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.

Study of cyclic crack‐tip opening displacement of microstructurally small fatigue crack using digital image correlation

“…With recent developments in contactless measurement techniques, such as digital image correlation (DIC), 36–38 the measurement process can be optimized, enabling high sample rate and full‐field displacements. DIC has been used to investigate both long and microstructurally small fatigue cracks emphasizing the early‐stage crack initiation, strain accumulation, and its dependence on microstructure 39–42 . The sub‐micron strain measurements using SEM‐DIC have shown that the strain is accumulated in the form of strain bands and that the grain boundaries have a role in the capability of transmitting or blocking slip 43,44 .…”

“…DIC has been used to investigate both long and microstructurally small fatigue cracks emphasizing the early-stage crack initiation, strain accumulation, and its dependence on microstructure. [39][40][41][42] The sub-micron strain measurements using SEM-DIC have shown that the strain is accumulated in the form of strain bands and that the grain boundaries have a role in the capability of transmitting or blocking slip. 43,44 Moreover, Abuzaid et al 38 observed several strain localizations that were prominent on one side of the grain boundary, while the adjacent grain showed little strain accumulation.…”

Virtual special issue: Fatigue 2021: The properties, processing, and performance of structural materials

“…Three complementary papers by Vasco-Olmo et al and Camacho-Reyes et al, [3][4][5] focusing upon crack propagation mechanisms, employed more established titanium, stainless steel, and aluminum alloys as the vehicle for detailed empirical research. Evaluation of surface crack growth, crack wake, and crack tip plasticity in compact tension specimens relied on optical microscopy and digital image correlation (DIC) to establish local strain fields and crack tip opening displacement.…”