bluuebunny/crossref_metadata_2025 huggingface dataset:
Recombinant Human Erythropoietin to Treat the Anemia of Prematurity
Authors: Strauss Ronald G.
Published: February 2008

Because plasma levels of erythropoietin are low in infants with the anemia of prematurity, it is logical to hypothesize that treatment with recombinant human erythropoietin (rHuEPO) would increase erythropoiesis and markedly diminish need for transfusions. Despite a large number of controlled clinical trials, the role of rHuEPO in neonatology practice is controversial. Clearly, it increases erythropoiesis in neonates and infants, but its efficacy in diminishing transfusions has been inconsistent, particularly in sick premature infants sustaining large phlebotomy loss for laboratory testing. Moreover, the ability to limit transfusions and donor exposures via modern transfusion practices coupled with concerns that the complete potential for adverse effects of rHuEPO is undefined have dissuaded widespread acceptance of rHuEPO as standard therapy to prevent or treat the anemia of prematurity.
Applications of Aprotinin in Cardiac Surgery
Authors: Levy Jerrold H.
Published: February 2008

Aprotinin has been studied extensively in cardiac surgery and is the only FDA approved pharmacological treatment to reduce blood transfusion in coronary artery bypass grafting (CABG) associated with cardiopulmonary bypass (CPB). Aprotinin has been evaluated in multiple double blind, placebo‐controlled, multicenter studies in cardiac surgery. In US studies, aprotinin has not been associated with an increased risk of post‐CPB myocardial infarction, graft closure, or increased risk of renal dysfunction, and may in fact be associated with a decreased risk of stroke. The mechanism of action is complex, but aprotinin displays antiinflammatory properties due to its complex array of protease inhibition. As with any polypeptide, there is a risk of anaphylaxis that is influenced by prior exposure. Cardiac surgery can be associated with significant bleeding and the need for allogeneic blood products. Although multiple approaches have been reported to reduce bleeding and transfusions, aprotinin represents an important pharmacologic strategy to reduce bleeding.
Cell Salvage in Trauma
Authors: Thomas Dafydd
Published: February 2008

Treatment of massive hemorrhage requires restoration of circulating blood volume to maintain oxygen delivery to the tissues. The maintenance of adequate cardiac output and restoration of intravascular volume can be achieved with non‐oxygen‐carrying volume expanders which may help restore blood pressure and maintain organ perfusion. Aims of treatment also include the avoidance of hypothermia and attempts to minimize the development of acidosis. The prompt use of cell salvage during early surgical intervention can help contribute autologous red cells to the total volume of red cells eventually transfused, thus minimizing allogeneic use. The autologous red cells have a higher 2,3‐diphosphoglycerate content than stored red cells and oxygen carriage may be better maintained in these earlier stages of resuscitation by the use of cell salvage devices.
A New Approach to Improve Material Models
Authors: Braasch H. , Duddeck H. , Ahrens H.
Published: February 2008

The inelastic behavior of materials is described most efficiently by unified models when their material functions are determined so that flow, hardening, creep etc. will be covered correctly. In this paper, the adaptation of a model is not confined to finding the optimal material parameters but is extended to the identification of the optimal shape of the material functions itself. Material functions given by series of simple shape functions defined in discrete sections which merge smoothly together lead to the best adaptation to experimental results. Furthermore, any remaining shortcomings of the model reveal deficiencies in the modelling of the microphysics of the material. Then by careful interpretation of the uncovered physical properties the original material model has to be amended leading to the derivation of even entirely new models. Thus, a powerful tool is presented here by which a unified model can be checked and improved.
The Mechanical Behavior of Zinc During Machining
Authors: Stevenson Robin , Stephenson David A.
Published: February 2008

It is well known that a nonzero force is obtained when cutting forces measured at different feed rates but otherwise constant cutting conditions are extrapolated to zero feed rate. In the literature, this nonzero intercept has been attributed to a ploughing effect associated with the finite sharpness of the cutting tool. However, the standard extrapolation method does not account for other variables such as strain, strain rate and temperature which also vary with feed rate and influence the work material flow stress. In this paper, the apparent flow stresses measured in high and low speed machining tests on zinc are compared with the flow stresses measured in compression tests. The results show that the flow stress measured in cutting is consistent with that measured in compression when all deformation variables are properly accounted for and that, contrary to the results obtained using the extrapolation approach, the ploughing force is negligible.
Elevated Temperature Axial and Torsional Fatigue Behavior of Haynes 188
Authors: Bonacuse Peter J. , Kalluri Sreeramesh
Published: February 2008

