Upper-bound Models Research Articles

Impact of Micromechanical Approaches on Wave Propagation of FG Plates via Indeterminate Integral Variables with a Hyperbolic Secant Shear Model

The aim of this paper is to analyze the impacts of micromechanical approaches on the wave propagation of a functionally graded (FG) plate via indeterminate integral variables with hyperbolic secant shear displacement models. This model is established based on a high-order theory and a new displacement field with four unknowns introducing indeterminate integral variables with a secant hyperbolic shear function. Six micromechanical approaches are applied to approximate the effective material properties of an FG plate, namely Voigt’s model, Reuss’ model, Hashin–Shtrikman’s lower, and upper bound models, Tamura’s model, and the LRVE model. The volume fractions are supposed to change corresponding to the power-law and sigmoid. By applying Hamilton’s principle, general formulae of the wave propagation were obtained to get the wave modes and phase velocity curves of wave propagation in FG plates, with the impact of Voigt’s, Reuss’, Hashin–Shtrikman’s bounds, Tamura’s, and LRVE explicit micromechanical models.

The penetration resistance of the elliptical tip of torpedo anchors in cohesive soil

Torpedo anchors are a new type of deep ocean anchor with a commonly elliptical anchor tip. However, little attention has been paid to theoretical research on the collapse load of the elliptical tip of the torpedo anchor. The lower and upper bound theorems are used to evaluate the penetration resistance of the anchor tip. A comparative analysis of the bearing capacity factor between the plastic limit solutions and the results presented in previous references is performed, and the feasibility of the lower and upper bound models is verified. As the aspect ratio of the anchor tip increases, the friction factor significantly affects the bearing capacity factor: the bearing capacity factor decreases with increasing the aspect ratio for smooth interface but increases with increasing the aspect ratio for the rough interface. Extended shape correction factors are obtained from the plane strain and axial symmetry results of the finite element method: 1.61 for a smooth interface, and 1.64 for a rough interface.

An Efficient Tree-Based Algorithm for Mining High Average-Utility Itemset

High-utility itemset mining (HUIM), which is an extension of well-known frequent itemset mining (FIM), has become a key topic in recent years. HUIM aims to find a complete set of itemsets having high utilities in a given dataset. High average-utility itemset mining (HAUIM) is a variation of traditional HUIM. HAUIM provides an alternative measurement named the average-utility to discover the itemsets by taking into consideration both of the utility values and lengths of itemsets. HAUIM is important for several application domains, such as, business applications, medical data analysis, mobile commerce, streaming data analysis, etc. In the literature, several algorithms have been proposed by introducing their own upper-bound models and data structures to discover high average utility itemsets (HAUIs) in a given database. However, they require long execution times and large memory consumption to handle the problem. To overcome these limitations, this paper, first, introduces four novel upper-bounds along with pruning strategies and two data structures. Then, it proposes a pattern growth approach called the HAUL-Growth algorithm for efficiently mining of HAUIs using the proposed upper-bounds and data structures. Experimental results show that the proposed HAUL-Growth algorithm significantly outperforms the state-of-the-art dHAUIM and TUB-HAUIM algorithms in terms of execution times, number of join operations, memory consumption, and scalability.

Microcoining ripples in metal foils

Experiments, upper bound models, and finite element simulations are used to determine forming loads needed to microcoin surface ripples in thin metal foils. Coining is traditionally performed in a closed die, however enclosing all non-patterned surfaces is difficult to directly scale down to sub-millimeter foils. We find different forming regimes can exist at this small scale in an open pressing configuration. We explore the effects of the metal foil thickness and its work hardening behavior, two primary factors controlling the microcoining ripple forming load. For very thin foils, the load needed to coin a ripple pattern is lower than the load needed to compress the foil so that the open pressing configuration behavior is effectively closed with pattern formation without thickness change. For moderate thickness foils, the load needed to coin significantly drops as the entire foil compresses. For thick foils approaching bulk materials, the pattern will not completely form as the die macroscopically indents into the metal. Work hardening is found to raise the forming load for the thin, effectively closed die scenario, however it is a secondary effect at moderate thickness. This insight is used to microcoin patterns in extremely hard, thin metal foils.

