The present study describes a novel approach applying 3D digital image correlation to a hole drilling method to measure residual stresses. Measurements were performed on a friction stir-welded joint ...made of ultrafine-grained aluminum. The results show that severe plastic deformation did not significantly change the residual stresses, while in the weld’s stir zone they increased to 100 to 200 MPa. The obtained results demonstrate the reliability of the applied residual stress measurement method.
In the present study, a commercially pure (CP) Ti and Ti–Re alloys containing 2 and 4 wt% of Re were manufactured by selective laser melting (SLM) and characterized in terms of microstructure, ...strength and fatigue crack propagation resistance. On the contrary to a homogenous lath-type martensitic α′ microstructure with no signs of directional solidification observed for CP Ti, the Re addition led to development of columnar prior β grains oriented along building direction with a much finer acicular α′ martensite in Ti–Re alloys. The width of martensitic α′ needles decreased with increasing Re content. Re affected also the formation of different phase constituents. The presence of ω phase precipitates as well as residual undissolved Re particles was noticed in Ti–Re alloys. Ti–Re alloys exhibited also the substantially increased ultimate tensile strength and drastically reduced ductility in comparison to CP Ti. These findings have been discussed in the paper considering the highly refined acicular α′ martensitic structure, the increased oxygen content as well as the presence of strengthening ω phase precipitates in Ti–Re alloys. Finally, the brittleness of Ti–Re alloys caused the deterioration of their fatigue crack propagation resistance.
Nowadays, post-surgical or post-accidental bone loss can be substituted by custom-made scaffolds fabricated by additive manufacturing (AM) methods from metallic powders. However, the partially melted ...powder particles must be removed in a post-process chemical treatment. The aim of this study was to investigate the effect of the chemical polishing with various acid baths on novel scaffolds' morphology, porosity and mechanical properties. In the first stage, Magics software (Materialise NV, Leuven, Belgium) was used to design a porous scaffolds with pore size equal to (A) 200 µm, (B) 500 µm and (C) 200 + 500 µm, and diamond cell structure. The scaffolds were fabricated from commercially pure titanium powder (CP Ti) using a SLM50 3D printing machine (Realizer GmbH, Borchen, Germany). The selective laser melting (SLM) process was optimized and the laser beam energy density in range of 91-151 J/mm³ was applied to receive 3D structures with fully dense struts. To remove not fully melted titanium particles the scaffolds were chemically polished using various HF and HF-HNO₃ acid solutions. Based on scaffolds mass loss and scanning electron (SEM) observations, baths which provided most uniform surface cleaning were proposed for each porosity. The pore and strut size after chemical treatments was calculated based on the micro-computed tomography (µ-CT) and SEM images. The mechanical tests showed that the treated scaffolds had Young's modulus close to that of compact bone. Additionally, the effect of pore size of chemically polished scaffolds on cell retention, proliferation and differentiation was studied using human mesenchymal stem cells. Small pores yielded higher cell retention within the scaffolds, which then affected their growth. This shows that
cell performance can be controlled to certain extent by varying pore sizes.
Research to better understand the phenomena influencing materials and components’ performance is important for increasing the safety of Generation II and III nuclear plants. A crucial step for ...improving nuclear safety is the development of new experimental techniques that can provide the necessary data. The three H2020 projects presented in this paper, MEACTOS (2017–2022), INCEFA-SCALE (2020–2025), and FRACTESUS (2020–2024), cover the steps needed to realize those safety improvements. The goal of the MEACTOS project is to improve the resistance of critical locations, including welds, to environmentally-assisted cracking through optimizing surface machining and treatments. The project is currently in its final stage, and the complete analysis of the data is finished. The objective of INCEFA-SCALE is to improve predictions of component fatigue lifetime when subjected to Environmentally-Assisted Fatigue (EAF). The strategy consists of producing guidance on how to appropriately accommodate variable amplitude and plant-relevant loading in EAF assessments. Increasing the understanding of the EAF mechanism based on substantial testing, characterization, and analysis program will support the INCEFA-SCALE strategy. The FRACTESUS project will validate the use of miniaturized compact tension specimens by comparing the results of master curve-oriented fracture toughness tests performed with small and large specimens. The round-robin exercises will use irradiated and non-irradiated Reactor Pressure Vessel (RPV) materials. The material selection process is complete in time for the project to enter the testing phase. The output of the project will be beneficial from a long-term operation perspective and a saving in the material amount needed for RPV surveillance programs. Even though each project is devoted to different research areas, common aspects are clearly visible. All three projects investigate phenomena that are relevant to the performance and safe operation of the nuclear plant. Moreover, each project will provide valuable databases and analyses of test results for materials relevant to components in the nuclear plant. The output of these projects will be of great value to the nuclear industry. This paper presents the current progress for each project, emphasizing the common research domains between the projects.
