Abstract
In situ scanning electron microscopy three-point bending test was employed in this study to investigate the crack initiation and propagation in 5A05 aluminum alloy. The microscale strain fields around the crack tip were measured by using the geometric phase analysis method. Results show that prior to the crack initiation, the normal strain εyy (y direction is perpendicular to the load direction) was tensile around the notch, whereas the normal strain εxx (x direction is parallel to the load direction) was compressive around the notch. The shear strain εxy was nearly zero. With the increase in load, the normal strains εyy and εxx gradually increased, but the change in shear strain εxy was not evident. When the stresses at several sharp points at the notch root reached the breaking strengths, a few microcracks initiated at these points. At this moment, the normal strains εyy and εxx were much greater than the shear εxy, and dominated the strain fields around the crack tip. In the crack propagation process, the normal strains εyy and εxx, and the shear strain εxy dominated the strain fields around the crack tip, thereby leading to a Z-form of crack propagation path in the specimen.
Highlights
IntroductionMaterial fracture may cause catastrophic failure. understanding the fracture behavior is of fundamental importance to improve the mechanical properties of materials and assess the reliability of engineering components [1,2]
In many cases, material fracture may cause catastrophic failure
The geometric phase analysis (GPA) method involves the filtering of an image with an asymmetric filter centered on a Bragg spot in the Fourier transform of an high-resolution transmission electron microscopy (HRTEM) lattice image and performing an inverse Fourier transform
Summary
Material fracture may cause catastrophic failure. understanding the fracture behavior is of fundamental importance to improve the mechanical properties of materials and assess the reliability of engineering components [1,2]. The microstructure and fracture evolution of a magnesium alloy AZ31 were characterized by conducting quantitative in situ SEM tensile tests [19] These studies mainly focused on the crack initiation and propagation behavior, but did not consider the deformation fields around the crack tip. Tong et al reported the first quantitative experimental evidence of near-tip strain ratchetting with cycles, as captured in situ by DIC technique on a compact tension specimen of stainless steel 316L, using both stereo and SEM systems [22]. These studies failed to discuss the crack initiation and propagation behavior. The microscale strain field evolution around the crack tip was analyzed by using the GPA method
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