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The suspensory apparatus of the distal phalanx (SADP) is an intricate adaptation of dermal and epidermal tissue that has a specialized role in the horse to absorb concussion while suspending the weight of the horse from within the hoof. The integrity of the hoof-bone connection is critical to the health of the horse and it can be affected by numerous disorders that cause it to fail. Accurate data on the ultimate tensile strength and other material properties of the SADP are important in modeling the behavior of the tissue under load and selecting appropriate prevention and treatment strategies for disorders of the SADP. The tensile load orientation and tissue sample size both have a profound effect on obtaining representative estimates for the material properties of a tissue. Consideration of the collagen fiber axis is important when selecting both. The purposes of this investigation were 1) to morphometrically determine the true collagen fiber axis in the SADP, 2) determine the most appropriate test sample size and tensile load orientation for materials testing, 3) to determine the ultimate tensile strength and other material properties of the SADP in healthy digits of adult horses, 4) to determine the site of tissue failure during testing, and 5) to determine whether freezing the SADP tissue samples prior to testing alters the material properties. Results of this investigation indicated that the true collagen fiber axis of the SADP in the toe region was predominantly vertical, in alignment with gravity. A vertical tensile load most closely matched the collagen fiber axis and was appropriate to model the load in the SADP for standing horses. A radial tensile load was appropriate to model the load in the SADP near the break over portion of the stride. Tissue blocks with a proximal-to-distal dimension of 1 cm tested less than 30% of the vertically oriented collagen fibers during radial tension testing and significantly underrepresented the ultimate tensile strength. The tissue failed in the deep dermis during radial tension testing and at the dermo epidermal junction during vertical tension testing. Freezing the tissue prior to testing significantly reduced the ultimate tensile strength.

The Punch test provides a technique for the determination of material properties from small specimens. Using the rectangular specimen, the test can be used to control the orientation of the cracking plane which was not possible in the ball punch on a circular disk design. A three dimensional quarter finite element model was formulated to simulate the punch test for 150°C and 300°C tests performed on So8 steel. The comparison of predicted and measured load-deflection and stress-strain curves showed good agreement between FE model and tests. A user interface, which allows for routine application, with the necessary postprocessing capabilities was developed and tested for the purpose of simulating miniature punch tests and estimating stress-strain data from measured load curves. / Thesis / Master of Applied Science (MASc)

Nanoindentation techniques have not been standardized for use on bone tissues, making comparison of bone material properties obtained via nanoindentation across studies difficult and unreliable. This study determined a set of optimal parameter values for thermal drift correction time, dwell time, and loading rate that can be used to obtain accurate and repeatable material properties from human femoral trabecular bone through experimentation and statistical analysis. All testing was conducted using a single nanoindenter on a single trabeculae, with the assumption that material properties within the individual trabeculae were internally consistent. Parameters not of interest during this study, such as ambient temperature, maximum load, and maximum indentation depth were held constant throughout all experiments. Elastic modulus and hardness data were calculated using the Oliver-Pharr technique. The optimal values for these parameters are as follows: 150 seconds for thermal drift correction time, 30 to 60 seconds for dwell time, and 0.4 to 0.8 mN/s for loading rate.

In this study, the seal bushings were designed to allow the lubricant stored in the screw and the nut system. Effect of thread clearance on the life of the screw were investigated. The screw and nut are made of S45C and HBsC3, respectively. Effects of material pairs on friction coefficient were investigated by using the pin on disk tester to simulate the friction condition between the screw and the nut. Result shows that the life of the screw increases with increasing thread clearance. The longest life for the maximum clearance can achieve 6790 cycles. Under the same surface pressure, the friction coefficients of HBsC3 on self-lubricating alloy and HBsC3 on SCM 440 are much smaller than self-lubricating alloy on self-lubricating alloy and self-lubricating alloy on SCM 440 by using nut on screw.

This research investigates the effects of the human body on the mechanical, chemical, and morphological properties of the surface of internal fixation devices. Stainless steel and titanium devices that had failed were provided from the Shandong Provincial Hospital in China, along with controls: implants that had never been used. Comparative study was conducted by evaluating properties of these implants before and after implanting. The first part of the research was simulation, and a model of the human femur was analyzed in Solidworks. The stress analysis software simulated the stress distribution, the strain distribution, and the deformation pattern. Two cases were simulated: walking and car accident. The simulations showed the points of highest stress and led to the analysis of the implants that were used in those regions. The next part of the research was to experimentally examine the properties and behavior of materials. Test samples fell into one of three categories: stainless steel femur implant, stainless steel tibia implant, and titanium femur implant. Material properties were characterized and effects of the human body on each of these groups were studied. Hardness was measured using Vickers hardness indentation. Surface roughness was analyzed using light interferometric technique. Potentiodynamic polarization analysis was performed to evaluate corrosive behavior before and after implanting. Scratch tests were conducted to evaluate wear resistance and the microstructure was analyzed to further understand the morphological changes that occurred of implanted samples. Results showed that the human body generally degraded the material properties of the stainless steel femur implant. There were no measurable effects of the same on stainless steel tibia and on titanium alloy.

