bluuebunny/crossref_metadata_2025 huggingface dataset:
A Unified Constitutive Model for the Inelastic Uniaxial Response of Rene’ 80 at Temperatures Between 538C and 982C
Authors: Ramaswamy V. G. , Stouffer D. C. , Laflen J. H.
Published: April 2008

The objective of this research is to develop a constitutive equation for the uniaxial monotonic and cyclic response of Rene’80 between the temperatures of 538C and 982C. The constitutive equation is accompanied by experimental data for the evaluation of the material constants. Extensive verification is achieved through the successful correlation of tensile and creep response and prediction of mechanical cycling experiments including mean stress shifts. These results also serve as a starting point for reformulating the model for the prediction of the high temperature multiaxial response of Rene’80 that includes torsion, proportional, and nonproportional uniaxial and torsional loading histories.
Application of the First Higher-Order (M21) Mode Rayleigh Wave to the Inspection of Stainless Steel Overlays
Authors: Bray D. E.
Published: April 2008

Efficient inspection of stainless steel overlays appears to present a particularly challenging problem due to the anisotropy that is characteristic of that material. An improved inspection technique may be available, however, when the dissimilar properties of the overlay and the base material are utilized. Higher order mode Rayleigh waves which at high frequencies remain confined to the upper layer of the stainless steel material are demonstrated to be able to detect welding defects in the overlay material in a field some distance away from the probe. With this technique, a larger area may be scanned with each probe placement rather than the point contact probe inspection method that is typically used.
Dispersion Investigation in the Split Hopkinson Pressure Bar
Authors: Gong J. C. , Malvern L. E. , Jenkins D. A.
Published: April 2008

Dispersion of an elastic wave propagating in a 76.2-mm-diameter (3 in.) Split Hopkinson Pressure Bar system was investigated with two consecutive pulses recorded in the transmitter bar. Assuming that the dispersive high frequency oscillatory components riding on the top of the main pulse originate from the first mode vibration, the dispersion was corrected by using the Fast Fourier Transform (FFT) and Fourier series expansion numerical schemes. The good agreement validates the assumption that only the first mode was significant. The dispersion correction technique was employed in a test of a concrete specimen having the same diameter as that of the SHPB. Better agreement of the two specimen-bar interface stresses versus time and fewer oscillations in the stress-strain curve demonstrated advantages of the application of dispersion corrections.
Strain Energy Release Rate Characterization of Structural Adhesive Bonds to Primer Electrodeposited on Steel
Authors: Schmueser D. W.
Published: April 2008

Structural applications of adhesive bonding have been increasing in recent years due to improvements in the types of adhesives available and in improved knowledge of bondline procedures. Consequently, there exists a demand for precise numerical modeling of adhesive joint behavior, particularly along bondline interfaces where low surface energy adhesives contact high surface energy metallic oxides. Recent experimental studies have shown that adhesive bond strength for steel substrates which had been cathodically electroprimed (ELPO-primed) before bonding were significantly higher than strengths for unprimed steel substrates. Subsequent finite element studies showed a correlation with the experimental results in that peak stress values at the midplane of single-lap-shear (SLS) joints were reduced for primed surfaces. The present study provides a qualitative examination of debond behavior at primed and unprimed bonded surfaces by applying finite element analyses to compute opening (Mode I) and shear (Mode II) components of the strain energy release rate for small debond lengths at selected locations through the bondline thickness of the SLS joint. The bondline-thickness locations where the total strain energy release rate was a minimum correlate well with experimentally observed failure surfaces. In addition, a significant reduction in Mode I was computed for the primed compared to the unprimed joint. This reduction in peel response is consistent with the enhanced strength of the primed joints.
Delamination Effects on Composite Shells
Authors: Chang Fu-Kuo , Kutlu Zafer
Published: April 2008

An analytical investigation was performed to study the effect of delamination on the response of cylindrical composite shells subjected to external loadings. It was of particular interest to determine the buckling load and the post-buckling behavior of externally pressurized cylindrical composite shells containing delaminations. An analytical model was developed that consists of a structural analysis for calculating the global deformations of the structures and a fracture analysis for determining the delamination growth in the structures. A nonlinear finite element code based on the updated Lagrangian formulation was developed for the model. Based on the results of calculations, it was found that delamination can significantly affect the buckling load and response of cylindrical composite shells subjected to externally pressurized loadings, depending upon the initial length and location of the delamination, ply orientation and laminate curvature. The calculated strain energy release rate at the crack tips indicates that delamination growth occurs in the wake of buckling due to Mode II shear fracture.
Creep Crack Growth in an Austenitic Cr-Ni-Mn Steel
Authors: Tanaka M. , Iizuka H. , Ashihara F.
Published: April 2008