Test and analysis of a new ductile shear connection design for RC shear walls

This paper presents a new and construction-friendly shear connection for the assembly of precast reinforced concrete shear wall elements. In the proposed design, the precast elements have indented interfaces and are connected by a narrow zone grouted with mortar and reinforced with overlapping U-bar loops. Contrary to conventional shear connections, the planes of the U-bar loops are here parallel to the plane of the wall elements. This feature enables a construction-friendly installation of the elements without the risk of rebars clashing. The core of mortar inside each U-bar loop is reinforced with a transverse double T-headed bar to ensure transfer of tension between the overlapping U-bars. Push-off tests show that a significantly ductile load–displacement response can be obtained by the new solution as compared to the performance of the conventional keyed shear connection design. The influence of the interface indentation geometry was investigated experimentally and the failure modes in the push-off tests were identified by use of digital image correlation (DIC). For strength prediction, rigid plastic upper-bound models have been developed with inspiration from the observed failure mechanisms. Satisfactory agreement between tests and calculations has been obtained.

EHAUPM: Efficient High Average-Utility Pattern Mining With Tighter Upper Bounds

High-utility itemset mining (HUIM) has become a popular data mining task, as it can reveal patterns that have a high-utility, contrarily to frequent pattern mining, which focuses on discovering frequent patterns. High average-utility itemset mining (HAUIM) is a variation of HUIM that provides an alternative measure, called the average utility, to select patterns by considering both their utilities and lengths. In the last decades, several algorithms have been developed to mine high average-utility itemsets (HAUIs). But most of them consume large amounts of memory and have long execution times, since they generally utilize the average-utility upper-bound ( auub ) model to overestimate the average utilities of itemsets. To improve the performance of HAUIM, this paper proposes two novel tighter upper-bound models as alternative to the traditional auub model for miningHAUIs. The looser upper-bound model considers the remaining-maximum utility in transactions to reduce the upper bound on the utilities of itemsets. The second upper-bound model ignores irrelevant items in transactions to further tighten the upper bound. Three pruning strategies are also designed to reduce the search space for mining HAUIs by a greater amount compared with the state-of-the-art HAUI-Miner algorithm. Experiments conducted on several benchmark data sets show that the designed algorithm integrating the two novel upper-bound models outperforms the traditional HAUI-Miner algorithm in terms of runtime, memory usage, number of join operations, and scalability.

Numerical Prediction of Young’s Modulus of MWCNTs/MnO2 Nanocomposite

This paper presents numerical analysis of Young’s modulus of MWCNTs/MnO2nanocomposite. The solution method has been usedto fabricate of 5, 10 and 15 wt% of MWCNTs/MnO2nanocomposite powder. The Young’s modulus of MWCNTs/MnO2nanocomposites was determined using analytical models include Voigt and Reuss bounds, Hashin and Shtrikman bounds, Halpin–Tsai model, Hui-Shia model. Voigt upper bound, Halpin-Tsai and Hui-Shia models predict nearly same Young’s modulus of MWCNTs/MnO2 nanocomposite in longitudinal direction. The various models also indicate that incorporating MWCNTSs in MnO2 matrix can potentially improve mechanical properties composites significantly.Halpin and Tsai proposed the equations for discontinuous short CNTs, randomly oriented in a matrix; the effective Young’s modulus of the nanocomposite also increases with wt% of MWCNTs.

Multi-commodity variable upper bound flow models

We perform a polyhedral study of a multi-commodity generalization of variable upper bound flow models. In particular, we establish some relations between facets of single- and multi-commodity models. We then introduce a new family of inequalities, which generalizes traditional flow cover inequalities to the multi-commodity context. We present encouraging numerical results.

Non-isothermal analysis of die corner gap formation for materials deformed by multi-pass ECAP

In this paper, the upper-bound solutions proposed by Eivani and Karimi Taheri [Comp. Mater. Sci. 42 (2008) 14] to calculate processing force and evaluate die corner angle Ψ formation in terms of tribology and die configurations during cold single pass equal channels angular pressed metals with constant flow stress were extended to work-hardening metals processed by two passes according to route A by using the Swift model combined to von Mises isotropic plasticity criterion. Also, adiabatic heat equation was coupled to solutions to express the final temperature of the workpiece. For that, thermomechanical properties of a hot-dip galvanized interstitial-free (IF) were considered and its behavior under pressing was evaluated to non-hardening and work-hardening conditions in all performed analyses. By including work-hardening in the models and for the critical friction factor of 0.4, theoretical predictions after single pass showed a decreasing of die corner angle and pressing force predictions and increasing of effective plastic strain and end temperature for all friction conditions and tooling geometries evaluated. In addition, after second pass, these responses showed higher values. Finally, with the proposed upper-bound models it was possible to analyze the dependency of angle Ψ, effective plastic strain, pressing load and sample temperature with the instantaneous workpiece height at the entry surface of deformation zone.

