Viscoelastic finite element analysis of the dynamic behavior of apple under impact loading with regard to its different layers

• The finite element model has been developed to simulate dynamic behavior of apple.
• Apple was considered as nonlinear viscoelastic material.
• The distribution trend of stress wave is from the collision point to the outside.
• Displacement in collisions is the most in skin and the least in the core of fruit.

Annually, large quantities of apple are destroyed and suffer from quality loss because of bruising and other mechanical damages during harvesting, transportation, storage and packaging. Bruising due to impact is one of the most important reasons for the quality loss in the fresh fruit market. Regarding to the accuracy and economic justification, Finite Element Method (FEM) is one of the best ways of investigating the effective factors in bruising produced as a result of impact. In this research, FEM is used to study the dynamic impact to apple. For soft and relatively large objects like apple, the dynamic waves are absorbed by the body of the object through decreasing the kinetic energy during the impact. The amount of energy absorption is dependent upon the viscoelastic properties, geometric size of the object during the collision, and collision velocity. Therefore, in such materials, contact area and the induced stress in contact region are time dependent. In finite element modeling, a nonlinear time-dependent contact is considered. Through the use of finite element models of a typical fruit, the apple, some collision processes of the fruit were studied. The 3D FEM models were created to illustrate, as closely as possible, the typical geometrical structure of an apple fruit, containing the basic inhomogeneous structure of the fruit. In the current study, using Finite element method, the behavior of the various layers of skin, cortex and core of apple was analyzed applying impact test to collision of the fruit with a flat rigid plate as well as the collision of an apple with another apple. The different layers of apple such as skin, cortex and core have not been yet analyzed dynamically so it plays a remarkably important role. The results showed that the parameters of displacement, velocity, acceleration, stress and hydrostatic pressure in the collision of apple to apple were less than that of apple to rigid object at the velocity of 1 m/s. Also, changes of these parameters were maximum in a skin and minimum in a core.