Effects of Time after Harvest and Rate of Loading on Force Relaxation Behaviour of Local Variety of Grapefruit (LemunTaba)

摘要

Force relaxation properties of a local variety of grapefruit (Lemuntaba) was determined under quasi-static compression loading using Instron UTM at three levels of time after harvest (freshly harvested, 7 days and 14 days after harvest) and three rates of loading (10, 5, 1 mm/s) for freshly harvested and 10 mm/s for one and two weeks after harvest. Fitting the obtained data for freshly harvested, loaded at 10 mm/s to a three-term Maxwell model; the resulted model equation was of F(t) = 743.521e~(-t/1.843)+592.817e~(-t/0.007)+474.254e~(-t/0.008), R~2 = 0.97. For freshly harvested loaded at 10 mm/s, die force relaxed (decayed) from an initial value of 2435.647 N to 743.521 N; about 69.473% in 1.834 s; Similar phenomenon was observed for other treatments. From the results, it can be deduced that when this cultivar is loaded with about 65% of the total force at rupture, about 69% of the imposed load will be dissipated upon removal of that in about 1.8 s; an evidence of high elasticity.