Herstellung und komplexe Charakterisierung von Metall‐Keramik‐Verbundschichten

Formation and characterization of metal‐ceramic coatings The influence of the formation process and used materials of metal‐ceramic coatings on the structural properties of the deposited layers were investigated and optimized to increase the mechanical properties. There the deposition of the metal‐ceramic‐layers occurred by a combination of electrophoretic and galvanic deposition with siloxane as bonding compound. Layers with a high ceramic content were successfully created. As ceramic components commercial silicon carbide and silicon nitride were used. Nickel and Copper respectively were applied as metal component to fill the porous ceramic structure with the aim to increase the strength of the layers, where nevertheless a pre nickel‐plating or pre cupper plating of the steel substrate X6Cr17 before ceramic component deposition had to be done to increase the adhesion of the layers. The layer characterization was made by optical microscopy and scanning and transmission electron microscopy, where especially the bonding of the single particles by the siloxane was in evidence.     

Aktivlöten von keramischen Segmenten für den Einsatz in verschleißkritischen Bereichen von Schmiedegesenken

Active brazing of ceramic inlays for the application in wear critical areas of forging dies The use of reinforcing ceramic segments in forging tools is investigated and has been successfully tested with model of dies recently. With reinforcing ceramic segments, however, the thermal widening of the steel tool is a major problem for forging dies. Further, only rotationally symmetrical ceramic inserts can be used as reinforcements which restricts the shape capabilities in tool design significantly. A considerably greater design flexibility is possible if the ceramic segments are brazed into the die body material. To this end, reactively brazed ceramic‐metal composites are to be developed and tested for feasibility in the forging process.     

Wechsellast‐Prüfung von Hüftgelenk‐Pfannen mit keramischen Einsätzen

Fatigue Test of Hip‐Joint Cups with Ceramic Inserts A safe design of hip‐joint components for the long‐term use in humans requires an evaluation of the fatigue lifetime under the in‐vivo loading conditions. For compound cups with ceramic inserts no standardized or commonly agreed procedure exists up to now. Therefore, a test is presented here which is practised by the authors and which possibly could be the basis for a standard. Because of the expensive testing procedure and the large number of possible cup‐insert combinations a failure test with only few samples was chosen.     

CVD‐Diamantschleifstifte für den Werkzeug‐ und Formenbau. Abrasive Pencils for Tool and Die Making Coated by Diamond CVD

Recently developed compeDIA®‐ abrasive pencils have been produced and tested for the machining of cemented carbide molding tools. In order to produce abrasive pencils, carbide base plates have been grinded and coated with a diamond layer by a Hot‐Filament‐CVD‐process. The testing of the abrasive pencils took place with an ultra‐precision grinding machine on carbide workpieces. Surface roughness of the workpiece and its wheel life were the criteria for evaluation. For the specific adjustment of the grain size of the abrasive pencils, the adequate coating parameters were worked out, and the dependencies on basic influencing variables at coating procedures, such as nominal diameter and grinding length, were calculated. In order to be able to coat the grinded base plates with enough film adhesion, a practical pre‐treatment method was developed and tested, which removes the fringe zone, that was damaged during the grinding process. At present, the costs for the coating process are uneconomically high, though. By means of large‐scale production in connection with an automated pre‐treatment and coating it would be possible to lower the costs so far that they are on the same cost level with other coatings like TiN or TiAlN. The CVD‐Diamond abrasive pencils are very appropriate for tool and die making. It is to be expected that through further development of tools and through process optimization, the quality of the wrought workpiece can be ameliorated and surface finishes of R_a < 0,3 μm can be reached. The wheel life could be increased to appropriate values by optimization of the coating technology. The range of the machining parameters, in which the grinding process can be accomplished expediently without leading to a broken die, have been worked out. Afterwards, a die‐casting component with typically shaped elements was designed and an adequate molding tool prototype was crafted. With that, the basic conditions for tool‐ and die‐making were worked out in order to put into practice a fast and flexible machining of cemented carbide molding tools with the aid of those innovative abrasive pencils. In contrast to the traditional molding tool material made of brass, clear advantages in tool life can be made in the production of miniature serial‐parts by drawing, deep‐drawing or extrusion.     

A FEM‐based virtual test‐rig for hybrid metal‐composites clinching joints

A 3D FEM‐based virtual test‐rig tool for the hybrid metal‐composites clinching technology is developed and built in the commercial finite element software Abaqus. The proposed tool consists of two modules: a module to simulate the hybrid clinching process and another to predict the strength of the clinched joints. At first, experimental results concerning the hybrid metal‐composites (EN AW‐5754‐PA6GF30) clinching are presented. Then, the developed virtual tool is described in detail outlining the constitutive models implemented for the hybrid pairing sheets as well as illustrating the proposed FE numerical procedures. Later, the developed tool is applied to the hybrid pairing EN AW‐5754‐PA6GF30. In comparison to the conducted experiments, the simulation results obtained show the applicability and accuracy of the developed virtual testing tool.     

