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

Abstract

ABSTRACT:Fatigue behaviors of short glass-fiber reinforced nylon6 (GF/Ny6) under three cyclic fatigue conditions, tension-tension (T-T), tension-compression (T-C) and compression-compression (C-C), were investigated on the basis of nonlinear dynamic viscoelastic analysis. A nonlinear viscoelastic parameter (NV P) was used for quantitative evaluation of nonlinear dynamic viscoelasticity for the (GF/Ny6) during the fatigue process. The magnitude of NV P increased with a decrease in the fatigue lifetime under three cyclic fatigue conditions. Under the T-T type cyclic deformation, glass-fibers that lay parallel to the cyclic deformation direction were broken during the fatigue process. After NV P attained a constant magnitude, cracks propagated perpendicularly to the cyclic deformation direction from the glass-fiber ends and ultimately, the (GF/Ny6) was fractured. The stress distribution in the matrix nylon6 became more inhomogeneous due to both glass-fiber breakage and crack propagation, resulting in an increase in NV P. In the case of the C-C type cyclic deformation, debonding at the (glass-fiber/matrix nylon6) interface occurred during the fatigue process, and the magnitude of NV P was strongly related to the progress of interfacial debonding between glass-fibers and the matrix nylon6. Under the T-C type cyclic deformation, the magnitude of NV P increased accompanying crack growth during the tensile deformation process and also, interfacial debonding during the compressive deformation process.KEY WORDS

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

“…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].…”

Universal Strain‐Life Curve Exponents for Thermoplastics and Elastomers under Tension‐Tension and Torsion

“…This power-law was found to be valid for metals, [5] as well as polymers. [6][7][8] In the present work, the total strain amplitude ( 0 ) is used to give [9][10][11][12] 0 = A TT N B TT f (tension − tension)…”

“…This power‐law was found to be valid for metals, [ 5 ] as well as polymers. [ 6–8 ] In the present work, the total strain amplitude ( ε 0 ) is used to give [ 9–12 ] For stress controlled measurements, the strain amplitude during testing highly depends on the material's modulus, intrinsically generated heating during testing or strain hardening/softening. As the material properties are changing with time during fatigue, the local strain amplitude changes as well.…”

Fatigue life prediction via the time‐dependent evolution of linear and nonlinear mechanical parameters determined via Fourier transform of the stress

“…In the literature, a stress analysis can be used to calculate a damage rate, to follow the dissipated energy based on the stress amplitude time evolution, or to describe specific events during fatigue. For example, failure onset was investigated via an increase of the so‐called viscoelastic nonlinear parameter (sum of n higher harmonics normalized to the fundamental one, with up to n = 100) or the occurrence of a macroscopic crack via the first even higher harmonic of the stress ( I 2/1 ) …”

“…In the literature, a stress analysis can be used to calculate a damage rate, 17,18 to follow the dissipated energy based on the stress amplitude time evolution, 19 or to describe specific events during fatigue. For example, failure onset was investigated via an increase of the so-called viscoelastic nonlinear parameter (sum of n higher harmonics normalized to the fundamental one, with up to n 5 100) 20,21 or the occurrence of a macroscopic crack via the first even higher harmonic of the stress (I 2/1 ). 12 The main objective of this work is to propose a new concept related to the cycle number (time) dependent evolution of the mechanical parameters G 0 , G 00 , and I 3/1 , allowing to predict the fatigue lifetime of each sample while the test is still ongoing.…”