Mechanical properties of the fresh control, frozen, and vitrified cartilaginous (cartilage and meniscus) samples were measured by microindentation. Indentation depth, elastic modulus, and indentation yield strength were obtained from the microindentation loading curves. Indentation deformation behavior was studied using Hertz contact model. The stress distribution of cartilaginous tissues under indentation loading was analyzed by finite element technique. It was found that fresh tissue shows the lowest indentation depth and the highest elastic modulus and indentation yield strength, followed by vitrified and frozen tissues. The vitrified tissue shows slightly lower but comparable mechanical properties with control tissue. The vitrification technique used in this study can preserve live cells with superior mechanical properties that make it an ideal technique for use in orthopedic and other biomedical applications. The microindentation tests and corresponding analysis methods used in this study offer a simple way to evaluate the mechanical properties of cartilaginous tissues. It suits small sample sizes and it may be used for other biological tissues.

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Friction stir welding (FSW) can produce superior mechanical properties in the weld zone. The purpose of this article is to find the optimum FSW process operating conditions for two plates of aluminum alloy AA5083 welded in butt joint. In addition to optimizing the performance characteristics, the cost is considered in the optimal FSW process. In the FSW procedure, there are four major controllable four-level factors, i.e. the tool rotation speed, transverse speed (feed rate), tool tilt angle with respect to the workpiece surface, and pin tool length. The uncontrollable factors are the ultimate tensile strength and elongation rate which can be converted to signal-to-noise ratios the larger the better. In order to achieve the aim of robustness in the multiple response process, the gray-based Taguchi method is proposed. A gray relational grade obtained from gray relational analysis is used as the multiple performance characteristic. The resulting optimum process parameters are rotation speed at 1800 rpm, transverse speed at 180 mm/min, tool tilt angle at 1 , and pin tool length at 2.9 mm for the best multiple performance characteristics with minimum cost.

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