Upper-bound analysis of die corner gap formation for strain-hardening materials in ECAP process

In this paper, the upper-bound solutions proposed by Eivani and Karimi Taheri (2008) to calculate processing force and evaluate die corner angle Ψ formation for distinct friction conditions and tooling geometry during single pass equal channels angular pressed perfectly plastic metals at room temperature were extended to work-hardening metals by using the Hollomon model combined to von Mises isotropic plasticity criterion. Also, plane strain finite-element models were developed to validate the proposed extended analytical solutions by comparing the predictions of angle Ψ, effective plastic strains and pressing force. Mechanical properties of an aluminum Al6070 alloy were considered and its behavior under pressing was evaluated to non-hardening and work-hardening conditions in all performed analyses. The theoretical predictions consistently showed that higher values of die corner angle Ψ and smaller predictions of both effective plastic strains and pressing force are obtained when the work-hardening behavior is included in the models independently of either tribology or tooling arrangements. These aspects were confirmed by comparison with the respective finite-element predictions. In addition, with the proposed upper-bound models it was possible to analyze the dependency of angle Ψ, effective plastic strain and pressing load with the instantaneous workpiece height at the entry surface of deformation zone.

Upper-bound and finite-element analyses of non-isothermal ECAP

Abstract In this paper, the thermomechanical properties of pure tantalum described by Liang and Khan [Int. J. Plast. 15 (1999) 963] through Johnson–Cook hardening law were used to propose a non-isothermal solution for estimating the temperature increasing during single-pass equal channel angular pressed metallic materials. The pressing force was determined with the upper-bound models developed by Perez and Luri [Mech. Mater. 40 (2008) 617] extended for elastic-plastic materials with the isotropic criteria of von Mises and Drucker. The von Mises plane-strain finite-element models were done with the program ABAQUS/Explicit to provide the pressing force, P , effective plastic strain, e ¯ p , and temperature along the workpiece and also to validate the proposed analytical solutions. By using Drucker's criterion, theoretical analyses showed that the decreasing of the sample temperature increment, Δ T , was primarily affected by higher values of die channels intersection angle, Φ , and moderately for its initial temperature and the tooling outer fillet radius, R outer . Also, the increasing of Δ T was more sensible for greater die inner fillet radii, R inner , and superior velocities, V 0 . In addition, the force dropped for elevated sample initial temperatures. For Φ = 90°, the finite-element models confirmed the decreasing of Δ T and P for 0 mm ≤ R outer ≤ 5 mm and their increasing for 10 mm/s ≤ V 0 ≤ 20 mm/s. Lastly, by comparing the numerical and theoretical results of P , e ¯ p and Δ T , the proposed solutions could be validated.

Materials Design of All-Cellulose Composite Using Microstructure Based Finite Element Analysis

A microstructure-based finite element analysis model was developed to predict the effective elastic property of cellulose nanowhisker reinforced all-cellulose composite. Analysis was based on the microstructure synthesized with assumption on volume fraction, size, and orientation distribution of cellulose nanowhiskers. Simulation results demonstrated some interesting discovery: With the increase of aspect ratio, the effective elastic modulus increases in isotropic microstructure. The elastic property anisotropy increases with the aspect ratio and anisotropy of nanowhisker orientation. Simulation results from microstructure-based finite element analysis agree well with experimental results, comparing with other homogenization methods: upper bound, lower bound, and self-consistent models. Capturing the anisotropic elastic property, the microstructure-based finite element analysis demonstrated the capability in guiding materials design to improve effective properties.

Combination of the Upper Bound and Potts Models for Simulation of Microstructure in Wire Drawing and Annealing Processes

For microstructure modeling of copper wire after wire drawing process and annealing, an algorithm based on the Upper Bound Method and Potts Model is developed. In the algorithm, the Upper Bound Method is utilized to calculate the stored energy distribution in the drawn wire and then the stored energy is used in the Potts Model to obtain the grain size distribution of the drawn wire after annealing. The microstructure modeling is carried out at different deformation and annealing conditions. In all of the conditions, the fine and coarse grains are achieved at the surface and center of the wire, respectively. Also, the grain size of the drawn wire after annealing is decreased with increasing die angle and reduction in area. The modeling results are verified by the experimental results and a good agreement is achieved.

