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The objective of the present study was to estimate the influence of laser shock peening on the fatigue properties of AA2024-T3 specimens with a fastener hole and to investigate the possibility to heal the initial cracks in such specimens. Fatigue cracks of different lengths were introduced in the specimens with a fastener hole before applying laser shock peening. Deep compressive residual stresses, characterized by the hole drilling method, were generated into the specimens by applying laser shock peening on both sides. Subsequently, the specimens were subjected to fatigue tests. The results show that laser shock peening has a positive effect regarding the fatigue life improvement in the specimens with a fastener hole. In addition, laser shock peening leads to a healing effect on fatigue cracks. The efficiency of this effect depends on the initial crack length. The effect of laser shock peening on the fatigue life periods was determined by using resonant frequency graphs.Metals 2020, 10, 495 2 of 13 and fatigue properties of the aluminum alloy LY12-CZ with various interference values (interference value describes how much a mandrel radius is larger than a hole radius), and it was shown that with increasing interference value from 0% to 6%, the fatigue life increases by a factor of six.Another promising way to improve the behavior of fatigue critical components is laser shock peening (LSP) [7]. LSP is a process in which under the influence of laser pulses, mechanical shock waves arise, propagating under the surface of the material [8]. When the peak pressure of waves exceeds the Hugoniot elastic limit (HEL) of the material, plastic deformation occurs, which leads to compressive residual stresses within the material, i.e., near the surface. The subsurface compressive residual stresses are balanced by the stress field within the material or in zones adjacent to the LSP-treated area. In recent years, various studies have been conducted on the effect of LSP on the fatigue properties of different metallic alloys. Ivetic et al. [9] investigated the effect of the sequence of processes (hole introduction and LSP) on the fatigue properties of AA6082-T6 specimens. The experiments showed that the sequence of processes is important for the improvement of the fatigue life. The beneficial effect of LSP is higher if the hole is introduced after LSP. This is linked to the fact that compressive residual stresses in LSP-treated specimen are compensated by tensile residual stresses [3], and in the case of applying LSP after drilling a hole, the magnitude of tensile stresses would be higher, which would lead to a shorter fatigue life. Achintha et al. [10] evaluated the effect of the size of the LSP-treated area on fatigue properties of AA2024-T3 specimens. Two cases were considered: (i) LSP was performed just around the hole, and (ii) LSP was applied across the entire width of the specimen. The results showed that specimens with a smaller treated area around the hole can withstand more loading cycles than specimens peened along the e...

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Titanium alloys are widely used in aerospace and automotive industries due to their excellent mechanical properties, however, the formability is limited, which is an issue during forming. In the present study, the effect of temperature and strain rate on the tensile properties of the titanium α-alloy KS1.2ASN was investigated. It was observed that there is initially no gain in ductility with increase in temperature until 400 °C, however, maximum formability is reached at maximum tested temperature of 600 °C. EBSD analysis revealed that twinning is the main deformation mechanism at room temperature, however, sliding deformation becomes more pronounced with increasing temperature. An increase in strain rate leads to a decrease in elongation, but the influence is less pronounced compared to temperature.