Effects of time and temperature on the tension-tension fatigue behavior of short fiber reinforced polyamides

摘要

To support the fatigue design of the cyclically stressed plastics parts, such as automotive under-the-hood and exterior components, we analyzed the short-term and long-term mechanical performance (tensile strength, fatigue strength, and fatigue life) of short glass fiber reinforced polyamides PA 6 and PA 66. Comprehensive tension-tension fatigue tests were conducted with reference to the latest ASTM, ISO, and Japanese industrial standards for plastics, at temperatures from -40 degrees C to 121 degrees C, on materials aged at 121 degrees C for 0, 100, 500, and 1000 h. Tests were conducted at a loading frequency f = 5 Hz, stress ratio R = 0.1, and in a wide range of cycles to failure from 2 x 10(3) to 2 x 10(6). Without aging and for both PA 6 and PA 66, the highest fatigue strength or fatigue life was found at -40 degrees C; it decreased significantly at 23 degrees C, and decreased further at 121 degrees C. The fatigue strength of PA 6 was found to be higher than that of PA 66 at -40 degrees C, but the reverse was seen at 23 degrees C. At 121 degrees C, the fatigue strengths of PA 6 and PA 66 were virtually the same. Aging at 121 degrees C improved the tensile strength of PA 6 and PA 66 as aging time increased ham 100 to 1000 h, and this process seemed to be more influential for PA 6. [References: 18]