Evaluation of small-scale yielding boundary using digital image correlation results

Abstract

In this work, the boundaries of small-scale yielding (SSY) and large-scale yielding (LSY) have been experimentally evaluated from the analysis of crack tip opening displacement (CTOD) measured by digital image correlation (DIC). According to a previous numerical work, the ratio between the elastic CTOD range and the total CTOD range (Δδe/Δδt) defines the boundaries of SSY conditions and LSY. Three materials have been studied, commercially pure titanium and 2024-T3 and 7050-T6 aluminum alloys, tested at different stress ratio values. SSY conditions are shown to dominate when Δδe/Δδt ≥ 79% and ≥78% for titanium and the two aluminum alloys, respectively. In addition, LSY can be established when Δδe/Δδt ≤ 66.3% and ≤67.2% for titanium and for 2024-T3 and 7050-T6 aluminum alloys, respectively. Transition or LSY conditions are more probable in fatigue tests conducted at low R ratio and for crack lengths above 40% with respect to the width of the specimen.