Detection of early stage of ductile and fatigue damage presented in Inconel 718 alloy using instrumented indentation technique

Abstract

Structural materials under various mechanical loads are damaged as a result of their plastic deformation and subsequent nucleation and propagation of cracks. Detection of damage in its initial phase is crucial to ensure safety and durability of construction elements. In this work, we proposed contact stiffness (SS) determined using the instrumented indentation technique as the damage indicator. New procedure for deformation-induced damage investigation is proposed and the indentation tests were performed in the specially designed specimens made from Inconel 718 alloy, which was previously subjected to mechanical loads. Damage parameter (Dε{D}_{\varepsilon }) determined on the basis of Johnson–Cook damage model was used as a reference measure of damage degree. Fracture analysis was carried out to investigate the early stage of damage development in the tested specimens. The value of contact stiffness determined from the instrumented indentation shows linear correlation with the value of damage parameter. This innovative approach was used in the presented investigation.

Keywords

• ductile
• fatigue
• damage
• indentation
• hardness
• inconel 718