bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling and Identification of Elastic-Plastic Systems Using the Distributed-Element Model
Authors: Chiang Dar-Yun
Published: February 2008

A modeling technique is proposed for a class of distributed-element models, which is able to account for the multi-axial Bauschinger effect without any additional kinematic hardening rules. The parameters associated with each of the elements in the model are specified by introducing an appropriate strength distribution function so as to make the model parsimonious in parameters regardless of the number of elements introduced in the model. Validity of the proposed modeling technique, in both modeling and identification of elastic-plastic systems, is demonstrated by biaxial tension-torsion applications using experimental results from the literature.
Parameter Estimation for an Internal Variable Model Using Nonlinear Optimization and Analytical/Numerical Response Sensitivities
Authors: Fossum A. F.
Published: February 2008

This paper demonstrates through examples that erroneous material constants for complex visco-plastic material models can be obtained from simultaneous parameter estimation by nonlinear optimization methods unless the laboratory load paths used in the fitting process give significant model response sensitivities to changes in all of the material parameters. A general procedure is proposed in which a nonlinear optimization algorithm is coupled with analytically/numerically derived response sensitivities to evaluate an unambiguous set of material parameters. Response sensitivities enter into the parameter estimation procedure in two ways. Relative response sensitivities are first used to identify an efficient test matrix that, when simulated with the model, give model responses that are sensitive to changes in each of the material parameters. Then the corresponding nonzero response sensitivities are used to construct the gradient and Hessian matrices in a gradient-driven optimization algorithm to evaluate the material parameters. A model for braze alloys is used to demonstrate that erroneous parameter values may result if not all of the relative response sensitivities are “nonzero” and distinct.
A Unified Damage Approach for Predicting Forming Limit Diagrams
Authors: Chow C. L. , Yu L. G. , Demeri M. Y.
Published: February 2008

Plastic deformation in sheet metal consists of four distinct phases, namely, uniform deformation, diffuse necking, localized necking, and final rupture. The last three phases are commonly known as nonuniform deformation. A proper forming limit diagram (FLD) should include all three phases of the nonuniform deformation. This paper presents the development of a unified approach to the prediction of FLD to include all three phases of nonuniform deformation. The conventional method for predicting FLD is based on localized necking and adopts two fundamentally different approaches. Under biaxial loading, the Hill’s plasticity method is often chosen when α(=ε2/ε1) <0. On the other hand, the M-K method is typically used for the prediction of localized necking when α > 0 or when the biaxial stretching of sheet metal is significant. The M-K method, however, suffers from the arbitrary selection of the imperfection size, thus resulting in inconsistent predictions. The unified approach takes into account the effects of micro-cracks/voids on the FLD. All real-life materials contain varying sizes and degrees of micro-cracks/voids which can be characterized by the theory of damage mechanics. The theory is extended to include orthotropic damage, which is often observed in extensive plastic deformation during sheet metal forming. The orthotropic FLD model is based on an anisotropic damage model proposed recently by Chow and Wang (1993). Coupling the incremental theory of plasticity with damage, the new model can be used to predict not only the forming limit diagram but also the fracture limit diagram under proportional or nonproportional loading. In view of the two distinct physical phenomena governing the cases when α(=ε2/ε1) < or α > 0, a set of instability criteria is proposed to characterize all three phases of nonuniform deformation. The orthotropic damage model has been employed to predict the FLD of VDIF steel (Chow et al, 1996) and excellent agreement between the predicted and measured results has been achieved as shown in Fig. 1. The damage model is extended in this paper to examine its applicability and validity for another important engineering material, namely aluminum alloy 6111-T4.
A Laminated Plate Model of an Adhesive-Bonded Taper-Taper Joint Under Tension
Authors: Helms Jack E. , Yang Chihdar , Pang Su-Seng
Published: February 2008

An analytical model of the strain and stress distributions in a taper-taper adhesive-bonded joint between two composite flat plates has been developed using first-order laminated plate theory. A correction for transverse shear deformation effects was included. The model was derived under the assumption of plane strain in the adherends and consists of eighteen first-order, linear, coupled ordinary differential equations with variable coefficients. The model was solved numerically using the Linear Shooting Method. Finite element models were also developed to verify the results of the analytical model using the COSMOS/M commercial software package.
Unified Constitutive Equations of Foam Materials
Authors: Chang Fu S. , Song Y. , Lu D. X. , DeSilva C. N.
Published: February 2008

A unified constitutive equation with the effect of compression strain rate, tension strain, and shear strain for foam materials with very low Poisson’s ratio has been developed. The mathematical derivation of the constitutive equation is described in detail. The effect of each parameter in the constitutive equation is studied. Numerical formula and procedure are also included in the paper. The test data of two types of energy absorbing foam materials are used for correlation study: polyurethane foam, which was tested at five compressive strain rates, and polypropylene foam, which was tested for quasi-static compression, tension, and shear. Good correlations have been concluded for both cases.
An Experimental Study of Ratchetting During Indentation of 316L Stainless Steel
Authors: Kaszynski P. , Ghorbel E. , Marquis D.
Published: February 2008