The results are reported for high-temperature axial and torsional low-cycle fatigue experiments performed at 760° C in air on thin-walled tubular specimens of Haynes 188, a wrought cobalt-base superalloy. Data are also presented for mean coefficient of thermal expansion, elastic modulus, and shear modulus at various temperatures from room to 1000° C, and monotonic and cyclic stress-strain curves in tension and in shear at 760° C. This data set is used to evaluate several multiaxial fatigue life models (most were originally developed for room temperature multiaxial life prediction) including von Mises equivalent strain range (ASME Boiler and Pressure Vessel Code), Manson-Halford, Modified Multiaxiality Factor (proposed in this paper). Modified Smith-Watson-Topper, and Fatemi-Socie-Kurath. At von Mises equivalent strain ranges (the torsional strain range divided by 3, taking the Poisson’s ratio to be 0.5), torsionally strained specimens lasted, on average, factors of 2 to 3 times longer than axially strained specimens. The Modified Multiaxiality Factor approach shows promise as a useful method of estimating torsional fatigue life from axial fatigue data at high temperatures. Several difficulties arose with the specimen geometry and extensometry used in these experiments. Cracking at extensometer probe indentations was a problem at smaller strain ranges. Also, as the largest axial and torsional strain range fatigue tests neared completion, a small amount of specimen buckling was observed.
A New Perspective on the Influence of Thickness and Post-Weld Heat Treatment for Large Scale Welded Joints
Authors: Hancock P. , Chubb J. P. , Spurrier J.
Published: February 2008

CTOD, Charpy, and wide plate results from welded constructional steels are collected from nine companies. The resulting large data bank is analyzed statistically to identify general trends in properties of welded constructional steels. The present paper uses the data bank to review the effect of post-weld heat treatment (PWHT) on the fracture behavior of the weldments. Analysis shows the beneficial effect of PWHT at all thicknesses. The results are subsequently used to question the normal practice of post-weld heat treating weldments of 50 mm and above in thickness while leaving weldments of below 50 mm thick in the as welded condition. It is suggested that there is no significant difference in as welded fracture properties in weldments until thicknesses are well in excess of 100 mm.
Deformation Analysis of Simple-Shear Sheet Specimens
Authors: Chen Fuh-Kuo
Published: February 2008

The shear properties of different simple-shear sheet specimens were investigated using the elastic-plastic finite element method. Tension loaded specimens with a shear zone formed at the center area between two transverse slots were adopted to analyze the shear properties of sheet metals under uniaxial tension. Specimens prepared by single material as well as by bonding two different strength materials together were both studied. Since the shear zone could not be kept free from bending stress during loading, the pure shear deformation was not possibly obtained. However, by varying the shape and the location of the slots, an optimum geometry of the shear zone which yields a nearly pure shear deformation in the plastic range was determined through the finite element analysis. The results also revealed when the shear zone was formed by a low strength material which was bonded on each side with a higher strength material, a nearly pure shear deformation could be obtained even in the elastic range.
Nonproportional Low Cycle Fatigue Criterion for Type 304 Stainless Steel
Authors: Itoh Takamoto , Sakane Masao , Ohnami Masateru , Socie Darrell F.
Published: February 2008

This paper describes a multiaxial low cycle fatigue parameter for correlating Hues under nonproportional loadings. Constant amplitude low cycle fatigue tests were carried out under 14 proportional and complex nonproportional cyclic strain paths using type 304 stainless steel hollow cylinder specimens at room temperature. In nonproportional loading tests, fatigue lives are decreased by as much as a factor of 10 in comparison with those in proportional loading tests with the same strain range. Reduction in fatigue life due to nonproportional loading is closely related to additional nonproportional cyclic hardening. The product of the maximum principal stress and strain ranges correlated the nonproportional fatigue data. A nonproportional cyclic hardening parameter computed from the strain path is also proposed that allows life estimates to be obtained directly from the strain history without the need for a cyclic plasticity model.
A Method for the Analysis of the Growth of Short Fatigue Cracks
Authors: McEvily A. J. , Shin Y.-S.
Published: February 2008

A method for the analysis of the fatigue crack growth rate for short cracks has been developed and is applied to the case of fatigue crack growth of short surface cracks in a 1045 carbon steel. The method entails three modifications to standard LEFM procedures. These modifications include the use of a material constant to bridge between smooth and cracked specimen behavior, consideration of the plastic zone size to crack length ratio, and incorporation of the development of crack closure. Comparisons are made between calculations based upon this approach and experimental data.
Universal Bounds for Overall Properties of Linear and Nonlinear Heterogeneous Solids
Authors: Nemat-Nasser Sia , Hori Muneo
Published: February 2008

