| 1. |
- Chen, Jun
(author)
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Optimizing Ice-Resistant Surfaces: Unifying Self-Healing, Durability, and Functional Design for Superior Anti-/De-Icing Performance
- 2024
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Doctoral thesis (other academic/artistic)abstract
- Snow and ice accumulation on critical infrastructure such as wind power turbines and power lines cause significant challenges and safety hazards in cold climate regions during wintertime. Research into anti-/de-icing technologies has been divided into two main streams, i.e., active, and passive approaches. Active technologies, including electric thermal, photothermal technologies, etc, are widely used in anti-/de-icing fields. Passive technologies, including hydrophobic and slippery surfaces, have gained increasing interest due to their low energy consumption and sustainable profile, but these passive technologies are often limited by relatively short service life and poor mechanical durability. A potential way of improving the anti-/de-icing performance would be to combine different technologies and create electric thermal superhydrophobic surfaces and/or photo-thermal superhydrophobic surfaces. Furthermore, the mechanical durability could be improved by developing self-healing superhydrophobic surfaces and wear-resistant electric thermal surfaces. However, some important studies of relevant mechanisms to achieve this are absent in the literature, such as the influence of self-healing on ice adhesion, and investigation on how to unify the durability and anti-/de-icing performances via molecular structure design. This thesis addresses these questions by focusing on enhancing the wear resistance and anti-/de-icing efficiency of anti-/de-icing materials through innovative material design. We conducted ice-phobic tests in lab environment, and long-term ice-phobic field tests, which helped us to further understand and optimize the design of ice-phobic surfaces. This thesis contributes to developing more durable, efficient, and sustainable anti-/de-icing solutions, addressing the critical need for reliable performance under adverse weather conditions. The key findings were: (1) A novel self-healing and low-ice adhesion poly silicon urea coating was developed, leveraging the intrinsic material structure for creating sufficient wear resistance and self-healing capabilities. The Poly silicon urea coating exhibits below 10kPa ice adhesion strength, which is far lower than the ice-phobic surface request(<100kPa). The molecular structure’s influence on self-healing and ice adhesion are specified in this work.(2) Inspired by the low-icing bonding properties of silicon urea, a graphene-enhanced siloxane urea multi-functional coating was designed, where the low-icing properties were combined with electric and thermal conductivity to achieve both active and passive anti-/de-icing effects. This graphene enhancement coating exhibits 10 minutes of removing all ice accretion under ~570W/m2 electric power on the lab scale test. The field tests, where a graphene enhancement coating surface can keep ice-free under ~310W/m2 during the whole winter in a harsh natural environment. (3) To explore the influence of mechanical durability on ice-phobic, a composite coating which integrates wear resistance and thermal conductive was formulated. Graphene was proven as a suitable additive to enhance thermal conductivity and wear resistance. Compared with the blank control coating and a boron nitride composite coating, the thermal conductivity of a graphene composite coating increased around 3 times, and the anti-wear performance based on wear depth was increased around 1.5 times. The wear mechanism and wear influence on anti-/de-icing behaviour are investigated in this work. (4) This work also explored the impact of surface functional groups on anti-/de-icing performance, uncovering that the force interactions and steric radius of these groups significantly influence surface element distribution and material strength, thereby affecting wettability and wear behaviour. The results show that the hydrophobicity of the groups is not the only factor to influence the surface properties. A smaller steric radius and strong interactions are beneficial for reducing the van der Waals' gap between groups which can inhibit the wetting of the water molecules. The influence of five different typical groups on mechanical durability and ice adhesion is investigated in this work.
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| 2. |
- Ding, Yu, et al.
(author)
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Hydrogen-enhanced grain boundary vacancy stockpiling causes transgranular to intergranular fracture transition
- 2022
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In: Acta Materialia. - : Elsevier. - 1359-6454 .- 1873-2453. ; 239
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Journal article (peer-reviewed)abstract
- The attention to hydrogen embrittlement (HE) has been intensified recently in the light of hydrogen as a carbon-free energy carrier. Despite worldwide research, the multifaceted HE mechanism remains a mat-ter of debate. Here we report an atomistic study of the coupled effect of hydrogen and deformation temperature on the pathway to intergranular fracture of nickel. Uniaxial straining is applied to nickel E5(210)[001] and E9(1-10)[22-1] grain boundaries with or without pre-charged hydrogen at various temperatures. Without hydrogen, vacancy generation at grain boundary is limited and transgranular frac-ture mode dominates. When charged, hydrogen as a booster can enhance strain-induced vacancy genera-tion by up to ten times. This leads to the superabundant vacancy stockpiling at the grain boundary, which agglomerates and nucleates intergranular nanovoids eventually causing intergranular fracture. While hy-drogen tends to persistently enhance vacancy concentration, temperature plays an intriguing dual role as either an enhancer or an inhibitor for vacancy stockpiling. These results show good agreement with recent positron annihilation spectroscopy experiments. An S-shaped quantitative correlation between the proportion of intergranular fracture and vacancy concentration was for the first time derived, highlight-ing the existence of a critical vacancy concentration, beyond which fracture mode will be completely intergranular.
