Defects in Al-7Si-Mg and Al-10Si-Mg alloys produced by selective laser melting are categorised into three types. The first type are large irregular-shaped defects with unmelted powder particles, ...formed due to a lack of fusion as a result of insufficient volumetric energy density. The second type are small round gas pores below 5µm in diameter, associated with high area energy density. These pores enlarge during solution heat treatment, but the enlargement is reduced significantly when the powder is pre-dried at 200°C for 16h under an argon atmosphere immediately before the build. The last type are large round keyhole type pores located at the base of melt pools. They can either form in contour scan regions, at the edges of core scans, or at island boundary overlap regions due to an excessive local energy density compared with the nominal energy density. Sub-surface porosity due to contour and core edge keyhole type defects can be more detrimental to the fatigue performance than net-shaped rough surfaces, but such sub-surface porosity can be minimised by either lowering the laser energy input for the contour scan and/or changing the way the laser turns between scan tracks.
The rapidly increasing production volume of clean hydrogen creates challenges for transport infrastructure. This study improves understanding of hydrogen transport options in Europe and provides more ...detailed analysis on the prospects for hydrogen transport in Finland. Previous studies and ongoing pipeline projects were reviewed to identify potential and barriers to hydrogen transport. A fatigue life assessment tool was built because material challenges have been one of the main concerns of hydrogen transportation. Many European countries aim at utilizing existing gas infrastructure for hydrogen. Conducted studies and pilot facilities have provided promising results. Hydrogen reduces the fatigue life of the pipeline, but existing pipelines can be used for hydrogen if pressure variation is maintained at a reasonable level and the maximum operation pressure is limited. Moreover, the use of existing pipelines can reduce hydrogen transport costs, but the suitability of every pipeline for hydrogen must be analyzed, and several issues such as leakage, leakage detection, effects of hydrogen on pipeline assets and end users, corrosion, maintenance, and metering of gas flow must be considered. The development of hydrogen transport will vary within countries depending on the structure of the existing gas infrastructure, and on the future hydrogen use profile.
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•H2 pipeline transportation projects in Europe were reviewed.•Use of linear elastic fracture mechanics fatigue assessment tool was demonstrated.•80 bar natural gas pipeline could be converted to 45–55 bar H2 pipeline.•Existing natural gas network will be utilized for H2 transportation in the future.•Further research needed to ensure feasibility of H2 transportation in existing grid.
The zirconia (ZrO2) ceramic dental implant abutment was prepared by DLP (Digital Light Processing) 3D printing technology. The effect of different heat treatment parameters on the sintering quality ...of ZrO2 was studied. According to TG-DSC, XRD, Raman, SEM and other characterization methods, it could be determined that best sintering parameter was set at 1450 °C for 1.5 h. The final product has a good morphology without holes and other defects, and the relative density is 99.48%. The ZrO2 samples printed in different directions have obvious anisotropy. The three-point bending strength of the sample in the horizontal direction is better than that in the vertical direction, and the strength is 600 MPa. The fatigue load simulation results show that the smaller the pre-angle is, the smaller the maximum stress is and the higher the safety factor is.
In the natural environment, concrete-built structures are frequently undergoing repetitive loadings, e.g., earthquake, automobile traffic, or wind during their entire service life. Those repetitive ...cyclic loadings trigger gradual initiation, expansion and coalesce of inner cracks, resulting in progressive deterioration of mechanical performance until eventual fatigue failure. This paper presents a hybrid fiber reinforcing strategy that could significantly increase the service life of concrete. In this work, the compressive fatigue performance of steel-polypropylene hybrid fiber reinforced concrete (HFRC) under fatigue compression was investigated. A total of 36 groups of prismatic specimens were tested for various stress levels (0.7, 0.8, and 0.9). With respect to the fatigue deformation, fatigue life, and fatigue strength, the effects of fiber parameters were analyzed, including steel fiber volume fractions (1%, 1.5%, and 2%) and aspect ratios (30, 60, and 80), as well as polypropylene fiber volume fractions (0.1%, 0.15%, and 0.2%) and aspect ratios (167, 280, and 396). The results showed that the incorporation of hybrid fiber exerts a pronounced impact on the fatigue performance of concrete. Specifically, in contrast to plain concrete, the ultimate fatigue deformation and fatigue strength of HFRC could be increased by up to 63.29% and 37.18%, respectively. In addition, owing to a positive synergetic effect generated in the hybrid system, HFRC is more superior to polypropylene fiber reinforced concrete (PFRC) or steel fiber reinforced concrete (SFRC) in fatigue performance. Furthermore, a unified fatigue model was proposed to estimate the fatigue strength of HFRC with consideration of fiber parameters. The predictions were found to correlate well with available experimental results, demonstrating a wide applicability of the model in prediction of fatigue life of concrete with reasonable accuracy.
•A quarter-scale specimen of ballastless track-bridge structural system was built.•No cracks were formed during the fatigue test of 18 million cycles.•The mechanical fatigue performance of the ...structural system performed well.•The service life of the beam was far beyond the design life under the train load.