For a sample of a general heterogeneous nonlinearly elastic material, it is shown that, among all consistent boundary data which yield the same overall average strain (stress), the strain (stress) field produced by uniform boundary tractions (linear boundary displacements), renders the elastic strain (complementary strain) energy an absolute minimum. Similar results are obtained when the material of the composite is viscoplastic. Based on these results, universal bounds are presented for the overall elastic parameters of a general, possibly finite-sized, sample of heterogeneous materials with arbitrary microstructures, subjected to any consistent boundary data with a common prescribed average strain or stress. Statistical homogeneity and isotropy are neither required nor excluded. Based on these general results, computable bounds are developed for the overall stress and strain (strain-rate) potentials of solids of any shape and inhomogeneity, subjected to any set of consistent boundary data. The bounds can be improved by incorporating additional material and geometric data specific to the given finite heterogeneous solid. Any numerical (finite-element or boundary-element) or analytical solution method can be used to analyze any subregion under uniform boundary tractions or linear boundary displacements, and the results can be incorporated into the procedure outlined here, leading to exact bounds. These bounds are not based on the equivalent homogenized reference solid (discussed in Sections 3 and 4). They may remain finite even when cavities or rigid inclusions are present. Complementary to the above-mentioned results, for linear cases, eigenstrains and eigenstresses are used to homogenize the solid, and general exact bounds are developed. In the absence of statistical homogeneity, the only requirement is that the overall shape of the sample be either parallelepipedic (rectangular or oblique) or ellipsoidal, though the size and relative dimensions of the sample are arbitrary. Then, exact analytically computable, improvable bounds are developed for the overall moduli and compliances, without any further assumptions or approximations. Bounds for two elastic parameters are shown to be independent of the number of inhomogeneity phases, and their sizes, shapes, or distribution. These bounds are the same for both parallelepipedic and ellipsoidal overall sample geometries, as well as for the statistically homogeneous and isotropic distribution of inhomogeneities. These bounds are therefore universal. The same formalism is used to develop universal bounds for the overall non-mechanical (such as thermal, diffusional, or electrostatic) properties of heterogeneous materials.
Failure Prediction for Cross-Rolled Beryllium Sheet Material
Authors: Roschke P. , Mascorro E.
Published: February 2008

A failure model for cross-rolled beryllium SR-200 sheets is developed for material loaded in a complex state of stress. Coefficients of the Tsai-Wu criterion are determined from a series of special laboratory experiments. Tests include circular plates loaded by a concentric ring, as well as in-plane compression and off-axis plate specimens. Complex states of stress lead to brittle failure of the anisotropic material. Failure surfaces obtained from the criterion form a family of ellipses when plotted in standard Cartesian coordinates. The criterion is incorporated into a general purpose finite element analysis code. Numerical simulation incrementally applies loads to a structural component that is being designed and checks each nodal point in the model for exceedance of the failure criterion. To demonstrate applicability of the predictive capability of the criterion, a 2.54-mm thick beryllium plate is placed under clamped edge conditions and loaded to failure by a central transverse point load. A numerical model of the structure predicts the failure load to within three percent.
Optimization of the Manufacturing Process of a Titanium Aluminide Metal Matrix Composite Using a Viscoplastic Constitutive Theory
Authors: Sherwood J. A. , Quimby H. M.
Published: February 2008

The thermomechanical behavior of a titanium aluminide metal matrix composite reinforced with silicon carbide fibers is computationally investigated to determine an optimum manufacturing process. The investigations are completed using the Ramaswamy-Stouffer constitutive model and the finite element method. Hold times at a given temperature were used in an effort to allow the residuals stresses to relax. However, the subsequent temperature changes erased the benefit of such holds. Thermomechanical cycling was determined to be the optimum method for reducing the residual stress field after cooldown from consolidation.
An Experimental Investigation Into the Relationship Between Temperature-Time History and Surface Roughness in the Spray Quenching of Aluminum Parts
Authors: Bernardin John D. , Mudawar Issam
Published: February 2008

Repeated heat-quench cycles of Al-1100 samples resulted in increased surface roughness and corresponding shifts in the temperature-time cooling curve towards shorter overall quench periods. Three different types of initial surface roughness were applied to the test samples: polished, particle blasted, and milled finishes. For each of the three test surfaces, cooling curve shifts during repeated heat-quench cycles were accompanied by surface roughening, the shift was smallest with the milled sample. The surface roughness was examined with the aid of scanning electron microscopy, surface contact profilometry, and X-ray photoelectron spectroscopy. Surface profiles obtained via the profilometer revealed, on a relative basis, significant changes in surface roughness on the polished and particle blasted surfaces but not on the milled (roughest) surface. The roughening was the result of (a) hydrogen diffusion associated with oxidation, (b) oxidation buildup, and, to a lesser extent, (c) expulsion of impurities along dendrite boundaries. The hydrogen diffusion caused localized pressure buildup within the surface and along grain boundaries resulting in the formation of both microscopic (1 to 10 μm) features on the polished and particle blasted surfaces and relatively large (20 to 1000 μm) bumps and blisters on the particle blasted surface. It is shown how these wide spectrum surface roughness features affect cooling rate by (a) raising the Leidenfrost temperature separating the film and transition boiling regimes, (b) increasing the number of boiling sites on the quenched surface, and (c) altering the impact dynamics of the spray drops.
Nonunique Dynamic Equilibrium Constitutive Relation of Metal Powder Depending on its Microstructure
Authors: Sano Yukio , Miyagi Kiyohiro , Arathoon Peter
Published: February 2008

