Abstract
Flexural creep tests on several engineering plastics were carried out for more than three years at room temperature.
Deflections after two or more than three years were estimated from the data in the first stage of the creep tests, and the accuracy of estimation was discussed by comparing the estimated values of deflections with observed ones.
The results obtained are as follows:
(1) Using the five data points obtained in the period from 96hrs to 504hrs (three weeks), the total deflection after two or more than three years can be estimated within about 5% error.
(2) The following two equations are applicable for the estimation:
logY=alogt+b (1)
log(Y-Y0)=a'logt+b' (2)
where Y is deflection, Y0 initial deflection, t time, and a, b, a', and b' are constants.
The values calculated from equation (2) are larger than those from equation (1), and equation (2) is better than equation (1) especially for estimating the deflection of glass-fiber reinforced thermoplastics.
(3) The constants a and a' in the equations are related to the rate of increase in total deflection and the creep speed and are independent of stress. Especially, the constant a' is almost independent of glass-fiber contents, and it takes a particular value for each plastics.
The constants b and b' depend on the modulus of specimen, so that their values are controlled by the loading stress.
