In this work the effects of long-term ageing of 9Cr-1Mo (T91) heat-resistant steel on its dynamic hydrogen embrittlement resistance in impact loading conditions were investigated. Altogether three heat-treated material states were studied, namely the initial normalized and tempered (N&T) state, i.e., 1050 degrees C/0.5 h + 750 degrees C/1 h and two long-term aged states, i.e., 600 degrees C/5000 hand 650 degrees C/5000 h. Charpy V-notch (CVN) impact bending tests were performed at room temperature for all the heat-treated material states in conditions either without or with electrochemical hydrogen charging. A brittle fracture resistance of the investigated material in individual material conditions was evaluated by the determination of Embrittlement Index (EI) values in terms of relative changes in CVN impact toughness with respect to variously selected initial and final material conditions. This approach enabled to differentiate the effects of long-term ageing, hydrogen charging, and their mutual superposition on the resulting brittle fracture resistance. The obtained results indicated excellent brittle fracture resistance of studied T91 steel in both the aged and hydrogen-charged material states at impact loading conditions.
The fatigue performance of 2024-T3 aluminum alloy is of critical importance in aerospace applications, yet the combined effects of stress ratio and geometry remain insufficiently explored. The objective of this study is to numerically investigate how different stress ratios (R = -0.2, 0.1, 0.4) and specimen geometries influence fatigue life, damage, and safety factor under varying tensile stresses (483, 241.5, and 120.75 MPa). Three specimen configurations-open-hole, transverse, and shear-were modeled and simulated using ANSYS Workbench, with input data obtained from literature-based mechanical properties and S-N curves. Results demonstrate that increasing tensile stress markedly reduces fatigue life and safety factor, whereas stress ratio exerts a non-linear influence, with intermediate values yielding the most detrimental effect. The findings reveal the interaction between stress ratio and geometry, providing new insights for fatigue life prediction and structural design of 2024-T3 aluminum alloy.
This study investigates the combined effect of temperature and notch depth on the Charpy impact toughness of API 5L X70 pipeline steel using an experimental approach coupled with statistical modeling. A 22factorial design of experiments was implemented to evaluate the influence of two factors: temperature (T), coded as X1, and notch depth (Nd), coded as X2. Charpy V-notch impact tests were performed according to the experimental matrix defined by the design of experiments, and the absorbed fracture energy (U) was measured for each condition. The results indicate that the notch depth has a more significant influence on the absorbed energy than temperature within the studied range. Furthermore, the fracture energy increases within creasing temperature, confirming the typical ductile-to-brittle transition behavior of HSLA steels. Response surface methodology was applied to model the variation of absorbed energy as a function of the studied parameters. A first-order interaction model was developed to correlate the experimental parameters (T, Nd) with the fracture energy (U) and to predict its values within the investigated domain. The obtained results contribute to a better assessment of the structural integrity of pipelines under different operating conditions.
The aim of the study is to investigate the effects on impact toughness properties of powder metallurgy (P/M) steels depending on different nickel ratios. For this purpose, ferrous P/M alloy samples containing 1.2 wt.% carbon and different nickel contents (0.5-5 wt.%) were compacted under 700 MPa pressure and sintered at 1200 degrees C under 5 & times; 10-2 Pa vacuum atmosphere. Following sintering, the densification rate and macrohardness (HV2) measurements of the samples were carried out. Fracture morphologies of the samples having different nickel content following impact toughness tests at various temperature (-40 to 40 degrees C) were imaged by scanning electron microscopy (SEM). Metallurgical characterizations of the samples with different nickel content were analyzed SEM and X-ray diffractometer (XRD). It was understood that pearlitic transformation was suppressed with the formation of nickel-rich austenitic areas in the microstructure of nickel-doped P/M steels. The hardness and impact toughness values of PM steel samples with 5 % nickel addition were increased by approximately 121 and 247 %, respectively, compared to samples without nickel addition, at all test temperatures.
The purpose of this article is the fatigue crack growth rate and stress-strain characteristic of a nickel superalloys ZhS6K. The da/dN(K) data from near-threshold to Paris regime and the stress-strain curve were obtained using a new methodology designed for bending small specimens using material extracted directly from the blade. The Hartmann-Schijve formula was fitted to describe the fatigue crack growth rate data. Failure mechanism was related to the crack propagation rate by help of fractographic analysis. A comparative analysis of the investigated material with the related alloy Inconel 718 was also performed. The tensile and compression stress-strain behavior, fatigue crack growth rate, and fracture toughness of the ZhS6K nickel superalloy were determined from a single turbine blade, with failure mechanisms examined using scanning electron microscopy. Compared to Inconel 718, ZhS6K offers higher resistance to fatigue crack growth but has significantly lower fracture toughness and stress-strain properties. The obtained results fill a gap in materials data necessary for the durability and damage tolerance assessment of turbine blades made of ZhS6K alloy. Although the primary focus is on the fracture behavior of the newly characterized material ZhS6K, the findings contribute to a broader understanding of the fracture mechanics within the entire class of structurally similar materials.
