Fatigue Strength of Poly-p-Phenylene Benzobisoxazole(PBO) Fibers

Abstract

In this paper, tensile and fatigue properties of poly-p-Phenylene benzobisoxazole (PBO) fiber have been investigated. The tensile test was carried out with a gauge length of 12.5 mm and displacement rate of 0.5 mm/min. The tensile strength data were analyzed in terms of the Weibull probability distribution function. Fatigue test was performed using an electromagnetic force fatigue tester. The fatigue testes were carried out at a frequency of 10 Hz with three stress ratios of 0.1, 0.5, and 0.7. It was found from the tensile strength test that the distribution of PBO fiber strengths expressed as Weibull distribution function with 2 parameters. The test results clearly showed that the fatigue behavior appeared in the S-N characteristic curves. The relation between the stress amplitude and the fatigue life depended on the stress ratio. However, the relation between the maximum stress and the fatigue life was independent of the stress ratio, and the maximum stress was most suitable parameter to describe the fatigue strength at the different stress ratios. Consequently, it became clear that the fatigue strength of the PBO fibers was not cycle dependent, but is time dependent. In addition, it is found by SEM observation that there are distinct differences between the surface image of tensile test specimen and that of fatigue test specimen, i.e., the crack length in the fatigue test specimens are much longer than that in the tensile test specimens.

The behavior of statically-indeterminate structural members and frames with cracks present

“…By contrast, this report focuses on HM type PBO fiber with tensile elastic modulus increased thermal treatment and identifies its tensile and fatigue properties as found by relevant tests on monofilaments. The findings are compared with the results from the AS type PBO fibers reported in the previous report [6]. Examined are change in the relationship between the internal fiber structure and the tensile and fatigue strength…”

“…Under such circumstances, the authors have focused their research on the fatigue properties of PBO fiber. In their previous research, they reported on the fatigue strength properties of AS type PBO fiber [6]. By contrast, this report focuses on HM type PBO fiber with tensile elastic modulus increased thermal treatment and identifies its tensile and fatigue properties as found by relevant tests on monofilaments.…”

“…In this report, such fibers are referred to as AS fibers as opposed to Zylon®-HM not heat processed to increase elasticity. The authors have reported on the tensile and fatigue properties of the AS fiber in a previous report [6]. For catalog data on both types of fibers, refer to Table 1 [7].…”

Rigid‐Rod Polymers

“…In addition, there are distinct differences between images of the surface of the tensile test specimen and that of the fatigue specimen. In other words, the crack length in the fatigue test specimen is much longer than that in the tensile test specimen (187). The rigid-rod polymer fibers also exhibit rather small creep and stress relaxation phenomena, which are indicators of viscoelastic behavior.…”

“…Both of the modes fit the Weibull statistical distribution (181,182). The distribution of PBO fiber strengths can be expressed as a Weibull distribution function with two parameters (187).…”