This paper deals with fatigue problems of 316L stainless-steel surgical structures used in the correction of pelvic obliquity. The structures consist of implants, milled rods, and screws. SEM observations show that fatigue degradation of the elements in complete contact under shearing forces is governed by blunting of the rod pyramid. This involves the occurrence of a micro-clearance at joints leading excessive damage of the junctions. An experimental procedure based on cyclic indentation tests is developed to predict the life of the prosthesis. Results indicate that components exhibit ratchetting. The progressive deformation associated with this phenomenon increases linearly with the logarithm of the number of cycles and leads to the degradation of the surgical assemblies by an excessive accumulated blunting of the rod pyramid. In addition, it appears that viscous effects and tensile, as well as compressive residual stresses of less than 200 MPa, do not play an important role on the ratchetting rate. However, load amplitude and maximum load are important. Phenomenological relationship describing this evolution is established.
Applicability of Neuber’s Rule to the Analysis of Stress and Strain Concentration Under Creep Conditions
Authors: Ha¨rkega˚rd G. , So̸rbo̸ S.
Published: February 2008

A differential form of Neuber’s rule, originally proposed by M. Chaudonneret, has been formulated for a generic viscoplastic notch problem, making extensive use of suitably normalised stress, strain and time. It has been shown that the stress-strain history at the root of a notch in a viscoplastic body can be determined directly from the elastic response, provided far-field viscoplastic strains can be neglected. Neuber’s rule has also been applied to the more general cases of stress and strain concentration at notches under (i) nominal creep conditions (constant nominal stress) and (ii) stress relaxation (constant nominal strain). Predictions are in good agreement with results from finite element analyses. Stress and strain concentration factors have been observed to approach stationary values after long-time loading. The stationary stress concentration factor under stress relaxation falls below that under nominal creep conditions.
A Method for Damage Evaluation of Laminated Composite Materials by Using Model Updating Techniques in Dynamics
Authors: Cunha Jesiel , Perreux Dominique
Published: February 2008

A method for damage identification in composite materials by model updating techniques in dynamics has been proposed. The modeling and the general aspects of the damage in composite materials have been briefly described. Damage is evaluated by using the sensitivity method (modal approach) which is employed to identify the stiffness properties of laminated composite tubes. Stiffness properties of extension, bending, twisting, and transverse shear effects have been identified from a single test. This will allow further damage quantification. Results obtained by numerical simulation show the feasibility of the proposed methodology.
Atomistic Finite Deformation Simulations: A Discussion on Length Scale Effects in Relation to Mechanical Stresses
Authors: Horstemeyer Mark F. , Baskes M. I.
Published: February 2008

In this study, atomistic finite deformation calculations employing the Embedded Atom Method show three items of interest related to continuum field theory. First, a spatial size scale effect on the yield stress is found. In these calculations, mechanical yield point occurred from dislocation initiation at the edge of the numerical specimens. The spatial size scale continued to affect the plastic response up to strains of 30 percent in simple shear for nickel oriented at 〈011〉. The second point is related to the continuum mechanics observation about oscillating global shear stress under simple shear conditions is shown to dampen as the spatial size scale increases. As the spatial length scale increases, the continuum rotational effect coupled with the increase in dislocation population reduces the oscillatory behavior. This confirms the notion proposed by Bammann and Aifantis (1987) in that when more dislocations are initiated with different orientations of the Burger’s vectors then the oscillations decrease. Finally, a length scale bridging idea is proposed by relating a continuum single degree of freedom loss coefficient, which relates the plastic energy to the total strain energy, to varying sizes of blocks of atoms. This study illustrates the usefulness of employing the Embedded Atom Method to study mechanisms related to continuum mechanics quantities.
Curved Parametric Segments for the Stress Field of 3-D Dislocation Loops
Authors: Ghoniem Nasr M.
Published: February 2008

Under applied mechanical forces, strong mutual interaction or other thermodynamic forces, dislocation shapes become highly curved. We present here a new method for accurate computations of self and mutual interactions between dislocation loops. In this method, dislocation loops of arbitrary shapes are segmented with appropriate parametric equations representing the dislocation line vector. Field equations of infinitesimal linear elasticity are developed on the basis of isotropic elastic Green’s tensor functions. The accuracy and computational speed of the method are illustrated by computing the stress field around a typical (110)-[111] slip loop in a BCC crystal. The method is shown to be highly accurate for close-range dislocation interactions without any loss of computational speed when compared to analytic evaluations of the stress field for short linear segments. Moreover, computations of self-forces and energies of curved segments are guaranteed to be accurate, because of the continuity of line curvature on the loop.
Stability of Dislocation Short-Range Reactions in BCC Crystals
Authors: Huang Hanchen , Ghoniem Nasr , Diaz de la Rubia Tomas , Rhee Moono , Zbib Hussein , Hirth John
Published: February 2008