Titanium alloys, mainly Ti–6Al–4V, are commonly used in biomedical applications as orthopedic implants. Due to the potential toxic influence of V and Al cations on health, a new alloy composition, ...Ti–24Nb–4Zr–8Sn, was introduced. However, Ti–24Nb–4Zr–8Sn has a much lower tensile strength by comparison with the Ti–6Al–4V alloy. The aim of this research was to determine whether high-pressure torsion (HPT) can be an efficient method for obtaining the desired properties in the case of the Ti–24Nb–4Zr–8Sn β-titanium alloy. This paper presents an analysis of the microstructural and mechanical properties of the Ti–24Nb–4Zr–8Sn alloy processed by HPT with various processing parameters. The obtained microstructures were examined using transmission electron microscopy (TEM). Mechanical properties, such as hardness and tensile strength, were also measured. The study demonstrates that HPT of the Ti–24Nb–4Zr–8Sn alloy leads to a significant reduction of grain size and this grain refinement gives a major improvement in tensile strength and hardness.
•Reactor pressure vessel weld material 73 W.•Flow curves from tensile test data and simplified coarse inverse finite element modelling were determined. Results are better than extrapolation of other ...existing popular models (power law, Voce model)•Tensile flow curves in irradiated and un-irradiated conditions at various temperatures (−100 °C up to room temperature) were obtained.•Application to fracture toughness of irradiated and un-irradiated pre-cracked Charpy V-notch specimens.•The extracted flow curves will be used to model mini compact tension (CT) and 1T-CT geometries in FRACTESUS.
The H2020 FRACTESUS project is aimed to validate miniaturized compact tension specimens usage for fracture toughness characterization of irradiated materials. One of the tasks in the project is devoted to the numerical simulations of the 0.16T and 1T-CT specimens and comparison of their stress/strain fields in. For this purpose accurate material flow curves are necessary to derive comparable mechanical response between the numerical models and experiments. This paper presents a simple technique of flow curve extraction from the tensile test using engineering stress–strain data. The proposed method utilizes a coarse meshed Finite Element Model and a manual flow curve data optimization procedure without additional scripting. The robustness of the method was shown on the example of the 73 W weld material in the unirradiated and irradiated states, tested at various temperatures from −100 °C to 125 °C. The obtained numerical flow curves are in a very good agreement with the experimental results. Moreover, the advantages of the proposed method were shown over either the methods based on extrapolation of the predictions of popular models with parameters fitted to prior necking or the method based on fracture diameter measurements. The final validation of the proposed methodology was demonstrated by numerical simulations of fracture toughness tests on precracked Charpy specimens.
This work presents the first observation of ultrasound and eddy currents coupling with Portevin–Le Chatelier serrations during tensile straining of aluminium-magnesium alloy small-size samples, of a ...gauge section 5.0 × 0.8 × 0.6 mm3. Significant changes in serration characteristics were detected and quantified using Fast Fourier Transform analyses in the 120–160 MPa stress range under the influence of 2.5 and 5.0 MHz ultrasound, and a 60 kHz eddy current. Digital Image Correlation measurements showed that the change in singular slip bands movement is surprisingly regular all along the sample gauge sections accompanied with a reduction in the serrations' frequency.
