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 polyc...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.展开更多
After a decade of periodic truss-,plate-,and shell-based architectures having dominated the design of metamaterials,we introduce the non-periodic class of spinodoid topologies.Inspired by natural self-assembly process...After a decade of periodic truss-,plate-,and shell-based architectures having dominated the design of metamaterials,we introduce the non-periodic class of spinodoid topologies.Inspired by natural self-assembly processes,spinodoid metamaterials are a close approximation of microstructures observed during spinodal phase separation.Their theoretical parametrization is so intriguingly simple that one can bypass costly phase-field simulations and obtain a rich and seamlessly tunable property space.Counterintuitively,breaking with the periodicity of classical metamaterials is the enabling factor to the large property space and the ability to introduce seamless functional grading.We introduce an efficient and robust machine learning technique for the inverse design of(meta-)materials which,when applied to spinodoid topologies,enables us to generate uniform and functionally graded cellular mechanical metamaterials with tailored direction-dependent(anisotropic)stiffness and density.We specifically present biomimetic artificial bone architectures that not only reproduce the properties of trabecular bone accurately but also even geometrically resemble natural bone.展开更多
In this paper we show that entropy can be used within a functional forthe stress relaxation time of solid materials to parametrise finite viscoplastic strainhardeningdeformations. Through doing so the classical empiri...In this paper we show that entropy can be used within a functional forthe stress relaxation time of solid materials to parametrise finite viscoplastic strainhardeningdeformations. Through doing so the classical empirical recovery of a suitableirreversible scalar measure of work-hardening from the three-dimensional stateparameters is avoided. The success of the proposed approach centres on determinationof a rate-independent relation between plastic strain and entropy, which is foundto be suitably simplistic such to not add any significant complexity to the final model.The result is sufficiently general to be used in combination with existing constitutivemodels for inelastic deformations parametrised by one-dimensional plastic strain providedthe constitutive models are thermodynamically consistent. Here a model for thetangential stress relaxation time based upon established dislocation mechanics theoryis calibrated for OFHC copper and subsequently integrated within a two-dimensionalmoving-mesh scheme. We address some of the numerical challenges that are faced inorder to ensure successful implementation of the proposedmodel within a hydrocode.The approach is demonstrated through simulations of flyer-plate and cylinder impacts.展开更多
The ceramic insulators of spark plugs in gasoline engines are especially prone to damage when deto-knock occurs.To under-stand the damage process and mechanism,the present work investigated the impact resistance of ce...The ceramic insulators of spark plugs in gasoline engines are especially prone to damage when deto-knock occurs.To under-stand the damage process and mechanism,the present work investigated the impact resistance of ceramic insulators using detonation waves as impact sources.A test device that generates detonation waves was developed,representing a novel means of evaluating the knock resistance of ceramic insulators.Various impact types and detonation intensities were employed,and detonation initiation and propagation at peak pressures greater than 100 MPa were assessed using synchronous high-speed direct photography and pressure measurements.The test results demonstrate that ceramic insulators tend to break at the base of the breathing chamber when damaged by a single high peak pressure detonation wave impact.In contrast,multiple low pressure impacts eventually break the insulator into multiple fragments.The data also show that the positioning of a ground electrode upstream of the ceramic insulator greatly increases the resistance of the ceramic to the detonation impact.A two-dimensional computational fluid dynamics simulation coupled with a chemical kinetics analysis demonstrated that this improved resistance can be ascribed to a reduced peak pressure that appears after the detonation wave diffracts from the electrode prior to contacting the ceramic insulator.展开更多
基金financially supported by the Research Council of Norway under the M-HEAT project(No.294689)the HyLINE Project(No.294739)All simulation resources are provided by the Norwegian Metacenter for Computational Science(Nos.NN9110K and NN9391K).
文摘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.
文摘After a decade of periodic truss-,plate-,and shell-based architectures having dominated the design of metamaterials,we introduce the non-periodic class of spinodoid topologies.Inspired by natural self-assembly processes,spinodoid metamaterials are a close approximation of microstructures observed during spinodal phase separation.Their theoretical parametrization is so intriguingly simple that one can bypass costly phase-field simulations and obtain a rich and seamlessly tunable property space.Counterintuitively,breaking with the periodicity of classical metamaterials is the enabling factor to the large property space and the ability to introduce seamless functional grading.We introduce an efficient and robust machine learning technique for the inverse design of(meta-)materials which,when applied to spinodoid topologies,enables us to generate uniform and functionally graded cellular mechanical metamaterials with tailored direction-dependent(anisotropic)stiffness and density.We specifically present biomimetic artificial bone architectures that not only reproduce the properties of trabecular bone accurately but also even geometrically resemble natural bone.
文摘In this paper we show that entropy can be used within a functional forthe stress relaxation time of solid materials to parametrise finite viscoplastic strainhardeningdeformations. Through doing so the classical empirical recovery of a suitableirreversible scalar measure of work-hardening from the three-dimensional stateparameters is avoided. The success of the proposed approach centres on determinationof a rate-independent relation between plastic strain and entropy, which is foundto be suitably simplistic such to not add any significant complexity to the final model.The result is sufficiently general to be used in combination with existing constitutivemodels for inelastic deformations parametrised by one-dimensional plastic strain providedthe constitutive models are thermodynamically consistent. Here a model for thetangential stress relaxation time based upon established dislocation mechanics theoryis calibrated for OFHC copper and subsequently integrated within a two-dimensionalmoving-mesh scheme. We address some of the numerical challenges that are faced inorder to ensure successful implementation of the proposedmodel within a hydrocode.The approach is demonstrated through simulations of flyer-plate and cylinder impacts.
基金This work was supported by National Natural Science Foundation of China(Grant Nos.91541206 and 51706121)China Postdoctoral Science Foundation(Grant No.2017T100076).
文摘The ceramic insulators of spark plugs in gasoline engines are especially prone to damage when deto-knock occurs.To under-stand the damage process and mechanism,the present work investigated the impact resistance of ceramic insulators using detonation waves as impact sources.A test device that generates detonation waves was developed,representing a novel means of evaluating the knock resistance of ceramic insulators.Various impact types and detonation intensities were employed,and detonation initiation and propagation at peak pressures greater than 100 MPa were assessed using synchronous high-speed direct photography and pressure measurements.The test results demonstrate that ceramic insulators tend to break at the base of the breathing chamber when damaged by a single high peak pressure detonation wave impact.In contrast,multiple low pressure impacts eventually break the insulator into multiple fragments.The data also show that the positioning of a ground electrode upstream of the ceramic insulator greatly increases the resistance of the ceramic to the detonation impact.A two-dimensional computational fluid dynamics simulation coupled with a chemical kinetics analysis demonstrated that this improved resistance can be ascribed to a reduced peak pressure that appears after the detonation wave diffracts from the electrode prior to contacting the ceramic insulator.