The stability of short-range reactions between two dislocations of parallel line vectors which glide on two parallel slip planes in BCC crystals is determined. The two dislocations are assumed to be infinitely long, and their interaction is treated as elastic. The interaction and self-energies are both computed for dynamically moving dislocations, where the dependence on dislocation velocity is taken into account. The stability of the reaction is determined as a function of the following phase space variables: relative angle, relative speed, dislocation mobility, Burgers vector, separation of slip planes, and external force. Our results indicate that the dynamic formation of dislocation dipoles or tilt wall embryos occurs only over a small range of the investigated phase space. Internal effects are shown to be important at close separation, because of the large force between the two dislocations comprising the dipole or tilt wall embryo. We find that destabilization of the dislocation dipoles or tilt wall embryos is enhanced by externally applied stresses or by stress fields of neighboring dislocations.
Gradient Deformation Models at Nano, Micro, and Macro Scales
Authors: Aifantis E. C.
Published: February 2008

Various deformation models incorporating higher-order gradients are discussed and their implications are considered in a variety of problems ranging from the determination of the size of dislocation cores or elastic dislocation interaction to the determination of wavelengths of dislocation patterns or heterogeneous dislocation distributions and the determination of the structure of solid interfaces and of localized strain zones during adiabatic shear deformation. Different scales are involved in each one of these problems: the nanoscale for single dislocations, the microscale for dislocation patterning, and the macroscale for adiabatic shear banding. Accordingly, different gradient models apply for each case, different types of gradient terms are involved and different expressions of the gradient coefficients are assumed.
Nonlinear Properties of High Strength Paperboards
Authors: Qiu Y. P. , Millan M. , Lin C. H. , Gerhardt T. D.
Published: February 2008

Paper is a highly anisotropic and nonlinear material. Solid mechanics research on paper structures has been hampered by limited data on the nonlinear material properties of paperboards. In particular, it has been difficult to measure shear and z-directional properties. In this paper, nonlinear material response of paper laminates under simple loading conditions (uniaxial compression in three directions and in plane shear) are presented. Also, data is presented for various Poisson’s ratios. It was found that paper behaves differently along the thickness direction than along the in-plane directions. Poisson’s ratios are usually nonlinear with large deformation. In-plane Poisson’s ratios decrease, while out-of-plane Poisson’s ratios increase with the applied load.
Fatigue Damage Initiation in Waspaloy Under Complex Cyclic Loading
Authors: Abdul-Latif A. , Ferney V. , Saanouni K.
Published: February 2008

The low-cycle fatigue damage initiation in Waspaloy under complex cyclic loading (out-of-phase) is studied from experimental and theoretical viewpoints. Special emphasis is put on the transgranular damage development and results are compared to those reproduced in the literature. A physico-phenomenological model based on slip theory is used to predict the damage initiation lives as well as the directional aspect of the damage distribution. In this model, the micro-damage is supposed to initiate and then evolve on the activated crystallographic slip systems. The theoretical results are compared to both the experimental ones concerning the same material (Waspaloy) as well as other experimental results extracted from the literature.
Multiaxial Fatigue Under Variable Amplitude Loads
Authors: Kim K. S. , Park J. C. , Lee J. W.
Published: February 2008

Multiaxial fatigue under variable amplitude loading is investigated using Kandil et al.’s parameter, rainflow cycle counting on the shear strain history, and the Miner-Palmgren damage rule. Fatigue data are obtained on tubular specimens of S45C steel under proportional and nonproportional tension-torsion loading. The approaches using the maximum shear strain range (Δγmax) plane and the maximum damage (Dmax) plane as the critical plane are investigated. The damage is computed for each reversal or for each cycle. The results show that both Δγmax and Dmax approaches yield acceptable fatigue lives irrespective of the damage computation method. Damage computation for each reversal tends to shift fatigue life toward the nonconservative side for some nonproportional loading. It is concluded that the overall procedure used in this study is viable for multiaxial life prediction under variable amplitude loading for the test material.
Fatigue Life Parameter for Type 304 Stainless Steel Under Biaxial-Tensile Loading at Elevated Temperature
Authors: Zouani Abdelkrim , Bui-Quoc Thang , Bernard Marie
Published: February 2008

This paper describes a damage Parameter for predicting fatigue life under biaxial-tensile loadings. Several studies have focussed in the past on the situations where the in-plane biaxial stress ratio is negative; however, little attention has been paid for the cases involving both principal stresses in tension. A new testing method is used to carry out biaxial fatigue tests, at room and 427°C, on Type 304 stainless steel for different positive values of the stress ratio. In the experimental procedure, a disk-shaped specimen was used in connection with a spatial-arms mechanism which converts the uniaxial force generated by a conventional testing machine to radial forces extending the disk specimen. A modified virtual strain energy parameter is then suggested to normalize fatigue data obtained under a wide range of stress states. The proposed parameter accounts for the mean stress and the mean strain effects in an explicit form. In addition, the COD equivalent stress and strain concepts are adopted to account for the stress state biaxiality. The predictions of the proposed parameter are compared with the obtained experimental data and the correlation between the applied stress states and the experimental fatigue lives is discussed.
Numerical Modeling of Resistance Brazing Process Behavior in Joining Electrical Contact Materials
Authors: El-Gizawy A. Sherif , Wood Randall A.
Published: February 2008

