| Popis: |
The rate of propagation of longitudinal and shear waves in polycaproamide (PCA) at frequencies of 5 and 1 MHz has been measured in the temperature interval of 4·2–240°K. It was found that below 58°K the speed of sound in PCA is independent of temperature and the extent of the low temperature plateau is dependent on the frequency of the ultrasonic vibrations and the shape of the wave being propagated in PCA. In samples with a low degree of crystallinity an anomalous relationship between the speed of sound and the degree of crystallinity was observed. At temperatures below 157°K the speed of sound decreases as the degree of crystallinity increases. Young's modulus, the shear modulus, the bulk modulus, Poisson's ratio, the Debye temperature and the heat capacity of PCA have been calculated from the acoustic measurements. |
