Department of Mechanical Engineering

Numerical modelling of thermal spray systems

Cristina H. Amon et al. — Fri, 04 May 2012 11:22:08 PDT

Abstract: "The purpose of this paper is to present a brief overview of the MD* thermal spray process, review the current existing models of heat transfer and fluid mechanics relevant to this process, outline a simplified thermal model implemented together with the results, and discuss the activities required for the implementation and verification of an accurate temperature model of the MD* thermal spray process. The termal model involves a mixed Lagrangian/explicit Eulerian algorithm to track the solidification for the time-dependent, one-dimensional heat equation. The effect of operating parameters (droplet/substrate temperatures, droplet size, etc.) on temperature distribution and remelting thickness is predicted. Furthermore, the motivation behind the desire for accurate spray temperature prediction of the ongoing Navigator project will be discussed."

A blend of different tastes : the language of coffee makers

Manish Agarwal et al. — Fri, 04 May 2012 11:22:06 PDT

Abstract: "Shape grammars, utilizing function labels, are shown to be applicable to product design. A grammar that describes a language of coffee makers is presented and shown to generate a large class of coffee makers currently on the market, as well as new designs that could be introduced to consumers."

The effect of filler type and volume fraction on the thermal conductivity of several polymer composites

Eric Egan et al. — Fri, 04 May 2012 11:22:03 PDT

Abstract: "To study the increase in the thermal conductivity of polymers embedded with conductive fillers, two fillers, BN particles and A1 wool fibers, are blended with two different polymers in various volume percentage fractions. As such, the effect of filler type and volume fraction is observed on the thermal conductivity enhancement of the polymer composite. The thermal conductivity is shown to rise most dramatically with Al wool but reaches its greatest magnitude using BN particles. For these material combinations, the increase in volume fraction of conductive filler is observed to be more significant than polymer type in the enhancement of thermal conductivity."

The function of value engineering

Robert H. Sturges et al. — Fri, 04 May 2012 11:22:01 PDT

Abstract: "Value Engineering (VE) techniques based on function have been the means to improved products and processes for several decades. It is a social design methodology that is usually episodic in application and often confused with narrow interests, such as cost cutting. This paper addresses the role, or function, of VE in a larger model of design practice to give insight into its use, non-use and misuse. The model identifies three levels of design practice, with a dual functional activity at its center. The process of innovative design shows tension between these functions. We conclude that VE is neither a different nor a sufficient way to design compared with more conventional analytical and synthesis techniques. It is rather a parallel and necessary process with different inputs and outputs."

Reduction of acquisition time through optimal component presentation at an assembly workstation

David O. Hunt et al. — Fri, 04 May 2012 11:21:59 PDT

Abstract: "An effective presentation of components at the workstation can have a significant impact in reducing assembly time. Our goal is to develop optimal presentation plans based on design for assembly theory. The assembly factors recognized as relevant to both parts acquisition and assembly workstation layout are recognition, orientation, weight, and handling distance. This study considers a single manual operator at an assembly station, with the components in rectangular bins of differing sizes and aspect ratios. Ninety degree rotations of the bins are allowed for minimizing potential handling distance. The assembly task is modeled with multiple assembly points representing the final location of the components. Components may or may not be preoriented in the bins, with preorientation removing the recognition and orientation time penalties. The problem formulation employs Mixed Integer Non-Linear Programming (MINLP), and numerical evidence suggests an NP-hard problem. Heuristic methods reduce computational effort to practical levels for realistic assembly tasks. Our results show that numerical optimization of assembly workstation layout can reduce the expected level of difficulty over random or manual workstation design methods."

Virtual wedging in three dimensional peg insertion tasks

Robert H. Sturges et al. — Fri, 04 May 2012 11:21:57 PDT

Abstract: "Quasi-static wedging of three-point contacts is investigated, wherein the concepts of virtual and redundant wedging due to a resultant force falling into a friction cone are proposed. We consider the fully-started case of a square peg and hole consisting of two point-surface contacts and one line-line contact. An analysis of the wedging diagram for this highly constrained configuration is carried out and compared to the two dimensional case. An approximate wedging diagram is constructed which shows that wedging of square pegs into square holes is more likely than cylindrical pegs and holes of similar sizes."

Reduction of acquisition time through new design for assembly heuristics

Robert H. Sturges et al. — Fri, 04 May 2012 11:21:54 PDT

Abstract: "Rearranging component positions and orientations inside products can reduce the acquisition times associated with handling distance and component orientation. Modeling the acquisition process with an information-based Design for Assembly methodology identifies and quantifies acquisition difficulty for manual and automatic processes. Heuristics based on evaluations of acquisition difficulty guide the relocation and orientation of components inside the product to reduce assembly time. Since acquisition time averages one third of the total assembly time, significant improvements are shown to be feasible."

