D:\Int. Agrophysics\19-4\KHAZAEI4.vp

A b s t r a c t. Basic rheological property (force relaxation) of a single kernel of chickpea under uni-axial compression was studied. Information on the force relaxation behaviour of chickpea kernels is not available. Meanwhile, no papers was found to study the effects of number of loadings on stress relaxation behaviour of grains and fruits. In this study the effects of moisture content and number of loadings were studied on force relaxation behaviour of chickpea kernels. The results showed that the chickpea kernels had a time dependent behaviour similar to other viscoelastic materials. The three-term Maxwell model with a maximum relative difference (MRD) of £5% and R 2 higher than 0.997 was chosen as the best fit equation to the relaxation data. Moisture content had a decreasing effect on the first term of the three-term Maxwell model (F 1 , t 1 ), but the number of loadings had an increasing effect on the first term of the Maxwell model. For all moisture contents and number of loadings, the grain tissue dissipates a major proportion of the initially applied force at a relatively slow rate. As the number of loading increases, the kernel becomes more elastic. Consequently, more force was required to maintain a certain deformation level. A master curve was proposed to determine the force relaxation behaviour of the chickpea kernels at moisture contents between 6.7 and 18% for 1 to 9 cycles of loadings. The Peleg and Pollak model was unsatisfactory for representing the relaxation force for chickpea kernels. K e y w o r d s: chickpea, relaxation force, rheology, stress INTRODUCTION During harvesting, handling, transport, processing, and storage, grains are subjected to a series of static and dynamic loads. These loads causes damage an d loss in food grains, decreases quality, and increases susceptibility to deterioration during storage The mechanical behaviour of agricultural products is time dependent and must be studied by applying the principles of viscoelasticity, in which both the viscous and elastic responses are considered Although there is some published works on the physical and mechanical properties of chickpea kernels and pods MODELING A generalized Maxwell model with 2 or 3 elements is generally used to represent stress or force relaxation data. Thus, the force relaxation behaviour can be represented by Int. Agrophysics, 2005, 19, 305-313 Effects of moisture content and number of loadings on force relaxation behaviour of chickpea kernel