Fatigue Damage and Degradation in Random Short-Fiber SMC Composite

Abstract

Damage accumulation and cyclic degradation in a random short-fiber SMC com posite subjected to tensile fatigue loading are studied. Fatigue damage in various forms of microcracking is examined. The transient nature of the nonlinear, monotonic stress- strain curve is investigated first, and subsequent property degradation and hysteresis loop changes are examined. Contrary to the behavior of certain metals and polymers, a cyclic stable state is never reached in general; cyclic softening is always observed in this class of materials. Owing to the random microstructure of the SMC material, the fatigue damage is viewed as being macroscopically homogeneous and uniform, and the damage growth is treated in a continuous sense. A parameter is then introduced to define the degree of the homogeneous damage. A power-law relationship among the rate of damage evolution, loading variables, and cyclic history is established. The homogeneous fatigue damage decreases rapidly with the loading cycle due to combined effects of rapid depletion of microcrack initiation sites and presence of various crack arrest mechanisms.

Fatigue behavior and modeling of short fiber reinforced polymer composites including anisotropy and temperature effects

“…Continuous cyclic softening was observed in SFRPCs due to initiation and growth of damage in the matrix, at fiber ends, or at fiber-matrix interface [2,3]. The viscous characteristics were found to be dependent on both temperature and frequency.…”

“…Fatigue damage in SFRPCs has been characterized and modeled based on their dissipative response under cyclic loading. Evolution of hysteresis loops in either their size or slope [2,5], hysteretic energy [7,8], strain energy [9,10], and nonlinear viscoelasticity [11,12] are the parameters typically used for modeling of fatigue damage and accumulation. Fiber orientation is another important factor controlling fatigue performance and the degree of anisotropy of SFRPCs [13][14][15].…”

“…As temperature increased, crazes in fibril structure were more pronounced. In matrix-dominant areas, cracks were formed normal to the loading direction, while in fiberdominant areas cracks were observed in matrix and along the interfacial bonding for aligned and off-axis fibers, respectively [2]. Fatigue damage mainly developed at the interfacial bonding of fiber and matrix, but matrix microcracks were dominant in the core layer [27].…”

Fatigue life prediction and failure mechanisms of composite materials

“…Recently, the residual strength degradation [1][2][3][4][5][6], and modulus degradation [7][8][9][10][11][12] approaches have been frequently used to predict fatigue life of composite materials.…”

“…The secant modulus degradation during fatigue tests is investigated by Hahn and co-workers [8,9]. Wang and Chim [10] proposed a fatigue damage model defined by elastic modulus. They assumed that a fatigue damage degradation rate is a power function of fatigue cycle n, and proportional to a parameter which is a function of damage.…”