Topology optimization of continuum structures with bi-modulus materials

Since the elasticity of bi-modulus materials is stress dependent, it is difficult to apply most conventional topology optimization methods to such bi-modulus structures owing to great computational expense. Therefore, this study employs the material-replacement method to improve the computational efficiency for topology optimization of bi-modulus structures. In this method, first, the bi-modulus material is replaced by two isotropic materials which have the same tensile or compressive modulus. Secondly, the isotropic materials for finite elements are determined by the local stress/strain states. The local elemental stiffness can be modified according to the current modulus and stress state of the element. Thirdly, the relative densities of elements, acting as the design variables, are updated using the optimality criterion method. Finally, the distributions of elemental densities and moduli are obtained for further applications. Several typical numerical examples are used to demonstrate the effectiveness of the proposed method.     

Topology optimization for compliant mechanisms,using evolutionary-hybrid algorithms and application to the design of auxetic materials

Designing micro-structures that lead to materials with negative Poisson’s ratio, the so-called auxetics, is studied here with techniques of topology optimization for compliant mechanisms. Compliant mechanisms are monolithic structures that are able to deliver two or more different motions depending on the applied loading. Single and multi-objective topology optimization problems for the design of compliant mechanisms are formulated. This formulation together with simple homogenization thoughts links the behavior of the flexible microstructure with the overall, homogenized continuum and, in particular, the negative Poisson’s ratio effect (auxetic material). Due to the local minima that arise, iterative local search methods are not very effective. On the other hand genuine global optimization algorithms may become too expensive, due to the large number of design variables. A hybrid method based on global optimization algorithms such as Particle Swarm Optimization (PSO) and Differential Evolution (DE), using an iterative local search method as an evaluation tool is proposed and tested. The iterative local method is based on discretization of the design space with truss elements.     

Topology optimization of functionally graded cellular materials

Design of functionally graded material (FGM), in which the mechanical property varies along one direction, is the focus of this study. It is assumed that the microstructure of the FGM is composed of a series of base cells in the variation direction and self-repeated in other directions. Bi-directional evolutionary structural optimization technique in the form of inverse homogenization is used for the design of the FGM for specified variation in bulk or shear modulus. Instead of designing a series of base cells simultaneously, the base cells are optimized progressively by considering three base cells at each stage. Thus, the proper connections between adjacent base cells can be achieved with high computational efficiency. Numerical examples demonstrate the effectiveness of the proposed method for designing microstructures of 2D and 3D FGMs with specified variation in bulk or shear modulus. The proposed algorithm can also be easily extended to design FGMs with other functional properties.     

Topology optimization design of flextensional actuators

Flextensional actuators can be defined as a piezoceramic (or a stack of piezoceramics) connected to a flexible mechanical structure that converts and amplifies the output displacement of the piezoceramic. Essentially, the actuator performance depends on the distribution of stiffness and flexibility in the coupling structure and, therefore, on the coupling structure topology. In this work, we propose a general method for designing flextensional actuators with large output displacement (or generative force) by applying the topology optimization method. The goal is to design a flexible structure coupled to the piezoceramic that maximizes the output displacement (or force) in some specified direction. Static and low frequency applications are considered. To illustrate the implementation of the method, 2-D topologies of flextensional actuators are presented because of the lower computational cost; however, the method can be extended to 3-D topologies. By designing other types of coupling structures connected to the piezoceramic, new designs of flextensional actuators that produce output displacements or forces in different directions can be obtained, as shown. This method can be extended for designing flextensional hydrophones and sonars.     

Topology optimization in micromechanical resonator design

A?topology optimization problem in micromechanical resonator design is addressed in this paper. The design goal is to control the first several eigen-frequencies of a micromechanical resonator using topology optimization. The design variable is the distribution of mass in a constrained domain which we model via (1)?the Simple Isotropic Material with Penalization Model and (2)?the Peak Function Model. The overall optimization problem is solved using the Method of Moving Asymptotes and a Genetic Algorithm combined with a local gradient method. A?numerical example is presented to highlight the features of the methods in more detail. The advantages and disadvantages of each method are discussed.     

Looking for design in materials design

Despite great advances in computation, materials design is still science fiction. The construction of structure-property relations on the quantum scale will turn computational empiricism into true design.     

