Fast global and partial reflective symmetry analyses using boundary surfaces of mechanical components

International audienceAxisymmetry and planar reflective symmetry properties of mechanical components can be used throughout a product development process to restructure the modeling process of a component, simplify the computation of tool path trajectories, assembly trajectories, etc. To this end, the restructured geometric model of such components must be at least as accurate as the manufacturing processes used to produce them, likewise their symmetry properties must be extracted with the same level of accuracy to preserve the accuracy of their geometric model. The proposed symmetry analysis is performed on a B-Rep CAD model through a divide-and-conquer approach over the boundary of a component with faces as atomic entities. As a result, it is possible to identify rapidly all global symmetry planes and axisymmetry as well as local symmetries. Also, the corresponding algorithm is fast enough to be inserted in CAD/CAM operators as part of interactive modeling processes, it performs at the same level of tolerance than geometric modelers and it is independent of the face and edge parameterizations

Atomistic Simulation Studies of Thin Film Growth and Plastic Deformation in Metals and Metal/Ceramic Nanostructures

Despite the significant improvements in manufacturing and synthesis processes of metals and ceramics in the past decades, there are still areas in which the procedure is still frequently more of an art or skill rather than a science. Therefore, systematic and combined experimental and computational studies are required to facilitate the development of techniques that offer thorough understanding of the events taking place during manufacturing and synthesis processes. With regard to these issues, it is paramount to address microscale characterizations and atomic scale understanding of the events during fabrication processes. One of the focuses of this study is unraveling fundamental events and mechanisms during thin film deposition of Cu on TiN substrates. It is demonstrated for the first time that at the very early stage of growth, BCC-Cu grows pseudomorphically on the TiN substrate as a very thin continuous film using a sequential molecular dynamics (MD)/time-stamped force-bias Monte Carlo (tfMC) algorithm. The Nishiyama-Wasserman mechanism, however, causes the Cu thin film to change from predominantly BCC-Cu to predominantly FCC-Cu with abundant nanotwins. As another topic, because of the tendency towards miniaturization in the past decades, studying the mechanical behavior of fabricated specimen at microscale or nanoscale via atomistic simulations is beneficial to characterize the deformation mechanisms associated with the observed phenomena in experiments. In that regard, we examined the impact of geometry and nanotwinned structure on the mechanical response and deformation mechanisms of nanoscale cylindrical Cu pillars capped between rigid substrates under tensile loading at a constant strain rate using MD simulation. The last topic in this dissertation is about the generalized stacking fault energy profile, which is a crucial component of alloy design since it is vital to models of metal plasticity. Models for thermal vibrations must take into account the stacking fault free energy profile; however, existing techniques can only determine how intrinsic stacking faults vary with temperature. We demonstrate how the PAFI linear scaling method, which completely takes into account anharmonic thermal vibrations that can be used to determine the complete stacking fault free energy profile

CHARACTERIZATION OF ENGINEERED SURFACES

In the recent years there has been an increasing interest in manufacturing products where surface topography plays a functional role. These surfaces are called engineered surfaces and are used in a variety of industries like semi conductor, data storage, micro- optics, MEMS etc. Engineered products are designed, manufactured and inspected to meet a variety of specifications such as size, position, geometry and surface finish to control the physical, chemical, optical and electrical properties of the surface. As the manufacturing industry strive towards shrinking form factor resulting in miniaturization of surface features, measurement of such micro and nanometer scale surfaces is becoming more challenging. Great strides have been made in the area of instrumentation to capture surface data, but the area of algorithms and procedures to determine form, size and orientation information of surface features still lacks the advancement needed to support the characterization requirements of R&D and high volume manufacturing. This dissertation addresses the development of fast and intelligent surface scanning algorithms and methodologies for engineered surfaces to determine form, size and orientation of significant surface features. Object recognition techniques are used to identify the surface features and CMM type fitting algorithms are applied to calculate the dimensions of the features. Recipes can be created to automate the characterization and process multiple features simultaneously. The developed methodologies are integrated into a surface analysis toolbox developed in MATLAB environment. The deployment of the developed application on the web is demonstrated

Analyse de forme appliquée à des modèles CAO B-Rep pour extraire des symétries locales et globales

Symmetry properties of objects described as B-Rep CAD models are analyzed locally as well as globally through an approach of type divide-and-conquer. The boundary of the object is defined using canonical surfaces frequently used when shaping mechanical components. Then, the first phase consists in generating maximal faces and edges that are independent from the object modelling process but that preserve its symmetry properties. These faces and edges form infinite sets of points that are processed globally. The second phase is the division one that creates candidate symmetry planes and axes attached to the previous maximal edges and faces. Finally, comes the propagation step of these candidate symmetry planes and axes forming the conquer phase that determines the local as well as the global symmetries of the object while characterizing its asymmetric areas.Les propriétés de symétrie d'un objet représenté sous la forme d'un modèle B-Rep CAO sont analysées localement et globalement à travers une approche de type diviser pour conquérir. La surface frontière de l'objet est décrite à partir de surfaces canoniques fréquemment utilisées dans les formes de composants mécaniques. La première phase de l'analyse consiste en la génération de faces et d'arêtes maximales indépendantes du processus de modélisation de l'objet mais préservant ses propriétés de symétrie. Ces faces et arêtes constituent des ensembles infinis de points traités globalement. La seconde phase est l'étape de division consistant en la création de plan et axes de symétrie de candidats pour les faces et arêtes maximales générées précédemment. Enfin, suit l'étape de propagation de ces plans et axes de symétrie représentant la phase de conquête et déterminant les propriétés de symétrie locales et globales de l'objet et caractérisant ses zones non-symétriques

