Microstructural optimization of cellular acoustic materials

A microstructure based acoustic model is introduced, which can be used to optimize the microstructure of cellular materials and thus to obtain their optimal acoustic property. This acoustic model is an unsteady one which is appropriate in the limit of low Reynolds numbers. The model involves three elements. This first involves the propagation of acoustic waves passing the cylinders whose axes are aligned parallel to the direction of propagation. The second model relates to the propagation of acoustic waves passing the cylinders whose axes are aligned perpendicular to the direction of propagation. In both cases the interaction between adjacent cylinders is taken into account by considering the effect of polygonal periodic boundary conditions. As these two models are linear they are combined to give the characteristics of propagation at arbitrary incidence. The third model involves propagation passing spheres in order to represent the joints. Heat transfer is also included. These three models are then used to expand the design space and calculate the optimum cell structure for desired acoustic performance in a number of different applications. Moreover, the application fields are also analyzed.

Development and validation of a new method for measuring friction between skin and nonwoven materials.

A new method for measuring the coefficient of friction between nonwoven materials and the curved surface of the volar forearm has been developed and validated. The method was used to measure the coefficient of static friction for three different nonwoven materials on the normal (dry) and over-hydrated volar forearms of five female volunteers (ages 18-44). The method proved simple to run and had good repeatability: the coefficient of variation (standard deviation expressed as a percentage of the mean) for triplets of repeat measurements was usually (80 per cent of the time) less than 10 per cent. Measurements involving the geometrically simpler configuration of pulling a weighted fabric sample horizontally across a quasi-planar area of volar forearm skin proved experimentally more difficult and had poorer repeatability. However, correlations between values of coefficient of static friction derived using the two methods were good (R = 0.81 for normal (dry) skin, and 0.91 for over-hydrated skin). Measurements of the coefficient of static friction for the three nonwovens for normal (dry) and for over-hydrated skin varied in the ranges of about 0.3-0.5 and 0.9-1.3, respectively. In agreement with Amontons' law, coefficients of friction were invariant with normal pressure over the entire experimental range (0.1-8.2 kPa).