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| 3. |
- Ding, Yu, et al.
(author)
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Hydrogen-induced transgranular to intergranular fracture transition in bi-crystalline nickel
- 2021
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In: Scripta Materialia. - : Elsevier. - 1359-6462 .- 1872-8456. ; 204
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Journal article (peer-reviewed)abstract
- It is known that hydrogen can influence the dislocation plasticity and fracture mode transition of metallic materials, however, the nanoscale interaction mechanism between hydrogen and grain boundary largely remains illusive. By uniaxial straining of bi-crystalline Ni with a Σ5(210)[001] grain boundary, a transgranular to intergranular fracture transition facilitated by hydrogen is elucidated by atomistic modeling, and a specific hydrogen-controlled plasticity mechanism is revealed. Hydrogen is found to form a local atmosphere in the vicinity of grain boundary, which induces a local stress concentration and inhibits the subsequent stress relaxation at the grain boundary during deformation. It is this local stress concentration that promotes earlier dislocation emission, twinning evolution, and generation of more vacancies that facilitate nanovoiding. The nucleation and growth of nanovoids finally leads to intergranular fracture at the grain boundary, in contrast to the transgranular fracture of hydrogen-free sample.
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| 4. |
- Ding, Yu, et al.
(author)
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Hydrogen trapping and diffusion in polycrystalline nickel : The spectrum of grain boundary segregation
- 2024
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In: Journal of Materials Science & Technology. - : Elsevier. - 1005-0302. ; 173, s. 225-236
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Journal article (peer-reviewed)abstract
- Hydrogen as an interstitial solute at grain boundaries (GBs) can have a catastrophic impact on the mechanical properties of many metals. Despite the global research effort, the underlying hydrogen-GB interactions in polycrystals remain inadequately understood. In this study, using Voronoi tessellations and atomistic simulations, we elucidate the hydrogen segregation energy spectrum at the GBs of polycrystalline nickel by exploring all the topologically favorable segregation sites. Three distinct peaks in the energy spectrum are identified, corresponding to different structural fingerprints. The first peak ( -0.205 eV) represents the most favorable segregation sites at GB core, while the second and third peaks account for the sites at GB surface. By incorporating a thermodynamic model, the spectrum enables the determination of the equilibrium hydrogen concentrations at GBs, unveiling a remarkable two to three orders of magnitude increase compared to the bulk hydrogen concentration reported in experimental studies. The identified structures from the GB spectrum exhibit vastly different behaviors in hydrogen segregation and diffusion, with the low-barrier channels inside GB core contributing to short-circuit diffusion, while the high energy gaps between GB and neighboring lattice serving as on-plane diffusion barriers. Mean square displacement analysis further confirms the findings, and shows that the calculated GB diffusion coefficient is three orders of magnitude greater than that of lattice. The present study has a significant implication for practical applications since it offers a tool to bridge the gap between atomic-scale interactions and macroscopic behaviors in engineering materials.& COPY; 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )
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| 5. |
- Ding, Yu, et al.
(author)
-
The dual role of hydrogen in grain boundary mobility
- 2023
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In: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 133:4
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Journal article (peer-reviewed)abstract
- The effect of solute hydrogen on shear-coupled grain boundary (GB) migration is investigated with the dislocation-array type sigma 25(430)[001] GB and a dual role of hydrogen on GB mobility is unraveled. In the low temperature and high loading rate regime, where hydrogen diffusion is substantially slower than GB motion, GB breaks away from the hydrogen atmosphere and transforms into a new stable phase with highly enhanced mobility. In the reverse regime, hydrogen atoms move along with GB, exerting a drag force on GB and decreasing its mobility. These findings provide rationale for the coexistence of hydrogen hardening and softening observed experimentally in polycrystalline materials.
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| 6. |
- Lin, Meichao, et al.
(author)
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A microstructure informed and mixed-mode cohesive zone approach to simulating hydrogen embrittlement
- 2022
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In: International journal of hydrogen energy. - : Elsevier. - 0360-3199 .- 1879-3487. ; 47:39, s. 17479-17493
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Journal article (peer-reviewed)abstract
- Hydrogen induced failure under uniaxial tension is simulated in a duplex stainless steel considering microstructural feature of the material. There are three key ingredients in the modelling approach: image processing and finite element representation of the experimentally observed microstructure, stress driven hydrogen diffusion and diffusion coupled cohesive zone modelling of fracture considering mixed failure mode. The microstructure used as basis for the modelling work is obtained from specimens cut in the transverse and longitudinal directions. It is found that the microstructure significantly influences hydrogen diffusion and fracture. The austenite phase is polygonal and randomly distributed in the transverse direction, where a larger effective hydrogen diffusion coefficient and a lower hydrogen fracture resistance is found, compared to the specimen in the longitudinal direction, where the austenite phase is slender and laminated. This indicates that the proper design and control of the austenite phase help improve hydrogen resistance of duplex stainless steel. The strength of the interface in the shear direction is found to dominate the fracture mode and initiation site, which reveals the importance of considering mixed failure mode and calibrating the hydrogen induced strength reduction in shear.
