In this dissertation, theoretical, computational, and experimental methodologies are introduced to determine the rate-dependent material properties of the brain tissue. Experiments have shown that the brain tissue is significantly rate-dependent. To examine the range of strain rates at which trauma might happen, a validated finite element (FE) human head model was initially employed to examine the biomechanics and dynamic behavior of the head and brain under impact and blast loads. The strain rates to cause traumatic brain injury (TBI) were found to be in the range of 36 to 241 1/s, under these types of loadings. These findings provided a good estimation prior to exploring the required experiments for characterizing the brain tissue. The brain samples were tested by employing unconfined compression tests at three different deformation rates of 10 (n= 10 brain samples), 100 (n=8), and 1000 mm/sec (n=12). It was found that the tissue exhibited a significant rate-dependent behavior with various compression rates. Two different material characterization approaches were proposed to evaluate the rate-dependent mechanical responses of the brain. In the first approach, based on the parallel rheological framework, a single-phase viscoelastic model which captures the key aspects of the rate-dependency in large strain behavior was introduced. The extracted material parameters showed an excellent constitutive representation of tissue response in comparison with the experimental test results (R^2=0.999). The obtained material parameters were employed in the FE simulations of the brain tissue and successfully verified by the experimental results. In the second approach, the brain tissue is modeled as a biphasic continuum, consisting of a compressible solid matrix fully saturated with an incompressible interstitial fluid. The governing equations based on conservation of mass and momentum are used to describe the solid-fluid interactions. This viscoelastic biphasic model can effectively estimate the rate-dependent tissue deformations, the hydrostatic pressure as well as fluid diffusion through the tissue. Although both single-phasic, as well as bi-phasic models, can successfully capture the key aspects of the rate-dependency in large strain deformation, it was shown the biphasic model can demystify more phenomenological behavior of this tissue that could not be perceived with yet established, single-phasic approaches.

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The complex interface between tyre and terrain is a largely studied topic in terramechanics and vehicle dynamics research. This interface, known as the contact patch, is however hidden from view and cannot easily be measured. Several studies have focused on measuring tyre strain on the inside surface of the tyre to indirectly determine tyre parameters. The inner surface is separated from the contact patch by the tyre thickness however this difference can be considered small in comparison to the bene t gained by a safe environment for measurement systems. Static studies of tyre strain have been successful however lacks the important phenomena occurring in a rolling tyre. Tyre strain measurements in dynamic tyres have been limited to discrete points and/or once per revolution, which is an insufficient sampling rate for vehicle stability controllers such as ABS. This study performs full-fi eld and point strain measurements of the inner tyre surface of a rolling agricultural tyre at low speeds. Stereo cameras mounted on a mechanically stabilised rim will record full-fi eld measurement of the contact patch kept in constant view. Digital Image Correlation techniques are used to determine full-fi eld deformation and strain from successively captured images. Point measurements, such as strain gauges, are included in the study for a comparative measurement. An agricultural tyre hosts large lugs which include large strain concentrations within the contact patch. The complex tyre structure signi ficantly influences the strain measurements, other factors such as inflation pressure, vertical load and slip angle is also studied. Since most vehicle forces are transmitted through the tyre at the tyre-terrain interface, capabilities to measure this area will be a great benefi t for tyre research and leading towards a smart tyre. / Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2020. / Mechanical and Aeronautical Engineering / MEng (Mechanical Engineering) / Unrestricted

Composites are now being incorporated into aircraft designs because of their high strength to weight ratio compared to traditional metal materials. Due to the complexity of the material, composite parts are presently being over designed to satisfy static and fatigue requirements. A greater understanding of composite fatigue behavior will allow for even greater weight savings leading to increased fuel economy. A critical part of an aircraft that is subjected to fatigue bending loads are its wings. The forces acting on the wings include its lift distribution, powerplant, and fuel which can be carried in the wing body. When in flight these forces repeatedly cause cyclic displacements which could ultimately lead to failure. It is important to design the wing spars which carry the bending loads, to be fatigue resistant so that damage or expensive inspections could be avoided. Wing models were be made from composite materials with a NACA 0016 airfoil shape, chord length of 9.25”, and a span of 15.25”. The C – channel spars were located at 22% and 72% of the chord. Strain gages on the wing model were used to measure strain at different locations. Static test were conducted on the specimens in order to validate a finite element analysis(FEA) model to be used for simulations. Overall, the strain measurements on the leading edge from two of the wings matched the model within 9% of the simulation results. Additional spar designs were then analyzed to determine the optimal one for static and fatigue bending loads. The wings were fatigue tested under displacement control at a test frequency. A model 8801 servo-hydraulic Instron machine and Wave Matrix software was used to fatigue the wings. After 100,000 cycles the test would be deemed a success and concluded.

