Mechanical behavior of jute hybrid bio-composites

Hybrid bio-composites are environmentally friendly and can provide a sustainable alternative to existing engineering materials in several applications. While these hybrid composites have relatively low modulus, their material consistency lend them to be used in many structural applications. Many low modulus natural fibers exhibit nonlinear axial stress strain relations. Orthotropic material nonlinearity is typically analyzed for composites in the transverse and shear directions, and very few computational models consider axial nonlinearity. In this manuscript two new macro and one micromechanical constitutive models are developed to characterize the nonlinear orthotropic behavior of these material systems in the axial, transverse and shear directions. These models are then implemented within finite element (FE) code. A hybrid bio-composite in the form of pultruded layers manufactured with jute bio-fibers, combined with unidirectional roving E-glass, and embedded in a polymeric matrix was chosen for this study. Stress strain curves are generated for these dually reinforced systems in transverse, axial and shear modes to calibrate the nonlinear parameters for computational models. Photomicroscopy was also used to characterize the microsctructure to calibrate the micromechanical constitutive model. All three models are then validated under a multi-axial state of stress by full-field stress/strain analysis via Digital Image Correlation (DIC) and Thermoelastic Stress Analysis (TSA) of open-hole specimens. The results show that all of the models match the full-field TSA and DIC results under a multi-axial state of stress; however, the Anisotropic Potential Theory (APT) model based on the work of Hahn Tsai showed more response at stress concentrations than the Anisotropic Deformation Theory (ADT) model based on the work of Hashin. Differences may have resulted from the correction scheme implemented in the APT model. Also the Nine-Cell micromechanical model in this study based on the work of Haj-Ali et al. was developed for comparison with the APT and ADT macromodels. The macromodels and micromodel presented here were implemented in ABAQUS user material subroutines, and are beneficial for analysis and design of structures with soft fiber constituents that have a nonlinear axial response. (C) 2016 Elsevier Ltd. All rights reserved.