Extreme events such as the Mont Blanc Tunnel fire in 1999 (Bettelini et al. 2001) or the Windsor Tower fire in 2005 (Calavera et al. 2005) have shown how concrete failure at elevated temperatures can be hazardous to the safety of members of the public. Generally, there is an absence of understanding of the mechanical behaviour of both plain and reinforced concrete at elevated temperatures, which is essential for computational modelling. Since fire is an extreme event, a certain amount of damage within the structure would be seen to be permissible within its performance objectives. This necessitates analysis in the post-peak regime. As a material, concrete has a very low value of thermal conductivity. This means that large thermal gradients often occur within concrete, causing differential expansion of the material. This, coupled with the change in mechanical properties at elevated temperatures, further complicates analytical analysis procedures. This study investigates issues associated with computational modelling of plain and reinforced concrete at elevated temperatures and its residual behaviour (behaviour when tested after the material has been heated, for example in a fire, and then cooled). In order to achieve this, first the constitutive material properties of both plain and reinforced concrete at ambient and elevated temperatures were investigated. The study showed that mesh sensitivity and localisation of strain softening occurs in plain concrete under both tensile and compressive loading. Path dependency of the stress-strain behaviour of plain concrete was also demonstrated, when it was subjected to loading and heating. Tension stiffening was included in the reinforced concrete material model, to represent the interaction between concrete and reinforcing steel. Complex behaviours were seen for simple reinforced concrete benchmark tests, due to changing material properties at elevated temperatures and differential thermal expansion of steel and concrete. Non-linear load-displacement relationships were seen as a result of complex load-sharing between concrete and reinforcement. A hypothesis was proposed – that variation of temperatures during heating and cooling of a specimen will cause damage, and hence material degradation, in plain and reinforced concrete. On investigation, it was seen that damage due to differential thermal expansion plays a small part in the reduction of elastic load-displacement slope and peak strength seen in experimental data on residual tests, indicating that other factors identified in previous research also affect the residual behaviour of plain and reinforced concrete. Indeed, in reinforced concrete, when tension stiffening was included, it was found that damage due to differential thermal expansion and contraction had a negligible effect on the residual response in the pre-peak regime. The study also found that for a simply supported beam pure thermal expansion caused a localised response, while pure thermal gradient gave distributed yield. When both were present, in this study, distributed yield with no mesh sensitivity was seen. Realistic heating of a restrained reinforced concrete plane strain model caused compressive stresses accompanied by tensile longitudinal total strains and tensile longitudinal plastic strains throughout the depth of the slab, with the largest values occurring near to the model supports. Damage and recovery variables were found to have no effect on the response of the model. When a portal frame was exposed to heating, plastic strains were distributed throughout the beam, with column rotation limiting downward thermal bowing due to a uniformly distributed load or thermal gradient present. Application of displacement loading causing plastic damage changed the behaviour of the structure under heating – instead of symmetrical compressive plastic strains being induced, areas of varying tensile and compressive strain were caused within the beam. Throughout, simple, easily reproducible simulations were used so that single parameters could be altered and considered. This was important, so that the important parameters to computational modelling could be identified. These can be used to guide experimental series to ensure that they are investigated, in order to improve computational material models. Not all variations of parameters were investigated in this study, but it is clear where further repetition would be beneficial (e.g. in varying thermal expansion and thermal gradient ratios in heating regimes). This study looks to address experimentalists and people working in structural analysis, who would be interested in the parameters investigated, as well as practitioners who may want to use these results.

When we stretch and contract a rubber band a hundred times, we expect the rubber band to fail. Yet our heart stretches and contracts the same amount every two minutes, and does not fail. Why is that? What causes the significantly higher elasticity of certain molecules and the rigidity of others? Equally importantly, can we use this information to design materials for precise mechanical tasks? It is the aim of this dissertation to illuminate key aspects of the answer to these questions, while detailing the work that remains to be done. In this dissertation, particular emphasis is placed on the nanoscale properties of elastomeric proteins. By better understanding the fundamental characteristics of these proteins at the nanoscale, we can better design synthetic rubbers to provide the same desired mechanical properties. / Ph. D.

No description available.

Understanding the origins of the multiaxial material properties of soft tissues is crucial for quantifying the tissue material properties that govern the material behavior for acurate predictive modeling of the biological systems. Unlike many engineering structural materials, biological materials exhibit complex material behavior due to structural anisotropy and various interactions between each of the microstructrual units of the tissue. Therefore, this study aims to quantify the shear material behavior of rabbit patellar tendon under simple shear loading along the fiber direction and perpendicular to the fiber direction and to understand the role of tissue shearing and its contribution to the overall mechanical behavior of the tendon. It was hypothesized that tendon demonstrates anisotropic material response under simple shear. Results suggests that tendon exhibits direction-dependent viscoelastic shear properties, reflecting structural anisotropy. The data obtained from our present study could be used for development of constituent models using internal state variable theory.