Mechanical behaviour of Macadamia nut under compression loading

The operation of cracking Macadamia nuts is the most critical and delicate step for achieving high-quality kernels. The nuts, usually at high moisture content, are dried to a recommended moisture, before cracking, in a process that takes from 3 to 4 weeks at the expense of large energy consumption. The present paper examines the basis of shell rupture which is needed for the development of new methodologies or techniques to reduce the drying period and to obtain a more efficient kernel extraction process. Requirements in terms of force, specific deformation and energy for initial rupturing of the macadamia nut shell under compression were experimentally investigated as a function of moisture content, nut size, and compression load position. The experiments have shown that there is a compression position for which force, specific deformation and energy values are minimal, independent of nut size and shell moisture. A damage evaluation of compressed nuts showed a trend for the void between kernel and shell to be the greatest at this position with the force acting longitudinally through the hilum. (C) 1999 Silsoe Research Institute.