Simultaneous Periodic Output Feedback Control for Piezoelectric Actuated Structures using Interval Methods

Abstract In this paper, the problem of modeling, output feedback control design and the experimental implementation for the vibration control of smart cantilever beam with parameter uncertainties represented in interval form is addressed. The interval model of the system is obtained by introducing variation in the parameter of the identified model. However, Uncertainties are assumed in the model, identified through on line recursive least square parameter estimation. The control and identification process is done by using Simulink modeling software and dSPACE DS 1104 controller board. The output feedback controller design for the interval model is carried out through simultaneous output feedback controller design methodology by considering lower, nominal and upper bound models. The controllers designed are periodic output feedback is experimentally evaluated for their performance in suppressing the first vibration mode.

A model for an adaptable axisymmetric extrusion die with a bearing length

Abstract The adaptable design method uses upper bound models to determine die shapes that meet specified criteria, such as minimizing distortion in the product. This method has been developed for the axisymmetric extrusion process. In order to extend the methodology to the three-dimensional extrusion of a non-axisymmetric shape, the deformation zone in the upper bound model would need to be extended into the bearing region of the extrusion die. The necessary equations and conditions needed to make such an extension are presented in this paper. Finite element modeling (FEM) is used to compare the results of extrusion through dies designed by the adaptable die design method, for a model with the deformation zone extended into the bearing region, to a model without such an extension. The results indicate that the upper bound model incorporating a bearing length provides a realistic flow field. The results also demonstrate that the upper bound model can be used to analyze a multi-sectioned die, so long as: (1) the die surface and first derivative of the surface are continuous between sections, and (2) calculation of the internal power of deformation is made for each section separately. The results provide further support for the findings that the average effective strain and the volumetric effective strain rate deviation are robust criteria, which can be used to determine optimal adaptable die shapes with an upper bound model.

Axisymmetric extrusion through adaptable dies—Part 3: Minimum pressure streamlined die shapes

In Part 1 of this series of papers, six kinematically admissible velocity fields, as well as the power terms, were developed for use in upper bound models for arbitrarily shaped dies for axisymmetric extrusion. Part 2 compared the results obtained in upper bound models for the six velocity fields through a spherical die shape and demonstrated that the sine-based velocity field was the best. In this final part, the application of the sine-1 field to extrusion through streamlined dies is developed. By fixing the values of two additional constants in the radial flow flexibility function, the two surfaces of velocity discontinuity, which separate the deformation zone from the incoming and outgoing material, will have no shear. In effect, the analysis for streamlined dies can be modeled without the surface of velocity discontinuity power terms. The results for an arbitrarily curved streamlined die, as proposed by Yang and Han, using the sine-1 velocity field and the cylindrical velocity field from the work by Yang and Han are compared. It is found that the upper bound model using the sine-1 velocity field predicts lower values for the extrusion pressure. A method to determine a streamlined die shape is proposed. The method allows flexibility between the entrance and exit by the use of a Legendre polynomial series for representation of the die surface. The method is termed an adaptable die design. The adaptable die design method is used to determine streamlined die shapes, which will minimize the pressure required for the extrusion process.

Axisymmetric extrusion through adaptable dies—Part 2: Comparison of velocity fields

In Part 1 of this series of papers, six kinematically admissible velocity fields, along with the power terms, were developed for use in upper bound models for arbitrarily shaped dies for axisymmetric extrusion. The three base velocity fields in the deformation zone were derived: (1) assuming proportional angles in the deformation zone, (2) assuming proportional areas in the deformation zone, or (3) assuming proportional distances from the centerline in the deformation zone. In each case the base velocity was modified by an additional term comprised of two functions, each function containing pseudo-independent parameters. One function allows extra flexibility in the radial direction, and the second function allows extra flexibility in the angular direction. In Part 2, the results obtained in upper bound models for the six velocity fields for extrusion through a spherical die are compared to one another. The velocity fields are compared based upon: (a) the base velocity field, (b) the number and distribution of pseudo-independent parameters in the flexible functions, and (c) the form of the angular flexible function. A spherical extrusion die shape is used to evaluate and compare the three velocity fields. The results demonstrate that the sine-based velocity field is the best. Furthermore, a natural boundary condition exists which allows the shear surface associated with the streamlined portion of a die to energetically disappear. Part 3 uses the best velocity field to determine an adaptable die shape, which minimizes the extrusion pressure and compares the shape to the arbitrarily curved and streamlined die shape of Yang and Han.

