Determination of in-plane elastic properties of rice husk composite Petch Jearanaisilawong a,⇑ , Shayanin Eahkanong a , Bundit Phungsara a , Anchalee Manonukul b a Department of Mechanical and Aerospace Engineering, Faculty of Engineering, King Mongkut’s University of Technology North Bangkok, 1518 Pracharat 1 Rd., Wongsawang, Bangsue, Bangkok 10800, Thailand b National Metal and Materials Technology Center, National Science and Technology Development Agency, 114 Thailand Science Park, Paholyothin Rd., Klong 1, Klong Luang, Pathumthani 12120, Thailand article info Article history: Received 2 July 2014 Revised 16 March 2015 Accepted 22 March 2015 Available online 24 March 2015 Keywords: Short fiber composite Rice husk Fiber orientation distribution Mori–Tanaka model abstract An approach to evaluate macroscopic elastic properties of rice husk composite from its morphology is demonstrated. Hard shells of rice husks were used as a low-cost reinforcing agent in thin polypropylene sheet. Composite samples containing 5–20% mass fractions of rice husks were formed by compression molding, and the orientation distributions of rice husks in the samples were evaluated from micrographs of the composite structure. Effective elastic properties of the composite were calculated from the Mori– Tanaka model that includes the effect of reinforcement orientation. The homogeneous Mori–Tanaka model was benchmarked against an equivalent composite model using explicit modeling of the reinforce- ments in a finite element simulation; good agreement between the in-plane moduli of the two models was confirmed. Predictive capabilities of the Mori–Tanaka model were demonstrated by matching the model responses to the composite response under uniaxial tensile tests and four-point bending tests. Predicted effective axial moduli compared favorably with the experimental values. However, discrepancy exists in the predicted flexural moduli due to the shortcoming of the Mori–Tanaka model in capturing the out-of-plane response. The comparisons show that the proposed approach is adaptable to predict the in-plane anisotropic elastic properties of compression-molded rice husk reinforced polypropylene composite. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Rice husks are hard empty shells of rice grains available as a byproduct from rice milling. They are currently utilized in a wide range of applications such as animal feeds, an ingredient in fer- tilizers and biofuels, and a reinforcing component in concrete and building materials. Interests have expanded to using dried rice husks as a reinforcing agent in polymer composites [1–8]. Manufacturing of rice husk polymer composite consists of mixing raw rice husks and coupling agent with polymers, such as polypropylene [1–6], epoxy resin [7], or elastomers [8], and form- ing the mixture into products using standard forming techniques such as extrusion, injection and compression molding. Current literature is focused on evaluation of effective properties of rice husk composite using standard techniques such as tension, flexure and fracture tests. Parameters that can influence composite prop- erties, including volume fraction of rice husks [1,3], temperature during deformation [3], compatibilizing agents [4], manufacturing processes [5], type of filler [2,6], and matrices [7,8], have been analyzed. Alternatively, properties of the rice husk composite can be ana- lytically evaluated using constitutive models for short fiber rein- forced polymer (SFRP) that take into account both the geometrical and mechanical properties of the constituents. These models employ the concept of homogenization where a non-uniform com- posite structure is idealized as an equivalent continuum medium. A pioneer approach by Hill [9], known as the self-consistent micromechanics model, was developed for an elastic isotropic matrix reinforced by perfectly aligned isotropic cylindrical fibers. This composite exhibited a transversely isotropic response along the fiber direction, and its elastic constants were derived from the volume fraction and arrangement of the fibers. Bonding between the fibers and the matrix was assumed to be rigid, and any interac- tions between fibers were neglected. For the special cases of spher- oidal or ellipsoidal fibers, the self-consistent model could be expressed in a closed form in accordance with the analysis of Eshelby’s inclusion [10]. Following the framework of the self- consistent model, Mori and Tanaka [11] introduced a fourth-order texture tensor that related an averaged strain of the ellipsoid inclu- sion to that of the matrix. The coefficients in the texture tensor were http://dx.doi.org/10.1016/j.matdes.2015.03.042 0261-3069/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: petchj@kmutnb.ac.th (P. Jearanaisilawong). Materials and Design 76 (2015) 55–63 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes