Search

Solving a multiple-criteria optimization problem with severe constraints remains a significant issue in multi-objective evolutionary algorithms. The problem primarily stems from the need for a suitable constraint handling technique. One potential approach is balancing the search in feasible and infeasible regions to find the Pareto front efficiently. The justification for such a strategy is that the infeasible region also provides valuable information, especially in problems with a small percentage of feasibility areas. To that end, this paper investigates the potential of the infeasibility-driven principle based on multiple constraint ranking-based techniques to solve a multi-objective problem with a small feasibility ratio. By analyzing the results from intensive experiments on a set of test problems, including the realistic multi-objective car structure design and actuator design problem, it is shown that there is a significant improvement gained in terms of convergence by utilizing the generalized version of the multiple constraint ranking techniques. [ABSTRACT FROM AUTHOR]

Multiple global trends and drivers have resulted in a steep escalation of tech-socio-economic inequities in basic human needs across industrialized as well as industrializing nations. This escalation is paralleled by the growing trend of novel and simple frugal innovations for meeting basic human needs, which are applied across various communities in the world towards bridging gaps of inequity. Frugality in this context is defined as minimizing the use of capital resources while delivering effective manufacturing product outcomes. It is noteworthy that frugal innovations are abundantly observed in the biological designs in nature. This paper is aimed at understanding the methodology of frugal engineering behind the resulting frugal manufacturing innovations through discovering the cross-section of frameworks of biological designs in nature and equitable social innovations. Authors have applied the framework of biological designs as these designs are observed to deliver multifunctionality, resilience, and sustainability, which are key to a frugal and equitable innovation platform and achieved by the frugal engineering process. As water is one of the most basic human needs, this paper uses water as an illustrative example to understand the frugal engineering process. The authors discuss designs in nature from cactus, tree roots, and human skin, and design parallels in related frugal innovations namely in fog-capturing nets, ice stupa, and Zeer (pot-in-a-pot), respectively, for equitable water access. The authors propose and discuss a resulting methodology for frugal engineering. This methodology can be utilized as a starting point for developing case-specific socially conscious manufacturing solutions. [ABSTRACT FROM AUTHOR]

As an ancient paper craft originating from Japan, origami has been naturally embedded and contextualized in a variety of applications in the fields of mathematics, engineering, food packaging, and biological design. The computational and manufacturing capabilities today urge us to develop significantly new forms of folding as well as different materials for folding. In this paper, by allowing line cuts with crease patterns and creating folded hinges across basic structural units (BSU), typically not done in origami, we achieve a new multiprimitive folding framework such as using tetrahedral, cuboidal, prismatic, and pyramidal components, called “Kinetogami.” “Kinetogami” enables one to fold up closed-loop(s) polyhedral mechanisms (linkages) with multi-degree-of-freedom and self-deployable characteristics in a single build. This paper discusses a set of mathematical and design theories to enable design of 3D structures and mechanisms all folded from preplanned printed sheet materials. We present prototypical exploration of folding polyhedral mechanisms in a hierarchical manner as well as their transformations through reconfiguration that reorients the material and structure. The explicit 2D fabrication layout and construction rules are visually parameterized for geometric properties to ensure a continuous folding motion free of intersection. As a demonstration artifact, a multimaterial sheet is 3D printed with elastomeric flexure hinges connecting the rigid plastic facets. [ABSTRACT FROM AUTHOR]

Mobile networks, constructed with simple linkages by tessellation, have great application potential in engineering as they could change their shapes according to the need of working state by one degree-of-freedom (DOF). However, the existing one-DOF networks are always composed of bar-like links, and cooperated membranes should be designed and fabricated additionally, which makes the design and the realization more complicated. This paper is to construct a one-DOF network of Bennett linkages with identical square panels. Geometric conditions to construct the network are derived by investigating the kinematic compatibility, kinematics is carried out to show the relationships among all Bennett linkages, and the discussion on the design parameter shows the extensibility and the deploying performance, which is validated by two physical prototypes. This work initials the construction of mobile networks with identical polygon-like links, which will simplify the fabrication and realization of deployable structures. [ABSTRACT FROM AUTHOR]

Miura and Miura-derivative rigid origami patterns are increasingly used for engineering and architectural applications. However, geometric modelling approaches used in existing studies are generally haphazard, with pattern identifications and parameterizations varying widely. Consequently, relationships between Miura-derivative patterns are poorly understood, and widespread application of rigid patterns to the design of folded plate structures is hindered. This paper explores the relationship between the Miura pattern, selected because it is a commonly used rigid origami pattern, and first-level derivative patterns, generated by altering a single characteristic of the Miura pattern. Five alterable characteristics are identified in this paper: crease orientation, crease alignment, developability, flat-foldability, and rectilinearity. A consistent parameterization is presented for five derivative patterns created by modifying each characteristic, with physical prototypes constructed for geometry validation. It is also shown how the consistent parameterization allows first-level derivative geometries to be combined into complex piecewise geometries. All parameterizations presented in this paper have been compiled into a matlab Toolbox freely available for research purposes. [ABSTRACT FROM AUTHOR]

Vibration is an environmental factor with hazardous effects on the instruments' precision, structural stability, and service life in engineering fields. Many kinds of energy dissipation devices have been invented to reduce the dynamic responses of structures and instruments due to environmental excitations. In this paper, a new kind of vibration isolation and suppression device with high damping performance, fine deformation recoverability, and bearing capacity for platform structures is developed, which is designed by considering the combination of the energy dissipation mechanisms of viscoelastic material, viscous fluid, and air spring. A series of dynamic properties tests on the device are carried out under different excitation frequencies and displacement amplitudes, and a mathematical model considering the coupling effects of energy dissipation of viscoelastic material, viscous liquid, and air spring is proposed. The research results indicate that the vibration isolation and suppression device has high damping capacity, and the proposed mathematical model can well describe the mechanical properties affected by excitation frequency and displacement amplitude. [ABSTRACT FROM AUTHOR]

In recent years, many applications in precision engineering require a careful isolation of the instrument from the vibration sources by adopting active vibration isolation system to achieve a very low remaining vibration level, especially for the very low frequency under 10 Hz vibration signals. This paper presents a 3-PUPU dual parallel manipulator for both rough positioning and active vibration isolation in a wide-range workspace based on our previous research experiences in the systematical modeling and study of parallel robots. The manipulator is designed as a kind of macro/micro hybrid robot. Both the kinematics model for macro motion and dynamics model for micro motion are established by using stiffness equation and the Kane's method, respectively. An active vibration control strategy is described by using the H2 method. Moreover, numerical simulations on the inverse solution for macro motion, workspace, and the active vibration control effects are performed at the end of this paper. [ABSTRACT FROM AUTHOR]

The combination of thin metal cases or tubes with a filling made of metal foams is interesting and promising for many applications, in mechanical engineering. Components made of an outer hollow thin compact metal structure and a cellular lightweight core are especially suited to energy absorption applications. In order to allow for an efficient product/process design with a concurrent engineering approach, reliable and computationally affordable finite element method (FEM) calculations are required by both product and process engineers. The structural performance of these complex composite parts must be numerically predicted, in order to find the optimal combination of outer structure and metal foam properties. While FEM simulation at large deformations of bending, crushing, etc. of thin sheets and tubes is state of the art, the accurate FEM simulation of the mechanical behavior of metal foams cannot be considered fully established. In this paper the three most common methods for FEM simulation of metal foam materials are discussed: (a) homogenization approach, (b) realistic reconstruction of tomographic data, and (c) repetition of standard unit cells. A new effective approach is proposed, suited for simulation of composite, metal foam filled, structures of realistic dimensions. The approach is based on meshing the metal foam by replicating a unit cell made of 32 triangular shell elements, and then by randomizing the nodal position in order to emulate the intrinsic homogeneity of foam morphology. The method is validated by means of different experimental tests. The results show that the proposed method correctly predicts the behavior of foam structures in axial compression. The method slightly overestimated the actual load registered in three point bending tests. Several improvements are described and discussed in the paper, such as randomization of nodal positions of the mesh, in order_ to reduce the overestimation of forces. An FEM approach for the simulation of large deformations of metal foam filled metal structure (e.g., tubes) suited for the design of realistic large dimensions structural components has been presented. The proposed method shows some innovative features with respect to the available scientific literature, such as a configuration based on octahedral unit cells with low number of triangular shell elements. Randomization of nodal positions of each unit cell has been implemented as a method for better representing the intrinsic variability of metal foams and for reducing the stiffness of the simulated structure. [ABSTRACT FROM AUTHOR]

This paper summarizes an attempt to devise an engineering method suitable for predicting fatigue lifetime of metallic materials subjected to both proportional and nonproportional multiaxial cyclic loadings. The proposed approach takes as a starting point the assumption that the plane experiencing the maximum shear strain amplitude (the so-called "critical plane") is coincident with the micro-/mesocrack initiation plane. In order to correctly account for the presence of both nonzero mean stresses and nonzero out-of-phase angles, the degree of multiaxiality/nonproportionalily of the stress state damaging crack initiation sites is suggested here to be evaluated in terms of the ratio between maximum normal stress and shear stress amplitude relative to the critical plane. Such a ratio is used then to define nonconventional Manson-Coffin curves, whose calibration is done through two strain-life curves generated under fully reversed uniaxial and fully reversed torsional fatigue loadings, respectively. The accuracy and reliability of our approach were systematically checked by using approximately 350 experimental data taken from the technical literature and generated by testing 13 different materials under both in-phase and out-of-phase loadings. Moreover the accuracy of our criterion in estimating lifetime in the presence of nonzero mean stresses was also investigated. Such an extensive validation exercise allowed us to prove that the fatigue life estimation technique formalized in the present paper is a reliable tool capable of correctly evaluating fatigue damage in engineering materials subjected to multiaxial cyclic loading paths. [ABSTRACT FROM AUTHOR]

In this paper, we derive some analytical solutions of the Kamal cure rate differential equation. The Kamal model is a first order quasilinear ordinary differential equation, describing the progress of the curing reaction of several thermosetting polymers. All the examined cases refer to isothermal curing processes. The solutions obtained in this paper are all of implicit form. The derived solutions are applied to a repair technique based on the adhesive bonding of polymer matrix composite patches onto damaged or corroded areas. Critical duration times of realistic cure cycles corresponding to composite patch repair are estimated. The practical importance of the proposed analytic solutions is demonstrated through the presented engineering application. [ABSTRACT FROM AUTHOR]

This paper presents a three-dimensional numerical elasto-plastic model for the contact of nominally fiat surfaces based on the periodic expandability of surface topography. This model is built on two algorithms: the continuous convolution and Fourier transform (CC-FT) and discrete convolution and fast Fourier transform (DC-FFT), modified with duplicated padding. This model considers the effect of asperity interactions and gives a detailed description of subsurface stress and strain fields caused by the contact of elasto-plastic solids with rough surfaces. Formulas of the frequency response functions (FRF) for elastic/plastic stresses and residual displacement are given in this paper. The model is verified by comparing the numerical results to several analytical solutions. The model is utilized to simulate the contacts involving a two-dimensional wavy surface and an engineering rough surface in order to examine its capability of evaluating the elasto-plastic contact behaviors of nominally flat surfaces. [ABSTRACT FROM AUTHOR]

In this paper we investigate oscillations of a dynamical system containing passive dynamics driven by a positive feedback and how spatial characteristics (i.e., symmetry) affect the amplitude and stability of its nominal limit cycling response. The physical motivation of this problem is thermoacoustic dynamics in a gas turbine combustor. The spatial domain is periodic (passive annular acoustics) which are driven by heat released from a combustion process, and with sufficient driving through this nonlinear feedback a limit cycle is produced which is exhibited by a traveling acoustic wave around this annulus. We show that this response can be controlled passively by spatial perturbation in the symmetry of acoustic parameters. We find the critical parameter values that affect this oscillation, study the bifurcation properties, and subsequently use harmonic balance and temporal averaging to characterize periodic solutions and their stability. In all of these cases, we carry a parameter associated with the spatial symmetry of the acoustics and investigate how this symmetry affects the system response. The contribution of this paper is a unique analysis of a particular physical phenomena, as well as illustrating the equivalence of different nonlinear analysis tools for this analysis. [ABSTRACT FROM AUTHOR]

This paper presents an extended stress-based forming limit curve (XSFLC) that can be used to predict the onset of necking in sheet metal loaded under non-proportional load paths, as well as under three-dimensional stress states. The conventional strain-based ϵFLC is transformed into the stress-based FLC advanced by Stoughron (1999, Int. J. Mech. Sci., 42, pp. 1–27). This, in turn, is converted into the XSFLC, which is characterized by the two invariants, mean stress and equivalent stress. Assuming that the stress states at the onset of necking under plane stress loading are equivalent to those under three-dimensional loading, the XSFLC is used in conjunction with finite element computations to predict the onset of necking during tubular hydroforming. Hydroforming of straight and pre-bent tubes of EN-AW 5018 aluminum alloy and DP 600 steel are considered. Experiments carried out with these geometries and alloys are described and modeled using finite element computations. These computations, in conjunction with the XSFLC, allow quantitative predictions of necking pressures; and these predictions are found to agree to within 10% of the experimentally obtained necking pressures. The computations also provide a prediction of final failure location with remarkable accuracy. In some cases, the predictions using the XSFLC show some discrepancies when compared with the experimental results, and this paper addresses potential causes for these discrepancies. Potential improvements to the framework of the XSFLC are also discussed. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) have great potential for use in the field of civil engineering. The authors of this paper have been involved, from 1996, in several experimental and theoretical studies of the application of SMAs in civil engineering, for national and international research projects. This paper provides an overview of the main results achieved, consisting of the conceptual design, implementation, and testing of three families of SMA-based devices, namely: (i) special braces for framed structures, (ii) seismic isolation devices for buildings and bridges, and (iii) smart ties for arches and vaults. The main advantage of using SMA-based devices in the seismic protection of structures comes from the double-flag shape of their hysteresis loops, which implies three favorable features, i.e., self-centering capability, good energy dissipation capability, and high stiffness at small displacements. The main advantage of smart ties comes from the thermal behavior of SMA superelastic wires, which is opposite to that of steel rod. This implies a strong reduction of the force changes caused by variations of air temperature. [ABSTRACT FROM AUTHOR]

This paper presents a summary of our most recent advances in Thermoeconomic Diagnosis, developed during the last three years, and how they can be integrated in a zooming strategy oriented toward the operational diagnosis of complex systems. In fact, this paper can be considered a continuation of the work presented at the International Conference ECOS'99 in which the concepts of malfunction (intrinsic and induced) and dysfunction were analyzed in detail. These concepts greatly facilitate and simplify the analysis, the understanding, and the quantification of how the presence of an anomaly, or malfunction, affects the behavior of the other plant devices and of the whole system. However what remains unresolved is the so-called inverse problem of diagnosing, i.e., given two states of the plant (actual and reference operating conditions), find the causes of deviation of the actual conditions with respect to the reference conditions. The present paper tackles this problem and describes significant advances in addressing how to locate the actual causes of malfunctions, based on the application of procedures for filtering induced effects that hide the real causes of degradation. In this paper a progressive zooming thermoeconomic diagnosis procedure, which allows one to concentrate the analysis in an ever more specific zone is described and applied to a combined cycle. In an accompanying paper the accuracy of the diagnosis results is discussed, depending on choice of the thermoeconomic model. [ABSTRACT FROM AUTHOR]

One of the major drawbacks of present cost estimation models is their incapability of embracing effectively complete product development stage. Parametric estimation works well in early design stage, but when it comes to detail design stage, a more complete estimation is provided by process model based and detail estimation techniques. A major paradigm shift is proposed in this paper whereby "Cost" is to be considered as a design parameter from scientific perspective and it is to be treated as a design consequence rather than as an operational outcome. A comprehensive framework using System Analysis fundamentals is designed to study "Process Cost" aspects of a part or a design. The paper gives detailed implementation of this new approach for objects manufactured largely by milling operation. The paper also suggests a methodology to extend this approach to other manufacturing processes. The proposed Generic Cost Estimation Model shows good agreement with cost estimation by commercial estimation software when applied to the objects manufactured by milling process. It also promises integration of "Cost" with other disciplines in Multidisciplinary Optimization and Collaborative Engineering. The integration is achievable through new information technology interface tools. [ABSTRACT FROM AUTHOR]

Chiral structures have many technologically significant applications in engineering. In this paper, we investigate, both theoretically and experimentally, the structural transformation from a symmetric X-shaped tensegrity to a chiral structure under uniaxial tension. When the applied tensile force exceeds a critical value, the initially achiral structure would exhibit snap-through buckling. At the critical state, the in-plane deformation mode of the tensegrity switches into an off-plane one. The critical condition of the structural transformation is provided in terms of structural parameters. An experiment was performed to validate the theoretical model. This work may not only deepen our understanding of the stability of tensegrities but also help design chiral structures for engineering applications. [ABSTRACT FROM AUTHOR]

Failure mode and fatigue behavior of dissimilar friction stir spot welds in lap-shear specimens of transformation-induced plasticity steel (TRIP780) and hot-stamped boron steel (HSBS) sheets are examined in this paper. Optical micrographs of the dissimilar TRIP780IHSBS friction stir spot welds made by a concave silicon nitride tool before and after testing are obtained and examined. These micrographs indicate that subject to quasi-static and cyclic loading conditions, the TRIP780/HSBS welds fail from cracks growing through the TRIP780 sheets where the tool was plunged into and the thickness was reduced. The bending moments and the transverse shear force near the welds are derived with consideration of the load offset, the weld gap, and the bend distance for calculation of analytical global stress intensity factor solutions for the welds in lap-shear specimens. A fatigue model of kinked crack growth is used to estimate fatigue lives based on the local stress intensity factor solutions for kinked cracks. The estimated fatigue lives with consideration of the weld gap and the bend distance are in agreement with the fatigue test results under low-cycle loading conditions and lower than the fatigue test results under high-cycle loading conditions. The estimated fatigue lives suggest that the weld gap and the bend distance can significantly affect fatigue lives of the friction stir spot welds in lap-shear specimens under cyclic loading conditions. [ABSTRACT FROM AUTHOR]

Roller clinching is an effective way to join continuous sheet metal components. In contrast to translational clinching, joining with rotational tool movement is a continuous process in which the semifinished parts can be fed through the joining device at a constant high velocity without stopping and accelerating. Because of the special kinematics, which differs from translational clinching, the clinchpoint reveals an asymmetric joint formation. This paper deals with the influence of different rolling radii of the tools and stripping forces on the clinchpoint formation and the resulting mechanical joint properties. Experiments are performed to determine tensile and shear strengths of the rotational clinchpoints. They are compared to the properties of translational clinchpoints. Furthermore, the kinematic mechanisms during roller clinching influencing the clinchpoint geometiy are identified. [ABSTRACT FROM AUTHOR]

A sound model for the prediction of the deformed roll profile during flat rolling is vital for the precision control of the strip profile and strip shape. However, preliminary inves-tigations reveal that the applicability of existing models may be limited due to their inher-ent predictions errors. In this paper, a new model is proposed which is capable of precisely predicting the deformed roll profile in a multihigh mill. The model, which is developed on the basis of the predictions from finite element simulation, is applied to the analysis of roll deformation in a 20-high Sendzimir mill under some special conditions, such as rigid outer rolls and no roll shifting, etc. The prediction accuracy of the new model is demonstrated through comparison with the predictions from the finite element simulation. [ABSTRACT FROM AUTHOR]

Sustainable manufacturing requires simultaneous consideration of economic, environmental, and social implications associated with the production and delivery of goods. Fundamentally, sustainable manufacturing relies on descriptive metrics, advanced decision-making, and public policy for implementation, evaluation, and feedback. In this paper, recent research into concepts, methods, and tools for sustainable manufacturing is explored. At the manufacturing process level, engineering research has addressed issues related to planning, development, analysis, and improvement of processes. At a manufacturing systems level, engineering research has addressed challenges relating to facility operation, production planning and scheduling, and supply chain design. Though economically vital, manufacturing processes and systems have retained the negative image of being inefficient, polluting, and dangerous. Industrial and academic researchers are re-imagining manufacturing as a source of innovation to meet society's future needs by undertaking strategic activities focused on sustainable processes and systems. Despite recent developments in decision making and process- and systems-level research, many challenges and opportunities remain. Several of these challenges relevant to manufacturing process and system research, development, implementation, and education are highlighted. [ABSTRACT FROM AUTHOR]

Petroleum Engineering Institute of Yanshan University, Qinhuangdao 066004, China Coiled tubing is widely used in oil drilling and production operations. However, extreme high stress variation of coiled tubing during the processes of pulling out, rolling in the reel, and passing through the gooseneck makes coiled tubing fatigue failure easily. Thus, it is of great importance to increase coiled tubing fatigue life. This paper introduces the new technology to improve the fatigue life of coiled tubing--the prebending coiled tubing technology; proceeds mechanical analysis and strength check of the prebending coiled tubing; analyzes stress cycling characteristics of the prebending coiled tubing in field operations; establishes the fatigue life prediction model of prebending coiled tubing under arbitrary cycle, on the basis of fatigue experimental data under the symmetric cycle and the pulsating cycle, with fitting and interpolation method; makes simple comparison of the fatigue life of the prebending coiled tubing with that of the straight coiled tubing. Preliminary calculations show that the prebending coiled tubing technology may improve the fatigue life of coiled tubing multiple times. [ABSTRACT FROM AUTHOR]

