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A finite element analysis approach is used to determine the susceptibility to wrinkles for thin sheets with clamped ends when subjected to tensile loading. The model problem chosen to do this analysis is the stretching of a thin sheet with clamped-ends. In the preliminary analysis, a stress analysis of thin sheets is done to study the stresses that develop under these boundary conditions. The analysis shows that there is a stretch-induced compressive stress in the transverse direction to the applied load that causes wrinkles. Then, the parametric study is conducted to determine the effect of aspect ratio and strain on the compressive stress. Based on the results of the parametric study, a critical strain value for each aspect ratio is determined for which the corresponding compressive stress is zero. Further buckling analysis is performed to find the buckling modes of the model problem that shows a limit of aspect ratio below which buckling is not possible under given conditions. Finally, post-buckling analysis shows the nature of wrinkles observed in the model problem for different aspect ratios. / text

In packaging industries, the demand for usage of Low Density Poly Ethylene foil is of profound interest. In the past, research was carried out on finite and infinite plates with varying crack lengths but having constant crack width. In this thesis, a detailed analysis on crack initiation is carried out on finite plates by varying width of the hole. The hole shapes for stress analysis include circle, ellipse and rectangular notch. Initially, maximum stress is found out using Linear Elastic Fracture Mechanics (LEFM) theory and compared with Finite element method (FEM) results. Secondly using Elastic Plastic Fracture Mechanics theory (EPFM), critical stress and geometric function are evaluated theoretically by Modified Strip Yield Model (MSYM) and numerically by ABAQUS. Finally, a tensile test is conducted to validate the theoretical and numerical results.  By varying the width of the hole, a study on the parameters like critical stress, geometric function is presented. A conclusion is drawn that the effect of hole width should be considered when calculating fracture parameters.

Disease and degeneration of articular cartilage and fibrocartilage tissues severely compromise the quality of life for millions of people. Although current surgical repair techniques can address symptoms in the short term, they do not adequately treat degenerative joint diseases such as osteoarthritis. Thus, novel tissue engineering strategies may be necessary to combat disease progression and repair or replace damaged tissue. Both articular cartilage and the meniscal fibrocartilage in the knee joint are subjected to a complex mechanical environment consisting of compressive, shear, and tensile forces. Therefore, engineered replacement tissues must be both mechanically and biologically competent to function after implantation. The goal of this work was to investigate the effects of oscillatory tensile loading on three dimensional engineered cartilaginous tissues in an effort to elucidate important aspects of chondrocyte and fibrochondrocyte mechanobiology. To investigate the metabolic responses of articular chondrocytes and meniscal fibrochondrocytes to oscillatory tensile loading, various protocols were used to identify stimulatory parameters. Several days of continuously applied tensile loading inhibited extracellular matrix metabolism, whereas short durations and intermittently applied loading could stimulate matrix production. Subpopulations of chondrocytes, separated based on their zonal origin within the tissue, differentially responded to tensile loading. Proteoglycan synthesis was enhanced in superficial zone cells, but the molecular structure of these molecules was not affected. In contrast, neither total proteoglycan nor protein synthesis levels of middle and deep zone chondrocytes were substantially affected by tensile loading; however, the sizes of these new matrix molecules were altered. Up to 14 days of intermittently applied oscillatory tensile loading induced modest increases in construct mechanical properties, but longer durations adversely affected these mechanical properties and increased degradative enzyme activity. These results provide insights into cartilage and fibrocartilage mechanobiology by elucidating cellular responses to tensile mechanical stimulation, which previously had not been widely explored for these tissues. Understanding the role that mechanical stimuli such as tension can play in the generation of engineered cartilaginous tissues will further the goal of developing successful treatment strategies for degenerative joint diseases.

Metastable austenitic and duplex stainless steels are widely used materials in industrial anddomestic applications, owing to their attractive characteristics such as good corrosion resistanceand favorable mechanical properties. Both types of steel experience enhanced mechanicalproperties during plastic deformation due to the formation of the martensite phase from theparent austenite phase, this is called deformation-induced martensitic transformation (DIMT).It is therefore of technical interest to study the transformation mechanism and its impact onmechanical properties for a better understanding and ultimately for developing new materialswith improved performance in certain applications. In the present thesis, two austenitic stainless steels (201Cu, HyTens® 301) and two duplexstainless steels (FDX25®, FDX27®) were investigated. Samples were tensile tested during insitusynchrotron radiation experiments performed at the Cornell High Energy SynchrotronSource (CHESS), Ithaca, USA. Tests were performed at both room temperature and at elevatedtemperatures. The collected diffraction data were then processed by software such as Fit2D andMATLAB. Quantitative phase fraction analysis based on the direct comparison method wasperformed successfully. Microstructural analysis of samples before deformation and after thefull tensile testing was also performed using electron microscopy. The deformation induced martensitic transformation took place in HyTens 301, FDX25 andFDX27, but in 201Cu the austenite was stable during the tensile tests conducted here. The a’-martensite formed in a significantly higher fraction than the ε-martensite in all alloys. At roomtemperature, the critical stress levels for martensitic transformation were 490 MPa, 700 MPaand 700MPa for HyTens 301, FDX25 and FDX27, respectively.

<p>The rotator cuff is a group of four muscles and tendons in the shoulder that function to lift and rotate the arm. Rotator cuff tendon tears are increasingly common: more than 545,000 rotator cuff surgeries occur annually in the US. However, treatment is often complicated by disorganized collagen matrix formed via fibrosis and results in high re-tear rates. Tendon tissue engineering seeks to solve the problem using biomaterials to promote neo-tendon formation to augment repair or regenerate tendon. However, while current biomaterials provide the opportunity to improve tendon healing, they frequently still exhibit fibrosis in preclinical studies. Therefore, a critical need exists to understand the mechanisms of aligned collagen formation when designing biomaterials for tendon tissue engineering. Matrix architecture and transient receptor potential cation channel subfamily V member 4 (TRPV4) regulate aligned collagen formation during tenogenesis in vitro, but the mechanism remains to be determined. Recently, TRPV4 stimulation was found to induce nuclear localization and activation of transcriptional co-activators Yes-associated protein (YAP). YAP expression is upregulated during tendon development, a process characterized by aligned collagen formation, and in response to physiological mechanical stimulation, suggesting it could play an important role in tendon. The objective of this work is to improve tissue engineering strategies and progress toward making a device that regenerate tendon after injury. Aim 1 incorporates tendon-derived matrix into synthetic polymer scaffolds to add biological signaling cues to induce tenogenesis. Aim 2 uses a 2D photolithography system (microphotopatterning) to optimize architectural and structural cues to promote stem cell differentiation toward tenogenic, chondrogenic, and osteogenic lineages. Aim 3 investigates dynamic tensile loading protocols to promote collagen matrix synthesis and improve engineered tendon mechanical function. Aim 4 investigates the role of TRPV4 and YAP in collagen alignment during engineered tendon development.</p>