Nonlinear constitutive models for pultruded FRP composites

Abstract

Three nonlinear multi-axial constitutive models for pultruded fiber reinforced plastic composites are proposed and examined in this study. The first two are macromechanical models that idealize the entire composite material as homogeneous orthotropic under plane stress conditions. The third is a new three-dimensional (3D) micromechanical model where the fiber and matrix responses are explicitly recognized and the nonlinear behavior is expressed at the matrix level. The pultruded composite material system considered in this study consists of two alternating layers of roving and continuous filament mat. The two layers have E-glass/vinylester fiber/matrix constituents. Coupon tests were performed for calibration and verification of the proposed models. Nonlinear response is calibrated using V-notch tests, to generate the axial-shear stress-strain, and uniaxial transverse tests. Off-axis coupons were cut with different roving orientations in order to generate in-plane multi-axial stress states. The nonlinear axial stress-strain curves of the off-axis tests are compared with the predicted curves from the three proposed models. Good agreement is shown for all off-axis angles when comparing the experimental stress-strain curves with those predicted by the 3D micromodel. The nonlinear curves predicted by the two nonlinear orthotropic models are also in good agreement with the experimental results but not for all off-axis orientations. All three models can be easily integrated within a finite element code for the general nonlinear analysis of pultruded composite structures using layered shell or 3D type elements.

A multi-scale framework for layered composites with thermo-rheologically complex behaviors

“…The axial, transverse, and 45°off-axis coupons are cut from 0.5 00 thick composite plates such that the orientation for the roving layers is controlled. The specimens used in this study are obtained from the same composite panels as previously tested by Haj-Ali and Kilic (2003a) to calibrate material nonlinear elastic properties. Fiber volume fraction (FVF), effective elastic modulus, and ultimate strength in this E-glass/vinylester system are reported in Table 1.…”

“…The above micromechanical models, which were derived with detailed stress-strain fields, can give exact response characteristics of composites; however, it is often difficult to obtain closed form solutions especially when material nonlinearity and complex loading, i.e., combined thermal and mechanical effects are also involved. Another micromechanical modeling approach is a unit-cell model based on a representative volume element (RVE), which can be found in Aboudi (1990), Aboudi (2005), van der Sluis et al (1999), Haj-Ali and Pecknold (1996), Haj-Ali et al (2001), Haj-Ali and Kilic (2003a). The unit-cell method allows modeling complex microstructural geometries and predicting overall composite responses at different geometrical features.…”

“…Effective compressive material properties for E-glass/vinylester system with FVF 34% measured at T = 75°F(Haj-Ali and Kilic, 2003a) …”

Nonlinear micromechanical formulation of the high fidelity generalized method of cells

“…Great care was given to the numerical formulation using consistent plasticity tangent operators and integration scheme suitable for cyclic loading and finite increments. Haj-Ali et al (2001), Haj-Ali andKilic (2003), Haj-Ali and Muliana (2004), Haj-Ali (2005, 2008) and Haj-Ali (2008, 2009 developed different numerical formulations for fiber reinforced plastic (FRP) class of composites applied for the GMC and other nonlinear micromechanical models including timedependent, nonlinear and damage effects.…”

Estimation of very narrow bounds to the behavior of nonlinear incompressible elastic composites

“…The nonlinearity considered here (Eq. (1.2)) corresponds to the incompressible case of the Ramberg-Osgood model of the J 2 deformation theory of plasticity [5,8]. By neglecting elastic effects in Eq.…”