Investigations into the damage mechanisms of glass fiber reinforced polypropylene based on micro specimens and precise models of their microstructure

Abstract Fiber reinforced thermoplastics are considered as promising candidates to enable the mass production of lightweight components. To assure their structural application, accurate methods to describe their mechanical behavior are mandatory. However, the modeling of the damage behavior of the thermoplastic matrix under multiaxial stress states within the microstructure still poses enormous challenges. In order to capture the in situ behavior, a novel methodology is applied. Tensile tests are conducted on micro specimens, which are manufactured from 100 μm thin slices of the material's cross section. A corresponding finite element mesh which precisely depicts the individual microstructure of each sample is reconstructed based on microscope images and computer tomographic (CT) scans. Since the dimensions of the specimens are sufficiently small, the position and orientation of each fiber can be directly mapped to the model. Furthermore, the evolution of deformation and damage within the microstructure is visible in microscope images. Inverse simulations are performed to separate the mechanical behavior of the matrix, the fiber-matrix interface and the fibers. On a first specimen with approximately 5 vol-% fiber fraction, the constituent properties are calibrated by an automated parameter optimization procedure until the global stress-strain curve of the simulation agrees well with the experiment. The approach is validated by the simulation of a second specimen with a strongly different fiber fraction (15 vol-%) and thus, a strongly different damage behavior. It is shown that the stress-strain curves and the observed damage evolution of both specimens can be accurately captured applying the same material parameters. As an outlook for potential industrial applications of the method, mesh free fast Fourier transform (FFT) simulations are performed. Such models are based on raw CT voxel data, rendering the extensive work of geometrically reconstructing the microstructure obsolete.

[1]  Laurent Delannay,et al.  First pseudo-grain failure model for inelastic composites with misaligned short fibers , 2011 .

[2]  N. Saintier,et al.  Multiscale fatigue damage characterization in short glass fiber reinforced polyamide-66 , 2014 .

[3]  T. Okabe,et al.  Micromechanical simulation of tensile failure of discontinuous fiber-reinforced polymer matrix composites using Spring Element Model , 2014 .

[4]  A. Scott,et al.  Fatigue micromechanism characterisation in carbon fibre reinforced polymers using synchrotron radiation computed tomography , 2014 .

[5]  Hervé Moulinec,et al.  A numerical method for computing the overall response of nonlinear composites with complex microstructure , 1998, ArXiv.

[6]  T. Vu-khanh,et al.  Morphology and mechanical performance of polyphenylenesulfide carbon fiber composite , 1991 .

[7]  Frank Henning,et al.  LFTs for automotive applications , 2005 .

[8]  M. Schneider,et al.  Efficient fixed point and Newton–Krylov solvers for FFT-based homogenization of elasticity at large deformations , 2014 .

[9]  J. C. Simo,et al.  Strain- and stress-based continuum damage models—I. Formulation , 1987 .

[10]  T. Kurauchi,et al.  Mechanism of fracture of short glass fibre-reinforced polyamide thermoplastic , 1984 .

[11]  S. Fliegener.  Micromechanical finite element modeling of long fiber reinforced thermoplastics , 2015 .

[12]  J. Spoormaker,et al.  Fibre-matrix debonding stress analysis for short fibre-reinforced materials with matrix plasticity, finite element modelling and experimental verification , 1998 .

[13]  M. Schneider,et al.  Mixed boundary conditions for FFT-based homogenization at finite strains , 2016 .

[14]  Nicolas Saintier,et al.  Damage mechanisms in short glass fibre reinforced thermoplastic during in situ microtomography tensile tests , 2016 .

[15]  J. Spahn.  An Efficient Multiscale Method for Modeling Progressive Damage in Composite Materials , 2015 .

[16]  D. Notta-Cuvier,et al.  Modelling of progressive fibre/matrix debonding in short-fibre reinforced composites up to failure , 2015 .

[17]  T. Kennerknecht.  Fatigue of Micro Molded Materials - Aluminum Bronze and Yttria Stabilized Zirconia , 2014 .

[18]  M. Piggott.  Why interface testing by single-fibre methods can be misleading , 1997 .

[19]  Norio Sato,et al.  Microfailure behaviour of randomly dispersed short fibre reinforced thermoplastic composites obtained by direct SEM observation , 1991 .

[20]  F. Cosmi,et al.  Micro-CT investigation on fatigue damage evolution in short fibre reinforced polymers , 2013 .

[21]  R. Young,et al.  Three techniques of interfacial bond strength estimation from direct observation of crack initiation and propagation in polymer–fibre systems , 2001 .

[22]  J. C. Simo,et al.  On continuum damage-elastoplasticity at finite strains , 1989 .

[23]  J. L. Spoormaker,et al.  Mechanisms of fatigue in short glass fiber reinforced polyamide 6 , 1996 .

[24]  L. Rebenfeld,et al.  Computer simulation of crystallization kinetics and morphology in fiber‐reinforced thermoplastic composites. I. Two‐dimensional case , 1993 .

[25]  S. Achard,et al.  Fatigue damage mechanisms in short fiber reinforced PBT+PET GF30 , 2011 .

[26]  Matti Schneider,et al.  Use of composite voxels in FFT-based homogenization , 2015 .

[27]  Peter Gumbsch,et al.  3D microstructure modeling of long fiber reinforced thermoplastics , 2014 .

[28]  Yves Chemisky,et al.  In situ damage mechanisms investigation of PA66/GF30 composite: Effect of relative humidity , 2014 .

[29]  J. Kenny,et al.  Crystallization kinetics of poly(phenylene sulfide) (PPS) and PPS/carbon fiber composites , 1991 .