The model describing the behavior of resistance brazing process developed here is a one-dimensional, explicit, finite difference model. The finite difference method uses a central difference scheme for the spatial approximation and a forward difference scheme for the transient iteration. The complex geometry of the contact is reduced to simple element via conformal mapping. The model incorporates joule heating, interfacial resistance, forced convective cooling of the electrodes. Radiation and ambient convection are neglected. The model simulates resistance brazing of powder metallurgy contacts to copper terminal quite well. The anticipated transient response is reproduced. The model, in conjunction with an experimental reference, could be used to troubleshoot or develop similar processes. As a result, it is concluded that the method is successful.
Optimum Forming Loading Paths for Pb-Sn Superplastic Sheet Materials
Authors: Khraisheh Marwan K. , Zbib Hussein M.
Published: February 2008

The bulge forming performance of Pb-Sn superplastic sheet materials is evaluated under different forming pressure-time profiles. In addition, an “optimum” pressure-time profile based on variable strain rates is proposed. Results of forming time, achieved amount of deformation, and thinning behavior are reported for the different forming pressure profiles. Not only the forming time was significantly reduced, when forming with the optimum pressure profile, but the integrity of the formed part was also maintained. Furthermore, the results show that forming profiles based on uniaxial models cannot successfully predict the actual forming behavior when the loading path is biaxial. In fact, the one-dimensional strain rate hardening relation, along with von Mises criterion, predict failure at a much higher strain (time) than the actual case.
Theoretical and Experimental Evaluation of Double-Notch Shear Strength of G-10CR Glass-Cloth/Epoxy Laminates at Cryogenic Temperatures
Authors: Shindo Y. , Wang R. , Horiguchi K. , Ueda S.
Published: February 2008

The cryogenic interlaminar shear behavior of G-10CR glass-cloth/epoxy laminates has been discussed through theoretical and experimental characterizations. The use of the double-notch shear test for measuring the interlaminar shear strength of glass-cloth/epoxy laminates at low temperatures is evaluated first. The interlaminar shear tests were carried out with double-notch shear specimens at room temperature, 77 K and 4 K to evaluate the interlaminar shear strength (ILSS) of G-10CR glass-cloth/epoxy laminates. The double-notch shear specimen was loaded on its ends in compression with a supporting jig to prevent buckling. These tests were conducted in accordance with ASTM D3846-79. The effects of temperature, specimen thickness, and notch separation on the apparent ILSS are shown graphically. Fracture surfaces were examined by scanning electron microscopy (SEM) and optical microscopy to verify the failure mechanisms. A three-dimensional finite element analysis was also performed to investigate the effect of specimen thickness and notch separation on the shear stress distribution in the expected fracture plane. Effective elastic moduli were determined under the assumption of uniform strain inside the representative volume element. The numerical findings are then correlated with the representative volume element. The numerical findings are then correlated with the experimental results. The validity of this test technique has been established.
Stress-Strain Analysis of a Taper-Taper Adhesive-Bonded Joint Under Cylindrical Bending
Authors: Helms Jack E. , Yang Chihdar , Pang Su-Seng
Published: February 2008

A model of a taper-taper adhesive-bonded joint under cylindrical bending has been derived using first-order laminated plate theory. Shear correction factors were used to account for transverse shear deformation. A FORTRAN program was written to integrate the resulting system of twelve simultaneous, linear, first-order, differential equations with variable coefficients. The Linear Shooting Method was used to solve the model. A finite element model was developed using the COSMOS/M commercial finite element package to verify the analytical model for a cross-ply laminate. The analytical model results agreed well with the finite element models and predicted peak adhesive stresses within about 2% of the finite element model.
Computer Simulation of 3-D Random Distribution of Short Fibers in Metal Matrix Composite Materials
Authors: Xiaoyu Jiang , Xiangan Kong
Published: February 2008

In this paper, the microstructure of “Saffil”-Al2O3 short fiber reinforced Al-Mg5.5 metal matrix composite material is simulated by computer. In the simulation it is taken into account of that the lengths, diameters, orientations, and locations of short fibers, etc. For the 3-D randomly distributed short fibers in composite materials, the typical distributions of short fiber microstructures on different planes are obtained for different short fiber volume fractions. The microstructural effects of average fiber length, diameter and their standard deviations on the overall strength of metal matrix composite materials are analyzed. From the short fiber microstructural distribution in metal matrix composite materials, the short fiber diameter coefficient ξd and short fiber length coefficient ξ1 are obtained for different standard deviations σd and σl, respectively. The short fiber orientation coefficient ξa is obtained, also. The results of these coefficients may be useful to the manufacture and use of short fiber reinforced composite materials. Considering these coefficients ξa ξd and ξl, the improved formula is given for the direct calculation of overall strength of short fibers reinforced composite materials. The improved formula may reflect the microstructural characteristics of short fibers reinforced composite materials.
The Effect of Transverse Shear on the Postbuckling and Growth Characteristics of Delaminations in Composites
Authors: Ferrie Catherine H. , Sheinman Izhak , Kardomateas George A.
Published: February 2008

