Effects of Moisture Content and Number ofLoadings on Force Relaxation Behavior ofChickpea Kernels

摘要

The objective of this study was to determine the effects of moisture content andnumber of loadings on force relaxation behavior of chickpea kernels under uni-axialcompression. Information on the force relaxation behavior of chickpea kernels is notavailable. Meanwhile, no papers was found to study the effects of number of loadings onstress relaxation behaviour of grains and fruits.Chickpea kernels of the cultivar ‘Kaka’ from the dry farms of Kangavar, Kermanshah, Iranwere selected for testing. For each test, the kernel was placed in the most stable positionbetween two parallel plates and was loaded until the grain deformation reached apredetermined strain of 2%. At this time, the deformation of the kernel was maintainedconstant and the force required to maintain this deformation was measured and recordeddirectly as a function of time. The time dependent force data was obtained for 120 s. Afterunloading and a 120 s delay, the same kernel was subjected to a second loading. Thisprocess was continued until nine loadings (i.e., nine successive relaxation tests) werecompleted. The results showed that the chickpea kernels had a time dependent behaviorsimilar to other viscoelastic materials. The three-term Maxwell model with a maximumrelative difference (MRD) of ￡ 5%and R2 higher than 0.997 was chosen as the best fitequation to the relaxation data. Moisture content had a decreasing effect on the first termof the three-term Maxwell model (F1, t1), but the number of loadings had an increasingeffect on the first term of the Maxwell model. A master curve was proposed to determinethe force relaxation behavior of the chickpea kernels at moisture contents between 6.7 and18% for 1 to 9 cycles of loadings. The Peleg and Pollak model was unsatisfactory forrepresenting the relaxation force for chickpea kernels.