Axisymmetric extrusion through adaptable dies—Part 1: Flexible velocity fields and power terms

An adaptable die is one that not only produces the correct geometrical shape, but also is designed through an adaptable method to impart other desirable properties to the product or process. In this first part of a series of papers, six kinematically admissible velocity fields are developed for use in upper bound models for axisymmetric extrusion through various dies, including extrusion through adaptable dies. Three base velocity fields are presented: (1) assuming proportional angles in the deformation zone, (2) assuming proportional areas in the deformation zone, or (3) assuming proportional distances from the centerline in the deformation zone. The base velocity is modified by an additional term comprised of two functions. One function allows extra flexibility in the radial direction, and the second function allows extra flexibility in the angular direction. There are two forms of the second function, which meet the required boundary conditions. The flexibility function in the radial direction is represented by a series of Legendre polynomials, which are orthogonal over the deformation region. The power terms derived for these velocity fields for use in upper bound models are also presented. Part 2 of this series compares the results obtained in upper bound models for the six velocity fields for a spherical extrusion die. In Part 3, the use of the best velocity field for extrusion through streamlined dies is developed to determine the adaptable die shape, which minimizes the required extrusion pressure. Additionally, the adaptable die shape is compared with results from Yang and Han for arbitrarily curved and streamlined dies.

Effect of texture and slip mode on the anisotropy of plastic flow and flow softening during hot working of Ti-6Al-4V

The effect of crystallographic texture and slip mode on the plastic flow of Ti-6Al-4V with either a colony- or globular-alpha microstructure was determined by conducting isothermal, constant-strainrate, hot-compression tests on specimens cut at various orientations (rolling direction (RD), transverse direction (TD), 45 deg, and normal) from hot-rolled plate. Testing was performed using a fixed strain rate (0.1 s−1) and various temperatures below the beta transus. The flow curves from all of the experiments exhibited a peak flow stress followed by a large and a small amount of flow softening for the colony and globular microstructures, respectively. Although the flow softening response did not depend noticeably on test direction for a given microstructure and test temperature, the peak flow stress and development of sample ovality did. This orientation dependence was interpreted using both lower-bound (isostress-type) and upper-bound (isostrain, Taylor/Bishop-Hill) models to deduce the operative slip systems in the alpha phase. These analyses suggested that prism 〈a〉 and basal 〈a〉 slip are considerably easier than pyramidal 〈c+a〉 or 〈a〉 slip at hot-working temperatures. A comparison of the flow curves for the colony and globular alpha microstructures suggested that slip transfer across alpha/beta interfaces and loss of Hall-Petch boundary strengthening can account for a substantial portion of the flow softening observed during hot working.

Geoelectrical soundings and their relationship to hydraulic parameters in semiarid regions of Jalore, northwestern India

Geoelectrical soundings using the Schlumberger configuration were carried out in the close vicinity of twelve pumping test sites in the Jalore district of Rajasthan, India, to relate geoelectric and hydraulic parameters. Geoelectrical sounding data were interpreted by partial curve matching technique to obtain the initial model parameters. This initial starter model was then used to obtain the final layer parameters through inversion technique. From the inversion technique, the best-fitting, lower bound (minimum) and upper bound (maximum) models were derived under 1% error level. The best-fitted models were correlated with the litholog. The resistivities for most of the aquifer zones are found to be very low which may be due to deteriorating quality of groundwater besides their packing and grain size. The resistivities of collected water samples were determined to compute the formation factor and porosity. Computed formation factor and porosity were correlated with hydraulic conductivity. The formation factor is directly related to hydraulic conductivity whereas porosity is inversely related. The normalised aquifer resistivity was correlated with hydraulic conductivity and normalised transverse resistance with aquifer transmissivity. The hydraulic conductivity is found to be closely related with normalised resistivity and the transmissivity with normalised transverse resistance.