A geometrically nonlinear formulation for the behavior of composite delaminated beams of arbitrary stacking sequence, and with the effects of transverse shear deformation included, is presented. The formulation is based on a first-order shear deformation kinematic model, which incorporates the bending-stretching coupling effect and also assumes an arbitrary initial imperfection. The nonlinear differential equations are solved by Newton’s method using a finite-difference scheme. The growth of the delamination is also studied by applying the J-integral in order to derive a formula for the energy release rate, which includes transverse shear. Results are presented which illustrate the shear effect, especially with respect to the ratio of the in-plane extensional over shear modulus and with respect to the ratio of plate length over thickness. It is seen that transverse shear can affect largely the displacement profiles, rendering the structure more compliant, and can promote growth by increasing the energy release rate, but this latter effect is moderate and mainly noticable only at the later stages in the postbuckling regime.
Bimaterial Interfacial Crack Growth With Strain Gradient Theory
Authors: Hao Su , Liu Wing Kam
Published: February 2008

The purpose of this paper is to investigate the effect of material heterogeneity on damage evolution and subsequent crack propagation in bimaterial systems. Strain gradient theory analysis reveals that a higher stress triaxiality always occurs on the softer material side due to the material mismatch in yield capacity and the corresponding strain gradient along the interface. High stress triaxiality is a major condition which promotes ductile damage and facilitates crack growth. To investigate this link, numerical simulations of ductile interface crack growth are performed using a damage based constitutive model. Both the numerical and experimental results show that a crack may grow along the interface or deviate into the softer material, but never turn into the harder material. The theoretical and numerical analysis reveal three factors which strongly affect the direction of crack growth and the resistance capacity of the bimaterial system against fracture. These are the boundary conditions which determine the global kinematically admissible displacement field, the stress/strain gradient near the interface due to the material mismatch, and the distance from the crack tip to the interface.
Evolution of Interlayer and Intralayer Cracks Under Compressive Fatigue in Composites
Authors: Pelegri Assimina A.
Published: February 2008

An investigation into the growth behavior of interlayer and intralayer cracks in delaminated cross-ply laminates subjected to fatigue compression is presented. Experimental data indicate different fatigue growth patterns for the two cases. The effects of mode mixity and position of the delamination in the formation of the cracks are studied. A mode-dependent fatigue growth law is applied in order to predict the behavior of the intralayer and interlayer cracks. Successful correlation of the analytical and test data is conducted for the interlayer cracks. For the intralayer cracks, addition of contact effects and local geometrical parameters in the model are suggested.
Static and High Strain Rate Compression Response of Thick Section Twill Weave S-2 Glass/Vinyl Ester Composites Manufactured by Affordable Liquid Molding Processes
Authors: Hosur M. V. , Vaidya U. K. , Abraham A. , Jadhav N. , Jeelani S.
Published: February 2008

Fiber reinforced composites, due to their higher specific strength and specific stiffness, are replacing many metallic structures. Of these, thick composite laminates are of high interest in various, millitary, transportation and marine applications for their use in ballistic and shock protection. One such application is in Composite Armored Vehicle (CAV) integral armor comprising of thick section composite that serves as the primary load-bearing component. The current solution of the structural backing laminate utilizes an S2-glass/epoxy system processed using automated fiber placement method. While proven structurally suitable, this method is time consuming as well as expensive. This paper presents several alternative cost-effective manufacturing solutions for fabricating composite laminates of 20 mm (0.8 in.) nominal thickness (made of 45 layer, 2 × 2 twill weave S2-glass with 933 sizing/vinyl ester C-50 resin), consisted with them CAV application in focus. They include Vacuum Assisted Resin Transfer Molding (VARTM) and Vacuum Assisted Resin Infusion Modeling (VARIM) and their variations. The effectiveness of different affordable processing approaches adopted in fabricating the structural laminate is compared in terms of static and dynamic compression response of the laminations. Static studies have been conducted on thick composites using specimen based on Army Material Technology Laboratory’s (AMTL) recommendation for thick section composites, while dynamic response is studied on cubic specimen samples using a Split Hopkinson Pressure Bar (SHPB).
Numerical Study of Damage Growth in Particulate Composites
Authors: Kwon Y. W. , Liu C. T.
Published: February 2008

A numerical study was conducted to simulate and predict damage initiation and growth around the crack tip crack tip in particulate composite specimens made of hard particles embedded in a soft rubber-like matrix material. Therefore, damage evolution in the matrix material around crack tips was investigated. The progressive damage was modeled using a micro/macro-approach which combined two levels of analyses like the micro-level and the macro-level analyses. Damage description was undertaken at the microlevel using a simplified three-dimensional unit-cell model and an isotropic continuum damage theory. The numerical study examined both him and thick specimens with a short or long edge crack to understand the effects of specimen thickness and crack size on the damage initiation, growth, and saturation. Numerical results were compared with experimental data.
Compressive Response and Failure of Circular Cell Polycarbonate Honeycombs Under Inplane Uniaxial Stresses
Authors: Chung Jaeung , Waas Anthony M.
Published: February 2008

