Mechanism Based Evaluation of Scratch Damage in Diatom Frustule Reinforced Epoxy Composites

ABSTRACT Epoxy composites are widely used in applications where surface integrity is critical, yet the relationship between penetration resistance and actual scratch damage remains unclear, particularly in systems containing rigid bio‐based fillers. This study presents a mechanism based interpretation of scratch damage by separating penetration resistance from material removal processes in epoxy composites reinforced with calcined diatom frustules, which possess a hierarchical porous silica structure distinct from conventional fillers. Scratch behavior was evaluated under varying normal loads and scratch velocities to examine the governing factors of surface deformation. Scratch hardness and relative cutting volume were used together to distinguish between deformation‐dominated and material removal‐dominated responses. Flexural tests were also conducted to relate bulk mechanical properties to surface damage behavior. In addition, response surface methodology was applied to assess the combined influence of load, velocity, and filler content. The results show that increasing filler content enhances stiffness but does not lead to a consistent improvement in overall scratch performance. Instead, the response evolves through different deformation regimes, shifting from plastic flow to material removal and, at higher filler contents, to more constrained deformation responses. These findings indicate that hardness alone is insufficient to describe scratch performance. The proposed approach provides a clearer framework for interpreting scratch damage in particle‐reinforced polymer systems by considering the interaction between penetration, deformation, and material removal mechanisms.