Grammatical design and bounded creativity

K. N. Brown et al. — Fri, 04 May 2012 11:21:52 PDT

Abstract: "In this paper, grammatical design and creative design are shown to be compatible by introducing the notion of bounded creativity, a recognition that grammars limit but do not determine the design process."

Material composition and localized heat generation effects on conjugate heat removal from electronic components

Cristina H. Amon et al. — Fri, 04 May 2012 11:21:49 PDT

Abstract: "A time-dependent conjugate conduction/convection numerical study of four electronic component configurations that differ in material composition and distribution of internal heat generation is conducted in parallel PCBs (Printed Circuit Boards) for laminar and transitional Reynolds numbers. Both material composition and concentration of heat generation are found to affect the spatial distribution of temperature, heat flux, and Nusselt number along the solid-fluid interface. Furthermore, it is found that the distribution of internal heat generation strongly affects the convective resistance at the solid-fluid interface of the component. This leads, for the configurations with local heat generation, to a non-monotonic relationship between the convective heat transport and the Reynolds number for the range of parameters investigated. It is found that conjugate heat transfer can significantly affect the temperature distribution."

Product design for the environment : an annotated bibliography

Alon Dominitz et al. — Fri, 04 May 2012 11:21:47 PDT

Concurrent thermal designs of PCB's : balancing accuracy with time constraints

Jay S. Nigen et al. — Fri, 04 May 2012 11:21:45 PDT

Abstract: "A thermal design methodology suitable for concurrent design of cost-driven electronic systems is proposed and exemplified for a sample printed circuit board (PCB). The design methodology utilizes an evolutionary concept, in which the analysis tools are capable of adjusting their level of complexity as the design evolves, initiating with rough approximate analyses and culminating with a conjugate conduction/convection simulation for a portion of the sample of the PCB. The level of approximation included at each stage is selected with consideration of both time and accuracy constraints. The importance of considering the conjugate problem in generating heat transfer coefficients for electronic packages is discussed. The proposed thermal design methodology is then applied to the Vu-Man artifact and the results are described to illustrate the effect that upstream thermal information can have on the evolution of a design."

A computer-aided function logic sketchpad

Robert H. Sturges et al. — Fri, 04 May 2012 11:21:42 PDT

Abstract: "Function logic has been an effective approach to improved preliminary and conceptual design for several decades. This paper describes a computer-based function block diagram development tool to aid a designer in the practice of preliminary design and analysis. Its functions include assistance in the identification and the definition of main and secondary functions, identifying links between interrelated functions, and automatic generation of functional block diagrams for the developing system. Limitations of the function logic method and the tool are discussed."

A computational model for conceptual design based on function logic

Robert H. Sturges et al. — Fri, 04 May 2012 11:21:40 PDT

Abstract: "Function logic and function block diagrams have been successfully employed in preliminary and conceptual design processes for several decades. This paper describes a computational model of this process with extensions of the manual approach. It provides for a systematic identification and definition of form and function variables and identifies a three-level function/allocation/component information structure to represent the state of the design. We outline the inputs, outputs and operations on the form and function variables as a key step prior to the synthesis process. We also illustrate by example how to transfer functional designs across specialist domains."

Shot peening in shape deposition manufacturing

J. W. Zinn et al. — Fri, 04 May 2012 11:21:37 PDT

Abstract: "Experimental results and their analysis are presented concerning the use of shot peening as a means of altering the geometries of residually stressed metals. The application of this research is to parts that are built up by the successive deposition of metal layers using shape deposition manufacturing. The goal of this work is to obtain qualitative and quantitative results which can be integrated into the design and planning of shape deposited parts. The results of shot peening experiments conducted on steel specimens are presented along with a model of shot peening. This model enables the calculation of the stresses, strains, and curvatures induced by shot peening, based on the measured strains, as a function of the amount of peening. Using this model, two types of analyses of the peening tests have been conducted including an analytical beam- based analysis and a numerical finite element analysis. Quantitative and qualitative results are presented concerning the effectiveness of shot peening in producing shape changes in a manufactured part. One of the primary conclusions drawn from these experiments is that the peening efficiency is a function of the thickness of the specimen, due to the manner in which compressive stresses develop in the shot peened portion of the part."