It was observed in an earlier work by Morimoto et al. [Inst. Phys. Conf. Ser. No. 70, Oxford 1984, p. 427] that the dynamic compact of an aluminium powder medium had greater flakiness and contiguity ratio than the static compact of the same density. This observed difference in micro structure is used to explain their result that the dynamic pressure of the medium is higher than the static pressure for a given density: the degree of rotation of particles during compaction is assumed to decrease for higher strain rates, because of the shorter time available, causing an increase in plastic particle deformation in the compaction direction, and increased resistance to the compaction. The normal Hugoniot equation derived, in which the mean strain rate averaged over a single steady wavefront is introduced, indicates that a rise of the normal Hugoniot with an increase in the strain rate results macroscopically from the increase in the propagation velocity of the wavefront. The multiwave Hugoniot equation is found to depend on the strain rate history of a given material. In compactions of a metal powder medium by punch impact, the wavefronts passing through the medium are approximately steady if the punch mass is sufficiently larger than the medium mass. But both the number of wavefronts arising during the compaction and the amplitudes of the strain waves, and hence the strain rate histories, vary with compaction conditions such as punch mass and initial punch velocity. This implies that a dynamic equilibrium constitutive relation for the medium will depend on the compaction conditions, and therefore cannot be determined uniquely for any two compactions.
Constitutive Modeling of the Visco-Plastic Response of Hastelloy-X and Aluminum Alloy 8009
Authors: Rowley M. A. , Thornton E. A.
Published: February 2008

The viscoplastic behavior of advanced, high temperature, metallic alloys is characterized using the Bodner Partom unified constitutive model. Material parameters for both Hastelloy-X and Aluminum alloy 8009 are obtained for this model. The Bodner Partom constitutive model is summarized, and a detailed approach for determining the model parameters from experimental data is reviewed. Experimental methods for obtaining the mechanical test data are described. Bodner-Partom model parameters are determined from data obtained in uniaxial, isothermal, monotonie tension or compression tests and isothermal creep tests. Model predictions from the parameters determined are generated and compared to experimental data.
Densification Forming of Alumina Powder—Effects of Power Law Creep and Friction
Authors: Kwon Y. S. , Kim K. T.
Published: February 2008

High temperature forming processes of alumina powder compacts were analyzed by using constitutive equations which are capable of predicting densification and grain growth under diffusional creep and power law creep. Experimental results for alumina powder compacts were compared with finite element calculations by using the constitutive equations. The effects of friction between alumina powder compact and punches during sinter forging of alumina powder compacts were also investigated. Densification mechanism maps of alumina powder, which can be used for the optimization of various process variables, were constructed under hot pressing and general states of stresses.
Carbide Coarsening During Creep in 12 Percent CrMoV Steel
Authors: Wu Rui , Sandstro¨m Rolf
Published: February 2008

Carbide coarsening has been investigated in a 12 percent CrMoV steel. Studies in the gauge length (creep exposed) and in the head (stress free ageing) for both interrupted and ruptured creep specimens tested at an initial stress of 80 MPa at various temperatures and at 600°C at different initial stresses have been performed. The measured quantities include hardness, carbide sizes in the tempered martensite, at the former austenite grain boundaries and at the δ-ferrite boundaries as well as mean free distance between carbides, total number of carbides, and carbide size distribution. The contributions to the increase of strain rate in the tertiary creep are discussed in terms of plastic deformation, cavitation accumulation, and microstructural degradation. By using a strain and strain rate relation, expressions to quantitatively account for each contribution to increase of strain rate are given. The increase of strain rate, thereby rupture, is mainly caused by the microstructural degradation due to carbide coarsening and by the cavitation accumulation.
A Unified Approach to Physically Based Weakest-Link Theories for Multiaxial Fracture of Ceramics
Authors: Furgiuele Franco M. , Luchi M. Laura
Published: February 2008

The paper discusses two physically based weakest-link approaches, commonly adopted to evaluate the reliability of ceramic components in multiaxial states of stress (namely, Evans’ multiaxial elemental strength method and Batdorf’s flaw density approach) whose equivalence has been recently proven. It is shown here how the two formulations can be simultaneously derived from the basic assumptions and simply regarded as two different ways to evaluate the same integral. Differences in computational efficiency yielded by the two different integration schemes are also illustrated.
Determination of Biaxial Residual Stresses by a Holographic-Hole Drilling Technique
Authors: Makino A. , Nelson D. V. , Fuchs E. A. , Williams D. R.
Published: February 2008

A technique is described for the rapid determination of residual stresses through the combined use of hole drilling and holographic interferometry. A small diameter blind hole is drilled into a part containing residual stresses and the displacement field caused by localized stress relief is registered using holographic interferometry instead of a strain gage rosette. The optical interference fringe pattern created in the hologram upon release of stress is analyzed by a fringe counting method that allows stresses to be computed quickly. A comparison of stresses determined by the holographic hole drilling technique with different known biaxial residual stresses is shown.
Determination of Shear Stress-Strain Curve From Torsion Tests for Loading-Unloading and Cyclic Loading
Authors: Wu Han-Chin , Xu Zhiyou , Wang Paul T.
Published: February 2008

