RESUMEN
Gradient structure (GS) is commonly designed and processed in engineering materials to improve mechanical properties especially fatigue performance by taking advantage of the strengthened surface. However, whether the very-high-cycle fatigue (VHCF) property can be improved by GS is questioning due to the different crack initiation mechanisms between low-, high-cycle and VHCF. In this paper, GS of a Ti-6Al-4V alloy is generated by pre-torsion and characterized by electron backscatter diffraction. Then the VHCF behavior of the GS specimen is studied. The fractography and synchrotron radiation X-ray microtomography presented detailed characteristics of the internal crack initiation region in VHCF of the titanium alloy with GS. The results indicated that, in contrast to the low- and high-cycle regimes, the VHCF strength is reduced for the specimens with GS. Thus, the GS induced by pre-torsion cannot enhance the VHCF strength of the titanium alloy. This implies that VHCF test (property) is an important consideration for the microstructural designed materials. The graphical abstract is available in Supplementary information.
RESUMEN
We report the experimental results of fatigue behavior of ultralow-binder-content inorganic-organic hybrid (IOH) based on lunar soil simulant, which may be viewed as a "lunar cement". Under the same loading condition, the fatigue life of the IOH is superior to typical steel-reinforced concrete, especially when the stress amplitude is relatively high. Fatigue damage mostly occurs in the binder phase, followed by rapid cleavage-like failure. The important material parameters include filler type, filler particle size, and filler-binder bonding.
RESUMEN
High-cycle and very-high-cycle fatigue tests via rotary bending (52.5 Hz), electromagnetic resonance (120 Hz) axial cycling, and ultrasonic (20 kHz) axial cycling were performed for a high-strength steel with three heat treatment conditions, and the effects of loading frequency and loading type on fatigue strength and fatigue life were investigated. The results revealed that the loading frequency effect is caused by the combined response of strain rate increase and induced temperature rise. A parameter η was proposed to judge the occurrence of loading frequency effect, and the calculated results were in agreement with the experimental data. In addition, a statistical method based on the control volume was used to reconcile the effect of loading type, and the predicted data were consistent with the experimental results.