.7, 18.3, and 1.3%, for day 1 vs. 2, 1 vs. 3, and 2 vs. 3. Poor inter-day reliability may be a result of the inability, at the time of this study, to apply the best computational EI model. It is concluded that tibial bone stiffness measurements with the MRTA are in the range of acceptability for same day inter- and intra-trial reliability when the 7-parameter analytic model of vibratory properties developed by McCabe et al. is used. / Master of Science

The use of electrospun polystyrene (PS) fibers to create continuous long range ordered multi-scale porous structures in titanium diboride (TiB2) is investigated in this work. The introduction of electrospun PS fibers as a sacrificial filler into a colloidal suspension of TiB2 allows for easy control over the pore size, porosity, and long range ordering of the porous structures of the sintered ceramic. Green bodies were formed by vacuum infiltrating an electrospun-fiber-filled mold with the colloidal TiB2 suspension. The size, volume, distribution, and dispersion of the pores were optimized by carefully selecting the sacrificial polymer, the fiber diameter, the solvent, and the solid content of TiB2. The green bodies were partially sintered at 2000 C in argon to form a multiscale porous structure via the removal of the PS fibers. Aligned continuous cylindrical pores were derived from the PS fibers in a range of ~5 - 20 μm and random porosity was revealed between the ceramic particles with the size of ~0.3 - 1 μm. TiB2 near-net-shaped parts with the multi-scale porosities (~50 to 70%) were successfully cast and sintered. The multi-scale porous structure produced from electrospun fibers was characterized both thermally and mechanically, at room temperature. The conductivity ranged from 12-31 W m^(-1) K^(-1) at room temperature and the compressive strength ranged from 2-30 MPa at room temperature. Analytical thermal and mechanical models were employed to understand and verify he processing-structure-properties relationship. Finally, a method was devised for estimating the effective thermal conductivity of candidate materials for UHTC applications at relevant temperatures using a finite difference model and a controlled sample environment. This low-cost processing technique facilitates the production of thermally and mechanically anisotropic structures into near-net shape parts, for extreme environment applications, such as ultra high temperature insulation and active cooling components. / MS / Society is on the cusp of hypersonic flight which will revolutionize defense, space and transport technologies. Hypersonic flight is associated with conditions like that of atmospheric re-entry, high heat and force or specific locations of a space craft. The realization of hypersonic flight relies on innovative materials to survive the harsh conditions for repeated flight. We have created a new material with tiny holes that can help prevent heat flow from the harsh atmosphere from damaging the hypersonic craft. Thesis tiny holes are made from placing a polymer fiber in an advanced ceramic (which withstand high temperatures) and removing the fiber to leave holes. The tiny hole’s effect on strength and heat flow have been studied, to understand how the tiny holes can be made better. It is difficult to test materials in the harsh atmosphere associated with hypersonic flight, so a program has been written to estimate thermal properties of candidate materials for hypersonic flight.

The design and construction of roads with longer service lives is a priority of civil engineers. The selection of appropriate highway materials with respect to climatic and loading conditions may significantly increase the lifespan of pavements. One material receiving interest in the area of improved roadway performance is polymer-modified binder. The complex behavior of polymer-modified binders, particularly over time, is not yet well-understood by engineers. Therefore, an experimental study was performed to determine the effects of four years of storage at room temperatures (23°C) on the dynamic mechanical properties of polymer-modified binders at intermediate and high temperatures. A typical paving grade (AC-20) and three elastomeric modifiers, each at three concentrations were used. Initial tests were performed in 1995 to evaluate the effects of short-term aging as simulated by the Rolling Thin Film Oven Test (RTFOT) procedure. This study encompasses a second phase of testing occurring after the modified binders were stored at ambient room temperature (23°C) for four years. The study found that significant changes affecting the dynamic response of binders occur during long term storage at a temperature of 23°C. These changes are dependent on the type and concentration of modifier and may be beneficial. Additionally, four mathematical models describing the dynamic response of binders were evaluated and found to be variable in their ability to accurately predict response of modified binders. Most of these models are not well suited for prediction of the response of stored binders. / Master of Science

