Thermomechanical and isothermal fatigue crack propagation testing method for 316LN austenitic stainless steel

Abstract

Investigating fatigue crack growth behavior of materials is crucial to the life design and safety evaluation of engineering structures. During the practical service condition, the temperature keeps changing, which cannot be studied by the traditional fatigue crack growth test method at constant temperature. In this study, we focus on constructing a new thermomechanical fatigue (TMF) crack propagation testing method, developing a thermal deformation compensation method, and proposing an equivalent compliance method suitable for variable temperature conditions based on ASTM E647 standard to measure the crack length. Furthermore, the load-and strain-controlled TMF tests under different phase angles are carried out to prove the validity of the new method.

Isothermal and thermomechanical fatigue crack growth behavior of 316LN stainless steel under load‐ and strain‐controlled modes

“…As illustrated in Figure 2A, the notched side of the specimen is employed for mounting a high‐temperature extensometer, combined with a modified compliance method, following the guidelines outlined in ASTM E647 31 . This method is utilized to gauge the precise length of the crack, with further elaboration and the material parameters required for the calculation process available in Zheng's earlier research 32 . The test was conducted using an MTS 370.02 loading frame as shown in Figure 2B.…”

“…In the load‐controlled TMFCG tests, cyclic stress ranging from 0 to 120 MPa was applied, while strain‐controlled tests were regulated using an extensometer to impose cyclic deformation between 0 and 0.2%. The selection of these load and strain magnitudes was primarily guided by previous research, ensuring a more consistent mechanical response under these loading conditions 32 . Considering industrial conditions, the temperature cycled between 350°C and 550°C.…”

“…31 This method is utilized to gauge the precise length of the crack, with further elaboration and the material parameters required for the calculation process available in Zheng's earlier research. 32 The test was conducted using an MTS 370.02 loading frame as shown in Figure 2B. Temperature monitoring and controlling were managed through a K-type TC (thermocouple), which was spot-welded at 5 mm below the center of the specimen gauge section.…”

“…The selection of these load and strain magnitudes was primarily guided by previous research, ensuring a more consistent mechanical response under these loading conditions. 32 Considering industrial conditions, the temperature cycled between 350 C and 550 C. In contrast, the IF tests were conducted at a constant temperature of 550 C. In all cases, the cycle period for these tests was set at 60 seconds. Two trials were conducted of each experimental parameter in this study to ensure the validity and reproducibility of the experimental data.…”

Guest editorial of virtual special issue: Structural integrity in the context of carbon neutrality

“…For the lifetime design and safety assessment of engineering structures, it is essential to investigate the crack growth behavior in materials. Zheng et al 10 proposed a new thermomechanical fatigue (TMF) crack growth testing method and developed a temperature compensation method test method considering the complex working conditions of constantly changing temperature in practical engineering. Based on ASTM E647, a modified compliance method is proposed to calculate the crack length under variable temperature conditions.…”