Monotonic and Cyclic Fatigue Behavior of a High Performance Ceramic Fiber
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Monotonic and Cyclic Fatigue Behavior of a High Performance Ceramic Fiber M. Kerr1, J.J. Williams1, N. Chawla1, and K.K. Chawla2 1
Department of Chemical and Materials Engineering Arizona State University P.O. Box 876006 Tempe, AZ 85287-6006 2
Department of Materials Science & Engineering University of Alabama at Birmingham Birmingham, AL 35294 ABSTRACT Monotonic and cyclic fatigue behavior of fibers are of general interest, regardless of the end use of the product whether in a composite or in a fabric. Study of cyclic fatigue behavior of fibers is particularly difficult because of their small diameter (~10 µm) and high aspect ratio. In this paper, we report some preliminary results of monotonic tension and tension – tension fatigue behavior of a ceramic fiber: Nextel 312 (Al2O3-SiO2-B2O3) fiber. This fiber has a nanocrystalline structure with B2O3 mostly in the form of a glassy phase. The tensile strength data of this fiber showed a Weibull modulus of 4.6, indicating a large degree of variability. Our experiments show clear indication of cyclic loading being more damaging than static loading for Nextel 312. The fracture surface observations of fatigues samples showed some distinctly different features from those observed in fibers subjected to monotonic tension. INTRODUCTION In structural applications, high performance fibers undergo monotonic and/or cyclic deformation, whether in the form of a fabric, rope, or as reinforcement in a composite. The mechanical behavior of fiber reinforced composites is inherently dependent on the constitutive properties of the fiber, matrix, and fiber/matrix interface [1]. In ceramic matrix composites reinforced with continuous fibers, the toughness and damage tolerance are obtained by a relatively weak fiber/matrix interface [2,3]. This weak interface, typically a fiber coating, promotes energyabsorbing mechanisms such as crack deflection and fiber pullout. Under cyclic loading conditions, gradual wear of the fiber coating makes the fiber surface susceptible to stress concentrations, which eventually lead to fiber fracture and composite failure [4,5]. The fatigue behavior of the fibers is particularly important in metal matrix composites, where the matrix is highly plastic and a high interfacial bond strength exists between fiber and matrix. Thus, a very important aspect of the fatigue behavior of composites, which has not been studied in detail, is the constitutive response of the ceramic fiber reinforcement to cyclic loading. In order to obtain a better understanding of the fatigue behavior of various composites, it thus becomes of interest to study the behavior of reinforcing fibers to subjected to cyclic fatigue conditions, in addition to monotonic loading.
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Relatively few studies have been conducted on the cyclic fatigue behavior of high performance fibers [6,7]. Bunsell and Somer [6] examined the fatigue behavior of carbon fibers and reported no significant change in tensile strength after (a) cyclic loading. Minoshima et al. [7] studied the cyclic behavi
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