Method for Varying the Strain in a Thermal Fatigue Test Cycle for Corset Specimens

• Published in: Russian metallurgy Metally 2022-12, Vol.2022 (13), p.1789-1794
• Main Authors: Degtyareva, S. P., Prokhorova, T. V., Sidokhin, E. F.
• Format: Article
• Language: English
• Subjects: Caskets; Chemistry and Materials Science; Crack initiation; Damage accumulation; Diameters; Fatigue cracks; Fatigue tests; Fracture mechanics; Materials Science; Metallic Materials; Nucleation; Plastic deformation; Plastic Deformation of Ferrous and Nonferrous Metals; Thermal cycling; Thermal cycling tests; Thermal fatigue
• ISSN: 0036-0295; 1555-6255; 1531-8648
• DOI: 10.1134/S0036029522130055

—The published results on studying thermal fatigue using thermal cycling tests of flat corset specimens (specimens with continuous radius between ends), which were performed under the thermal operating conditions of the materials of products, are analyzed. The tests are accompanied by metallographic examination of the structural changes occurring in the materials during operation. These data allowed us to reveal the specific features of the development of thermal fatigue in corset specimens. Metallographic examination has shown that cracks in corset specimens appear everywhere in the first few test cycles. This finding indicates that the material is immediately in a state favorable for crack nucleation, bypassing the long stage of damage accumulation inherent in the Coffin tests. Therefore, we can conclude that thermal cycling tests performed on corset specimens are a preferred method for studying and modeling the thermal fatigue in products. However, in tests on corset specimens, it is not possible to use the techniques used in the Coffin method to vary the plastic deformation in a cycle (ε pl ), and this is done by changing thermal test conditions, which can negatively affect the results due to the influence of temperature on the physicomechanical properties of the material. To solve this problem, we propose the following method for varying ε pl : tests are carried out on specimens, the shoulders of which are rectangular for flat specimens and are cylindrical for cylindrical ones, and ε pl is varied by changing the width or length of the former and the diameter or length of the latter.