Residual stress-driven delamination in deposited multi-layers

Jack L. Beuth et al. — Fri, 04 May 2012 11:21:34 PDT

Abstract: "An analysis is presented of the problem of residual stress-driven delamination in materials or parts manufactured by successive layer deposition. A direct application of this work is to parts that are built using rapid prototyping-based layered manufacturing methods. A two- dimensional model is presented that allows calculation of steady-state energy release rates for delamination cracks. Results from a finite element model of the problem are also presented. The results verify the steady-state analysis and show that it is applicable over a wide range of part dimensions. Crack displacement modes are also extracted from the finite element model. Results are presented for two and four layer bi- material configurations, over a large range of material mismatches. Examples are given of how this work can be used to identify critical interfaces where delamination is most likely to occur and to thus predict the susceptibility of multi-layers to delamination."

Interfacial fracture testing in shape deposition manufacturing

Nathan W. Klingbeil et al. — Fri, 04 May 2012 11:21:32 PDT

Abstract: "Shape Deposition Manufacturing (SDM) is a manufacturing process in which three dimensional parts are built up layer by layer, realizing a computer-generated solid model. Because materials are deposited at high temperatures, residual stresses are induced throughout the process. Consequently, there can exist both warping of the part and a tendency to delaminate or fracture between layers, especially between those of dissimilar materials. Thus, in the design of SDM parts, it is important to know the critical energy release rate and mode of crack extension governing interfacial fracture for particular material combinations. Interfacial toughness tests using three layer composite beam specimens under four point bending are examined. Such a test on a two layer specimen has been considered in the literature. A steady-state energy release rate (independent of crack length) is deduced analytically for both the two and three layer specimens. Finite element models verify the analytical predictions and are used to extract the mode of crack extension. Experimental results are obtained for two bimaterial interfaces."

Droplet-level thermo-mechanical analysis of the microcasting process

R. K. Chin et al. — Fri, 04 May 2012 11:21:29 PDT

Abstract: "Thermal and mechanical modeling of the microcasting stage of Shape Deposition Manufacturing is presented. Thermal modeling is needed because during the solidification and subsequent cooling of deposited molten metal, thermal aspects determine important effects such as substrate remelting, microstructure development, and build-up of residual stress. Also, temperature control is needed to protect existing machined features. Mechanical modeling is needed because thermally-induced residual stresses can lead to detrimental effects such as part warping, debonding between deposited layers, and reduced apparent strength or life. In this study, thermo-mechanical models of carbon steel deposited onto an existing carbon steel substrate are described. Current thermal modeling is centered on reliably predicting localized remelting of previously deposited substrate material by newly deposited molten droplets. Temperatures from a one-dimensional model are compared to those obtained at the axis of an axisymmetric model. In this region, the axisymmetric model predicts temperatures that agree with those from the simpler one-dimensional model for times less than that needed for complete droplet solidification. Current mechanics modeling is centered on the issue of residual stress buid-up. The effects of yielding and creep on the build-up of residual stresses are shown. Results show that thermal cycling from newly applied droplets drastically changes the stress state in the top of the substrate. Originally unstressed regions go through a cycle of yield in compression followed by yield in tension. Residual stresses close to the yield stress are predicted during part manufacture. It is likely that these stresses will be substantially relaxed, however, after a part is completed and then separated from the pallet upon which it is built."

An improved shape annealing algorithm for truss topology generation

Giridhar Reddy et al. — Fri, 04 May 2012 11:21:27 PDT

Abstract: "An improved shape annealing algorithm for truss topology generation and optimization, based on the techniques of shape grammars and simulated annealing, is introduced. The algorithm features a shape optimization method using only simulated annealing with a shape grammar move set; while no traditional gradient-based techniques are employed, the algorithm demonstrates more consistent convergence characteristics. By penalizing the objective function for violated constraints, the algorithm incorporates geometric constraints to avoid obstacles. The improved algorithm is illustrated on various structural examples taking into account stress, Euler buckling and geometric constraints, generating a variety of solutions based on a simple grammar."

Optimally directed truss topology generation using shape annealing

Giridhar Reddy et al. — Fri, 04 May 2012 11:21:25 PDT

Abstract: "This paper presents a technique for the generation and optimization of truss structure topologies based on the shape annealing algorithm. Feasible topologies for the truss are generated through a shape grammar, in an optimally directed manner, using simulated annealing. The algorithm can incorporate stress and buckling constraints as well as assembly and manufacturing constraints, during design topology generation."

Linear quadratic optimal control design using Chebyshev-based state parameterization

Ssu-Kei Wang et al. — Fri, 04 May 2012 11:21:22 PDT

Abstract: "A computationally attractive method for determining the optimal control of unconstrained linear dynamic systems with quadratic performance indices is presented. In the proposed method, the difference between each state variable and its initial condition is represented by a finite-term shifted Chebyshev series. The representation leads to a system of linear algebraic equations as the necessary condition of optimality. Simulation studies demonstrate computational advantages relative to a standard Riccati-based method, a transition matrix method, and a previous Fourier-based method."