Measurement Analysis of Contact Pressure Distribution of Apple under Compression
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Abstract:
In this study, the pressure distribution of apple subjected to static loading was measured by the pressure sensitive film technique. The effects of apple maturity and curvature radius at contact location of fruit on pressure area were focused on. The results were calculated by Hertz equation; meanwhile, the calculation accuracy of the equation on contact pressure area was analyzed. The result showed that the contour of pressure distribution was near elliptical, and the discontinuous distributed pressures had the variation feature of rising and falling. The pessure less than 0.2 MPa occupied at the edge of the contact region, while the area of pressure over 0.5 MPa distributed at tiny spots. When the apple was loaded over 100 N, the pressure areas of two different maturity apples showed significant difference. With the increase of curvature radius, the pressure areas of apple at same load increased to varied extent due to maturity difference. Compared with film measurements of apple pressure area, the calculations with Hertz equation showed larger deviation. Hence, a correction coefficient (λ=1.5780 -0.0042F) was introduced to modify the equivalent elastic modulus in the Hertz equation. As a result, there was a good agreement between the measured contact areas and the predications using the modified Hertz equation. This indicated that the modified Hertz equation could precisely estimate pressure area of apple under static load.
