Effect of Fatigue Loading Mode on 718 Alloy Fatigue Properties

Abstract

In materials science, fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. If the loads are above a certain threshold, microscopic cracks will begin to form at the stress concentrators such as the surface, persistent slip bands (PSBs), interfaces of constituents in the case of composites, and grain interfaces in the case of metals. Eventually a crack will reach a critical size, the crack will propagate suddenly, and the structure will fracture. The first works about fatigue phenomenon were published since 1837 and intensively was investigated by Wöhler in 1860. With needs of using the progressive materials such titanium and Ni-base superalloys become more significant to put under the various fatigue loading these sorts of alloys. Presented article deals with how the various condition of loading influenced an IN718 alloy fatigue lifetime especially. The fatigue tests provided on this kind of material was done via low frequency loading and push-pull or rotation-bending stress up to this time. Fatigue tests of experimental material was carried out at two different frequencies, 20 kHz with stress ration R = - 1 (push – pull, σm = 0 MPa) as well as the three-point bending load R ˂ 1 (σom = 526.8 MPa) at low frequency 150 Hz at room temperature. The microstructure characterization and Scanning Electron Microscopy (SEM) fractography analysis of fatigue process were done as well. The main goal of study was analyze obtained data after fatigue test and consider, if the various loading modes have influence on fatigue lifetime (initiation sites, crack propagation character, etc.).

Archives of Metallurgy and Materials

“…Fatigue tests were performed at low frequency sinusoidal cyclic push-pull loading (stress ratio R = -1) at frequency f ≈ 75 hz at ambient temperature (T = 23 ± 5°C) using the fatigue testing machine zwick/roell amsler 150hfp 5100 (fig. 2b, 2c) according to stn 42 0362; the Wöhler curve (relationship between stress amplitude σ a and number of cycles to failure N f ) and fatigue limit σ c for N = 10 7 cycles were determined [21,22].…”

Fracture Behaviour of Aluminium Alloys under Coastal Environmental Conditions: A Review

“…Researchers primarily rely on valuable techniques such as digital image correlation (DIC) [143] and optical microscopy for this purpose [144]. Fatigue loading repeatedly stresses the material, leading tiny cracks or imperfections on the surface to grow into small cracks over time [145]. These cracks can be challenging to detect with the naked eye.…”

Testing Techniques and Fatigue of Additively Manufactured Inconel 718 – A Review

“…Type of loading has a significant influence on the fatigue life of SLM IN718; this is due to the dependence of stressed volumes of a sample and different loading types. Belan [72] studied the effect of type of loading on fatigue life of wrought IN718; the author compared data generated from push-pull and three point bending tests (Figure 29). As expected, fatigue lives of samples in bending tests are significantly longer than those from push-pull tests; samples in bending test subjected to high stress at the outer surface while uniform stress is seen for the entire cross section of sample in push-pull test.…”