Characterization and Modeling of Polymeric Matrix Under Static and Dynamic Loading
A polymeric matrix (3501-6) used in composite materials was characterized under multi-axial loading at strain rates varying from quasi-static to dynamic ones. Tests were conducted under uniaxial compression, tension, pure shear and combinations of compres
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Characterization and Modeling of Polymeric Matrix Under Static and Dynamic Loading Brian T. Werner and Isaac M. Daniel
Abstract A polymeric matrix (3501-6) used in composite materials was characterized under multi-axial loading at strain rates varying from quasi-static to dynamic ones. Tests were conducted under uniaxial compression, tension, pure shear and combinations of compression and shear. Quasi-static and intermediate strain rate tests were conducted in a servo-hydraulic testing machine. High strain rate tests were conducted using a split Hopkinson Pressure Bar (Kolsky bar) system built for the purpose. This SHPB system was made of a glass/epoxy composite (Garolite) bars having an impedance that is closer to that of the test polymer than metals. The typical stress-strain behavior of the polymeric matrix exhibits a linear elastic region up to a yield point, a nonlinear elastoplastic region up to an initial peak or “critical stress,” followed by a strain softening region up to a local minimum and finally, a strain hardening region up to ultimate failure. A general three-dimensional elasto-viscoplastic model was developed incorporating strain rate effects, and including the large deformation region. The model was formulated in strain space unlike most models in the literature. The stress-strain curves obtained were used to develop and validate the new elasto-viscoplastic constitutive model. Keywords Polymer characterization • Multi-axial testing • Dynamic testing • Strain rate effects • Elasto-plastic behavior • Constituive modeling
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Introduction
Recent and ongoing research in fiber reinforced polymer composites (FRPC) has shown that there is a significant rate effect on the resin dominated stiffness and strength properties (E2, G12, F2c, F2t, F6) of these materials [1, 2]. Fabrication and testing of these composites is costly due to the expense of the material itself, and its anisotropic behavior that requires time consuming multi-axial testing. In the case of carbon/epoxy composites, the fiber itself shows no rate dependence in its mechanical response. This suggests that all of the rate effects on the composite can be traced to the matrix. Since the polymer matrix is basically isotropic, a much less costly evaluation of a composite can be achieved by characterizing the bulk matrix at various strain rates. The constitutive and strain rate behavior of epoxies under various loading conditions has been studied by many researchers [3–13]. Some studies focus on characterization of the resin at various rates [3, 4]. Many investigators have focused on viscoelastic analysis and the determination of shift factors used in temperature-time superposition modeling [5–8]. Some have attempted to link the monomer structure to the bulk properties [9]. Goldberg et al. have published works on both testing various resins under multiaxial conditions at various rates as well as modeling with a state variable approach [10–12]. The objective of this study was to characterize the matrix resin under multi-axial loading at diffe
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