Fracture Resistance of Unsplit Pistachio (Pistacia vera L.) Nuts against Splitting Force, under Compressive Loading

Mechanical properties of non-split pistachio nuts are among the lada required for the design of equipment needed for processing of the nut. Unsplit pistachio nut samples were uniaxially loaded to determine the nut’s needed splitting force and energy, as well as Poisson’s ratio and Young’s modulus of elasticity. The tests were carried out at four moisture contents (5, 10, 15 and 20% wb), under four loading rates (10, 20, 30 and 40 mm min-1), and on two varieties (O’hadi and Badami) of the nut. The highest splitting forces for the varieties (281.9 N for Badami and 102.4 N for O’hadi) were obtained at a moisture content of 5% wb and loading rate of 40 mm min-1, while the lowest forces, 97.0 N for Badami and 16.8 for the case of O’hadi, occured at moisture contents of 20% wb along with loading rate of 10 mm min-1. Different trends were observed between O'hadi and Badami varieties for the required energy to split nuts with increasing moisture content and loading rates. By increasing moisture content, Poisson’s ratio for unsplit pistachio nuts increased from 0.374 to 0.388 and from 0.326 to 0.337 for O’hadi and Badami varieties, respectively. Young’s modulus exhibited an indirect relationship with moisture content while a direct relationship with loading rate, in either of the varieties. Increase in moisture content from 5 to 20% wb led to a decrease in Young's modulus, from 322.59 to 223.23 MPa and from 816.25 to 719.28 MPa, for O’hadi and Badami variety nuts, respectively.