An experiment was carried out in order to locate and quantify osteon types within a sample of cortical bone taken from a human tibia. This was done using a microscope-camera assembly and the BioQuant computer software. The results of this were correlated with a previous experiment’s results on fracture toughness so that an analysis could be run on the data in order to determine the factors that most affect the value of fracture toughness of this cortical bone. Results were examined closely and the analysis repeated until the author was satisfied that the best possible model for fracture toughness had been achieved. A combination of usable parameters included: region, porosity, volume fraction of lightfield osteons, volume fraction of hooped osteons, volume fraction of dark osteons, volume fraction of alternating osteons, volume fraction total, density, average diameter total, average diameter of hooped osteons, average diameter of lightfield osteons, average diameter of darkfield osteons and average diameter of alternating osteons. This model explains the parameters that most affect fracture toughness by using a regression analysis, which also provides a regression equation to show exactly how much each specific parameter affects the fracture toughness value

Geostructures experience repetitive load cycles, which gradually affect their long-term performance. This thesis explores the long-term response of soils subjected to mechanical load-unload, heat-cool, freeze-thaw, and atmospheric pressure oscillations. The research methodology involves new instrumented cells (oedometer, temperature-controlled triaxial chamber, and pressure-controlled drying chamber), various geophysical monitoring methods (X-ray micro-CT, NMR, S-wave, and EM-waves), and simulations using discrete element modeling. Results show that soils subjected to repetitive mechanical or environmental loading experience shear and volumetric strain accumulation and changes in saturation (during barometric pressure cycles). In all cases, soils evolve towards an asymptotic terminal void ratio; the change in void ratio is pronounced when the soil exhibits grain-displacive ice formation during freeze-thaw cycles. The initial stress obliquity defines the shear strain response, which may be either shakedown -at low stress obliquity-, or ceaseless shear strain accumulation in ratcheting mode when the maximum stress obliquity approaches failure conditions. Finally, we provide simple engineering guidelines to estimate the long-term behavior of soils subjected to repetitive mechanical or environmental loading.

Presented work deals with the strain-stress analysis of a spinal segment while monitoring the influence of total disk replacement Maverick on the global behaviour of the spinal segment. It also assesses the influence of this implant on the nearest upper intervertebral disk. On the basis of CT images was in the program Rhinoceros created the geometry model of spinal segment Th12-L2. The geometry model of implant was applied between vertebra L1 and L2 instead of intervertebral disk from which the whole core was removed, while in the immediate surrounding of implant the part of disk was left, which is important from the view of stability. Subsequently were in the program Ansys Workbench created finite element models for two states: - healthy (unbroken) status - status with applied implant Then the calculations for movements were realized: lateral flexion, flexion, extension, rotation. For the same movements were realized calculations of the model simulated spinal fusion of the vertebras L1-L2. Finally an influence both of methods (total disk replacement, spinal fusion) on the intervertebral disk Th12-L1 was compared.

The subject of this diploma thesis is to optimize the shield of asynchronous motor. In the thesis are given results of modal and the strain-stress analysis made for model of the shield, which is currently produced. To resolve this issue was used CAE programming system Pro/MECHANICA, which is based on method of geometric elements – GEM. The main output of this work is proposal of two new optimized shields of asynchronous motor and for these are presented results of modal analyse and the strain-stress analysis. Part of the thesis is design and technical-economic evaluation of casting methods for new shield production.

Master thesis deals with design of "student" pneumatic car equipped by pneumatic elements of a chosen firm. The introductory part is devoted to mapping the Hungarian competition. The idea of designing such vehicles comes from this competition. Next step is analysis of vehicles that are present in this competition. The main part describes the development of vehicle from the initial design, through analysis of main components, through to the production and presentation. The work contains a strain-stress analysis of the frame which is made by using the finite element method. The work ends with the conclusion which assesses the results.

The project elaborated in frame of engineering studies branch M-STG describe characteristics of plasticity of non-anneal materials E 235, E 190 and E 220. Materials characteristic was receive by static and dynamical tests. Based on the literature study it was conducted survey of the current state of experimental techniques for high-speed deformation. The materials were designed by Holomon approximation of rigid-plastic material model without hardening. It was conducted force analyses for machine Unison MG 2790 for rewind bending and bend with compressive force considering the identified material model. It was describe the impact passive and active forces to move the neutral axis.