Topology design for composite components of minimum weight

This work presents a new philosophy for optimisation of composite structures in relation to lightweight design. It is based on Michell optimum lay-out theory, which uses orthogonal mesh structures disposed in the direction of principal stress trajectories, associated with an absolutely uniform distribution of stress in the fibres. The fibres in the composite component micro structure are disposed orthogonally like the minimum weight Michell structures, with voids filled with resin. This is the same mechanical principle which governs the optimisation of natural composites such as bones, horn, trees etc. Based on this natural rule, a procedure to find the optimum topology for the design of optimum composite mechanical components has been developed. A CAD-CAE software system based on finite element analysis using ABAQUS produces interactively on a screen the structure of optimum topology where the optimum fibre arrangement will be made.     

基于多目标进化算法的压电换能器优化设计

为了解决单目标优化无法满足实际工程应用需求的问题,通过对一个约束性多目标优化问题的分析,以最大振幅和最小输入电压做为优化目标,设计参数包括连续变量(换能器的尺寸)和离散变量(材料类型),利用基于分析模型的传递矩阵法对压电换能器进行建模,进而导出优化问题的数学描述式,最后应用多目标进化算法NSGA-Ⅱ,估算一系列的pareto优化设计值,分析优化结构,并确定最优设计参数.     

Compliant mechanism design with non-linear materials using topology optimization

In this paper, compliant mechanism design with non-linear materials using topology optimization is presented. A general displacement functional with non-linear material model is used in the topology optimization formulation. Sensitivity analysis of this displacement functional is derived from the adjoint method. Optimal compliant mechanism examples for maximizing the mechanical advantage are presented and the effect of non-linear material on the optimal design are considered.     

Integrated structures and materials design

This paper introduces the concept of␣Integrated Structures and Materials Design (ISMD). ISMD combines materials engineering and structural engineering for the purpose of more effectively achieving targeted structural performance, by adopting material composite properties as the shared link. An application example, design of a bridge deck link-slab, is used to illustrate the essential elements of ISMD. It is shown that the composite hardened properties—tensile strain capacity, microcrack width, and Young’s Modulus, as well as composite self-consolidating fresh properties, are amongst the most important composite parameters that govern the targeted structural performance of safety, durability and ease of design and implementation. These are also properties that can be controlled in an Engineered Cementitious Composite—an ultra ductile concrete, by tailoring the ingredients for desired fiber, matrix and interface micromechanical parameters. Broad implications of ISMD on educational approach, research collaboration, and next generation infrastructure development, are briefly discussed.     

光谱分析仪光学系统的优化设计方法

提出一种光谱分析仪光学系统的优化设计方法。该方法以光线光学为依据,在光源和光瞳上以高密度取样,将追迹实际取样光线得到的点列图作为评价依据, 根据光谱分析系统的评价指标,将整个系统以单色器入口为分界点分为两个子系统,分别对其进行优化设计,研制了对结果的后处理模块,并将其集成到光学设计软件中去。给出了一个原子吸收分光光度计光学系统实例,使用波段为 190~860nm。设计结果和样品实验表明,该系统达到 0.3nm 的光谱分辨力要求。     

Challenge,response and serendipity in the design of materials

A number of condensed case-histories of successful materials innovations are presented to illustrate the author’s thesis that happy accident favouring the prepared mind (i.e. serendipity), or alternatively a response to a challenge from competing materials, are circumstances favouring effective innovation.     

Alternative materials and processing techniques for optimized nanostructures in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) represent an exciting application of nanotechnology and offer an appealing alternative to conventional solar cells based on photovoltaic devices, with significantly reduced production and material costs. However, further improvements are required to enhance the commercial viability of these solar cells. These improvements may be achieved through the careful manipulation of the structure at the nanoscale and the application of novel processing techniques, which may help to increase the efficiency of these solar cells, improve the ease of manufacture and allow the production of flexible, solid-state solar cells. For example, the use of a nanometre-thick coating of an insulating oxide over the semiconducting film in these solar cells may reduce recombination losses. Also, selective heating techniques such as microwave heating may assist in the production of efficient solar cells on polymer, rather than glass, substrates, by allowing a rapid heat treatment to be applied to the titanium dioxide film at a higher temperature than would be possible with conventional heating. Some novel approaches to the production of semiconducting thin films for dye-sensitized solar cells, as well as the use of alternative materials and nanostructures, are reviewed.     

