Limit values of impact energy determined from contours and surface pressure distribution of apples under impact loads

During the harvest, handling, transport, sorting and other operations, apples are exposed to different static and dynamic loads. However, impact loads are the main causes of apple surface bruising and grower losses. Under impact loads, biological material has elastic characteristics. Due to this dynamic process, fluid and air in the intercellular spaces cannot move to areas with a lower load, which results in the formation of cracks and irreversible tissue damage. The mechanism of damage to the structure of apple flesh under impact loads differs qualitatively from damage generated under quasi-static loads. Therefore, it is essential to determine the critical impact energy for which deformation of the elastic apple moves toward permanent deformation. To define and determine the boundary impact energy including tissue damage, it was hypothesized that whether a permanent deformation occurs during a collision corresponds to the initial phase of maximal surface pressure stabilization. Therefore, apples with different elasticity moduli may have characteristic surface pressures above which the flesh tissue is destroyed. The maximum values for contour surface pressure are at the central point of contact. In this area, there is no evidence of flesh tissue destruction. Evaluating the maximum surface pressure over the apple surface, contours are formed near the central point of contact. This study also determined the energy required to cause permanent deformations.