Complex molds and dies often need grinding to achieve the required surface finishes and tolerances. Due to complex part geometry and multiple-axis motion, the wheel-workpiece engagement conditions may vary drastically during grinding, which imposes challenges to choose the appropriate workspeeds. This paper presents a modeling approach to optimize mold and die grinding to reduce cycle time while maintaining process parameters such as grinding force and specific removal rate below critical limits. The wheel-workpiece engagement conditions are calculated for each grinding step by processing the NC program, part and wheel geometries. Grinding forces, power1, and temperature are calculated and used as decision variables to optimize workspeed to reduce cycle time. Results for grinding a half bottle shaped mold show that the grinding process parameters vary significantly along the wheel axis at any instant and along the grinding path. The grinding process is far from optimum if a constant workspeed is used. Model-based optimization has been shown to reduce cycle time by 50% while achieving much lower grinding forces and power. [ABSTRACT FROM AUTHOR]

Theoretical prediction of percolation thresholds universally applicable for various composites remains a major theoretical challenge. In the work done by Xu (2011, "Ellipsoidal Bounds and Percolation Thresholds of Transport Properties of Composites," Acta Mech., 223, pp. 765-774), a variational method is developed to predict optimal percolation thresholds for transport properties of three dimensional composites subjected to full dispersion of fillers. In this paper, simplified formulae are provided for engineering applications of 3D composites. New formulae are derived for optimal percolation thresholds of 2D composites, i.e., laminates and thin films, and for composites containing a combination of fillers with different aspect ratios. The effects of dimensionality and waviness are especially discussed. [ABSTRACT FROM AUTHOR]

This paper provides full asymptotic crack-tip field solutions for an antiplane (mode-III) stationary crack in a functionally graded material. We use the complex variable approach and an asymptotic scaling factor to provide an efficient procedure for solving standard and perturbed Laplace equations associated with antiplane fracture in a graded material. We present the out-of-plane displacement and the shear stress solutions for a crack in exponentially and linearly graded materials by considering the gradation of the shear modulus either parallel or perpendicular to the crack. We discuss the characteristics of the asymptotic solutions for a graded material in comparison with the homogeneous solutions. We address the effects of the made-Ill stress intensity factor and the antiplane T-stress onto crack-tip field solutions. Finally, engineering significance of the present work is discussed. [ABSTRACT FROM AUTHOR]

This paper presents a major step in the development and validation of a systematic prototype-based methodology for designing multilayer feedforward neural networks to model nonlinearities common in engineering mechanics. The applications of this work include (but are not limited to) system identification of nonlinear dynamic systems and neural-network-based damage detection. In this and previous studies (Pei, J. S., 2001, "Parametric and Nonparanietric Identification of Nonlinear Systems," Ph.D. thesis, Columbia University; Pei, J. S., and Smyth, A. W, 2006, "A New Approach to Design, Multilayer Feedforward Neural Network Architecture in Modeling Nonlinear Restoring Forces. Part I: Formulation," J. Eng. Mech., 132(12), pp. 1290-1300; Pei, J. S., and Smyth, A. W, 2006, "A New Approach to Design Multilayer Feedforward Neural Net- work Architecture in Modeling Nonlinear Restoring Forces. Part II: Applications," J. Eng. Mech., 132(12), pp. 1301-1312; Pei, J. S., Wright, J. P., and Smyth, A. W, 2005, "Mapping Polynomial Fitting Into Feedforward Neural Networks for Modeling Nonlinear Dynamic Systems and Beyond," Comput. Methods Appl. Mech. Eng., 194(42-44), pp. 4481-4505), the authors do not presume to provide a universal method to approximate any arbitrary function. .Rather the focus is given to the development of a procedure which will consistently lead to successful approximations of nonlinear functions within the specified field. This is done by examining the dominant features of the function to be approximated and exploiting the strength of the sigmoidal basis function. As a result, a greater efficiency and understanding of both neural network architecture (e.g., the number of hidden nodes) as well as weight and bias values is achieved. Through the use of illuminating mathematical insights and a large number of training examples, this study demonstrates the simplicity, power and versatility of the proposed prototype-based initialization methodology. A clear procedure for initializing neural networks to model various nonlinear functions commonly seen in engineering mechanics is provided. The proposed methodology is compared with the widely used Nguyen-Widrow initialization to demonstrate its robustness and efficiency in the specified applications. Future work is also identified. [ABSTRACT FROM AUTHOR]

The classification of workpiece surface patterns is an essential element in trying to understand how functional performance is influenced by the surface geometry. Filter banks have been investigated in literature for capturing the multiscale characterization of the engineering surfaces. Conventionally, parametric representations of the filter outputs were used for classification. In this paper the histogram estimators of the filter bank outputs from engineering surfaces in combination with, the nearest neighbor method for classification are investigated to improve the classification accuracy, which are accomplished by utilizing distribution dissimilarity measures to compare histograms. Further- more, for large and complex surfaces, the histogram estimators of local surface flatness parameters are also proposed for the purpose of simple computation. Two case studies have been conducted to demonstrate the proposed methods. Influence of the histogram bins for histograms and the dissimilarity measures on classification performance is studied in detail. Results from the first case study show that the proposed method is less effective in classifying small surfaces with clear surface patterns, because the filtering is influenced by. the quality of the surface data collected from the measurement sensor In comparison, results from the second case study show that the proposed method performs better in classifying large surfaces with mild surface pattern differences. The classification accuracy using the conventional method drops from 100% to around 50% in the second case study. In general, one can achieve misclassification errors below 5% in both case studies with the histogram representations of surface parameters and the appropriate selection of the number of bins for histogram construction. [ABSTRACT FROM AUTHOR]

In this paper, we present a new model to predict the fracture in brittle materials from a geometrical weakness presenting an arbitrary stress concentration. The main idea is to combine the strain gradient elasticity with a cohesive model that includes both the displacement and the rotation jumps between the cohesive surfaces in the separation law. Three material parameters were used in the establishment of the fracture criterion. The first two parameters are the commonly used σc, the ultimate stress, and Gc, the critical energy release rate. The third parameter is the characteristic length l as in most of the strain gradient models. The proposed three-parameter model enables to take the different stress concentration levels into account, thus providing a criterion to predict fractures for any stress concentration, whether it is singular or not. Experimental results were selected to verify the accuracy and efficiency of the criterion. It was shown that the proposed model is physically reasonable, highly accurate, and easy to apply. It can be used in crack initiation prediction of engineering structures made of brittle materials. [ABSTRACT FROM AUTHOR]

The present paper is aimed at investigating the dynamics of release of objects in freefalling conditions typical of space applications. In the presence of surface interaction forces, a quick separation of the released from the constraining body will result in a momentum transfer, provided that the inertial forces exceed the maximum attractive force. The release conditions as well as the related parameters affecting the momentum acquired by the released body through the adhesion rupture play a fundamental role. Therefore, an analytical model has been set up to predict the imparted momentum in the case of conservative interaction forces. Furthermore, an experimental technique aimed at measuring the momentum transfer has been analyzed. Particular attention has been placed on the capability to accurately reproduce the stress status on the contact patch, on the noise sources affecting the measurement, and on the performances of a noise optimal-filtering technique in terms of achievable measurement resolution. [ABSTRACT FROM AUTHOR]

A physically-motivated, reduced representation of a general one-dimensional frictional interface is developed. Friction is introduced into the system as a state variable and is modeled by nonlinear springs of large but finite stiffness. The set of equations for the interface is reduced in a procedure similar to Guyan reduction by assuming that the system must deform in its quasistatic displacement shapes. The result of this reduction is that the degrees of freedom internal to the interface are removed from the analysis and only the boundary degrees of freedom are retained. The reduced system is then specialized to the case of a bar on a frictional surface. For this problem, a second reduction is made by noting that the time derivative of the friction force on the stuck block nearest the slip zone is much greater than the time derivatives of the friction forces elsewhere. Therefore only the friction force on the stuck block nearest the slip zone needs to be updated at each time step. The reduced representation developed in this paper is compared with a formulation from the literature and it is seen that the two match very closely and that the reduced representation is far less computationally intensive. [ABSTRACT FROM AUTHOR]

This paper is concerned with the nonlinear oscillations and dynamic behavior of a rigid disk-rotor supported by active magnetic bearings (AMB), without gyroscopic effects. The nonlinear equations of motion are derived considering a periodically time-varying stiffness. The method of multiple scales is applied to obtain four first-order differential equations that describe the modulation of the amplitudes and the phases of the vibrations in the horizontal and vertical directions. The stability and the steady-state response of the system at a combination resonance for various parameters are studied numerically, applying the frequency response function method. It is shown that the system exhibits many typical nonlinear, behaviors, including multiple-valued solutions, jump phenomenon, hardening, and softening nonlinearity. A numerical simulation using a fourth-order Runge-Kutta algorithm is carried out, where different effects of the system parameters on the nonlinear response of the rotor are reported and compared to the results from the multiple scale analysis. Results are compared to available published work. [ABSTRACT FROM AUTHOR]

This paper describes the findings from an empirical study carried out with engineers in senior roles within a large company manufacturing complex products. This research aimed to identify the types of knowledge that are important for design engineers. Twenty four knowledge categories were identified and the importance of these for design engineers in industry was investigated. In addition, the number of years of relevant experience required to become an expert in these types of knowledge was investigated. Knowledge related to the process was perceived as more important to those related to the product. However, the number of years to become an expert in process knowledge was found to be lower than for product knowledge, despite process knowledge being perceived as more important. The findings of this research contribute to the education and training of design engineers. [ABSTRACT FROM AUTHOR]

In this paper we provide two different symmetry cells to describe the shot-peening process. In this multiple impingement model, we study the dynamic behavior of TI-6Al-4V targets subjected to a large number of shots. Three-dimensional elastoplastic finite element analysis (FEA) of the process was conducted using these two symmetry cells for strain-rate sensitive targets and rigid shots. The basic symmetry cell is assigned a target surface area C X C, where C is one half of separation distance between adjacent shots. The second ‘enhanced’ symmetry cell is assigned a target surface area 2C × 2C thus allowing higher density of impact point locations. Average residual stresses inside the target predicted by FEA were compared with experimental measurements using the hole- drilling technique. In. order to do this, a new averaged technique was developed to obtain the stress distribution inside the symmetry cell. The results reveal that both symmetry cell models could be used for shot-peening modeling. However, the use of the enhanced symmetry cell leads to a better agreement with the measured residual stresses. In addition, the enhanced symmetry cell model allowed us to overcome some of the shortcomings of the basic symmetry cell for cases involving high peening velocity and intensity. [ABSTRACT FROM AUTHOR]

The present paper deals with the strain energy release rate of three woven fabric reinforced thermoplastic composites. The interlaminar fracture behavior was studied using the mode 1, double cantilever beam test and the mode II, end notched flexure test, in order to determine the energy required for the initiation and growth of an artificial crack. The materials used were made of two types of glass fiber weave (2/2 Twill, 8H Satin) and a carbon fiber (8H Satin). The matrix was polyetherimide. The delamination energy of these two materials was compared in order to study the effect of weave and reinforcement on mechanical properties. The fracture mechanism was also analyzed by means of scanning electron microscopy. [ABSTRACT FROM AUTHOR]

This paper studies intergranular creep failure of high-temperature service material under a stress-controlled unbalanced cyclic loading condition. The experimentally verified Murakami-Ohno strain-hardening creep law and Norton's creep law are incorporated into the Tvegaard's axis-symmetric model for the constrained grain boundary rupture analysis. Based on the physically realistic Murakami-Ohno creep law, it is shown that the cavity growth becomes unconstrained upon the stress reversal from compression to tension. This leads to the prediction that the material life under a cyclic loading condition is shorter than that under a constant loading. Based on the classical Norton's law, the predicted material life under a cyclic loading condition remains the same as that under a constant loading. The obtained numerical results qualitatively match recent experimental results by Arai, where the life under a cyclic loading can be much shorter than that under a constant loading. There are many cases where engineers use a simple Norton's creep law because of its simplicity. The present work suggests that more physically realistic creep laws should be used when cyclic loading must be considered. [ABSTRACT FROM AUTHOR]

This paper presents an upper bound approach to analyze axisymmetric extrusion processes. A cylindrical and a spherical coordinate system are defined to represent the die geometry and the velocity field, respectively. For various curved dies, minimized upper bound results can be obtained by relating these two coordinate systems. Based on this modeling technique, the effects of die geometry, reduction ratio, and friction are investigated. Axisymmetric extrusion through various curved dies can be easily optimized with the proposed methodology. [ABSTRACT FROM AUTHOR]

Both modular product design and reconfigurable manufacturing have a great potential to enhance responsiveness to market changes and to reduce production cost. However, the two issues have thus far mostly been investigated separately, thereby causing possible mismatch between the modular product structure and the manufacturing or assembly system. Therefore, the potential benefits of product modularity may not be materialized due to such mismatch. For this reason, this paper presents a concurrent approach to the product module selection and assembly line design problems to provide a set of harmonic solutions to the two problems and hence avoid the mismatch between design and manufacturing. The integrated nature of the problem leads to several noncommensurable and often conflicting objectives. The modified Chebyshev goal programming approach is applied to solve the multi-objective problem. A genetic algorithm is further developed to provide quick and near-optimum solutions. The proposed approach and the solution procedure have been applied to an ABS motor problem. The performance of the genetic algorithm has also been examined. [ABSTRACT FROM AUTHOR]

Rotary ultrasonic machining (RUM) is a relatively low cost and environmentally benign process for machining of advanced ceramics. Much effort has been made to theoretically and experimentally investigate material removal rate, surface roughness, and tool wear in RUM. However, there is no report on systematic study of edge chipping in RUM drilling of ceramics. This paper presents the results of a study on edge chipping in RUM drilling of advanced ceramics. The study is conducted by an integrated approach, combining designed experiments and FEM (finite element method) analysis. The designed experiments will reveal the main effects as well as interaction effects of process variables (spindle speed, ultrasonic power, feedrate, and grit size) on cutting force and chipping thickness. FEM simulations will provide the stress and strain distributions in the work-piece while being drilled by RUM. Furthermore, the relationship between chipping thickness and cutting force obtained from the FEM simulations will be compared with that obtained from the designed experiments. [ABSTRACT FROM AUTHOR]

In AFM measurements of surface morphology, the locality is a traditional assumption, i.e., the load recorded by AFM is simply the function of the distance between the tip of AFM and the point on a sample right opposite the tip [Giessibl, F J., 2003, "Advances in Atomic Force Microscopy," Rev. Mod. Phys., 75, pp. 949-983]. This paper presents that nonlocality effect may play an important role in atomic force microscopic (AFM) measurement. The nonlocality of AFM measurement results from two different finite scales: the finite scale of the characteristic intermolecular interaction distance and the geometric size of AFM tip. With a coupled molecular-continuum method, we analyzed this nonlocality effect in detail, it is found that the non locality effect can be formulated by a few dimensionless parameters characterizing the ratio of the following scales: the characteristic intermolecular interaction distance between the AFM tip and the sample, the characteristic size of the tip and the characteristic nano-structure and/or the nanoscale roughness on the surface of a sample. The present work also suggests a data processing algorithm—the approaching method, which can reduce the nonlocality effect in AFM measurement of surface morphology effectively. [ABSTRACT FROM AUTHOR]

This paper documents the pioneering work of Dr. Max Bentele during his long and distinguished career in Germany, the UK, and the United States. His early work on turbojets at the Heinkel-Hirth Corporation in conjunction with his life-long friend, Dr. Hans von Ohain, culminated in the development of the advanced HeS 011 turbojet. Dr. Bentele's pioneering work in the area of blade vibration is documented along with details of his spectacular solution of the turbine blade vibration problem of the Junkers 004B engine which propelled the world's first operational jet fighter--the Me-262. Also covered are his pioneering contributions to turbine blade cooling and blade manufacturing and his important work at Curtiss--Wright and Avco Lycoming prior to his retirement. [ABSTRACT FROM AUTHOR]

The present paper describes the key steps and issues involved in performing a quantitative risk analysis (QRA) for a dynamically positioned (DP) offshore vessel that is used to perform a short-term production test (PT) in North Atlantic deep waters. The bask approach is to focus on the "incremental" risk that would occur if the PT were run from a DP vessel as opposed to a fixed structure. The analysis is structured around two basic groups of risk: those specifically associated with DP vessel disconnection decisions and activities (all of which are seasonal), and those occurring during normal operation of the DP vessel In the case of disconnection caused by hazards such as severe weather,ice, equipment or reference system malfunction, or human/operating error, a large variety of event sequences is assumed, each resulting in different consequences and risks. These are formulated for each analysis outcome in terms of loss of life, release of chemicals into the environment, and damage and loss of assets and equipment, as well as overall failure cost It is shown that the QRA provides a very useful basis for optimal decision making with respect to the feasibility, the planning, and the risk/benefit of deep-water production testing from a DP vessel. [ABSTRACT FROM AUTHOR]