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Microstructural analysis of new bainitic steel subject to heat treatment was performed and directly compared with those achieved from the microstructure of R-260 pearlitic rail steel. Mechanical ...properties, fracture behaviour, and low-cycle fatigue (LCF) tests of the bainitic steel were also evaluated and collated with those achieved from pearlitic rail steel. The LCF tests were performed at room temperature at varying strain amplitudes under total strain control. The basic characteristics of the relationship between the low - cycle fatigue parameters of steels were evaluated based on the Coffin – Manson formula. The obtained test results demonstrate that the two microstructures exhibit different cyclic stress responses, i.e. the cyclic strengthening of pearlitic steel and a cyclic softening in bainitic steel. The variations in the amount of retained austenite in the bainitic structure, before and after LCF, were evaluated by X-ray diffraction and electron transmission microscopy (TEM). The results indicate that during deformation, a partial transformation of the residual austenite into the deformed martensite α' has taken place. Moreover, the quasi-cleavage character of the fracture surface was observed for bainitic steel with a higher deformation degree during the LCF test.
Samples from commercially pure aluminium were subjected to various number of passes of Incremental Equal Channel Angular Pressing (I-ECAP) and subsequently welded using Friction Stir Welding (FSW). ...Similar and dissimilar welds were obtained and investigated in terms of their microstructure and mechanical properties. In the case of similar weld from coarse grained aluminium in the stir zone a decreased average grain size was obtained, which resulted in enhanced microhardness. In the case of samples after I-ECAP, the ultrafine grained regime has not been preserved, which caused a drop in microhardness in the stir zone. Nevertheless, obtained results were still higher than those for coarse grained sample. In all welds the average grain size of 2.1–3.7 μm was obtained. No correlation between the microstructure of base material and stir zone has been found. Tensile tests revealed, that the localization of deformation was obtained in each weld in the area of the biggest average grain size. For dissimilar welds from deformed and undeformed samples a gradient change in microstructure and microhardness was obtained on the cross-section of the welds.
The low carbon P110 steel has been recently considered as a potential pipeline material for shale gas sequestration using CO2-based fracturing technique. The significant problem in such natural gas ...production and transportation system is a CO2 corrosion, especially the stress corrosion cracking (SCC) of pipelines. Due to the possible operating conditions, the aim of the present work was to investigate the susceptibility of P110 pipeline steel to SCC in CO2-rich environments. It was determined based on the stress corrosion test of U-bended specimens in the technically pure CO2 and wet CO2 (CO2 + H2O), tensile tests of miniaturized samples cut from different regions of U-bended specimens as well as slow strain rate bending tests in the wet CO2 followed by SEM observations. No clearly visible long SCC cracks and microstructural changes after exposure in CO2 and CO2 + H2O were observed. Nevertheless, some corrosion pits with micro-cracks in their vicinity were formed in the stressed/deformed areas of U-bend SCC specimens. Moreover, the results of tensile and slow strain rate tests indicated that P110 pipeline steel is susceptible to SCC in CO2-rich environments. It was manifested by a significant reduction of ductility in the stressed regions of U-bended specimens exposed to CO2 and CO2 + H2O. Besides, small cracks with brittle fracture characteristics were observed for P110 steel bended in the wet CO2 at the strain rate of 2 × 10−6 s−1. All observed phenomena indicated that the susceptibility of P110 steel to SCC in CO2-rich environments is associated with activity of anodic dissolution process and hydrogen involvement.
•P110 pipeline steel was investigated in case of SCC in CO2-rich environments.•Corrosion pits with micro-cracks were formed in the stressed areas of SCC specimens.•The exposure in CO2 caused also significant reduction of ductility of P110 steel.•Small cracks occurred after slow strain rate tests in CO2 confirming the SCC.•SCC resulted from the activity of anodic dissolution and hydrogen involvement.
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