In this paper, a 1:4 scale specimen of concrete box bridge with ballastless track was constructed. The deflection evolution and stiffness degradation of the Crts Ⅱ ballastless track-bridge structural system were studied by carrying out a multistage fatigue loading test with 1.8 × 107 cycles. The results showed that, first, no cracks were formed on the surface of structural system during the test, the dynamic and static deflection ratio of the mid-span section of the structure changed from 108.49% to 106.74%, and the dynamic deflection and static deflection ratio gradually decreased. The cumulative dynamic deflection ratio of the structure exhibited obvious characteristics of the “three-stages” of evolution of the structural fatigue mechanical properties. Second, the static stiffness of the structural mid-span section, which had the most significant change compared to that of the other sections, decreased by 23.82% after the fatigue test. The static stiffness of stage 2, which had the greatest number of cycles, decreased the most compared to that of the other stages. Third, the dynamic stiffness degradation rates of sections L/4, L/2 and 3L/4 of the structure were 18.99%, 19.25%, and 18.59%, respectively. The dynamic stiffness degradation of the structure exhibited the evolution law of “three stages”, and the dynamic stiffness of the structure decreased most significantly in the initial stage of the fatigue test compared to that during the other stages. Moreover, the theoretical results of the stiffness decreasing rate of the mid-span section of the structure were consistent with the experimental results, and the service life of the beam in the structural system was far beyond the design life under the fatigue train load.
Ultrasonic-assisted technology has proven effective for Inconel 718 milling. This study compared tool life and tool wear forms and wear mechanisms at different wear states in high-speed Ultrasonic ...Peening Milling (UPM) and Conventional Milling (CM). The influence of different tool wear states on the surface integrity index and fatigue performance were systematically analyzed. The results showed 32.5% increase in tool life in UPM owing to lower tool wear compared to that in CM. More important, UPM was significantly more effective in improving machined surface quality and fatigue life with an average increase of 4–17 times.
This paper investigates the fatigue failure mechanism of mono- and multilayer coatings on the fatigue performance of TC11 titanium alloy under tension-tension. The morphology, phase composition, ...mechanical properties were measured by scanning electron microscope, X-ray diffractometer and nanoindentation. Electron back scatter diffraction was employed to investigated the failure mechanism. Fatigue limits obtained of uncoated TC11, TC11 with TiN coating, TiN/Ti multilayer (ML-6, ML-3, ML-1) and after 1×107 cycles are 855 MPa, 550 MPa, 525 MPa, 500 MPa and 400 MPa. Under fatigue loading, the hard-coating/TC11 substrate experiences fatigue failure through coating cracking hastens the substrate's fatigue failure. EBSD analysis results indicate that the main slip system of TC11 titanium alloy under tension-tension fatigue load is α phase (10-10) -12-10. After 1×107 cycles at fatigue limits, the average dislocation density on the surface of the TC11 with TiN coating is lower than that of TC11. Due to the surface defect induced by coating preparation and high crack propagation velocity, the hard coating significantly deteriorates fatigue property of TC11 by reducing fatigue crack initiation period. Therefore, instead of approaching from the perspective of coating structure design to increase the fatigue crack propagation cycles, it is more effective to reduce the surface roughness of the coating and enhance the fatigue crack initiation cycles.
The stress analysis of micro-arc oxidation (MAO) coated aero Al alloys is the basis to reveal the mechanism of fatigue deterioration. To clarify effects of the coating defects on fatigue life, a ...stress calculation model with micropores and residual stress is established based on shear lag model in this study. The effects of porosity, substrate elastic modulus, coating thickness and residual stress on the stress are explored. The results indicate that the coating porosity and thickness are the critical factor affecting coating normal stress and interfacial shear stress, respectively. In addition, the residual stress significantly affects the interfacial normal stress. The increasing stress caused by low porosity and residual tensile stress and stress concentration at the large-sized defects are the key factors for fatigue degradation.
•Stress calculation model considering micropores and residual stress is established.•Micropores affect coating normal stress and interfacial shear stress.•Effect of coating thickness and porosity on its normal stress is negatively correlated.•A method for analyzing the coupling effect of defects on fatigue degradation is proposed.
Electromagnetic riveting (EMR) can effectively form large-diameter rivets and produce high-quality joints. In this paper, the effect of rivet arrangement on fatigue performance of electromagnetic ...riveted joint was investigated. Quasi-static shear tests, fatigue tests, numerical simulation and microstructure observation were carried out. The results showed that the rivet arrangement had little effect on the shear performance and had a great impact on the fatigue performance of the EMR joint. Specifically, the difference between the average maximum shear load of the V-joints (60.49 kN) and the H-joints (60.41 kN) was small. The fatigue life of the H-joints was higher than that of the V-joints at high fatigue load levels (Fmax>30.225 kN), while the result was opposite at low fatigue load levels (Fmax<30.225 kN). Furthermore, the fatigue fracture analysis showed that there were two typical failure modes for the joints: (I) the rivet fracture, and (II) the sheet fractured on the manufactured head side. The V-joints mainly displayed the coexistence of failure mode I and mode II, while the H-joints displayed failure mode II at all fatigue load levels. At high fatigue load levels, the significant stress concentration in both rivets resulted in the rivet fracture of the V-joints within a relatively short time. Due to multiple extension directions and a smaller extension zone, the fatigue life of H-joints was lower than that of the V-joints at low fatigue load levels. Therefore, the fatigue performance of the component could be improved by choosing a different rivet arrangement.
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•The fatigue performance of EMR joint with different rivet arrangement was compared.•The fatigue behavior and failure modes under different load levels was investigated.•Differences of fatigue performance and applicable working conditions were analyzed.
