摘要:

Nano‐structured composite ceramic coatings such as TiN with Si3N4or TiSi2prepared by various forms of plasma assisted CVD composed of crystalline components of equiaxed TiN of several nm diameter, surrounded by amorphous Si3N4intercrystalline layers of roughly 0.2 volume fraction have exhibited hardnesses in the range of 70–100 GPa—quite commensurate with polycrystalline diamond layers—and thermal stability up to 1000C. Best present considerations indicate that such ultra‐hardness is not governed by processes of crystal plasticity in the crystalline component but by the characteristics of flow mechanisms of the often topologically continuous amorphous component exhibiting “liquid‐like” behavior in the constrained spaces between the crystalline components. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1766493

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The paper describes some recent developments in finite element methods for analysis of bulk forming and sheet stamping processes. The developments include new stabilized linear tetrahedra for non linear solution of problems in solid and fluid mechanics and an enhanced version of the three node rotation‐free BST shell triangle for analysis of thin shells. Applications of the new elements to casting and sheet metal forming problems are shown. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1766494

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Microstructure development of polymer blends in chaotic mixing flows is studied, using a model that idealizes the microstructure as ellipsoidal droplets of the minor phase. The model includes the effects of viscosity ratio and interfacial tension. Calculations are performed for a two‐dimensional, time‐periodic flow between eccentric cylinders, using a protocol that is globally chaotic. A Lagrangian particle method is used to follow the microstructure. The flow strength is described by a global capillary number. Flows with a global capillary number greater than about 30 give exponential stretching of the long axes of the droplets, with a Gaussian global distribution, similar to previous results with zero interfacial tension. Sheet‐like microstructures can be generated by using very large global capillary numbers, but in the absence of breakup these always relax to thread‐like structures at long times. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1766495

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Methods for simulating macroscopic and microscopic behaviors in powder forming and sintering processes are presented. In the finite element method, the volume change in deforming material is taken into consideration by obeying the macroscopic constitutive equations allowing for the volume change. The microscopic rotation of powder particles during compaction is dealt with on the basis of the Cosserat continuum theory. In addition, a micro‐macro method for simulating a sintering process of ceramic powder compacts based on the Monte Carlo and finite element methods is presented. The macroscopic non‐uniform shrinkage during the sintering is calculated by the viscoplastic finite element method. In the microscopic approach using the Monte Carlo method, powder particles and pores among the particles are divided into many cells, and the growth of grains in the particles and the disappearance of pores are simulated by means of the Potts model. The microscopic and macroscopic approaches are coupled by exchanging microscopic and macroscopic results in each step. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1766496

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The solution of forming processes requires reliable and efficient finite element methods to model the various complex physical phenomena encountered. The objective in this presentation is to focus on the current state of finite element methods with respect to reliability and efficiency in modeling forming processes. The finite element procedures pertain to the simulation of sheet metal forming, bulk forming, extrusion and drawing, rolling, welding, cutting processes, etc. It is emphasized that the appropriate finite element methods for a specific problem should be used, and that indeed procedures are available which are effective in many situations. The presentation briefly considers the state of modeling of solids, shell structures, contact conditions, friction, inelastic material response in large strains, thermo‐mechanical coupling and fluid‐solid interactions, as encountered in forming process simulations. The solutions of the governing finite element models are obtained using sparse direct or iterative solvers. The oral presentation will include the results of various example simulations. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1766497