Mixed Ionic and Electronic Conductor for Li‐Metal Anode Protection

Li‐metal is the optimal choice as an anode due to its highest energy density. However, Li‐anodes suffer safety problems from dendritic Li‐growth and continuous corrosion by liquid electrolytes. Here, an effective strategy of using ultrathin and conformal mixed ionic and electronic ceramic conductor (MIEC) is proposed to stabilize Li‐anodes. An ultrathin Li_0.35La_0.52[V]_0.13TiO₃ (LLTO) ceramic film with superior ionic conductivity is first obtained by sintering single‐crystal LLTO nanoparticles, which have controlled surface facets and particle sizes. Then the MIEC property is developed in the LLTO film by introducing toluene as catalyst, which triggers the chemical reactions between LLTO and Li‐metal, leading to high electronic conductivity in the LLTO film. After evaporating toluene, a hybrid LLTO/Li anode with a conformal and stable interface is formed. When applying the hybrid anodes in Li‐metal batteries, the MIEC ceramic film blocks Li‐corrosion from electrolyte and the formation of Li‐dendrites by buffering the Li‐ion concentration gradient and leveling secondary current distribution on Li‐metal surface. At the same time, the Coulombic efficiency of batteries reaches to 98%. This finding will impact the general approach for tailoring the properties of Li‐metal anodes for achieving better Li‐metal battery performance.     

Experimental and numerical studies on the determination of twist drill temperature in dry drilling: A new approach

In this paper, the influences of the spindle speed and feed rate on the drill temperature responses have been investigated. A new experimental approach was developed to measure drill temperature in drilling process. Drill temperatures were measured by inserting standard thermocouples through the coolant (oil) hole of TiAlN-coated carbide drills. Experimental parameters used in the study has based on Taguchi’s method. Experimental study was conducted by using two different workpiece materials, AISI 1040 steel and Al 7075-T651. The drill bit temperature was predicted using a numerical calculation with Third Wave AdvantEdge^TM Lagrangian based on explicit finite element analysis software. The results obtained from experimental study and finite element analyses (FEA) were compared. Good agreement between the measured and analyzed temperature results was found in dry drilling process.     

Finite element simulation and experimental research on rotary ultrasonic grinding of titanium alloy北大核心CSCD

In order to study the effects of the abrasive grain size of core tool on grinding force in rotary ultrasonic grinding titanium alloy, abrasive grain in the shape of irregular polyhedron was modeled by cutting regular hexahedron with random interception plane on a hexahedron. Based on virtual grid method, a simulation model of core drill with multi abrasive grains randomly distributing on the end face of tool was built. A 3D finite element model of rotary ultrasonic grinding of titanium alloy was developed by using Deform-3D. The simulation value of grinding force in rotary ultrasonic grinding of titanium alloy Ti6Al4V with multi abrasive grains was obtained by Lagrangian incremental algorithm, and the effects of the abrasive grain size on grinding force was investigated. A series of experiments were conducted to validate the grinding force in rotary ultrasonic grinding of titanium alloy. The result proved that rotary ultrasonic grinding force decreased as abrasive grain size increased and the experimental result agreed well with the simulation result. The result shows that the multi abrasive grain tool model and the finite element model of rotary ultrasonic grinding have certain accuracy. A new way for multi abrasive grain tool relational investigation in rotary ultrasonic grinding has been provided.     

Finite‐element analysis of a combined fine‐blanking and extrusion process

This paper presents the characteristics of the combined fine‐blanking and extrusion process and gives a detailed analysis of the process with the finite‐element method. To carry out the simulation step by step and avoid the tendency to diverge in the calculations, the remeshing, tracing and golden section methods were developed and introduced into the finite‐element program. Different boundary conditions were used in the simulation; the mesh distortion, field of material flow, and the stress and strain distributions were obtained. From the simulated results, the deformation characteristics under different boundary conditions were revealed. An experiment was also carried out to verify the simulated results. A large strain analysis technique was chosen to determine the effective strain distribution based on the experiment. The effective strain distributions from the simulation are in accordance with the effective strain distributions and the hardness distributions from the experiment. Copyright © 2005 John Wiley & Sons, Ltd.     

