Viscoelastic properties of seed cotton and their effect on module shape and density

Modules for cotton storage and transport should be constructed with a shape that will resist collecting water to maintain the quality of seed cotton during storage. Meeting this specification requires knowledge of the relationship between the applied compressive force, deformation, and time for seed cotton. Several factors were tested to determine their effects on the height and density of seed cotton during compression, creep loading, and recovery. Models were used to describe these processes. These results were used to develop an algorithm capable of providing information on module shape to the module builder operator. The initial loading density did not affect the compressed density, but a slight effect was observed in the recovered density, due to the weight of the seed cotton. Picker harvested cotton was compressed to a greater density than stripper harvested cotton, but expanded more during recovery, resulting in similar final densities. Multiple compressions increased the density, but this increase was not physically significant after the third compression. Higher moisture content increased the density seed cotton could be compressed to slightly. Viscoelastic behavior was observed; however, the effect on density was small. Both the compression and creep curves were described using mathematical models. A compression model using an asymptotic true strain measure yielded high R2 values; however, some aspect of this process remained unexplained and the equation was limited in its predictive ability. Creep behavior was described using a modified Burgers model. This model was more accurate than the creep model, although a definite trend existed in the creep model residuals. A feedback algorithm was developed based on the observation that the compressed density was primarily dependent on the mass of seed cotton and not the initial density. By measuring the compressed depth of cotton in a module and the hydraulic pressure of the tramper foot cylinder, the resulting shape of the module can be predicted. Improved loading of the module builder is necessary to produce a desirably shaped module. More seed cotton needs to be placed in the center of the module, resulting in a surface that slopes down towards the outer edges.