Fracture Toughness of Walnut Particles (Juglans regia L.) and Coconut Fiber-Reinforced Hybrid Biocomposite Dinesh Kumar Rao, Prakash Chandra Gope Mechanical Engineering Department, College of Technology, G.B. Pant University of Agriculture & Technology, Pantnagar, India The rectangular specimens with an edge crack were subjected to symmetric three-point bending and asym- metric four-point bending to determine the mode I and mode II fracture toughness of the walnut particle and coconut fiber-reinforced biocomposite. Epoxy resin was used as matrix material and 10 wt% of coconut fiber and 20 wt% of walnut shell particle were used as reinforcing materials. The mode I and mode II fracture toughness and mechanical tests were conducted on a servo hydraulic universal testing machine and the results were analyzed and discussed. POLYM. COMPOS., 36:167–173, 2015. V C 2014 Society of Plastics Engineers INTRODUCTION There is an increasing demand for alternative raw material as wood in the furniture, household, and agro- product industries because of depletion of the natural resources. This need has directed researchers toward non- wood bio-based alternatives for composite manufacturing. Researchers [1–6] suggested many biomaterials-based composites that can be used as an alternative to wood. The mechanical and thermal characteristics of such bio- composites made from natural fibers or particles are also available in the literature. Nevertheless, all such studies are limited to the behavior of the material in absence of flaws or cracks, whereas the presence of flaws and cracks are very often inevitable in engineering structures and components. The crack may be generated during the man- ufacturing processes or during the operation due to cyclic loading or environmental causes. Pure mode I and pure mode II are two modes of deformation that take place in a cracked component subjected to in-plane loading. Frac- ture toughness is usually used to measure material resist- ance to extension of a crack. The stress intensity factor is mostly used as a fracture parameter. The material defor- mation behavior describes which parameter is to be used as fracture toughness and fracture method. For brittle fracture, the fracture toughness is characterized by the stress intensity factor. A limited research on the fracture toughness studies of biocomposites is available in the lit- erature [7–13]. Use of fracture mechanics methods in engineering design and analysis requires fracture toughness to serve as a material property. In this article, the frac- ture toughness behavior under mode I and mode II loading conditions are determined and examined for walnut particles and coconut fiber-reinforced hybrid biocomposite. MATERIAL AND METHODS In this study, 20 wt% of walnut particles and 10 wt% of coconut fiber were added as reinforcing material to epoxy resin CY 230 and hardener HY 951. 10 wt% of hardener was mixed in the solution of walnut shell par- ticles, coconut fibers, and epoxy resin at 40  C, which were preheated to 100  C and held for 2 h at 100  C in an electric oven. The solution thus obtained was used to cast sheet of 10 mm thickness in a mould of size 300 mm 3 250 mm 3 10 mm [Fig. 1]. The mould box was prepared from 10 mm thickness Perspex sheet. A detailed proce- dure of casting and curing process is described in Ref. [14, 15]. In the present investigation, 20 wt% of walnut shell particles and 10 wt% of coconut fibers were selected on the basis of recommendations and results of H. Pirayesh et al. [1, 4, 5]. The walnut shells were supplied by a dry fruit walnut manufacturer in India. Prior to the use, the shells were first cleaned of dirt and impurities and then were ground into particles using a Wiley miller. The walnut shell particle size varied between 1.618 lm and 2.685 lm. The walnut particles were oven dried at 100 6 5  C to reach the target moisture content (<2%) before using them as reinforcing material. Coconut fibers were extracted from exocarp, washed with distilled water, and dried at 100  C for 24 h. The length and diameter of coconut fibers used in the present investigation varied Correspondence to: Dr. Prakash Gope; e-mail: pcgope@rediffmail.com DOI 10.1002/pc.22926 Published online in Wiley Online Library (wileyonlinelibrary.com). V C 2014 Society of Plastics Engineers POLYMER COMPOSITES—2015