This paper discusses a method, based on Nadai’s solution, which can be used to determine the true (Cauchy) shear stress-strain curve of a material by means of torsion test of a solid shaft. The method is shown to be applicable to loading, unloading and cyclic loading. It is also applicable to fixed-end torsion of a solid shaft in the large shear strain range. A modified method has also been derived for the case of free-end torsion of a tubular specimen in the large strain range.
Modeling of High Homologous Temperature Deformation Behavior Using the Viscoplasticity Theory Based on Overstress (VBO): Part II—Characteristics of the VBO Model
Authors: Tachibana Yukio , Krempl Erhard
Published: February 2008

Characteristics of the high homologous temperature VBO model under extreme conditions such as very fast and very slow tensile tests, long-term-creep and relaxation tests are investigated via numerical experiments and analysis. To this end, material constants of Alloy 800H determined from other tests in Part I were utilized for the prediction. Although no experiments are available for the extreme conditions, the predictions are plausible. For cyclic, strain controlled hold-time tests the predictions compare well with sparse experimental data. The results give confidence that VBO can be used to predict the long-term behavior at high homologous temperature once the constants have been determined from regular, short-term tests.
On the Stability of Biaxial Stretching With Application to the Optimization of Superplastic Blow-Forming
Authors: Ding X. D. , Zbib H. M. , Hamilton C. H. , Bayoumi A. E.
Published: February 2008

The instability of biaxial stretching of thin sheets of viscoplastic metals under plane stress conditions is investigated using a linear stability analysis. An instability criterion for biaxial stretching is developed based on the assumption that localized necking initiates along the direction perpendicular to the major principal stress direction. Various “optimum” variable strain rate paths, which ensure a stable deformation of the sheet without neck formation, are computed for different strain ratios based on the instability analysis. The variable strain rate paths are applied in the finite element modeling of the superplastic uniaxial extension of a tabular specimen and supe´rplastic blow-forming of a hemisphere. A reduction of forming time is achieved compared with the established constant strain rate forming method, while uniformity in the thickness distribution of the formed parts are maintained.
A Phenomenological Model for Cyclic Plasticity
Authors: Chiang Dar-Yun
Published: February 2008

A phenomenological model is proposed for cyclic plasticity based on the concept of distributed elements, which is capable of reflecting microstructural behavior of real materials under multiaxial cyclic loading conditions. By investigating the detailed behavior of the model, various important phenomena and effects of materials in cyclic plasticity can be elucidated. Generalization of the model is also done to include cyclic hardening effects. A thorough understanding of these complicated response mechanisms and material properties provides useful insight and guidelines for validating analytical models and for performing experimental studies in the related areas of cyclic plasticity.
Process-Independent Force Characterization for Metal-Cutting Simulation
Authors: Stephenson D. A. , Bandyopadhyay P.
Published: February 2008

Obtaining accurate baseline force data is often the critical step in applying machining simulation codes. The accuracy of the baseline cutting data determines the accuracy of simulated results. Moreover, the testing effort required to generate suitable data for new materials determines whether simulation provides a cost or time advantage over trial-and-error testing. The efficiency with which baseline data can be collected is limited by the fact that simulation programs do not use standard force or pressure equations, so that multiple sets of tests must be performed to simulate different machining processes for the same tool-workpiece material combination. Furthermore, many force and pressure equations do not include rake angle effects, so that separate tests are also required for different cutter geometries. This paper describes a unified method for simulating cutting forces in different machining processes from a common set of baseline data. In this method, empirical equations for cutting pressures or forces as a function of the cutting speed, uncut chip thickness, and tool normal rake angle are fit to baseline data from end turning, bar turning, or fly milling tests. Forces in specific processes are then calculated from the empirical equations using geometric transformations. This approach is shown to accurately predict forces in end turning, bar turning, or fly milling tests on five common tool-work material combinations. As an example application, bar turning force data is used to simulate the torque and thrust force in a combined drilling and reaming process. Extrapolation errors and corrections for workpiece hardness variations are also discussed.
Strain Measurement in the Wavy-Ply Region of an Externally Pressurized Cross-Ply Composite Ring
Authors: Gascoigne H. E. , Abdallah M. G.
Published: February 2008

Ply-level strains are determined in the cross-section of an externally pressurized cross-ply (3:1 circumferential to axial fiber ratio) graphite-epoxy ring containing an isolated circumferential wavy region. A special test fixture was used which permitted measuring orthogonal displacement components in the wavy area using moire´ interferometry as the pressure was increased. Strain components were determined at selected locations in the wavy area up to approximately 90 percent of failure pressure. The study shows: (1) Large interlaminar shear strains, which are non-existent in the “perfect” ring, are present near the wave inflection points; (2) The wavy plies generate increased interlaminar normal compressive strains in both circumferential and axial plies along a radial line coinciding with maximum wave amplitude; and (3) Nonlinear strain response begins at approximately 60 percent of failure pressure.
Analysis of the Failure of Ceramics Due to Subcritical Crack Growth
Authors: Hild Franc¸ois , Marquis Didier , Kadouch Olivier , Lambelin Jean-Pierre
Published: February 2008

