| 1 | Solid-State Metal Additive Manufacturing for Structural Repair显示文摘CONSPECTUS:Structural metal components play a vital role in a broad range of industries,from aerospace and automotive to infrastructure and defense.In service,these components can experience substantial wear,thermal fatigue,erosion,corrosion,or chemical reactions,resulting in significant surface or even volumetric damages.Replacement of these components is often energy-intensive and economically impractical.Structural repair,which aims to restore the original geometry while enabling good mechanical performance postrepair,can offset the costs dramat-ically.Depending on the additive capabilities and bonding mechanisms,structural repair technologies can be divided into four categories:nonadditive,nonmelting-based;nonadditive,melting-based;additive,nonmelting-based;additive,melting-based.Although melting-based approaches can be applied to various repair geometries with good precision,the underlying melting and solidification processes inevitably lead to crucial problems impacting the mechanical performance,such as solidification porosity,high residual stresses,dendritic microstructure formation,elemental segregation,hot cracking,and stress corrosion cracking.To fundamentally solve or minimize these problems,one may employ solid-state technologies that leverage ultrasonic vibration,friction stirring,or particle impact to facilitate metallurgical bond formation.For robust geometry restoration,an additive capability needs to be incorporated for continuous material feeding and precise deposition path control.Currently,two solid-state technologies satisfy the requirement,cold spray and additive friction stir deposition.In this Account,we discuss the structural repair enabled by solid-state metal additive manufacturing,focusing on(i)cold spray,which is a relatively established process,and(ii)additive friction stir deposition,which is an emerging process recently triggering significant research effortsthe authors are particularly invested in this process and are pioneering the research on process fundamentals and structural repair applications.In cold spray,a substrate is bombarded with small metal particles at high speed;upon impact,the particles and substrate co-deform,resulting in interfacial bonding and mechanical interlocking.In additive friction stir deposition,frictional heat is created after the rapidly rotating feed-rod contacts the substrate,followed by co-plastic deformation and mixing between the deposited material and substrate surface.This renders a strong interface with complex 3D features.Both cold spray and additive friction stir deposition can be applied to a wide range of repair geometries while preventing hot cracking and high thermal exposure.Although cold spray has better portability and spatial resolution than additive friction stir deposition,we believe that additive friction stir deposition is the top choice for repairing load-bearing components given its unparalleled capabilities of rendering equiaxed microstructures and wrought-like mechanical properties.Regarding niche repair applications,cold spray is particularly suited for field repair of surface damage;our previous work has shown great promise of using additive friction stir deposition for underwater and large component repair.For future research in cold spray,strategies are needed to eliminate porosity and improve the as-repaired mechanical properties,especially when depositing high strength-to-weight ratio materials.For additive friction stir deposition,we hope to improve the spatial resolution and portability,possibly by down-scaling,and to enable robust repair of components made of high-temperature,high-strength materials. | Ryan B.Gottwald R.Joey Griffiths Dylan T.Petersen Mackenzie E.J.Perry Hang Z.Yu | 2021 | Accounts of Materials Research2021，2，9： | 1 |
| 5 | Adaptive Finite Element Modeling Techniques for the Poisson-Boltzmann Equation显示文摘We consider the design of an effective and reliable adaptive finite element method(AFEM)for the nonlinear Poisson-Boltzmann equation(PBE).We first examine the two-term regularization technique for the continuous problem recently proposed by Chen,Holst and Xu based on the removal of the singular electrostatic potential inside biomolecules;this technique made possible the development of the first complete solution and approximation theory for the Poisson-Boltzmann equation,the first provably convergent discretization and also allowed for the development of a provably convergent AFEM.However,in practical implementation,this two-term regularization exhibits numerical instability.Therefore,we examine a variation of this regularization technique which can be shown to be less susceptible to such instability.We establish a priori estimates and other basic results for the continuous regularized problem,as well as for Galerkin finite element approximations.We show that the new approach produces regularized continuous and discrete problemswith the samemathematical advantages of the original regularization.We then design an AFEM scheme for the new regularized problem and show that the resulting AFEM scheme is accurate and reliable,by proving a contraction result for the error.This result,which is one of the first results of this type for nonlinear elliptic problems,is based on using continuous and discrete a priori L¥estimates.To provide a high-quality geometric model as input to the AFEM algorithm,we also describe a class of feature-preserving adaptive mesh generation algorithms designed specifically for constructing meshes of biomolecular structures,based on the intrinsic local structure tensor of the molecular surface.All of the algorithms described in the article are implemented in the Finite Element Toolkit(FETK),developed and maintained at UCSD.The stability advantages of the new regularization scheme are demonstrated with FETK through comparisons with the original regularization approach for a model problem.The convergence and accuracy of the overall AFEMalgorithmis also illustrated by numerical approximation of electrostatic solvation energy for an insulin protein. | M.Holst J.A.McCammon Z.Yu Y.C.Zhou Y.Zhu | 2012 | Communications in Computational Physics2012，11，1： | 0 |
| 6 | 二维盆地模拟模型中可溶性的三相流体运移显示文摘在二维盆地模拟模型上进行了可溶性三相流体运移研究。对于由差异压实所致的超压、控制不同相态流体的浮力和毛细压力等驱动力,都应用达西定律。建立相对渗透率与每种相态流体在孔隙空间中所占的饱和度的关系。试验结果表明,溶解度对烃类的一次运移和二次运移以及烃类的聚集具有重大的影响。可溶性烃类的运移和聚集的时空模式是多种多样的,这主要取决于特定的地质、地热及地化条件。因为烃类运移的动力学特征通过相对渗透率变化与相饱和度相连系,且通过温度和压力依赖关系而与相溶解度相连系,所以本研究指出,在盆地的勘探评价中必须考虑油气聚集史。与相态有关的运移模型在巴伦支海Hammerfest盆地的地质剖面描述中的应用表明,第三系的上抬和侵蚀,导致了烃类泄漏,可能是造成Hammerfest盆地中大多数井无开采价值的主要原因。 | Z.Yu I.Lerche 傅广 | 1995 | 国外油气勘探1995，7，6： | 0 |
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