Poly(vinylidene fluoride) (PVDF) receives an increasing amount of attention because it exhibits the strongest piezoelectric response of any commercially available polymer. These piezoelectric properties have proved useful as actuators and sensors. Current manufacturing processes limit PVDF to thin films and restricting their uses largely to sensors. Further applications utilizing the changes in mechanical properties of piezoelectric polymers are being realized. Evaluating to what extent the mechanical properties will change with applied electric field and finding new ways to manufacture PVDF will lead to new applications of piezoelectric polymers. In-situ mechanical testing of biased piezoelectric PVDF films successfully measured changes in loss and storage modulus. In-situ creep testing measured an increase in stiffness while in-situ dynamic mechanical analysis (DMA) measured and overall decrease in loss and storage modulus. Differences in results between the two experiments are attributed to orientation of the polymer and piezoelectric forces acting on the equipment. DMA results are accepted as being the most accurate and measured changes of over 20% in elastic modulus. Results were believed to be greatly influence by attached electrodes and actuation forces. Cryogenic mechanical milling successfully converted a phase PVDF powder to b phase as measured with wide-angle x-ray diffraction. This is the first recorded instance of b phase powders forming from the a phase through ball milling. These b phase powders maintained their crystal structure during compression molding at 70&#176;C. / Master of Science

The objective of this research project was to evaluate the mechanical, morphological, and permeability properties of electrospun blends of polydioxanone and poly(lactic acid) for application as vascular grafts. Mechanical analysis was performed by uniaxial tensile testing to examine the peak load, peak stress, elastic modulus, and strain at break of the fibrous materials. The morphological characteristics of the polymer blends were analyzed using phase contrast microscopy, scanning electron microscopy, and image analysis software. Scanning electron microscopy and image analysis software were used to assess fiber diameter and pore size of electrospun scaffolds. Scaffold permeability measurements were also used to calculate fiber diameter and pore size, and the values were compared to those obtained using image analysis. The material property results acquired from the research suggest that the electrospun polymer blends have potential for use in vascular graft applications.

Ce travail présente les résultats d'un modèle théorique de précipitation de particules Al$_2$Cu dans un alliage d'aluminium de fonderie de type 319 traité thermiquement T7, prenant en compte les équations de la théorie de la coalescence. L'utilisation d'une distribution de taille de particules expérimentale discrétisée comme point de départ du modèle rend possible l'utilisation d'une équation de flux afin de modéliser l'évolution du rayon moyen des particules dans un élément de volume représentatif de l'alliage. L'utilisation d'un schéma numérique implicite permet de ramener la résolution du problème physique à l'inversion d'une matrice tridiagonale. Ainsi, l'évolution du rayon critique de coalescence, du nombre total et de la fraction volumique de précipités sont obtenus pour plusieurs vieillissements. Les résultats du modèle a été confrontés aux résultats des mesures expérimentales qui ont été réalisées à l'aide d'observations en microscopie électronique à transmission et qui ont permis une mesure de la taille des précipités. Ces derniers ont été assimilés à des sphères de volume équivalent aux plaquettes réelles et ont été analysés numériquement. Les résultats fournis par le modèle théorique sont en bon accord avec les mesures expérimentales et ont permis le couplage du modèle de coalescence avec un modèle micromécanique fondé sur la théorie des dislocations et calibré à l'aide d'essais de traction en température. Il permet de déterminer la limite d'élasticité de l'alliage pour un vieillissement jusqu'à 1000h compris entre 23°C et 300°C. La limite d'élasticité est alors assimilée à une somme de trois contraintes~: une contrainte liée à la friction de réseau (contrainte de Peierls), une contrainte liée au contournement des précipités par les dislocations (contrainte d'Orowan) et une contrainte liée à la présence de solution solide. Enfin, des essais de fatigue oligocyclique à différentes températures ont permis de déterminer les variables internes de la loi de comportement macroscopique. Il s'agit d'une loi élasto-viscoplastique de type Lemaitre et Chaboche, à laquelle la limite d'élasticité calculée par le modèle micromécanique est couplée. Ainsi, le comportement physique macroscopique de l'alliage est fonction de la coalescence des précipités. Des calculs 1D ou 3D, par éléments finis, permettent alors de déterminer le comportement général d'une culasse soumise à de la fatigue thermomécanique / This work highlights the results of a theoretical Al$_2$Cu particles coarsening model in a T7 thermal treated 319 aluminum alloy. As an input of the model, the experimental and discretised size distribution of the precipitates, in a 1$mu$m$^3$ representative volume element of the alloy, is used and coupled to a flux equation. The use of a numerical implicit scheme allows us to solve the problem by the inversion of a tridiagonal matrix. Thus, the evolution of the critical radius of coarsening, of the total number and of the volumical fraction of particles are modeled in a range of temperature going from 23°C to 300°C up to 1000h ageing time. Results were then compared to transmission electron microscope observations and are in good agreement with experimental measurements. Hence, the model was then coupled to a micro-mechanical model which is based on the theory of dislocations. It determines the real yield stress of the alloy generated by the interaction of the dislocations with the lattice (Peierls stress), with the precipitates (Orowan stress) and with the atoms in solid solution. Both models were then combined into a mechanical macro-scale model in order to represent the LCF behavior of the material. An elasto-viscoplastic law has been used and all the internal variables were experimentally determined using LCF stress/strain loops for the mechanical steady state. The simulation results are in good agreement with the experiments. Finally, 1D and 3D finite element computations could be run, taking into account the evolution of the microstructure during ageing and its impact on the evolution of the mechanical properties, to determine the head cylinder behavior under thermomechanical fatigue