Effects of grain-boundary sliding and strenthening by serrated grain boundaries on creep-crack growth are investigated using an austenitic 21Cr-4Ni-9Mn steel at 973 K in air. In surface notched specimens, crack growth rate is lower in specimens with serrated grain boundaries than in those with normal straight grain boundaries at the same stress intensity factor (K1), but the difference in crack growth rate between these specimens decreases with crack growth. In smooth bar specimens, growth rate of the largest surface crack is correlated with the average amount of grain-boundary sliding, although a unique relationship is not found between them. Grain-boundary sliding controls the crack growth when the crack size is small, but total creep deformation becomes important and crack linkage occurs with increasing crack length, thus reducing the strengthening effects of serrated grain boundaries.
A Bilinear Constitutive Model for Isotropic Bimodulus Materials
Authors: Vijayakumar K. , Ashoka J. G.
Published: April 2008

Proper formulation of stress-strain relations, particularly in tension-compression situations for isotropic biomodulus materials, is an unresolved problem. Ambartsumyan’s model [8] and Jones’ weighted compliance matrix model [9] do not satisfy the principle of coordinate invariance. Shapiro’s first stress invariant model [10] is too simple a model to describe the behavior of real materials. In fact, Rigbi [13] has raised a question about the compatibility of bimodularity with isotropy in a solid. Medri [2] has opined that linear principal strain-principal stress relations are fictitious, and warned that the bilinear approximation of uniaxial stress-strain behavior leads to ill-working bimodulus material model under combined loading. In the present work, a general bilinear constitutive model has been presented and described in biaxial principal stress plane with zonewise linear principal strain-principal stress relations. Elastic coefficients in the model are characterized based on the signs of (i) principal stresses, (ii) principal strains, and (iii) on the value of strain energy component ratio ER greater than or less than unity. The last criterion is used in tension-compression and compression-tension situations to account for different shear moduli in pure shear stress and pure shear strain states as well as unequal cross compliances.
Effect of Delamination on the Nonlinear Behavior of Composite Laminated Beams
Authors: Sheinman I. , Soffer M.
Published: April 2008

This paper presents a parametric study of the effect of delamination, and of initial imperfection, on the overall nonlinear behavior of laminated composite beams. The study is based on geometrical nonlinear analysis with the Von-Karman kinematic approach. It is shown that the bifurcation point provides not more than an indication of the buckling behavior, and that the full nonlinear analysis is needed for predicting the load-carrying capacity. It was also found that the delaminated beam is sensitive to initial imperfection.
Dynamic Crushing of Strain-Softening Cellular Structures—A One-Dimensional Analysis
Authors: Shim V. P. W. , Tay B. Y. , Stronge W. J.
Published: April 2008

A one-dimensional model for impact deformation of open-celled structures is used to examine the effects of material elasticity, cell inertia, cell compliance characteristics and limited crushability. Analyses show that these parameters govern the development, distribution and severity of crushing in periodic, open-celled structures where individual cells strain-soften; coupled with impact velocity, they dictate the deceleration imparted to a colliding body. Comparisons with experiments on the impact crushing of metal tube arrays and rigid polyurethane foam yield reasonable qualitative correlation. A conclusion is drawn on the desired nature of cellular systems for efficient impact dissipation.
An Assessment of Add-on Energy Absorbing Devices for Vehicle Crashworthiness
Authors: Lin Kuang-Huei , Mase G. Thomas
Published: April 2008

An alternative approach to vehicle crashworthiness improvement by inserting add-on nonstructural energy absorbing (EA) devices in the unutilized space in series with existing load paths is studied conceptually. Vehicle-barrier impact simulations are conducted to determine the energy absorption and crushable space requirements for the add-on devices. Based on the experimental data available in the literature, a number of materials are identified as being capable of meeting these requirements. Simple tubes and honeycombs in axial crushing mode are found to be more effective as add-on EA devices than complex devices such as inversion tubes. Foam filling of primary structural members in bending mode is found to be less effective in increasing energy absorbing capacity than add-on EA devices. While the study indicates a theoretical assessment of these devices, physical limitations may inhibit their usefullness. In particular, many of the devices are highly directional in nature.
Characterization of Notched Ductile Failure With Continuum Damage Mechanics
Authors: Chow C. L. , Sze K. Y.
Published: April 2008

A recently developed anisotropic model of continuum damage mechanics has been applied successfully to characterize ductile fracture of cracked plates under mode I and mixed mode failures. The damage model is further extended in this investigation to examine its applicability to include notch ductile fracture of thin plates containing a circular hole. Two hole sizes of 16 mm and 24 mm diameters are chosen and the specimen material is aluminum alloy 2024-T3. Fracture loads of the plates are predicted by the damage model and compared satisfactorily with those determined experimentally. This investigation provides an important confirmation that not only the anisotropic model of continuum damage mechanics but also the same failure criterion developed can be effectively employed to characterize both ductile fracture for plates containing an isolated macro-crack or circular hole which would otherwise not be possible using the conventional theory of fracture mechanics. The successful development of the unified approach to characterize ductile failure provides a vital impetus for design engineers in the general application of the theory of continuum damage mechanics to solve practical engineering problems.
Notch Root Displacement (NRD) Approach to Predict Crack Initiation Life of Notched Specimen in High-Temperature Multiaxial Low Cycle Fatigue
Authors: Umeda Hiroshi , Sakane Masao , Ohmani Masateru
Published: April 2008