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The development of finite element simulation of material forming processes started about 30 years ago in academic laboratories, while the introduction of the corresponding commercial computer codes in industry is less than twenty years old. The main mechanical integral formulations for solid or viscous liquids are briefly recalled: classical Eulerian, Eulerian with a characteristic function, updated Lagrangian and arbitrary Euler Lagrange, with some comments on the finite element discretization using a mixed formulation and mini tetrahedral elements. The crucial remeshing issues are analyzed for non steady‐state processes with different levels of sophistication: Updated Lagrangian for solids, or Euler and a characteristic function, possibly combined with error estimation and adaptivity. As real problems are usually very complex in industry, we must consider different levels of coupling such as thermal and mechanical coupling with the tools in forging and gas — liquid — solid coupling as in polymer foaming. In an attempt to model microstructure evolution of the work‐piece during the different stages of forming, three approaches are reviewed. In the first example the physical evolution of metal is described by macroscopic parameters and their laws of evolution, while the second one is based on a finite element modeling of the two‐phase material at the microscopic level. Finally the third case is the presentation of a new approach of polymer crystallization during injection molding and its introduction in a computer code. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1766498

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

It is well known that injection molding is the most effective process for mass‐producing discrete plastic parts of complex shape to the highest precision at the lowest cost. However, due to the complex property of polymeric materials undergoing a transient non‐isothermal process, it is equally well recognized that the quality of final products is often difficult to be assured. This is particularly true when a new mold or material is encountered. As a result, injection molding has often been viewed as an art than a science.During the past few decades, numerical simulation of injection molding process based on analytic models has become feasible for practical use as computers became faster and cheaper continually. A research effort was initiated at the Cornell Injection Molding Program (CIMP) in 1974 under a grant from the National Science Foundation. Over a quarter of the century, CIMP has established some scientific bases ranging from materials characterization, flow analysis, to prediction of part quality. Use of such CAE tools has become common place today in industry.Present effort has been primarily aimed at refinements of many aspects of the process. Computational efficiency and user‐interface have been main thrusts by commercial software developers. Extension to 3‐dimensional flow analysis for certain parts has drawn some attention. Research activities are continuing on molding of fiber‐filled materials and reactive polymers. Expanded molding processes such as gas‐assisted, co‐injection, micro‐molding and many others are continually being investigated.In the future, improvements in simulation accuracy and efficiency will continue. This will include in‐depth studies on materials characterization. Intelligent on‐line process control may draw more attention in order to achieve higher degree of automation. As Internet technology continues to evolve, Web‐based CAE tools for design, production, remote process monitoring and control can come to path. The CAE tools will eventually be integrated into an Enterprise Resources Planning (ERP) system as the trend of enterprise globalization continues. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1766499

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The paper deals with problems related to full/macro scale simulations of industrial forming processes. Large‐scale numerical simulations and virtual modeling are replacing prototypes in order to reduce costs and time. This requires accurate and reliable predictions. To satisfy these requirements, sophisticated material models including micro‐structural phenomena as phase transitions, aging, and recrystallization have to be considered on macro scale level simulation. Solution strategies are discussed and some examples are given of complex thermo‐ mechanically coupled forming simulations. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1766500

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A microstructure‐based finite element formulation for the mechanical response of friction stir welded AL‐6XN stainless steel is presented. The welding process generates regions of substantial variations in material state and properties that contribute to strong heterogeneities in the mechanical behavior of welded components We modeled the system with a multiscale elastoplastic formulation in which polycrystalline behavior is computed as the integrated responses of constituent crystals. Model validation is made through comparisons to post‐test measurements of shape and hardness and to lattice strain measurements fromin situneutron diffraction experiments. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1766501

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Internal interfaces in metals and alloys provide a convenient and natural basis for the construction of 3‐D meshes employed in finite element calculations. For moderate anisotropy (orthotropic symmetry) the spatial variation of the intercept density of test lines with internal interfaces can be expressed as an Orientation Distribution Function (ODF) that can be approximated by a polynomial in powers of the components of the unit vector parallel to the direction of the test line. It is suggested that finite element meshes derived from measurements of actual grain boundary networks can be similarly described. A local finite strain can be defined based on the distortion of the representation quadric for the intercept density relative to a hypothetical isotropic distribution having the same average intercept density. This measure can be a useful means of describing the spatial variation of internal total distortion within an inhomogeneously deformed body. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1766502

出版商:AIP    

年代:1904

数据来源: AIP