An Energy Based Model for the Compressive Behavior of Goose Down
Wilde, Timothy Philip
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Very little work has been done to study and understand the internal mechanisms that provide goose down with its resiliency under repeated compression. We have employed low magnification optical microscopy to identify some of these important mechanisms. Microscopy showed that a small tertiary structure exists on most goose down fibers and creates an important point of contact when two fibers interact. This tertiary contact mechanism has been coupled with fiber orientation and incorporated into a unique strain-energy function. The principal stresses for an initial compression cycle can be determined from this strain-energy function according to the hyperelastic constitutive theory. Irreversible deformation and hysteresis necessitate another means to determine the stresses during unloading and reloading. For these stages, the framework used by Beatty et al. (2002) for an ideal Mullins material will be utilized in conjunction with a shift in the stress-free state to determine the principal stresses. The proposed model is then evaluated for uniaxial compression and shown to capture the general behavior of goose down in compression including the irreversible deformation and hysteresis.