The objective of this study is to investigate the influence mechanism of martensite multi-scale interfaces on the fatigue small cracks propagation behavior in super martensite stainless steel. The findings revealed that crack propagation slows during the transition from early to steady stages. Multiscale martensite interfaces can cause varying degrees of crack deflection, and cracks tend to propagate along-boundaries during the early propagation stage. Martensite lath is the basic unit that affects the fatigue performance and the behavior of small crack propagation.
High-tension structural steels are prone to accelerated fatigue damage from pitting corrosion and high-temperature. Despite adverse effects, research on their low cycle fatigue (LCF) behavior is limited. Specifically, studies analyzing temperature-dependent pit sensitivity effects, considering pit-related material’s susceptibility to surface topographic features variation and stress concentration are lacking. This study conducts LCF tests on pitting corroded killed E350 BR structural steel at multiple strain amplitudes and high temperatures. It develops temperature-dependent parameters, such as the cyclic softening pit sensitivity factor, suitable for integration into existing approaches like total cyclic plastic strain energy density (CPSED), power-law, average strain energy density (SED), Coffin-Manson, and pit stress intensity factor (pit-SIF). Further, it proposes multiple linear regression-based prediction models relating total CPSED and average SED with strain amplitude and temperature. Corroded specimens show higher plastic deformation and reduced peak stress, fatigue life, and total CPSED compared to uncorroded ones. The developed parameters, integrated with average SED approach, predicts LCF life within an error band of ±1.5, while power-law relationship reduces it to ±1.2. Moreover, pit-SIF approach estimates fatigue life within an error band of ±1.5. The findings provide critical knowledge for enhanced component design, leading to structural safety, performance, and fire resilience.
The influence of microstructural attributes on fatigue crack propagation in titanium matrix composite remains largely unexplored. The impact of α-lamella crystallographic and spatial orientations on fatigue crack propagation in an as-forged TiB/near α-Ti composite was investigated using innovative quantitative tilt fractography and electron backscattered diffraction techniques. Crack initiation was observed from TiB cluster defects, followed by faceted fatigue crack propagation across α lamellae. In long-life failure, facet formation appears to be driven by a combination of slip and resolved normal stress across the facet plane, with facet angles relative to the loading direction (LD) predominantly ranging between 30.0° and 50.0°. In contrast, short-life failure exhibited shear deformation as the primary mode, with facet angles relative to LD mainly between 40.0° and 50.0°. Crystallographic orientation analysis revealed that facets predominantly formed near the basal plane in both long-life and short-life failures. Crack-initiation microstructural neighborhoods favoring basal slip increased effective slip length over α lamellae, reducing resistance to crack propagation. This led to a rise in basal geometrically necessary dislocation (GND) density from 1.2 × 1013 m−2 in long-life to 3.6 × 1013 m−2 in short-life failures. These observations highlight the dominance of spatial and crystallographic orientations of α lamellae in controlling fatigue crack propagation.
Cold spray presents a promising solution for repair of damaged material within high-value components. However, before employing cold spray for component repair, it is crucial to assess its damage tolerance and durability. This study focuses on evaluating the fatigue behavior of helium-sprayed AA6061 applied to an A356-T6 cast substrate compared to the same specimen geometry made entirely of the A356-T6 material. Fatigue testing was conducted using a marker band schedule to analyze fatigue crack growth rates in the cold spray and substrate materials. To complement the fatigue testing, experimental uncertainties and variabilities were incorporated into a crack growth model using a Monte Carlo approach to probabilistically assess reliability. The results indicate that the AA6061 cold spray material exhibited faster crack growth, resulting in a ∼25% lower life compared to the baseline A356-T6 material. Given the cost effectiveness of the cold spray repair process, it appears to be a viable approach, with the caveats that the residual life is expected to be less than the pristine substrate material and the cold spray interface is prone to delamination during crack impingement.