Abstract:Short fiber-reinforced polypropylene is largely used in the automotive industry. Fatigue failure is one of the most failure modes observed in this class of materials. In order to better understand the damage mechanisms and plasticity evolution, this article provides an overall experimental investigation of the mechanical properties of a PPGF40 composite (polypropylene matrix reinforced by a 40% weight content of short glass fibers) including monotonic and cyclic loading. The effect of various parameters such a… Show more
“…The same phenomenon has also been experimentally observed by Imaddahen. 38 Despite the fact that specimens in various orientations degraded globally in a similar manner, the 0° specimens ruptured at a significantly lower degradation degree than the specimens at the other orientations. This indicates a more concentrated damage distribution in the 0° specimens due to their higher stiffness in the loading direction.Figure 5.Measured elastic stiffness (a) and stiffness degradation (b) in load-unload tests on specimens with three orientations (0°, 45°, 90°).…”
It is challenging to predict the material degradation and crack initiation of short fiber reinforced thermoplastics (SFRT) components with high computation efficiency and low parameter identification effort. To achieve that, this work utilizes a hybrid method combining micro- and macro-mechanical approaches to describe the damage-coupled material behavior of SFRT. The Mori-Tanaka mean-field homogenization method is used to determine the effective linear elastic properties of SFRT, whereas the consideration of plasticity is based on a macro-mechanical anisotropic viscoplastic model. The effect of micro-damage in the matrix material on the macroscopic behaviors of SFRT is considered within the Continuum Damage Mechanics (CDM) framework. A nonlinear damage evolution law is implemented to account for the nonlinearity in the damage evolution. Targeting industrial applications, the proposed damage-coupled material model is implemented into the commercial FE software ANSYS with a novel stepwise damage updating process, requiring no user-defined subroutine. The model is calibrated with experimental data on flat specimens under monotonic and cyclic tensile loading. The FE simulation with the calibrated material model accurately describes the anisotropic deformation and crack initiation of the investigated SFRT material observed in experiments.
“…The same phenomenon has also been experimentally observed by Imaddahen. 38 Despite the fact that specimens in various orientations degraded globally in a similar manner, the 0° specimens ruptured at a significantly lower degradation degree than the specimens at the other orientations. This indicates a more concentrated damage distribution in the 0° specimens due to their higher stiffness in the loading direction.Figure 5.Measured elastic stiffness (a) and stiffness degradation (b) in load-unload tests on specimens with three orientations (0°, 45°, 90°).…”
It is challenging to predict the material degradation and crack initiation of short fiber reinforced thermoplastics (SFRT) components with high computation efficiency and low parameter identification effort. To achieve that, this work utilizes a hybrid method combining micro- and macro-mechanical approaches to describe the damage-coupled material behavior of SFRT. The Mori-Tanaka mean-field homogenization method is used to determine the effective linear elastic properties of SFRT, whereas the consideration of plasticity is based on a macro-mechanical anisotropic viscoplastic model. The effect of micro-damage in the matrix material on the macroscopic behaviors of SFRT is considered within the Continuum Damage Mechanics (CDM) framework. A nonlinear damage evolution law is implemented to account for the nonlinearity in the damage evolution. Targeting industrial applications, the proposed damage-coupled material model is implemented into the commercial FE software ANSYS with a novel stepwise damage updating process, requiring no user-defined subroutine. The model is calibrated with experimental data on flat specimens under monotonic and cyclic tensile loading. The FE simulation with the calibrated material model accurately describes the anisotropic deformation and crack initiation of the investigated SFRT material observed in experiments.
“…Experimental studies revealed that damage evolution inside the polymer matrix and the resulting stiffness degradation of the composite material is indeed influenced by the load amplitude [99][100][101]. Moreover, a recent study of Imaddahen et al [102] reports that the fatigue process in short-glass fiber reinforced polypropylene depends on the strain rate or frequency. They observed an improvement of the fatigue strength at higher frequencies, i.e., a higher number of bearable load cycles at higher frequencies.…”
Under fatigue loading, the stiffness decrease in short-fiber reinforced polymers reflects the gradual degradation of the material. Thus, both measuring and modeling this stiffness is critical to investigate and understand the entire fatigue process. Besides evolving damage, viscoelastic effects within the polymer influence the measured dynamic stiffness. In this paper, we study the influence of a linear viscoelastic material model for the matrix on the obtained dynamic stiffness and extend an elastic multiscale fatigue-damage model to viscoelasticity. Our contribution is two-fold. First, we revisit the complex-valued elastic models known in the literature to predict the asymptotic periodic orbit of a viscoelastic material. For small phase shifts in an isotropic linear viscoelastic material, we show through numerical experiments that a real-valued computation of an “elastic” material is sufficient to approximate the dynamic stiffness of a microstructure with a generalized Maxwell material and equal Poisson’s ratios in every element as matrix, reinforced by elastic inclusions. This makes standard solvers applicable to fiber-reinforced thermoplastics. Secondly, we propose a viscoelastic fatigue-damage model for the thermoplastic matrix based on decoupling of the time scales where viscoelastic and fatigue-damage effects manifest. We demonstrate the capability of the multiscale model to predict the dynamic stiffness evolution under fatigue loading of short-fiber reinforced polybutylene terephthalate (PBT) by a validation with experimental results.
“…Meanwhile, the failure modes change from fiber pull-out to fiber breakage with increasing strain rate. Imaddahen et al 8 demonstrated that the ultimate stress and Young's modulus are highly sensitive to the strain rate. Brown et al 9 investigated the strain rate-dependent mechanical behavior of E-glass/polypropylene woven fabric composite.…”
In the present work, the interfacial behavior of overmolded hybrid fiber reinforced polypropylene composites (hybrid composites) under the loading rate of 1, 10, and 100 mm/min are studied by experimental methods. The interfacial mechanical properties of hybrid composites are determined by monotonic and cycle loading-unloading single-lap-shear tests. The experimental results reveal that interfacial shear strength increases with loading rate, while the shear stiffness shows insensitive to loading rate. A regression function is built to describe the variation of interfacial shear strength with loading rate. The cyclic loading-unloading curves of hybrid composites samples indicate that loading rate effects on the interfacial nonlinear behavior of hybrid composites are considered by affecting plastic deformation. In addition, scanning electron microscopy and digital image correlation observations reveal the failure mechanisms of overmolded hybrid composites. The failure behavior of overmolded hybrid composites is mainly CFRT laminate failure for all cases.The evolution of non-uniform strain fields indicates that the fracture of overmolded thermoplastic composites may initiate at the edges and spread out to the far fields.
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