The crushing response of polycarbonate circular cell honeycomb to inplane uniaxial loading under displacement control is analyzed through a combination of experiment and numerical simulation. The experiments, which correspond to two different uniaxial loading conditions, are performed using honeycomb material which has a nearly periodic microstructure. In the initial part of the response, the specimens deform in a uniform fashion. Next, a nonlinear phase characterized by progressive localization of deformation is observed. The progressive localization causes the walls of each cell to contact. These experimental results are simulated through numerical analysis using the finite element method. The reasons for the orthotropic response of the honeycombs are discussed.
An Information System for Damage Tolerance of Polymer Matrix Composites
Authors: Turkgenc Ozgur , Dianati Reza , Mitrovic Milan , Hahn H. Thomas , Shyprykevich Peter
Published: February 2008

Much research has been conducted to understand the damage tolerance behavior of polymer matrix composites, but there are so many parameters involved that the development of a generic model is rather difficult. The present paper proposes an information system, which can overcome such difficulty. In this system, a list of possible parameters is generated and used as input. The output contains compression strength after impact, dent depth and damage area as well as pertinent reference information. The information system is constituted in a relational database environment and tools from expert system technology are incorporated. Case examples are included to demonstrate the practical use of the software for both data retrieval and similarity studies.
Mechanical Oscillations in TiNi Under Synchronized Martensite Transformations
Authors: Belyaev S. P. , Volkov A. E. , Voronkov A. V.
Published: February 2008

Experimentally studied have been oscillations of a rotating pendulum with a TiNi elastic element subjected to periodic heat impulses synchronized with the period of oscillations. This methodology allowed controlling oscillations by stimulating the reverse phase transformation. Conditions for obtaining high damping, support of sustained vibrations, oscillations generation have been established. The observed dependence of the oscillations decrement has been explained with the account of the basic functional mechanical properties of shape memory alloys.
On Deformation of A-M Interface in Single Crystal Shape Memory Alloys and Some Related Issues
Authors: Sun Qing-Ping , Xu Terry Ting , Zhang Xiangyang
Published: February 2008

Recent experimental results on the deformation field of single crystal CuNiAl shape memory alloys (SMA) by using Moire´ interference technique are reported and two kinds of austenite-martensite (A-M) interfaces with different deformation features are identified. The experimental discovery questioned the invariant plane hypothesis used in crystallographic theory of martensitic transformation. Some fundamental issues on the property of A-M interface and the related micro- and macro-deformation features are discussed.
Anisotropy of Cu-Based Shape Memory Alloys In Tension/Compression Thermomechanical Loads
Authors: Sˇittner P. , Nova´k V.
Published: February 2008

Tension/compression thermomechanical experiments were performed on oriented CuAlNi shape memory alloy single crystals and CuAlZnMn single and polycrystals. Response of the single crystals in thermomechanical loads was strongly anisotropic, dependent on the orientation of the load axis and sense of the load. Tension/compression stress-temperature diagrams were constructed from experimentally determined transformation stresses and temperatures. It was shown that the history dependent strain response of the single crystal in a complex tension/compression thermomechanical cycle could be predicted from the diagram. Thermomechanical behaviors of the CuAlZnMn polycrystal under tension/compression were reported and discussed on the basis of the knowledge of the single crystal anisotropy.
R-Phase and Precursory Structures
Authors: Potekaev A. I. , Khaimzon B. B.
Published: February 2008

An analysis of plausible crystal structures of R-phase and precursory structures in Ti-Ni based on solely kinematical data on presence and equivalence of extra-reflections of diffraction patterns, as well as further data on symmetry of structure was carried out. A character of possible ordering and displacements, required to form these phases from parent BCC lattice, was determined. A classification of possible structures was given.
High Temperature Shape Memory Alloys
Authors: Van Humbeeck Jan
Published: February 2008

Several alloy systems can be selected for high-temperature shape memory alloys, defined as alloys with stable reverse transformation temperatures above 120°C. However, due to the lack of minimum quality standards for stability, ductility, functional behavior and reliability, no successful applications have been realized so far. Research on high temperature shape memory alloys (HTSMA) is, nevertheless, an important topic not only for scientific reasons but also due to the market pull. This paper reviews existing systems of HTSMA pointing out their weak and strong parts.
Navier-Stokes Analysis of the Pump Flow Field of an Automotive Torque Converter
Authors: By R. R. , Kunz R. , Lakshminarayana B.
Published: February 2008