This paper focuses on the development of optimal deterministic, nonlinearly coupled barge motion models, identification of their system parameters, and calibration of their prediction capability using experimental results. The ultimate objective is to develop accurate yet sufficiently low degree-of-freedom stochastic models suitable for efficient probabilistic stability and reliability analyses of US Naval barges for preliminary design and operation guideline development (see Part II). First a three-degree-of-freedom (3DOF) fully coupled roll-heave-sway model, which features realistic and practical high- degree polynomial approximations of rigid body motion relations, hydrostatic and hydro- dynamic force-moment specifically suitable for barges, is examined. The hydrostatic force- moment relationship includes effects of the barge `s sharp edge and combined roll-heave states, and the hydrodynamic terms are in a "Morison" type quadratic form. System parameters of the 3DOF model are identified using physical model test results from several regular wave cases. The predictive capability of the model is then calibrated using results from a random wave test case. Recognizing the negligible sway influence on coupled roll and heave motions and overall barge stability, and in an attempt to reduce anticipated stochastic computational efforts in stability analysis, a two-degree-of-freedom (2DOF) roll-heave model is derived by uncoupling sway from the roil-heave governing equations of motion. Time domain simulations are conducted using the 3DOF roll-heave- sway and the 2DOF roll-heave models for regular and random wave cases to validate the model assumptions and to assess their (numerical) prediction capabilities. [ABSTRACT FROM AUTHOR]

In machining titanium alloys with cemented carbide cutting tools, crater wear is the predominant wear mechanism influencing tool life and productivity. An analytical wear model that relates crater wear rate to thermally driven cobalt diffusion from cutting tool into the titanium chip is proposed in this paper. This cobalt diffusion is a function of cobalt mole fraction, diffusion coeficient, interface temperature and chip velocity. The wear analysis includes theoretical modeling of the transport-diffusion process, and obtaining tool—chip interface conditions by a nonisothermal visco-plastic finite element method (FEM) model of the cutting process. Comparison of predicted crater wear rate with experimental results from published literature and from high speed turning with WC/Co inserts shows good agreement for different cutting speeds and feed rate. It is seen that wear rates are independent of cutting time. [ABSTRACT FROM AUTHOR]

A new approach used for single crystal (SC) materials analysis is described. Its principle is based on the extension of predictive models for isotropic material behavior to anisotropic materials such as SC nickel base superalloys. A viscoplastic model describes the material in the macroscopic level while a factor, based on the crystallographic approach, accounts for the global state of micro slip on the crystal. The combination of both elements defines the so-called ‘combined approach’ (CA). This paper presents the development of the theory and its applications to the determination of initial yielding and tension-compression asymmetry. [ABSTRACT FROM AUTHOR]

This paper presents the results of recent studies of cyclic microbend experiments and their consequences for plasticity length-scale phenomena in LIGA Ni microelectromechanical systems (MEMS) thin films. The strain-life fatigue behavior of LIGA Ni thin films is studied by performing fully reversed cyclic microbend experiments that provide insights into cyclic stress/strain evolution and cyclic failure phenomena. The effects of cyclic deformation on the plasticity length-scale parameters are also considered within the context of strain gradient plasticity theories. The implications of the results are then discussed for the analysis of plasticity and cyclic deformation in MEMS structures and other microscale systems. [ABSTRACT FROM AUTHOR]

A multistage compressor test facility, fully instrumented with a dedicated data acquisition and processing system, has been developed to conduct experimental research work at the University of Ferrara. This paper provides a systematic description of the uncertainty analysis procedures required for compressor testing, including preliminary performance test results, in addition to a brief description of the test facility and its capabilities. [ABSTRACT FROM AUTHOR]

The features of linear performance diagnostic methods are discussed, in comparison to methods based on full nonlinear calculation of performance deviations, for the purpose of condition monitoring and diagnostics. First, the theoretical background of linear methods is reviewed to establish a relationship to the principles used by nonlinear methods. Then computational procedures are discussed and compared. The effectiveness of determining component performance deviations by the two types of approaches is examined, on different types of diagnostic situations. A way of establishing criteria to define whether nonlinear methods have to be employed is presented. An overall assessment of merits or weaknesses of the two types of methods is attempted, based on the results presented in the paper. [ABSTRACT FROM AUTHOR]

This paper investigates the applicability and effect of the crack-free electrical boundary conditions in piezoelectric fracture. By treating flaws in a medium as notches with a finite width, the results from different electrical boundary condition assumptions on the crack faces are compared. It is found that the electrically impermeable boundary is a reasonable one for engineering problems. Unless the flaw interior is filled with conductive media, the permeable crack assumption may not be directly applied to the fracture of piezoelectric materials in engineering applications. [ABSTRACT FROM AUTHOR]

This paper presents a new approach to multiple fault diagnosis for sheet metal fixtures using designated component analysis (DCA). DCA first defines a set of patterns based on product/process information, then finds the significance of these patterns from the measurement data and maps them to a particular set of faults. Existing diagnostics methods has been mainly developed for rigid-body-based 3-2-1 locating scheme. Here an N-2-1 locating scheme is considered since sheet metal pans are compliant. The proposed methodology integrates on-line measurement data, pan geometry, fixture layout and sensor layout in detecting simultaneous multiple fixture faults. A diagnosability discussion for the different type of faults is presented. Finally, an application of the proposed method is presented through a computer simulation. [ABSTRACT FROM AUTHOR]