Simulation analysis of micron-scale indentation damage in a multilayer apple structure comprising wax, peel, and flesh

Mechanical damage is one of the main causes of quality deterioration during mechanized apple harvesting. In this study, a multilayer finite element model of apple tissue was developed using ABAQUS to investigate microscale failure behavior under localized contact loading. The model included wax, peel, and flesh layers, while zero-thickness cohesive elements were inserted at the interfaces to simulate delamination behavior. Different elastoplastic properties were assigned to each layer, whereas creep and permeability effects were incorporated into the flesh to reproduce its time-dependent mechanical response. Three indenter geometries, including Berkovich, Flat, and Spherical indenters, were used to analyze their effects on deformation, stress distribution, damage evolution, and energy dissipation. The Berkovich indenter generated the strongest local stress concentration, with an influence depth of 180 μm, and produced a maximum principal stress that was 60% higher than that of the Spherical indenter, indicating greater a tendency for peel cracking. The Flat indenter caused the largest permanent deformation and pronounced edge stress concentration, whereas the Spherical indenter distributed stress more uniformly and resulted in the lowest residual stress after unloading. Micro-indentation experiments showed trends consistent with the simulation results, thereby validating the proposed model. Interfacial damage initiated first at the wax-peel interface at indentation depths of 50–120 μm, while more severe failure occurred at the peel-flesh interface at depths of 150–250 μm, where complete separation and increased energy dissipation were observed. These results reveal a hierarchical damage mechanism in apple tissue and provide theoretical guidance for reducing mechanical damage during mechanized harvesting.