A three-dimensional, incompressible, viscous flow code, developed by NASA AMES (INS3D) using the pseudo-compressibility method, is modified for torque converter flow field computations. The code is used to predict the velocity and pressure fields in the pump of an automotive torque converter. Numerical results are compared to measured static pressure and velocity distributions. Results show that: 1) the code can fairly well predict the Cp distribution, the distribution of the through-flow velocity, and the secondary flow field, 2) pump rotation has a major effect on the secondary flow field and on the mass-averaged total pressure loss, and 3) inlet velocity profiles have a profound effect on the mass-averaged total pressure loss.
Investigation of Centrifugal Pump Performance Under Two-Phase Flow Conditions
Authors: Noghrehkar G. R. , Kawaji M. , Chan A. M. C. , Nakamura H. , Kukita Y.
Published: February 2008

A one-dimensional two-fluid model has been used to study the centrifugal pump head degradation phenomena and to analyze the gas-liquid interaction within the pump impeller under high pressure, steam-water two-phase flow conditions. The analytical model was used to predict the two-phase pump head data for the small-scale and full-scale nuclear reactor pumps and the predictions of the head degradation compared favorably with the test data for different suction void fractions. The physical mechanisms responsible for head degradation were also investigated.
Dispersion of Ellipsoidal Particles in an Isotropic Pseudo-Turbulent Flow Field
Authors: Fan Fa-Gung , Ahmadi Goodarz
Published: February 2008

Dispersion of ellipsoidal particles in a simulated isotropic pseudo-turbulent field is studied. A procedure using Euler’s four parameters in describing the particle orientations is used, and the governing equations for the translational and rotational motions of particles are outlined. Turbulence fluctuation velocity field is simulated by a Gaussian random model. Motions of ellipsoidal particles of different sizes and lengths are analyzed. Ensemble and time averagings are used for evaluating various statistics of particle motion. Effects of size, shape, and density ratio on the mean-square particle velocities and the relative particle diffusivities are studied. By applying the orientation-averaging procedure, an analytical model for estimating the mean-square particle velocities and the relative diffusivities is developed. The predictions of the approximate model are compared with the simulation results and discussed.
Effect of Hydrofoil Planform on Tip Vortex Roll-Up and Cavitation
Authors: Fruman D. H. , Cerrutti P. , Pichon T. , Dupont P.
Published: February 2008

The effect of the planform of hydrofoils on tip vortex roll-up and cavitation has been investigated by testing three foils having the same NACA 16020 cross section but different shapes. One foil has an elliptical shape while the other two are shaped like quarters of ellipses; one with a straight leading edge and the other with a straight trailing edge. Experiments were conducted in the ENSTA, Ecole Navale and IMHEF cavitation tunnels with homologous foils of different sizes to investigate Reynolds number effects. Hydrodynamic forces as well as cavitation inception and desinence performance were measured as a function of Reynolds number and foil incidence angle. Laser Doppler measurements of the tangential and axial velocity profiles in the region immediately downstream of the tip were also performed. At equal incidence angle and Reynolds number, the three foils show different critical cavitation conditions and the maximum tangential velocity near the tip increases as the hydrofoil tip is moved from a forward to a rear position. However, the velocity profiles become more similar with increasing downstream distance, and at downstream distances greater than one chord aft of the tip, the differences between the foils disappear. The rate of tip vortex roll-up is much faster for the straight leading edge than for the straight trailing edge foil and, in the latter case, a significant portion of the roll-up occurs along the foil curved leading edge. The minimum of the pressure coefficient on the axis of the vortex was estimated from the velocity measurements and correlated with the desinent cavitation number for the largest free stream velocities. The correlation of data is very satisfactory. At the highest Reynolds number tested and at equal lift coefficients, the straight leading edge foil displays the most favorable cavitation desinent numbers.
Separating and Reattaching Flow Structure in a Suddenly Expanding Rectangular Duct
Authors: Papadopoulos G. , O¨tu¨gen M. V.
Published: February 2008

The incompressible turbulent flow over a backward-facing step in a rectangular duct was investigated experimentally. The side wall effects on the core flow were determined by varying the aspect ratio (defined as the step span-to-height ratio) from 1 to 28. The Reynolds number, based on the step height and the oncoming free-stream velocity, was 26,500. Detailed velocity measurements were made, including the turbulent stresses, in a region which extended past the flow reattachment zone. Wall static pressure was also measured on both the step and flat walls. In addition, surface visualizations were obtained on all four walls surrounding the separated flow to supplement near-wall velocity measurements. The results show that the aspect ratio has an influence on both the velocity and wall pressure even for relatively large aspect ratios. For example, in the redevelopment region downstream of reattachment, the recovery pressure decreases with smaller aspect ratios. The three-dimensional side wall effects tend to slow down the relaxation downstream of reattachment for smaller aspect ratios as evidenced by the evolution of the velocity field. For the two smallest aspect ratios investigated, higher centerplane streamwise and transverse velocities were obtained which indicate a three-dimensional mean flow structure along the full span of the duct.
Nonsteady Stagnation-Point Flows Over Permeable Surfaces: Explicit Solutions of the Nevier-Stokes Equations
Authors: Burde G. I.
Published: February 2008