Highly Efficient Grinding of Ceramic Parts by Electrolytic In-Process Dressing (ELID) Grinding

In the manfacture of structural ceramic components, it has been well documented that the grinding costs can be as high as 90% of the total cost. Grinding costs of ceramics can be reduced by maximizing the material removal rates (MRR). A novel grinding technology that incorporates in-process dressing of metal bonded superabrasive wheels, known as Electrolytic In-Process Dressing (ELID) has been developed (1) which can significantly increase the MRR. This technique uses a metal bonded grinding wheel that is electrolytically dressed, during the grinding process, for continuous protrudent abrasive from superabrasi ve wheels. The principle of ELID grinding technology will be discussed in this paper as will its application for rough grinding. The effects of various parameters such as wheel bond type and type of power supply on the ELID grinding mechanism will also be addressed in this paper.     

Performance Improvement of Grinding of SiC Using Graphite as a Solid Lubricant

Grinding is a widely employed finishing process for different materials. It is inherently characterized by its high specific energy requirement unlike other machining processes. This leads to a high grinding zone temperature, which impairs the workpiece quality by inducing thermal damage in the form of surface and subsurface cracks, phase transformations, tensile residual stresses, etc. The microcracks and residual stresses induced in the surface of the ceramics during grinding can severely limit the application of ceramic components. This article deals with an investigation on using graphite as a solid lubricant to reduce friction and thereby improve the surface integrity of ground silicon carbide (SiC). An experimental setup has been developed, and experiments have been conducted to study the effect of using a graphite lubricant on the surface roughness, grinding forces, and specific energy while grinding SiC material. Results indicate that there is a considerable improvement in the performance of grinding SiC using graphite as a solid lubricant when compared with dry grinding in terms of specific energy requirements, surface roughness, and damage. The employment of graphite as a solid lubricant in ceramic grinding makes the process more economical and reliable.     

陶瓷表面复合电镀Ni - Ti改性及其钎焊性

为使陶瓷表面金属化,本文对陶瓷进行了Ni-Ti复合电镀.利用辉光钎焊的方法,在低真空下对复合电镀Ni-Ti陶瓷与钢板进行了无钎剂钎焊.试验表明,选用Ni作为基质金属,能够有效地缓解接头的残余应力;钎焊接头的剪切强度达到100MPa以上;在钎焊接头陶瓷一侧的界面处存在Ti的成分分布,活性元素Ti的存在增强了金属化层与陶瓷的界面反应.     

An over‐current protection module for telephone network line cards—an analysis of electro‐thermal properties

In this paper the results of a finite‐element analysis of the electro‐thermal behaviour of an over‐current protection thick‐film hybrid module are presented. The module was designed for protecting the line card of a telephone network against an abnormal surge of current, resulting from accidental shorts between adjacent power feed lines. The switching time of the device is crucial to its effectiveness as a protective element. A transient finite‐element thermal analysis was performed in order to predict the dynamic temperature states at the critical points of the circuit design and to evaluate the influence on the switching characteristics. A comparison between simulated and practical results is given. Copyright © 2002 John Wiley & Sons, Ltd.     

面齿轮磨削齿面力热耦合及残余应力研究

根据面齿轮磨削残余应力的产生机理和Prandtl-Reuss方法,建立磨削表层热弹塑性力学本构关系;基于面齿轮磨削方法和Gleason接触原理,得出碟形砂轮磨削点接触椭圆方程参数、磨削力和磨削热流量的数学模型。构建面齿轮磨削单齿3D有限元模型,采用小步距移动法模拟磨削载荷的移动,仿真磨削温度场,得到磨削瞬态最高温度位于磨削接触弧中心区域。采用力热耦合间接法仿真分析了磨削表层残余应力,得出磨削齿面上为残余压应力,齿面里层为残余拉应力;随磨削深度和砂轮速度增大,齿面残余应力增加显著;但随展成速度增大,齿面残余应力增幅减小。采用X射线衍射法实验,对比分析了面齿轮磨削表层残余应力的实测值与仿真值,其相对误差最大值17.8%在精度控制范围内,说明力热耦合有限元分析残余应力有效,为改善面齿轮磨削质量提供了依据。     

Lead Halide Post‐Perovskite‐Type Chains for High‐Efficiency White‐Light Emission

Hybrid metal halides containing perovskite layers have recently shown great potential for applications in solar cells and light‐emitting diodes. Such compounds exhibit quantum confinement effects leading to tunable optical and electronic properties. Thus, broadband white‐light emission has been observed from diverse metal halides and, owing to high color rendering index, high thermal stability, and low‐temperature solution processability, these materials have attracted interest for application in solid‐state lighting. However, the reported quantum yields for white photoluminescence (PLQY) remain low (i.e., in the range 0.5–9%) and no approach has shown to successfully increase the intensity of this emission. Here, it is demonstrated that the quantum efficiencies of hybrid metal halides can be greatly enhanced if they contain a polymorph of the [PbX₄]^2? perovskite‐type layers: the [PbX₄]^2? post‐perovskite‐type chains showing a PLQY of 45%. Different piperazines lead to a hybrid lead halide with either perovskite layers or post‐perovskite chains influencing strongly the presence of self‐trapped states for excitons. It is anticipated that this family of hybrid lead halide materials could enhance all the properties requiring the stabilization of trapped excitons.     

