The Method of Measuring Modulus Change Continuously during Fatigue Test of Plastics

Abstract

In this report a new method of explaining the fatigue of plastics in terms of the change of their properties is proposed. The fatigue testing machine used here is ASTM (D 671-63 T, Method B) type, constant amplitude of force, cantilever flexural fatigue, and is equipped with differential transformer displacement meter and the moment bar with strain gage. According to the dynamic rheological theory, |E*|=σ0/ε0=KP0/d0 where |E*|: absolute value of complex dynamic Young's modulus, σ0·ε0·P0·d0: peak value of stress·strain·load·deflection respectively, K: size parameter of specimen, and K was derived as follows. In the case of rectangular specimen K=4L3/bh3 and ASTM type triangular specimen K≈3L2/tan θ h3 where L·b·h·θ: distance between both grips·width·thickness·inclination angle of side line, of specimen respectively. When K, P0 are given, the change of |E*| can be observed during the fatigue test by measuring d0 continuously with dynamic displacement meter.The results of experiment show that the change of d0 and the temperature rise of specimen are characteristic of the materials, though the calculation of |E*| has sometimes been disturbed by the rise and growth of crack in the specimen. It is concluded that this method is applicable to the study of the fatigue of polymeric materials.