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| 7. |
- Lin, Meichao, et al.
(author)
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A predictive model unifying hydrogen enhanced plasticity and decohesion
- 2022
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In: Scripta Materialia. - : Elsevier. - 1359-6462 .- 1872-8456. ; 215
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Journal article (peer-reviewed)abstract
- The detrimental effect of hydrogen on metals which manifests itself as a transition from a ductile to a brittle failure mode is, for the first time, incorporated into a unified continuum-scale predictive framework. The complete Gurson model, designed to predict ductile failure by voiding, is extended to include failure by deco-hesion. Hydrogen enhanced plasticity is accounted for through acceleration of the voiding process while hydrogen induced decohesion is realized by a degradation of the decohesion threshold. The interplay between these two failure modes driven by hydrogen concentration are well captured. This model can predict a realistic level of embrittlement as well as the suppression of dimples in a hydrogen induced fracture surface. Being generic, versatile, and easy to implement, the model may serve as a basis for interpretation of laboratory ex-periments and enable the transferability of the laboratory results to the integrity assessment of engineering components in hydrogen environment.
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| 8. |
- Lin, Meichao, et al.
(author)
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Experimental and numerical study on hydrogen-induced failure of X65 pipeline steel
- 2024
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In: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 894
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Journal article (peer-reviewed)abstract
- Hydrogen-induced fracture of X65 pipeline steel under in -situ electrochemical charging is investigated by using slow strain-rate tensile (SSRT) test, hydrogen diffusion test, fractography analysis, and finite element simulation. Smooth and notched tensile specimens with varying notch radii are utilized to ascertain the impact of stress triaxiality on hydrogen embrittlement (HE) susceptibility. A fully coupled model, H-CGM+, capable of simulating the synergy between hydrogen-enhanced plasticity and decohesion, is employed. The simulation proficiently replicates both the global stress-strain trajectories and the local failure initiation sites of the in -situ SSRT tests. The findings indicate a predominance of dislocation trapping hydrogen mechanism in HE, with crack inception at the notch surface where local plastic strain peaks, subsequently advancing towards the center of the specimen. Notably, an inverse relationship is observed between HE susceptibility and stress triaxiality. A hydrogen-induced failure criterion, defined as a critical combination of local hydrogen concentration and plastic strain, is derived. The failure criterion is found to be independent of stress triaxiality, which serves as a good reference for safety assessment of hydrogen pipelines.
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| 9. |
- Lin, Meichao, et al.
(author)
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Simulation of ductile-to-brittle transition combining complete Gurson model and CZM with application to hydrogen embrittlement
- 2022
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In: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 268
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Journal article (peer-reviewed)abstract
- A general simulation framework for modelling ductile-to-brittle transition in metals is proposed. The method combines the complete Gurson model and cohesive zone model, which brings ductile and brittle fracture mechanisms into one play. We found that the transition of failure mode is the result of a competition between fracture due to micro-void growth and coalescence and fracture in the cohesive zone. It is found that the fracture mode is dependent on the ratio between the cohesive strength and the yield strength of the material; brittle fracture only occurs when the strength ratio is below a critical value. This generic rule can be used to rationalize various failure scenarios featured by ductile-to-brittle transition, such as low temperature embrittlement and hydrogen embrittlement. As an application of the general framework, hydrogen embrittlement is simulated. It is revealed that a critical hydrogen concentration has to be achieved in order to trigger brittle fracture, which is consistent with many experimental observations.
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| 10. |
- Ma, Delong, et al.
(author)
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The role of deep-seated half-grabens in the evolution of Huoerguosi-Manasi-Tugulu fold-and-thrust belt, northern Tian Shan, China
- 2019
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In: Journal of Geodynamics. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0264-3707 .- 1879-1670. ; 131
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Journal article (peer-reviewed)abstract
- The Huoerguosi-Manasi-Tugulu fold-and-thrust belt, which is located in the southern Junggar Basin, has formed in response to contraction during Late Cenozoic. However, the tectonic environment for its formation before Late Cenozoic is still controversial. In this paper, we use surface data, recently collected and processed subsurface seismic refection data, isopach map of Lower Jurassic and balanced sections to propose pre-existing half-graben system developed in the Lower Jurassic with this fold-and-thrust belt. We also use results of a series of scaled sandbox analogue models, where industrial CT apparatus was used to monitor deformation, to simulate the evolution of this fold-and-thrust belt. We suggest that the segmented shape of the Huoerguosi-Manasi-Tugulu fold-and-thrust belt is a response to the presence of thrust ramps, which were formed during Early Jurassic. During Late Cenozoic shortening, the Lower Jurassic syn-rift sediments served as major detachment horizon, making a pre-existing normal fault act as a stress concentration zone leading to steeping of a thrust-ramp over the normal fault and cover detachment overstep the underlying half-grabens. Modeling results reveal that the presented structural framework has close resemblance with paleostructures especially in the intracontinental environment, which underwent a complex multicycle evolution process, and provide a new prospective for the interpretation of natural examples.
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