Abstract
The paper presents results of SEM analysis of fatigue fracture surface of thin-walled tubular specimen manufactured from PA38-T6 aluminum alloy. In the previous research specimens were subjected to multiaxial loadings. They were axial, torsional, in-phase, 90º out-of-phase and asynchronous loadings. During the fatigue experiments, the process of initiation and development of cracks was tracked using the surface replication technique, using cellulose acetate thin foils. In the present work, SEM observations of fatigue fracture surface were conducted and compared to previously obtained data. It was confirmed, that the dominating mechanism of fatigue crack formation was the coalescence of small crack, regardless of loading type and level.
Highlights
Microscopic analysis of phenomena occurring in the material under fatigue loadings is an important issue, because the stages of initiation and propagation of small cracks take, in most cases, a significant part of the fatigue life [1]
The development of fatigue cracks may be different depending on the material and the loading case, and on the scale of observation: the crack can grow on the planes of maximum shear strain [1], the planes of maximum principal stress [3], or on the planes of maximum shear strain to some length, and change the propagation direction [4]
The research confirmed the coalescence of small cracks, and at the same time showed that the cracks propagated towards the center of the specimen’s cross-section
Summary
Microscopic analysis of phenomena occurring in the material under fatigue loadings is an important issue, because the stages of initiation and propagation of small cracks take, in most cases, a significant part of the fatigue life [1]. The development of fatigue cracks may be different depending on the material and the loading case, and on the scale of observation: the crack can grow on the planes of maximum shear strain [1], the planes of maximum principal stress [3], or on the planes of maximum shear strain to some length, and change the propagation direction [4]. The study of the fatigue crack development mechanism, depending on the loading case and on the material, is important for the analysis of experimental results and the improvement of fatigue failure accumulation and fatigue life prediction models. These models are based on the critical plane [8], principal strains [9] or energy parameters [10]
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