The finite element method (FEM) has been widely applied to various medical imaging applications over the past two decades. The remarkable progress in high-resolution imaging techniques has allowed FEM to draw great research interests in computing trabecular bone (TB) stiffness from three-dimensional volumetric imaging. However, only a few results are available in literature on applying FEM to multi-row detector CT (MDCT) imaging due to the challenges posed by limited spatial resolution. The research presented here develops new methods to preserve TB structure connectivity and to generate high-quality mesh representation for FEM from relatively low resolution images available at MDCT imaging. Specifically, it introduced a space-variant hysteresis algorithm to threshold local trabecular structure that preserves structure connectivity. Also, mesh generation algorithms was applied to represent TB micro-architecture and mesh quality was compared with that generated by traditional methods. TB stiffness was computed using FEM simulation on micro-CT (µ-CT) and MDCT images of twenty two cadaveric specimens of distal tibia. Actual stiffness of those specimens were experimentally determined by mechanical testing and its correlation with computed stiffness was analyzed. The observed values of linear correlation (r2) between actual bone stiffness and computed stiffness from µ-CT and MDCT imaging were 0.95 and 0.88, respectively. Also, reproducibility of the FEM-based computed bone stiffness was determined from repeat MDCT scans of cadaveric specimens and the observed intra-class correlation coefficient was a high value of 0.98. Experimental results demonstrate the feasibility of application of FEM with high sensitivity and reproducibility on MDCT imaging of TB at distal tibia under in vivo condition.

The research contained within this thesis formed part of an Engineering and Physical Sciences Research Council (EPSRC) funded project based at Loughborough University, which aimed to investigate the use of additive manufacturing (AM), and in particular sintering technologies, for the production of running footwear sole units. Laser sintering (LS) is an AM process which produces parts directly from a computer aided design (CAD) file by selectively fusing successive layers of powdered material using a CO2 laser. LS imparts significant advantages over traditional manufacturing techniques including extensive design freedom, the ability to manipulate the local properties of a single material part as well as economical manufacture of bespoke items due to the elimination of tooling. Modifying the mechanical properties and/or geometry of sole units has been shown to provide benefits in the areas of performance, injury risk reduction and comfort, especially when considering elite athletes on a subject specific basis. Given the attributes of LS outlined above, the technology offers significant potential to produce sole units offering high added-value compared to conventional counterparts which are limited by the constraints of traditional processing techniques such as injection moulding. However, the mechanical capacity of LS polymers in context of such application was unknown. Accordingly, this research investigated the suitability of a laser sintered elastomer (LSE) material, in view of key selected mechanical properties, for the manufacture of running shoe midsoles. The midsole is the primary functional component in the sole unit of a running shoe used for distance running on hard surfaces. Following a preliminary assessment of the selected LSE (TPE 210-S), a new dynamic test method was designed to assess the compressive, fatigue and time dependent recovery properties of midsole material specimens under loading conditions representative of in-service use. The method was successfully implemented on an electro-mechanical test apparatus (previously unreported upon in literature) and used firstly, to benchmark the aforementioned properties of a range of ethylene vinyl acetate (EVA) and polyurethane (PU) midsole foams representative of the range currently used in production, and secondly, to establish the same property set for TPE 210-S specimens produced across a range of laser powers (LP's). Initial cycle operating ranges in terms of key compressive properties were established for EVA and PU materials. All conventional variants showed considerable deterioration from these initial values over the 125,000 cycle test regime, but subsequently demonstrated partial recovery when left unloaded post-test. PU grades generally exhibited better fatigue performance and findings were consistent with those of previous studies. Whilst variation in LP facilitated linear variation in displacement and stiffness properties for TPE 210-S, all specimens yielded a stiffer and more elastic response than that of conventional foams at the outset; initial compressive operating ranges, whilst within close proximity, did not overlap. However, fatigue performance was found to be superior with only relatively small property changes occurring over the test regime regardless of LP. Furthermore, no signs of catastrophic specimen failure (e.g. cracking) were visually apparent. In this respect the material showed good suitability for midsole applications, but further work is required to address increasing the available compressive property range which fell outside the scope of this work.