Failure conditions are assessed when ceramics exhibit Subcritical Crack Growth from preexisting flaws. In the framework of the weakest link theory and independent events hypothesis, a reliability analysis is carried out by modeling flaw distributions and crack growth laws. Experimental data obtained on a spinel Mn Zn ferrite subjected to five different load rates are analyzed by using an expression for the failure probability accounting for Subcritical Crack Growth.
Surface Strains Due to Face Loading of a Slot in a Layered Half-Space
Authors: Prime M. B. , Finnie I.
Published: February 2008

A solution is presented that will allow the compliance method for residual stress measurement to be applied to layered materials. The solution is for surface strains due to arbitrary normal stress loading on the faces of a slot in a layered half-space. The materials are homogeneous isotropic elastic with different elastic constants and the slot may penetrate into the substrate. The solution is accomplished using the body force method and the solution for a point force in two bonded half spaces. The results indicate that, for residual stress measurement, the effects of the substrate properties are significant for materials with elastic moduli differing by 50 percent or more when the slot penetrates to at least one-half of the layer thickness.
Cutting Forces in Orthogonal Cutting of Unidirectional GFRP Composites
Authors: Caprino G. , Nele L.
Published: February 2008

The results of orthogonal cutting tests carried out on unidirectional glass fiber reinforced plastic composites, using HSS tools, are presented and discussed. During the tests, performed on a milling machine at very low cutting speed to avoid thermal effects, the cutting speed was held constant and parallel to the fibre direction. Three parameters, namely the tool rake angle α, the tool relief angle γ, and the depth of cut t, were varied. According to the experimental results, the horizontal force per unit width, Fhu, undergoes a dramatic decrease, never verified for metals, with increasing α. Besides, Fhu is only negligibly affected by the relief angle, and linearly increases with t. Similarly to metals, an effect of the depth of cut on the specific energy (size effect) is found also for composites. However, the presented results indicate that the size effect can be analytically modeled in a simple way in the case of composites. The vertical force per unit width, Fvu, exhibits a marked reduction when the relief angle is increased. Fvu, is also very sensitive to the rake angle: the lower α the higher is Fvu. It is shown that this behavior probably reflects a strong influence of the rake angle on the forces developing at the flank. A linear dependence of the vertical force on the depth of cut is also demonstrated. Finally, the experimental data are utilized to obtain empirical formulae, allowing an approximate evaluation of cutting forces.
Shear Strength of a Thermal Barrier Coating Parallel to the Bond Coat
Authors: Cruse T. A. , Dommarco R. C. , Basti´as P. C.
Published: February 2008

The static and low cycle fatigue strength of an air plasma sprayed (APS) partially stabilized zirconia thermal barrier coating (TBC) is experimentally evaluated. The shear testing utilized the Iosipescu shear test arrangement. Testing was performed parallel to the TBC-substrate interface. The TBC testing required an innovative use of steel extensions with the TBC bonded between the steel extensions to form the standard losipescu specimen shape. The test method appears to have been successful. Fracture of the TBC was initiated in shear, although unconstrained specimen fractures propagated at the TBC-bond coat interface. The use of side grooves on the TBC was successful in keeping the failure in the gage section and did not appear to affect the shear strength values that were measured. Low cycle fatigue failures were obtained at high stress levels approaching the ultimate strength of the TBC. The static and fatigue strengths do not appear to be markedly different from tensile properties for comparable TBC material.
Easy-to-Compute Tensors With Symmetric Inverse Approximating Hencky Finite Strain and Its Rate
Authors: Bazˇant Zdeneˇk P.
Published: February 2008

It is shown that there exist approximations of the Hencky (logarithmic) finite strain tensor of various degrees of accuracy, having the following characteristics: (1) The tensors are close enough to the Hencky strain tensor for most practical purposes and coincide with it up to the quadratic term of the Taylor series expansion; (2) are easy to compute (the spectral representation being unnecessary); and (3) exhibit tension-compression symmetry (i.e., the strain tensor of the inverse transformation is minus the original strain tensor). Furthermore, an additive decomposition of the proposed strain tensor into volumetric and deviatoric (isochoric) parts is given. The deviatoric part depends on the volume change, but this dependence is negligible for materials that are incapable of large volume changes. A general relationship between the rate of the approximate Hencky strain tensor and the deformation rate tensor can be easily established.
Prediction of Extent of Heat Affected Zone in Laser Grooving of Unidirectional Fiber-Reinforced Plastics
Authors: Pan C. T. , Hocheng H.
Published: February 2008

