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Transferring load to flesh: part IX. Cushion stiffness effects
Bulletin of Prosthetics Research
|January 1, 1979
Summary
Switching to a softer cushion offers minimal additional comfort once a soft cushion is already in use. While compressive stress slightly decreases, tensile and shear stresses show little change, indicating limited benefits for seating comfort.
Area of Science:
- Biomechanics
- Materials Science
Background:
- Understanding stress distribution in soft tissues is crucial for designing comfortable seating and support surfaces.
- Previous research has not fully quantified the impact of cushion stiffness on internal flesh stresses.
Purpose of the Study:
- To analytically investigate the stresses (compressive, tensile, shear) developed within flesh in contact with cushions.
- To determine the influence of cushion stiffness and flesh Poisson's ratio on these stresses.
Main Methods:
- Analytical examination of stress development in flesh under cushion pressure.
- Modeling stresses as a function of cushion stiffness (PSI) and flesh Poisson's ratio.
Main Results:
- Tensile and shear stresses in flesh plateau with decreasing cushion stiffness below 10 PSI.
- Compressive stress shows a modest reduction (approx. 20%) with a 50% decrease in cushion stiffness in the soft range.
- Diminishing returns in stress reduction are observed with softer cushions.
Conclusions:
- Significant improvements in comfort from switching to even softer cushions are limited once a soft cushion is used.
- Compressive stress is the primary stress component that benefits from further softening of cushions.
- Designers should consider the non-linear stress response of flesh to cushion stiffness for optimal ergonomic solutions.