Is the temperature plateau of a self‐heating test a robust parameter to investigate the fatigue limit of steels with thermography?

Abstract

A critical aspect of standard test methods for fatigue characterization is that they do not provide any information on heat dissipation in the material and involve very expensive experimental campaigns in time and costs. In recent years, thermographic methods capable of reducing testing time have been developed, also providing more information on damage occurring in the material. A commonly used approach is based on the assessment of the temperature plateau during a stepwise loading procedure. At times, however, this approach can fail if temperature stabilization is not achieved. In this regard, in this paper, a new approach based on the assessment of 3 different thermal indexes was proposed to estimate the fatigue limit of 3 stainless steels: AISI 316, 17‐4PH, and ASTMA890 grade 4a, respectively, exhibiting fully austenitic, fully martensitic, and duplex biphasic microstructure. The fatigue tests were carried out by using a stepwise loading procedure, under loading ratio of 0.5. The analysis demonstrated the possibility to further reduce testing time and, consequently, the fatigue experimental campaign. Moreover, some ideas are discussed about how to justify the different thermal behaviour of a biphasic stainless steel, in total temperature variation. Moreover, a discussion of results regarding the various thermal behaviours of the investigated steels and a possible correlation with the microstructure has been proposed.

Fatigue of Friction Stir Welded Aluminum Alloy Joints: A Review

“…In the fatigue crack growth tests, standard CT specimens were loaded on electrohydraulic machine and the crack length on the crack front was measured by a stereomicroscope [99]. To assess the location and the time of damage onset, thermographic methods have been used to achieve information about the damage [100][101][102][103][104]. Palumbo et al [105] monitored the AA5754-H111 specimens by infrared detector during experiment and the thermal signal is related to the energy dissipated in the material plastic deformation zones.…”

Effects of Heterogeneous Microstructures on the Strain Hardening Behaviors of Ferrite-Martensite Dual Phase Steel

“…Moreover, the evolution of plastic local deformation and strain distribution of DP steel has been researched considering the microstructure features [11][12][13][14]. In addition, the effects of the microstructures, ferrite content, and test temperature on the mechanical properties (i.e., tensile properties, fatigue behaviors, and crack propagation properties) of austenitic-ferrite duplex stainless steel were researched as well [15][16][17][18][19][20][21][22].…”

Energetic approach to study the plastic behaviour in CT specimens

“…Different authors found that in presence of a dissipative phenomenon such as a crack, in a material undergoing a cyclic loading, it is possible to define the plastic volume which, dissipates energy around the crack [23][24][25].…”

“…By considering a bilinear hysteresis loop where kinematic and isotropic hardening phenomena are neglected Figure 2, at stress ratio of R=-1, for sake of simplicity. Until the load is elastic, the behaviour of material is described by a full recovery of elastic energy per cycle and irreversible dissipative sources are zero [23]. The cyclic loading produces a delay between strain and stress involving the occurrence of the hysteresis loop.…”