Laser has been widely used in various industrial applications including machining. However, in shaping operation of composite material after curing, thermal damage associated with laser energy can be produced. It leads to poor assembly tolerance and long-term performance deterioration. The current research investigates the anisotropic formation of the heat affected zone (HAZ) in unidirectional fiber-reinforced plastics induced by laser grooving. Preliminary analytical and experimental analysis reveal that the laser energy per unit length and fiber orientation-dependent thermal conductivity primarliy determine the induced thermal damage. The extent of HAZ is estimated by the isotherm of the matrix char temperature. Heat conduction is maximum along the fibers, and the HAZ shape is thus affected by the beam scanning direction relative to fiber orientation. The study investigates the grooving of laminated unidirectional carbon/epoxy, which demonstrates clear thermal damage in 90 degree (i.e., perpendicular grooving), 60 degree, 30 degree, and 0 degree (i.e., parallel grooving) relative to the fiber axis. A theoretical analysis based on moving point heat source is adopted to determine the extent of thermal damage in correlation with process parameters and material properties. Mirror Image Method is used for specimen of finite thickness. Considerations of temperature-dependence of thermal conductivity and the emmerged heat source further improve the prediction of HAZ. While HAZ in grooving along the principal material axes can be solved analytically, conductivity ellipsoid and finite difference can calculate the extent of HAZ induced by grooving in any direction relative to fiber axis.
Dynamics of Thick Viscoelastic Beams
Authors: Johnson A. R. , Tessler A. , Dambach M.
Published: February 2008

A viscoelastic higher-order thick beam finite element formulation is extended to include elastodynamic deformations. The material constitutive law is a special differential form of the Maxwell solid, which employs viscous strains as internal variables to determine the viscous stresses. The total time-dependent stress is the superposition of its elastic and viscous components. In the constitutive model, the elastic strains and the conjugate viscous strains are coupled through a system of first-order ordinary differential equations. The use of the internal strain variables allows for a convenient finite element formulation. The elastodynamic equations of motion are derived from the virtual work principle. Computational examples are carried out for a thick orthotropic cantilevered beam. Relaxation, creep, relaxation followed by free damped vibrations, and damping related modal interactions are discussed.
Analysis for Cold Die Compaction of Stainless-Steel Powder
Authors: Kwon Y. S. , Lee H. T. , Kim K. T.
Published: February 2008

Densification behavior of 316L stainless-steel powder under die pressing was studied. The friction effects between the powder and the die wall under different die pressing modes were also investigated. The elastoplastic constitutive equations, based on the yield functions by Fleck and Gurson and by Shima and Oyane, were implemented into a finite element program to simulate die compaction processes. The friction coefficient between the powder and the die wall was determined from the relationship between the compaction pressure and the ejection pressure. Finite element calculations were compared with experimental data for densification and deformation of 316L stainless-steel powder under single and double action die pressing.
Mechanical Properties of Aircraft Materials Subjected to Long Periods of Service Usage
Authors: Scheuring J. N. , Grandt A. F.
Published: February 2008

This paper evaluates changes in the behavior of aircraft materials which result from aging and/or corrosion that occurs during long periods of service usage. The primary objective was to determine whether damage tolerant analyses for older aircraft should employ updated properties that more accurately represent the current state of the material, or if the virgin material properties continue to properly characterize the aged/corroded alloy. Specifically, tensile stress-strain curves, cyclic stress life (SN) tests, and fatigue crack growth tests were used to characterize the “aged aircraft” material. These properties were compared with handbook properties for virgin material of the same pedigree. The aluminum alloys tested were obtained from fuselage and wing panels of retired KC-135 aircraft. Computer controlled tests were conducted using specimens machined from the retired aircraft components. Different configurations were used to observe the effects of aging and/or corrosion on material behavior. In the crack growth specimens, various levels of corrosion were observed, thus the crack growth rates could be categorized as a function of the level of corrosion present. The SN and da/dN-ΔK curves for the “aged” only materials were compared with the fatigue properties of virgin material of the same alloy. Similar comparisons were performed for the tensile stress-strain properties.
Modeling of High Homologous Temperature Deformation Behaviour Using the Viscoplasticity Theory Based on Overstress (VBO): Part III—A Simplified Model
Authors: Tachibana Yukio , Krempl Erhard
Published: February 2008

A simplified version of the Viscoplasticity Theory Based on Overstress (VBO) is applied to modeling of Alloy 800H at homologous temperatures between 0.6 and 0.8 The present formulation is simplified to the extent that omission of any constant would deprive the model to represent phenomena. Examples of such a phenomenon are tertiary creep and static recovery. The three-dimensional formulation of the simplified model for Alloy 8OOH at high homologous temperature needs a total of 10 constants. The parent theory from which the simplified model is derived has 18 constants that must be determined from experiments. The simplified theory has essentially the same modeling capability as the parent theory. There are differences in the predictions of the two versions for very long-time behaviour for which no test data are available. When material data are available for comparison the modeling of the regular and the simplified versions are very good and show roughly the same amount of deviation. The results suggest that the simplified version should be tried first when a given material has to be modeled.
Application of the Taylor Polycrystal Plasticity Model to Complex Deformation Experiments
Authors: Butler G. C. , Graham S. , McDowell D. L. , Stock S. R. , Ferney V. C.
Published: February 2008

