Effect of Interfacial Interaction between Glass-Fiber and Matrix Nylon-6 on Nonlinear Dynamic Viscoelasticity and Fatigue Behavior for Glass-Fiber Reinforced Nylon-6

Abstract

ABSTRACT:Effect of (glass-fiber/matrix nylon-6) interfacial interactions on fatigue behaviors of glass-fiber reinforced nylon-6 (GF/Ny6) under a strain controlled condition was investigated on the basis of in situ nonlinear dynamic viscoelasticity. Ny6s mixed with surface-modified and -unmodified short glass-fibers (SMSGF and SUSGF) were used as specimens. An extent of nonlinearity of dynamic viscoelasticity was expressed by nonlinear viscoelastic parameter, NVP, which was calculated from coefficients of the Fourier expanded series of the response signal during a fatigue cycle. The nonlinear dynamic viscoelasticity for both (GF/Ny6)s became remarkable with the progress of fatigue damage. The magnitude of NVP for the (SUSGF/Ny6) was always greater than that for the (SMSGF/Ny6) at a given fatigue time. Since the interface between SUSGF and Ny6 was peeled off during the fatigue test due to the weak interaction, the fatigue damage easily occurred for the (SUSGF/Ny6). Such leads to the non-uniform propagation of the imposed strain through the (SUSGF/Ny6), resulting in an increase of NVP. In the case of the (SMSGF/Ny6), the fatigue damage slowly progressed due to the strong interfacial interaction. Consequently, the nonlinearity of the dynamic viscoelasticity for the (SMSGF/Ny6) was depressed in comparison with the (SUSGF/Ny6).KEY WORDS Fatigue Behavior / Short Glass-Fiber Reinforced Nylon-6 / Interfacial Interaction / Nonlinear Viscoelastic Parameter / Polymer composites are a class of materials that polymer matrix is reinforced by fillers such as glassfibers or carbon-fibers with a small amount. Recently, polymer composites have been widely used for structural components of transports and constructions as substitutes of metal materials due to their comparatively high specific strength and modulus. When polymer composites are applied to the above-mentioned purpose, it is important to understand the fatigue mechanisms, and to predict the fatigue lifetime. This is because the fatigue fracture of them could cause fatal accidents.Fatigue mechanisms of fiber-reinforced polymers have been discussed on the basis of scanning electron microscopy (SEM) observations of fractured surfaces. 1, 2 In general, a fatigue damage of polymer composites starts from debonding at fiber ends. Then, the debonding progresses along the (fiber / polymer) interface, and eventually, polymer composites are fractured. In the case of weak interfacial interaction, debonding easily progresses even at the initial stage of fatigue cycles. On the contrary, interfacial debonding is hard to occur for composites with strong interfacial interaction and thus an imposed load effectively transfers from matrix polymer to fibers, resulting in an improvement of fatigue strength. 1,[3][4][5][6][7] Although SEM is an useful apparatus, fatigue tests must be interrupted to observe sample surfaces. Therefore, it seems difficult by SEM observation to follow how fatigue damages such as interfacial debonding progress in a specimen. In order to clarify the fatigue fracture...

Effect of Cyclic Fatigue Conditions on Nonlinear Dynamic Viscoelasticity and Fatigue Behaviors for Short Glass-Fiber Reinforced Nylon 6

“…11 As shown in Figure 3, the magnitudes of NVP under three type cyclic deformations markedly increased at a critical fatigue time after several hundred seconds from the start of fatigue tests and then, remained constant values which were defined as NVP S in this study. Figure 4 shows the relationship between the imposed strain amplitude, ε d being lower than 1.2% and the magnitude of NVP S under three type cyclic deformations at 11 Hz and 303 K. The magnitude of NVP S increased in the order of the C-C, T-C, and T-T type cyclic deformation.…”

“…11 Sinusoidal strain with the constant amplitude was imposed on the specimen. The frequency of cyclic straining was 11 Hz and the ambient temperature under nitrogen gas atmosphere was 303 K. The cyclic fatigue conditions were the tension-tension (T-T), the tensioncompression (T-C) and the compression-compression (C-C) type cyclic deformations.…”

“…[3][4][5][6][7][8][9][10][11] The magnitude of NVP was calculated from the coefficients of fourier expanded series of a response stress signal during the fatigue process, as follows:…”

“…1,2 Fractography of the fatigue fracture surface revealed that the fatigue damage of polymer composites starts from debonding at fiber ends, being followed by progressive debonding along the (fiber/polymer) interface until final fracture occurs. In order to investigate the principal change in mechanical properties under cyclic fatigue, the in situ measurement of nonlinear viscoelasticity has been proposed by Kajiyama et al [3][4][5][6][7][8][9][10][11] They evaluated a nonlinear viscoelastic parameter, NVP, to discuss the nonlinear dynamic viscoelasticity and fatigue mechanisms of polymers during the fatigue process. The magnitude of NVP increased with macroscopic structural damage of short glass-fiber reinforced nylon6 (GF/Ny6) under the tension-compression type cyclic deformation.…”

“…The magnitude of NVP increased with macroscopic structural damage of short glass-fiber reinforced nylon6 (GF/Ny6) under the tension-compression type cyclic deformation. 11 Since stress-strain behaviors of polymers depend on the deformation mode such as tensile and compressive deformations, it is important to discuss the fatigue behaviors in tensile and compressive processes during cyclic fatigue deformations. The effects of cyclic fatigue conditions on the fatigue behaviors of polymers have been studied.…”