Effect of frequency upon fatigue strength of a short glass fiber reinforced polyamide 6: A superposition method based on cyclic creep parameters

Abstract

The fatigue behavior of a conditioned short glass-fiber reinforced polyamide 6 was studied and the effect of the cyclic frequency investigated. Load controlled fatigue tests were performed, and the strains and surface temperature of specimens were recorded continuously. The number of cycles to failure was found to be dependent upon cyclic creep rate, as is typical for short glass fiber reinforced polyamides in the conditioned state. A strong reduction of fatigue strength was observed for increasing cyclic load frequency. This was mainly related to the specimen temperature increase due to hysteretic self heating and its effect on the cyclic creep speed. A frequency superposition method is proposed, expressing the relationship between temperature rise, applied stress, and cyclic creep speed in terms of a parameter derived from the Larson-Miller steady creep parameter. POLYM. COMPOS.,

Effect of cycling frequency and self-heating on fatigue behavior of reinforced and unreinforced thermoplastic polymers

“…If the area inside the loop is multiplied by the frequency, the result is the dissipated energy per unit volume and time. A linear relationship between the temperature rise and dissipated energy per unit volume and time was suggested in , as presented in Eq . .…”

“…In a study by Bernasconi and Kulin on axial load‐controlled fatigue behavior of conditioned short glass fiber reinforced polyamide‐6, surface temperature rise was found to be dependent on stress and frequency. Conditioning consisted of submerging specimens in distilled water for 7 days at room temperature and then allowing them to reach equilibrium with ambient moisture at 23°C and 50% relative humidity.…”

Fast prediction of the Wöhler curve from heat build-up measurements on Short Fiber Reinforced Plastic

“…The second main factor for these injection molded parts is the very strong coupling between the microstructure on the one hand and the geometry and the process parameters on the other hand. The characterization of the influences of these numerous environment and process parameters on the fatigue properties therefore requires wide fatigue campaigns, which are even more time consuming than for metallic materials because this viscous material exhibits a high heat build-up generating artifacts for fatigue tests lead at high frequencies [15,23,24]. It would therefore be very useful to speed-up the characterization of the fatigue properties of these materials, which is the goal of this study.…”

“…Restricted a few years ago to automotive applications with limited mechanical requirements, these materials, filled with glass fibers up to 50% in mass, are now used for structural components [1][2][3][4][5]. Designing those parts against fatigue has therefore become a serious issue during the last years, generating an extended literature [6][7][8][9][10][11][12][13][14][15]. Solving this issue is clearly not an easy task because of two main factors.…”

Fatigue properties of vibration‐welded postindustrial waste nylon with glass fibers at room and elevated temperatures

“…Another phenomenon that is inherent to polymers subjected to prolonged cyclic loading is cyclic creep, which is also exacerbated by hysteretic heating. However, in this work, cyclic creep is not expected to play a significant role in low temperature fatigue tests as compared to the crack nucleation‐growth mode because all specimens tested in this work are in the dry as molded condition which enhances resistance to creep. At 120°C, the cyclic creep component during fatigue seems to manifest through necking in the vicinity of the fracture surface.…”