A B S T R A C TPermeable microporous foams and membranes of biodegradable polyesters are currently used in the area of tissue engineering and drug delivery systems. Their mechanical properties are useful in the medical applications. The foams should mechanically fit to the tissues where the foams were implanted. In this study, we investigated the mechanical properties of the foams of biodegradable polyesters by compression tests. Microporous foams of poly(L-lactic acid), poly (ε-caprolactone), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) were prepared by thermally induced phase separation method. The compression tests were performed at 23-24 C with a universal testing machine. The structure of the microporous foams depended on the kinds of polymers, polymer concentrations, and quenching temperatures. The cell size of the foams was smaller when the polymer concentration was higher or the quenching temperature was lower. We analyzed the stress-strain diagrams of the foams in the compression test. The lower the relative density of the foams to the solid materials the lower the elastic limit stress was. The relative Young's modulus and relative elastic limit stress of the foams were approximately proportional to the square of their relative density and less dependent on their cell size. The dependences were similar to those of open-cell foams of polyurethane.

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Cymbals are percussion instruments that vibrate and radiate sounds when hit with a stick. A bell is the raised section in the middle of the cymbal and its size produces different sounds. In this study, we investigate the effect of bell size on the sound characteristics of cymbals. The radiated sounds and vibrations for cymbals with two different bell sizes are measured. In addition, the natural frequency and mode shape are obtained by finite element analysis and the sound radiation efficiency is calculated for each mode. The measured results indicate that the sound frequency characteristics for the large bell show three peaks with large sound pressure within the range of 1000 to 3000 Hz and the sound pressure for the small bell is larger than that for the large bell within the range of 4000 to 5000 Hz. The vibration frequency characteristics show there is no remarkable difference between the large and small bells. The sound radiation efficiencies indicate that the large bell has many modes with high radiation efficiency within the range of 1000 to 3000 Hz and their modes have a small number of nodal diameters and a large deformation at the bell. The small bell has many modes with high efficiency within the range of 4000 to 5000 Hz. This is reason for the difference in sound characteristics between the large and small bells.

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