3-D eddy-current computation with a self-adaptive refinementtechnique

A method for the adaptive computation of 3-D eddy-current problems is presented. The 3-D eddy-current problem is formulated in terms of the electric intensity (E formulation). Edge elements that impose tangential continuity of the approximation function are employed for the discretization of the problem with the finite element method. An a-posteriori error estimation technique is proposed with the introduction of two error criteria: a) the tangential discontinuity of the magnetic intensity H, and b) the normal discontinuity of the eddy current density J_e. The proposed error estimation technique is employed in a 3-D self-adaptive refinement procedure. Sufficient approximation of the skin effect and calculation of the eddy current distribution is obtained with the proposed method. The implementation of the proposed technique in a problem of 3-D eddy-current computation in a multiply connected conducting body is discussed     

Reactive self-tracking solar concentrators: concept, design, and initial materials characterization

étendue limits angular acceptance of high-concentration photovoltaic systems and imposes precise two-axis mechanical tracking. We show how a planar micro-optic solar concentrator incorporating a waveguide cladding with a nonlinear optical response to sunlight can reduce mechanical tracking requirements. Optical system designs quantify the required response: a large, slow, and localized increase in index of refraction. We describe one candidate materials system: a suspension of high-index particles in a low-index fluid combined with a localized space-charge field to increase particle density and average index. Preliminary experiments demonstrate an index change of aqueous polystyrene nanoparticles in response to a low voltage signal and imply larger responses with optimized nanofluidic materials.     

On design of multi-functional microstructural materials

The design of periodic microstructural composite materials to achieve specific properties has been a major area of interest in material research. Tailoring different physical properties by modifying the microstructural architecture in unit cells is one of the main concerns in exploring and developing novel multi-functional cellular composites and has led to the development of a large variety of mathematical models, theories and methodologies for improving the performance of such materials. This paper provides a critical review on the state-of-the-art advances in the design of periodic microstructures of multi-functional materials for a range of physical properties, such as elastic stiffness, Poisson’s ratio, thermal expansion coefficient, conductivity, fluidic permeability, particle diffusivity, electrical permittivity and magnetic permeability, etc.     

Micro-structural reliability design of brittle materials

The paper analyses the effects of statistical distribution of micro-structural defect sizes concerning a scatter of brittle material fracture toughness. The results can be utilized for reliability assessment of selected engineering components operating under conditions of imminent brittle fracture. The reliability, taken as a complementary probability of brittle fracture initiation, is discussed, taking into account the character of the defect size statistical distribution, material mechanical properties, and varying loading and stress conditions of the component. Application of this method on Ni-Cr steel has demonstrated that there is very good agreement of the fracture behaviour predicted scatter with experimental results. This probability approach is compared with a deterministic reliability method originating from computations of safety factors. Its rational evaluation, as a function of the acceptable probability of fracture instability, provides a highly effective tool for designing of engineering components.     

Computer aided materials selection and design

The design of an end-product and the choice of the material from which it should be made are interdependent activities which nevertheless have separate and different requirements for supporting data. The provision of such data is not quite as straightforward as it might seem at first sight, mainly because the properties of a moulded item vary from point to point and differ from the properties exhibited by idealized specimens. At the very least this complicates the task of evaluation and on occasions it leads to the charge that the data provided bear little relation to service performance, but such situations are common whenever complex materials are used in exacting applications and are in no sense peculiar to plastics and the automotive industry which are the focus of this paper. Our comprehension of the materials is continually enhanced by new research results and the means by which that comprehension can be translated into data of value to the end-user industries improve in step with the advances in computer technology.One can now envisage an efficient flow of pertinent data across the interface between the end-user industries and the plastics industry. The first steps towards that ideal were discussed in two papers presented at SITEV 79^1,2; they described new results emerging from work in the research laboratories of thee Plastics Division¹ of ICY that offered a possible route to data that are both more concise and more relevant to downstream applications than earlier data described ways in which such data and more iraditional information can be manipulated by computer and “tailored” to the specific needs of particular users. This new paper develops that theme further and possibly marks the point at which responsibility for later developments should pass from research workers to those professionally concerned with the transfer of information from one group to another, for there now exists a prototype data system. The only issues to be resolved now are what information should be incorporated rather than how should the task be done. The paper is concerned primarily with the data and the underlying rationale rather than with the software that controls the various operations.