Automatic constraint-based synthesis of non-uniform rational B-spline surfaces

In this dissertation a technique for the synthesis of sculptured surface models subject to several constraints based on design and manufacturability requirements is presented. A design environment is specified as a collection of polyhedral models which represent components in the vicinity of the surface to be designed, or regions which the surface should avoid. Non-uniform rational B-splines (NURBS) are used for surface representation, and the control point locations are the design variables. For some problems the NURBS surface knots and/or weights are included as additional design variables. The primary functional constraint is a proximity metric which induces the surface to avoid a tolerance envelope around each component. Other functional constraints include: an area/arc-length constraint to counteract the expansion effect of the proximity constraint, orthogonality and parametric flow constraints (to maintain consistent surface topology and improve machinability of the surface), and local constraints on surface derivatives to exploit part symmetry. In addition, constraints based on surface curvatures may be incorporated to enhance machinability and induce the synthesis of developable surfaces;The surface synthesis problem is formulated as an optimization problem. Traditional optimization techniques such as quasi-Newton, Nelder-Mead simplex and conjugate gradient, yield only locally good surface models. Consequently, simulated annealing (SA), a global optimization technique is implemented. SA successfully synthesizes several highly multimodal surface models where the traditional optimization methods failed. Results indicate that this technique has potential applications as a conceptual design tool supporting concurrent product and process development methods

Seven properties of self-organization in the human brain

The principle of self-organization has acquired a fundamental significance in the newly emerging field of computational philosophy. Self-organizing systems have been described in various domains in science and philosophy including physics, neuroscience, biology and medicine, ecology, and sociology. While system architecture and their general purpose may depend on domain-specific concepts and definitions, there are (at least) seven key properties of self-organization clearly identified in brain systems: 1) modular connectivity, 2) unsupervised learning, 3) adaptive ability, 4) functional resiliency, 5) functional plasticity, 6) from-local-to-global functional organization, and 7) dynamic system growth. These are defined here in the light of insight from neurobiology, cognitive neuroscience and Adaptive Resonance Theory (ART), and physics to show that self-organization achieves stability and functional plasticity while minimizing structural system complexity. A specific example informed by empirical research is discussed to illustrate how modularity, adaptive learning, and dynamic network growth enable stable yet plastic somatosensory representation for human grip force control. Implications for the design of “strong” artificial intelligence in robotics are brought forward

Utilizing equivalent circuits to describe the strain- and temperature-dependence of electromagnetic metamaterials

Electromagnetic metamaterials have demonstrated unique and unprecedented behaviors in a laboratory setting. They achieve these novel properties by utilizing geometry and structure, as opposed to a strict reliance on chemical composition, to dictate their interactions with electromagnetic (EM) radiation. As such, metamaterials significantly expand the toolkit from which engineers can draw when designing devices that interact with EM waves. However, the flexibility afforded by these structures also implies environmental sensitivities not seen in traditional material systems. Some recent efforts have borne this out, demonstrating significant strain- and temperature-dependence in metamaterial samples. To date, little has been done to fundamentally understand the mechanisms driving these dependencies. This understanding is crucial for developing engineering-quality predictions of the EM performance of metamaterial structures in a relevant environment, a crucial step in transitioning this technology from laboratory novelty to fielded capability. This study leverages equivalent circuit models to understand and predict the strain- and temperature-dependent EM properties of metamaterial structures. Straightforward analytic expressions for the equivalent circuit parameters (resistance, inductance, capacitance) detail the strain-induced changes in geometry as well as the temperature-dependence of the metamaterials constituent materials. These expressions are initially utilized to predict the strain-dependent shift in resonant frequency, a key descriptor of the metamaterial\u27s EM behavior. These same expressions are then utilized to describe the metamaterial\u27s strain- and temperature-dependent EM constitutive properties (permittivity, ε, and permeability, μ), which are critical for solving Maxwell\u27s equations and performing EM simulations within the material. This study focused on the Electric-LC (ELC) resonator, a design commonly used to provide a tailored response to the electric field of the EM wave. However, the author believes that the same process, and similar analytic expressions for the circuit parameters and constitutive properties, could be used to successfully predict the strain- and temperature-dependence of other metamaterial structures, to include Split-Ring-Resonators (SRRs), a design commonly used to provide a tailored magnetic response to EM waves.\u2

Effects of non-unique friction forces on the dynamic behavior of turbine bladed disks with contact interfaces

L'abstract è presente nell'allegato / the abstract is in the attachmen

Methods for heat transfer and temperature field analysis of the insulated diesel phase 2 progress report

This report describes work done during Phase 2 of a 3 year program aimed at developing a comprehensive heat transfer and thermal analysis methodology for design analysis of insulated diesel engines. The overall program addresses all the key heat transfer issues: (1) spatially and time-resolved convective and radiative in-cylinder heat transfer, (2) steady-state conduction in the overall structure, and (3) cyclical and load/speed temperature transients in the engine structure. During Phase 2, radiation heat transfer model was developed, which accounts for soot formation and burn up. A methodology was developed for carrying out the multi-dimensional finite-element heat conduction calculations within the framework of thermodynamic cycle codes. Studies were carried out using the integrated methodology to address key issues in low heat rejection engines. A wide ranging design analysis matrix was covered, including a variety of insulation strategies, recovery devices and base engine configurations. A single cylinder Cummins engine was installed at Purdue University, and it was brought to a full operational status. The development of instrumentation was continued, concentrating on radiation heat flux detector, total heat flux probe, and accurate pressure-crank angle data acquisition