Some new explicit solutions of the unsteady two-dimensional Navier-Stokes equations describing nonsteady stagnation-point flows with surface suction or injection are presented. The solutions have been obtained using a new approach for finding explicit similarity solutions of partial differential equations. As distinct from the common Birkhoff’s similarity transformation, which permits only one form of an unsteady potential flow field and only one form of time dependence for suction (or blowing) velocity, the transforms obtained permit consideration of a variety of special solutions differing in the forms of time dependence.
Relationship Between Unsteady Flow, Pressure Fluctuations, and Noise in a Centrifugal Pump—Part A: Use of PDV Data to Compute the Pressure Field
Authors: Chu S. , Dong R. , Katz J.
Published: February 2008

Velocity distributions determined by using Particle Displacement Velocimetry are used for computing the pressure field within the volute of a centrifugal pump. It is shown that blade-tongue interactions and nonuniform outflux from the impeller are primary contributors to local pressure fluctuations and far field noise. Consequently, a slight increase in the space between the impeller and the tongue causes significant changes in flow structure and reductions in the resulting noise. The impact is significant as long as the tongue-impeller gap is less than 20 percent of the impeller radius. It is also shown that the vorticity distributions, particularly the large vortex trains associated with the jet/wake phenomenon, dominate variations in the total pressure. Thus, it is unlikely that a potential flow model can provide any realistic description of the flow structure.
Relationship Between Unsteady Flow, Pressure Fluctuations, and Noise in a Centrifugal Pump—Part B: Effects of Blade-Tongue Interactions
Authors: Chu S. , Dong R. , Katz J.
Published: February 2008

Maps of pressure distributions computed using PDV data, combined with noise and local pressure measurements, are used for identifying primary sources of noise in a centrifugal pump. In the vicinity of the impeller pressure minima occur around the blade and near a vortex train generated as a result of non-uniform outflux from the impeller. The pressure everywhere also varies depending on the orientation of the impeller relative to the tongue. Noise peaks are generated when the pressure difference across the tongue is maximum, probably due to tongue oscillations, and when the wake impinges on the tip of the tongue.
Fluid Flow Structures in Staggered Banks of Cylinders Located in a Channel
Authors: Braun M. J. , Kudriavtsev V. V.
Published: February 2008

This paper contains numerical experiments that model fluid flow through a staggered array of cylinders and represents a continuation of work previously performed by the authors (Braun et al., 1993; Kudriavstsev et al., 1993). The results shown here concentrate on the analysis of the physics of flow and pressure distribution in (i) one row of cylinders, and (ii) seven rows of cylinders. The test section is the same square channel described by Braun et al. (1993). The numerical experiments were run in transient mode at Reynolds numbers (Re = umaxd/v) ranging from 86 to 869. The primary purpose of this paper is to report qualitative results regarding the attached near-wall jet phenomenon and to discuss its flow mechanics. The authors compare various stages of the transient evolution of the flow structures for geometric configurations that contain one, and seven rows of pins respectively. The associated pressure distributions in the arrays of pins are also discussed.
Prediction of the Flow Around an Airfoil Using a Reynolds Stress Transport Model
Authors: Davidson Lars
Published: February 2008

A second-moment Reynolds Stress Transport Model (RSTM) is used in the present work for computing the flow around a two-dimensional airfoil. An incompressible SIMPLEC code is used, employing a non-staggered grid arrangement. A third-order QUICK scheme is used for the momentum equations, and a second-order, bounded MUSCL scheme is used for the turbulent quantities. As the RSTM is valid only for fully turbulent flow, an eddy viscosity, one-equation model is used near the wall. The two models are matched along a preselected grid line in the fully turbulent region. Detailed comparisons between calculations and experiments are presented for an angle of attack of α = 13.3 deg. The RSTM predictions agree well with the experiments, and approaching stall is predicted for α = 17 deg, which agrees well with experimental data. The results obtained with a two-layer κ – ∈ model show poor agreement with experimental data; the velocity profiles on the suction side of the airfoil show no tendency of separation, and no tendency of stall is predicted.
Propagation of the Velocity Shear Front in Spin-up From Rest in a Cut-Cone
Authors: Kim Jae Won , Hyun Jae Min
Published: February 2008

The behavior of the dominant azimuthal velocity field during spin-up from rest of a homogeneous fluid in a cut-cone is investigated. The fundamental mechanism of spin-up process is recapitulated. In line with the classical flow model of Wedemeyer, the importance of the meridional circulation, driven by the Ekman layers, is stressed. The experimental apparatus, together with the image processing technique of the visualized flow data, is described. The reliability and accuracy of this experimental method are validated by performing parallel measurements using an LDV system. The experimental results clearly indicate that the azimuthal velocity shear front propagates faster as the incline angle of the side wall decreases. In the rotating zone of the interior, the azimuthal velocities are larger in magnitude in a cut-cone than in a circular cylinder of comparable size. Plausible physical explanations are offered, and the experimental observations are supportive of these physical arguments.