Correlation between pattern density and linewidth variation in silicon photonics waveguides

We describe the correlation between the measured width of silicon waveguides fabricated with 193 nm lithography and the local pattern density of the mask layout. In the fabrication process, pattern density can affect the composition of the plasma in a dry etching process or the abrasion rate in a planarization step. Using an optical test circuit to extract waveguide width and thickness, we sampled 5841 sites over a fabricated wafer. Using this detailed sampling, we could establish the correlation between the linewidth and average pattern density around the test circuit, as a function of the radius of influence. We find that the intra-die systematic width variation correlates most with the pattern density within a radius of 200 gm, with a correlation coefficient of 0.57. No correlation between pattern density and the intra-die systematic thickness variation is observed. These findings can be used to predict photonic circuit yield or to optimize the circuit layout to minimize the effect of local pattern density. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

Plastometric Simulation of the Hot Rolling Process of Al/B4C Powder Composite

The actual problem of nuclear machine building is mastering the manufacture of Al/B4C powder composite cladded with layers of aluminum alloy in a rigid technological casing by a high-production method of rolling. Simulation tests of cylindrical samples were carried out using a uniaxial compression method on a cam plastometer with an evaluation of the influence of the strain on the density of the Al/B4C powder compact with the aim of optimizing the rolling technology. The strain rate and strain correspond to the ones for the rolling process, and the compression process of samples was divided into three stages. The temperature of deformation and strain of the powder compound of aluminum and dispersed particles of boron carbide Al/B4C were varied according to the experiment plan. The final density of the powder compound after each compression stage was accepted as an experimental variable as well as its cutting ability according to which the manufacturability of the obtained composite was evaluated. According to the simulation experiment results, the conditions of hot compaction of the Al/B4C powder composite were evaluated and recommendations for temperature–deformation regimes were formulated.     Keywords: powder composite, plastometric tests, compression, hot rolling, Al/B4C composite, densification, boron carbid

Near net shape manufacturing of metal : a review of approaches and their evolutions

In the last thirty years the concept of manufacturability has been applied to many different processes in numerous industries. This has resulted in the emergence of several different "Design for Manufacturing" methodologies which have in common the aim of reducing productions costs through the application of general manufacturing rules. Near net shape technologies have expanded these concepts, targeting mainly primary shaping process, such as casting or forging. The desired outcomes of manufacturability analysis for near-net-shape (NNS) processes are cost and lead/time reduction through minimization of process steps (in particular cutting and finishing operations) and raw material saving. Product quality improvement, variability reduction and component design functionality enhancement are also achievable through NNS optimization. Process parameters, product design and material selection are the changing variables in a manufacturing chain that interact in complex, non-linear ways. Consequently modeling and simulation play important roles in the investigation of alternative approaches. However defining the manufacturing capability of different processes is also a “moving target” because the various NNS technologies are constantly improving and evolving so there is challenge in accurately reflecting their requirements and capabilities. In the last decade, for example, CAD, CNC technologies and innovation in materials have impacted enormously on the development of NNS technologies. This paper reviews the different methods reported for NNS manufacturability assessment and examines how they can make an impact on cost, quality and process variability in the context of a specific production volume. The discussion identifies a lack of structured approaches, poor connection with process optimization methodologies and a lack of empirical models as gaps in the reported approaches

Bottom-up design of porous electrodes by combining a genetic algorithm and a pore network model

The microstructure of porous electrodes determines multiple performance-defining properties, such as the available reactive surface area, mass transfer rates, and hydraulic resistance. Thus, optimizing the electrode architecture is a powerful approach to enhance the performance and cost-competitiveness of electrochemical technologies. To expand our current arsenal of electrode materials, we need to build predictive frameworks that can screen a large geometrical design space while being physically representative. Here, we present a novel approach for the optimization of porous electrode microstructures from the bottom-up that couples a genetic algorithm with a previously validated electrochemical pore network model. In this first demonstration, we focus on optimizing redox flow battery electrodes. The genetic algorithm manipulates the pore and throat size distributions of an artificially generated microstructure with fixed pore positions by selecting the best-performing networks, based on the hydraulic and electrochemical performance computed by the model. For the studied VO2+/VO2+ electrolyte, we find an increase in the fitness of 75 % compared to the initial configuration by minimizing the pumping power and maximizing the electrochemical power of the system. The algorithm generates structures with improved fluid distribution through the formation of a bimodal pore size distribution containing preferential longitudinal flow pathways, resulting in a decrease of 73 % for the required pumping power. Furthermore, the optimization yielded an 47 % increase in surface area resulting in an electrochemical performance improvement of 42 %. Our results show the potential of using genetic algorithms combined with pore network models to optimize porous electrode microstructures for a wide range of electrolyte composition and operation conditions.</p

Efficient Design Optimization Methodology For Nonconventional Laminated Thin-Walled Composite Structures

Structural designers seek the best possible design of a structure that optimally meets the requirements of a specific application. The measure of the quality of the final design can often be related to specific stiffness and strength of the structure. Because of their superior mechanical and environmental properties compared to traditional metals, fiberreinforced composite materials have earned a widespread acceptance for different structural applications. The tailoring potential of composites to achieve high specific stiffness and strength has promoted them as promising candidates for constructing lightweight structures. From that aspect, designers have tackled the problem of designing composite laminates, which is inherently challenging due to the presence of non-linear, non-convex, and multi-dimensional problems with discrete and continuous design variables. Witnessing new manufacturing technologies also granted engineers the capability of exploiting the full potential of composites by using nonconventional laminates leading to more complex design problems. To circumvent this difficulty, designers have used lamination parameters as intermediate variables to achieve global optimization. Parameterizing the optimization problem in terms of lamination parameters retains the convex nature of the problem aiming to attain a global optimum design. This thesis aims to demonstrate the use of lamination parameters for efficient multi-level optimization of robust nonconventional laminates by integrating the optimization process with industry design guidelines. In the first optimization step, a theoretical optimum stiffness, parameterized in terms of lamination parameters, is obtained that accounts for optimum v structural performance while maintaining robustness. The second optimization step aims to retrieve the optimal stacking sequence matching the optimum stiffness properties, while accounting for laminate design guidelines to attain adequate industry performance. An important aerospace application incorporates the design of the fuselage in the aircraft, which can be divided into portions of cylindrical shells with a complex array of stiffeners, stringers, and rings that include large and small cutouts. The design of cylindrical shells under bending with a specified cutout is chosen as an application to demonstrate the effectiveness of using nonconventional laminates with arbitrary fiber orientation angles compared to conventional laminates composed of 0°, ±45°, and 90° fiber orientation angles. Constant stiffness laminates are designed for buckling and strength while imposing laminate design rules to achieve robustness. The designed laminates are compared using linear and non-linear analysis with progressive failure analysis to present the performance gains achieved by using nonconventional constant stiffness laminates compared to conventional ones. The presence of the cutout in the cylindrical shell also imposes severe stress concentrations yielding a need to use variable stiffness laminates that have continuously varying fiber orientation angles to redistribute the stresses and obtain a structurally optimal design. The first optimization step of the optimum variable stiffness design is demonstrated in the present study, whereas the optimal fiber angle distribution and fiber path generation are left for future work. A future goal of the research is to also extend the capability to address the design of more realistic fuselage structures including stiffening elements using nonconventional laminates. This aims to prove that structural improvements can be vi achieved by using nonconventional laminates for realistic design problems, which can be a major task towards their industry adoption and certification in the future