PHYSICAL, MECHANICAL AND VISCOELASTIC PROPERTIES OF CORN KERNELS AND THEIR RELATION TO IMPACT FRACTURE RESISTANCE (DAMAGE, BREAKAGE, SUSCEPTIBILITY)

Damage to corn results primarily from the impact stresses encountered in normal harvesting and handling operations. Recent technological changes in grain production and handling, especially the introduction of field shellers, high temperature dryers and high speed handling equipment, have added to the problem.; This work was intended mainly to determine physical, mechanical and viscoelastic behavior of corn kernels and to find their relations to kernel fracture resistance as measured by the damage susceptibility tester.; The physical properties determined were: kernel size, shape, density and test weight. The results show that susceptibility to kernel fracture increased with kernel size. The flat kernels were more resistant to fracture than the round kernels. Kernel damage resistance increased with kernel density and test weight, but the test weight was weakly correlated with it.; Mechanical properties of two dent and one flint corn hybrids were determined. The properties evaluated were: maximum load, ultimate stress, ultimate strain, modulus of resilience and modulus of toughness. Each of these excepting the strain decreased as moisture increased. The modulus of toughness and ultimate stress were highly correlated with the breakage resistance, but the resulting correlation coefficients were only significant for modulus of toughness in the desired moisture range (12-18% wb).; Viscoelastic response of a dent and a flint corn kernel was investigated through relaxation tests. The intact corn kernels appeared to be a hydro-rheologically simple material. A generalized Maxwell model with six elements and a spring in parallel was adequate to describe the master relaxation function. Time of relaxation was relatively unaffected by the corn type and kernel moisture. For moistures above 20% wb, the combined influence of moisture, strain, deformation velocity and time on both stress and relaxation modulus responses was studied using a 2('4) factorial design. All the four parameters significantly affected the kernel responses for flint corn; however, the deformation velocity appeared unimportant for dent corn in the tested range.