Phase‐Field Modeling of Microstructural Evolution by Freeze‐Casting

Freeze‐casting has attracted great attention as a potential method for manufacturing bioinspired materials with excellent flexibility in microstructure control. The solidification of ice crystals in ceramic colloidal suspensions plays an important role during the dynamic process of freeze‐casting. During solidification, the formation of a microstructure results in a dendritic pattern within the ice‐template crystals, which determines the macroscopic properties of materials. In this paper, the authors propose a phase‐field model that describes the crystallization in an ice template and the evolution of particles during anisotropic solidification. Under the assumption that ceramic particles represent mass flow, namely a concentration field, the authors derive a sharp‐interface model and then transform the model into a continuous initial boundary value problem via the phase‐field method. The adaptive finite‐element technique and generalized single‐step single‐solve (GSSSS) time‐integration method are employed to reduce computational cost and reconstruct microstructure details. The numerical results are compared with experimental results, which demonstrate good agreement. Finally, a microstructural morphology map is constructed to demonstrate the effect of different concentration fields and input cooling rates. The authors observe that at particle concentrations ranging between 25 and 30% and cooling rate lower than ?5° min^?1 generates the optimal dendrite structure in freeze casting process.

     

Constraint effects on the elastic–plastic fracture behaviour in strain gradient solids

ABSTRACT Crack‐tip constraint effects (or T‐stress effects) on the elastic–plastic fracture behaviour in strain gradient materials are analysed in the present study. The T‐stress effects on the stress distributions along the plane ahead of the stationary and growing crack tip, respectively, are analysed by using the Fleck and Hutchinson strain gradient plasticity formation. For a steadily growing crack, the T‐stress effects on the steady‐state fracture toughness are analysed by adopting the embedded fracture process zone model. In addition, the analysis for the growing crack is applied to an interfacial cracking experiment for a metal/ceramic system, and the material length‐scale parameter appearing in the strain gradient plasticity theory is predicted. In the present analyses, a new finite element method specially designed for strain gradient problems by Wei and Hutchinson is adopted.     

Finite element formulation for anisotropic coupled piezoelectro‐hygro‐thermo‐viscoelasto‐dynamic problems

A finite element algorithm has been developed for the efficient analysis of smart composite structures with piezoelectric polymer sensors or/and actuators based on piezoelectro‐hygro‐thermo‐viscoelasticity. Variational principles for anisotropic coupled piezoelectro‐hygro‐thermo‐viscoelasto‐dynamic problems have also been proposed in this study. As illustrative studies, dynamic responses in laminated composite beams and plates with PVDF sensors and actuators are obtained as functions of time using the present finite element procedures. The voltage feedback control scheme is utilized. The proposed numerical method can be used for analysing problems in the design of smart structures as well as smart sensors and actuators. Copyright © 1999 John Wiley & Sons, Ltd.     

金属板料冲压成形过程有限元分析软件的开发

报道了最新开发的金属板料冲压成形过程有限元分析软件－SheetForm,它是一个将大变形弹塑性有限元法应用于金属板料冲压成形过程的模拟分析软件。它能模拟成形过程中出现的起皱和破裂等成形缺陷,对其功能、特点、使用方法和适用条件分别进行了介绍,并对大量的实例进行了分析模拟,得到了很好的模拟结果。     

The generation of triangular meshes for NURBS‐enhanced FEM

This paper presents the first method that enables the fully automatic generation of triangular meshes suitable for the so‐called non‐uniform rational B‐spline (NURBS)‐enhanced finite element method (NEFEM). The meshes generated with the proposed approach account for the computer‐aided design boundary representation of the domain given by NURBS curves. The characteristic element size is completely independent of the geometric complexity and of the presence of very small geometric features. The proposed strategy allows to circumvent the time‐consuming process of de‐featuring complex geometric models before a finite element mesh suitable for the analysis can be produced. A generalisation of the original definition of a NEFEM element is also proposed, enabling to treat more complicated elements with an edge defined by several NURBS curves or more than one edge defined by different NURBS. Three examples of increasing difficulty demonstrate the applicability of the proposed approach and illustrate the advantages compared with those of traditional finite element mesh generators. Finally, a simulation of an electromagnetic scattering problem is considered to show the applicability of the generated meshes for finite element analysis. ©2016 The Authors. International Journal for Numerical Methods in Engineering published by John Wiley & Sons Ltd.