What does residual Indentation mean?

Residual indentation refers to the permanent deformation or mark left on a material's surface after an external force or load has been removed. This occurs when the material does not fully recover its original shape, often due to plastic deformation. Residual indentation is commonly assessed in materials testing to evaluate properties such as hardness and ductility. It can provide insights into the material's behavior under stress and its long-term durability.