Fatigue performance of notched and hot-dip galvanized laser and mechanically cut S960 steel components considering local defects with the theory of critical distances

Abstract Experimental fatigue tests were performed for a S960 steel grade, including hot-dip galvanized (HDG) round base material specimens, and laser cut, and machined notched component-sized specimens made of t = 6 mm S960 ultra-high-strength steel (UHSS) plates. Cracking after the HDG was found to have a major influence on fatigue strength and thus reducing the effect of surface quality on the fatigue performance. Design guidelines for notched HDG components are proposed, and HDG with UHSSs was found suitable for structures with geometrical notches. Multiparametric TCD-based 4R method application was introduced, and it was found to be applicable for the fatigue strength assessment of structural details with initial cracks

Fatigue strength assessment of cut edges considering material strength and cutting quality

Abstract In the present study, statistical analysis for previously reported cut edge fatigue test results is performed. Experimental fatigue tests are conducted for machined, plasma, and fiber laser-cut S960 edges to verify the effect of yield strength and cut edge quality, and to study the effect of the cutting method on fatigue performance. Experimental fatigue tests were complemented with hardness and residual stress measurements and metallurgical analyses with electron backscatter diffraction (EBSD) to characterize cut edge fatigue properties and to verify statistical analysis findings. The results show that cut edges can be divided into high- and low-quality categories. On the basis of these high- and low-quality categories, material strength, and applied cutting methods, FAT classes and recommended fatigue design practices are proposed

Effects of notch-load-defect interactions on the local stress-strain fields and strain hardening of additively manufactured 18Ni300 steel

Abstract This study investigates the influence of geometrical notches on the local (true) stress-strain curves, deformations, and strain hardening behavior of maraging tool steel 18Ni300 processed via the laser powder-bed fusion method as an additive manufacturing approach. For this purpose, five types of specimens with different notch designs were manufactured; these samples were considered to study the effects of the notch stress concentration factor and the notch position on the material's mechanical response against the applied external load. Accordingly, using the digital image correlation technique, true stress-logarithmic strain curves were plotted and compared for various points in the vicinities of the notches while the specimens were subjected to quasi-static tensile loads. Further, the strain (work) hardening behavior of the material at each point was then evaluated and compared with other points by plotting their strain hardening diagrams from the first derivative of the stress-strain curves. The results showed that the strain hardening of the samples increased with the stress concentration factor (notch sharpness) while its ductility decreased accordingly. Furthermore, notch location and shape also showed determining roles in defining the material behavior. Ultimately, higher stress concentrations, internal positioning, and less gradual changes in geometric features (C-shaped notches compared to V-shaped ones) can result in higher defect sensitivity, more decrease in ductility, and more likely catastrophic failures in metals processed by additive manufacturing

Fatigue performance of stainless tool steel CX processed by laser powder bed fusion

Abstract This study investigates the fatigue performance of additively manufactured steel CX under uniaxial high cycle loading. The results show that surface quality was the most influential parameter that changed the fatigue behavior of the material, compared to combinations of building orientation and heat treatment as other fabrication parameters. Consequently, improving the surface quality from Ra = 3 μm–1 μm increased the fatigue limit from 170 MPa to 250 MPa. However, heat treatment did not significantly influence the fatigue performance of the material, although it increased the hardness of the material from 320 HV to 460 HV