The economical and environmental issues associated with fossil fuels have been urging the automotive industry to cut the fuel consumption and exhaust emission levels, mainly by reducing the weight of vehicles. However, customers increasing demands for safer, more powerful and luxurious vehicles have been adding more weight to the various categories of vehicles, even the smallest ones. Leading car manufacturers have shown that significant weight reduction, yet satisfying the growing demands of customers, would not be feasible without the extensive use of lightweight materials. Magnesium is the lightest constructional metal on earth, offering a great potential for weight-savings. However, magnesium and its alloys exhibit inferior ductility at low temperatures, limiting their practical sheet metal applications. Interestingly, some magnesium alloys exhibit superplastic behaviour at elevated temperatures; mirrored by the extraordinarily large ductility, surpassing that of conventional steels and aluminium alloys. Superplastic forming technique is the process used to form materials of such nature, having the ability to deliver highly-profiled, yet very uniform sheet-metal products, in one single stage. Despite the several attractions, the technique is not widely-used because of a number of issues and obstacles. This study aims at advancing the superplastic forming technique, and offering it as an efficient process for broader utilisation of magnesium alloys for sheet metal applications. The focus is primarily directed to the AZ31 magnesium alloy, since it is commercially available in sheet form, possesses good mechanical properties and high strength/weight ratio. A general multi-axial anisotropic microstructure-based constitutive model that describes the deformation behaviour during superplastic forming is first developed. To calibrate the model for the AZ31 magnesium alloy, systematic uniaxial and biaxial stretching tests are carried out over wide-ranging conditions, using 3 specially-designed fixtures. In a collaborative effort thereafter, the calibrated constitutive model is fed into a FE code in conjunction with a stability criterion, in order to accurately simulate, control and ultimately optimise the superplastic forming process. Special pneumatic bulge forming setup is used to validate some proposed optimisation schemes, by forming sheets into dies of various geometries. Finally, the materials post-superplastic-forming properties are investigated systematically, based on geometrical, mechanical and microstructural measures.

The demands for high density, fine pitch interconnections in electronics systems has seen solder-based approaches for such interconnections miniaturized to the scale of tens of micro meters. At such a small scale, such 'micro joints' may contain only one or a few grains and the resultant mechanical behaviour may not be that for a polycrystalline aggregate, but rather for a single crystal. Since the ~-Sn matrix of SnAgCu solder has a contracted body-centred tetragonal (BCT) structure, such a solder grain is expected to demonstrate a considerably anisotropic behaviour. In such cases the reliability of a Phfree solder is strongly dependent on the local microstructural features, such as the size and orientation of the grains. This thesis presents the investigation of the evolution of microstructure within a joint or at the interface and, the influence of such microstructural features on the meso-scale mechanical behaviour of the Ph-free solder. It includes Evolution of the interface between a molten solder and the Cu substrate To form a joint, the solder alloy is heated and molten, wetting a solid under-bump metallization. After solidification, layers of brittle intermetallic compounds (IMCs) are formed at the interface. In this project, facilities were set up to obtain interfacial reactants at an arbitrary moment of the liquid/solid reaction. Formation and evolution ~ during reflow of SnCu IMCs at the interface between the molten SnAgCu alloy and the Cu UBM was captured and presented for the first time. Formation of phases and IMCs with the body of a liquid SnAgCu solder during solidification The formation behaviour of basic components for a SnAgCu grain (including Sn dendrites, AIDSn and Cu6Sns IMCs) during solidification was investigated. Relationships between the growth behaviour of these components and their internal lattice orientation were studied. The characteristic growth and coupling of AIDSn IMCs and the Sn matrix to form eutectics has been elaborated and presented in this study for - 1- the first time. Based on the results, the forming process of a eutectic SnAgCu grain under the non-equilibrioum solidification condition was illustrated; and major factors that determine the lattice-orientation, size and substructure of the grain were discussed. Meso- and Micro- scale mechanical behaviour of a SnAgCu solder joint To study the size effect on the microstructure, and subsequently, the meso-scale mechanical behaviour, solder joints were manufactured with varying geometries. Shearing tests were performed on these meso-scale joints. The results first demonstrated that the anisotropic characteristics of a SnAgCu grain play an important role in the mechanical behaviour of both a meso-scale solder joint and the adjacent interfacial IMCs. To further investigate the micro-scale deformation and damage mechanisms, micro-mechanical tests were preformed within a SnAgCu grain. Constitutive equations for a SnAgCu grain Based on the experimental results, a crystal model was established to describe the local microstructure-dependent mechanical behaviour. The constitutive equation was implemented by means of the finite element approach, and applied in solder joints of a Flip Chip (FC) package by a multi-scale method. To describe the crystal behaviour at the higher temperature, the model was improved to account for deformations due to vacancy diffusion and thermal expansion. This model was integrated by an implicit approach, and implemented in a full three dimension (3D) finite element (FE) model.