Some engineering properties of yam setts from two species of yams

Abstract

Yam production is still mainly carried out manually by peasant farmers using yam setts as planting material. Adequate knowledge of their engineering properties is an essential prerequisite for the scientific design and development of equipment for planting and handling yam setts mechanically. Some engineering properties of yam setts from two species of yams, namely white yam ( D. rotundata) and yellow yam ( D. cayenensis), were investigated at different moisture contents. The properties investigated include sett density, static coefficient of friction on plywood, galvanized steel and formica surfaces, force–deformation behaviour during quasi-static radial compression, stiffness moduli and sett toughness. The coefficient of friction of yam setts of both species on formica was considerably lower than the corresponding coefficients on wood and galvanized steel, respectively. The results further showed that a considerable reduction in the coefficient of friction was achieved (0.41–0.29 and 0.45–0.25 on formica, for D. rotundata and D. cayenensis, respectively) by air-drying freshly prepared setts at ambient room temperature for at least 4 days. Sett density over the drying period ranged between 1020 and 1180 kg m −3 for D. rotundata and between 1030 and 1140 kg m −3 for D. cayenensis. The stiffness moduli were 3.53 and 5.36 kN m −1 for freshly prepared yam setts of D. rotundata and D. cayenensis, respectively. However, sett stiffness generally decreased as sett moisture content decreased. The toughness of freshly prepared yam setts initially increased, attaining a maximum value within the first 4 days of air-drying, and subsequently decreased with further sett drying.