The extended Taylor assumption of uniform deformation gradient among grains was applied in 3-D polycrystal plasticity simulations for complex loading paths at finite strain for OFHC Cu using the Los Alamos polycrystal plasticity (LApp) code (Kocks et al., 1994). Comparisons of both stress-strain behavior and texture evolution, with and without the inclusion of latent hardening effects, show that the theory overpredicts the rate of development of texture in both torsion and compression. Compression stress-strain behavior was accurately predicted, but the effect of the prestrain, either compressive or torsional, on subsequent nonproportional deformation response was inadequately modeled. Some possible sources of the discrepancies are discussed, including the low order nature of the extended Taylor model for intergranular interactions as compared to self-consistent models, low order formulation of slip system hardening, lack of accounting for formation of dislocation substructure within grains, and the possible role of anisotropic elasticity. Deformation-induced anisotropy and accommodation of intergranular constraint afforded by geometrically necessary dislocation substructure formation is viewed as the key neglected element of the formulation.
Analysis of Forming Limits Using the Hill 1993 Yield Criterion
Authors: Xu Siguang , Weinmann Klaus J. , Chandra Abhijit
Published: February 2008

Forming limits of thin sheets are investigated using a yield criterion recently proposed by Hill (1993). This criterion utilizes five independent material parameters, which can be determined from uniaxial and balanced biaxial experiments, to describe a wide range of material properties of sheet metals, including the anomalous behavior of aluminum. In the present work, a bifurcation analysis is pursued to predict the onset of localized necking in strain rate insensitive sheet materials. A detailed parametric study is then conducted to evaluate the effect of various material parameters on the positive minor strain side of the forming limit diagram. It is observed that limit strains are strongly dependent on the shape of the yield locus. Forming limits predicted using Hill’s 1993 yield criterion are compared with those predicted using Hill’s 1948 and 1979 criteria. Results from the bifurcation analysis are also compared with experimental observations, as well as the limit strain predicitons based on the M-K analysis.
The Interaction Between Point Defects and Edge Dislocation in BCC Iron
Authors: Shastry Vijay , Diaz de la Rubia Tomas
Published: February 2008

We present results of atomistic simulations of the interaction between self interstitial atoms and vacancies with edge dislocations in BCC iron. The calculations are carried out using molecular dynamics with an energy minimization scheme based on the quasi-Newton approach and use the Finnis-Sinclair interatomic potential for BCC iron developed by Ackland et al. Large anisotropy in the strain field of self interstitials is observed and it causes strong interaction with edge dislocations even when the defect is located on the dislocation glide plane. For vacancies, the relaxation volume is smaller and much more isotropic, which results in a far weaker interaction with the dislocation. A temperature dependent capture radius for vacancies and self interstitials is extracted from the simulations. The difference between the capture radii of vacancies and self interstitials is used to define the sink strength of the dislocation. Large deviations are observed from the predictions of elasticity based on treating point defects as isotropic dilatational centers. Further, the capture radius of edge dislocations in BCC iron is observed to be small and is of the order of 1–3 nm for self interstitials.
Experimental Study of Internal Variable Evolution in SS304L, at Multiple Rates and Temperatures
Authors: Harley E. J. , Miller M. P. , Bammann D. J.
Published: February 2008

Most metals exhibit a deformation-induced uniaxial yield strength asymmetry. Interpreted within the context of macroscale viscoplastic models, it is conventional to describe this yield strength asymmetry with an isotropic hardening variable, κ, and a kinematic hardening variable, α. The focus of this work was to conduct a series of reverse yield experiments to directly measure the evolution of α and κ in 304L stainless steel (SS304L) over large ranges of temperatures and strain rates. We found that the material exhibited inelastic behavior immediately on changing the straining direction. We discussed the ramifications of this behavior on our goal to directly measure α and κ within the context of an isotropic/kinematic hardening model framework. We also explored the capability of the model to simulate the behavior of SS304L under different loading conditions across a wide range of temperatures and strain rates.
Laser-Induced Deformation Patterns in Thin Films and Surfaces
Authors: Walgraef Daniel
Published: February 2008

The coupling between surface deformation and defect motion may be at the origin of deformation patterns in thin films under laser irradiation. We analyze the dynamics of laser-induced vacancy densities and deformation fields and show how it triggers deformational instabilities, in the case of uniform and focused laser irradiation. Pattern selection analysis is performed, through linear, nonlinear, and numerical methods. In irradiation with extended beams, we show that, according to the relative importance of nonlinearities arising from the defect or from the bending dynamics, square, hexagonal or even quasi-periodic patterns are selected. It appears, furthermore, that one-dimensional gratings are always unstable in isotropic systems. In irradiation with focused laser beams, rose deformation patterns, with petal number increasing with laser intensity, naturally arise in this model, in qualitative agreement with experimental observations. These results claim for more systematic and quantitative experimental investigations of deformational pattern formation under laser irradiation.