This paper describes the notch root displacement (NRD) approach to assess the crack initiation life of notched specimens in high-temperature multiaxial low cycle fatigue. Two and three-dimensional finite element method (FEM) analyses were made to estimate the local displacement at the notch root in tension, torsion, and combined tension/torsion. From the FEM analysis, a simple equation which expresses the intensity of the notch root displacement was derived and it was applied to the experimental data. The equation well correlates the crack initiation life of the notched specimen in high-temperature multiaxial low cycle fatigue.
Effect of Deformation-Induced Heating on the Cold Drawing of Polymeric Films
Authors: Tugˇcu P. , Neale K. W. , Ma´rquez-Lucero A.
Published: April 2008

The destabilizing effect of deformation-induced heating on the cold drawing of polymeric films is investigated under adiabatic and plane-strain loading conditions. An approximate method, previously devised to study the steady-state cold drawing of polymers with viscoplastic properties, is further modified to incorporate the softening effects due to temperature. Parametric studies are carried out showing the interaction of material properties with the kinematics of the process.
Microhardness of the Surface Layer of Tungsten and Molybdenum After Recrystallization With Laser Radiation
Authors: Kostrubiec F. , Walczak M.
Published: April 2008

We present results of microhardness measurements in melted local regions in molybdenum and tungsten. Microhardness has been measured by the Vickers method. Melted regions have been produced by pulsed Nd-glass laser. The emphasis is on correlation between conditions of recrystallization (energy of laser beam and method of irradiation-single pulse or multiple pulse) and the microhardness value.
Fracture Toughness JIC Prediction From Super-Small Specimens (0.2CT, 0.5MM Thick) of a Martensitic Stainless Steel HT-9
Authors: Mao Xingyuan
Published: April 2008

The fracture toughness of alloy HT-9, a martensitic stainless steel under consideration for fusion reactor applications, was determined from 0.2CT (0.5mm thick) specimens. Specimens with thicknesses of 25 (1CT), 10 (0.4CT), 3 and 0.5 (0.2CT)mm were tested to investigate the effects of specimen size on fracture toughness. 0.2CT (0.5mm thick) specimens did not satisfy ASTM E813 size requirements for a valid JIc. Fractographic examinations of the variation of stretch zone width and fracture modes along the specimen thickness were performed by scanning electron microscopy (SEM), where flat and shear fracture regions had been distinguished. A new JIc evaluation procedure for invalid specimen size is proposed using rigid plastic analysis and shear fracture measurements with fractographic observations. Predicted JIc values were compared with the JIc values obtained from valid specimen sizes. This miniaturized specimen technique may be applicable to post-irradiation fracture toughness testing.
Single Crystal Modeling for Structural Calculations: Part 1—Model Presentation
Authors: Me´ric L. , Poubanne P. , Cailletaud G.
Published: April 2008

A micro-macro model derived from slip theory is shown. It is applied to the modeling of nickel base single crystal superalloys. The experimental data include monotonic and cyclic solicitations at 950°C. The general agreement between tests and numerical simulations is good for all the studied orientations: 〈001〉, 〈011〉, 〈111〉, and 〈123〉. The model is simple enough to be implemented in a finite element code as shown in a future part of the paper.
Constitutive Modeling of Metals Under Nonproportional Cyclic Loading
Authors: Doong S. H. , Socie D. F.
Published: April 2008

A two-surface kinematic hardening model for the stress-strain response of metals under nonproportional tension-torsion cyclic loading is developed and verified with critical experiments. In this model, both the yield and limit surfaces are assumed to be ellipses in the two-dimensional stress plane to account for anisotropic cyclic hardening. Areas of the yield and limit surfaces are changed in order to model the overall isotropic cyclic hardening (or softening) behavior. The strength anisotropy is modeled by changing the ellipticity and orientation of the elliptical surfaces with respect to the stress axes. A nonproportionality parameter based on the plastic strain history is developed to estimate the cyclic hardening level under nonproportional loading. It is shown that this model is able to model a number of important deformation features of metals under complex nonproportional cyclic loading.
Measuring Residual Stresses by Hole-Drilling and Coherent Optics Techniques: A Numerical Calibration
Authors: Furgiuele F. M. , Pagnotta L. , Poggialini A.
Published: April 2008

Hole-drilling is a widely accepted method for determining residual stresses from the relaxation data obtained by a strain-gage rosette. Several researchers have recently investigated the alternative of employing interferometric techniques to reveal the displacement field produced by hole-drilling. As in the case of the standardized hole-drilling strain-gage method, proper calibration constants must be assessed so that this procedure can be effectively employed. This paper reports the displacement calibration constants derived from the results of an extensive numerical analysis. The constants proposed enable a uniform residual stress field to be determined, whatever the displacement component detected. The most commonly employed coherent optics techniques have been considered; computer-generated fringe patterns are reported and criteria are suggested to derive the stress field from fringe readings taken around the edge of the hole.
A Study on Burr Formation Mechanism
Authors: Ko Sung-Lim , Dornfeld David A.
Published: April 2008

A quantitative model of burr formation for ductile materials which does not include fracture during orthogonal machining is proposed. The burr formation mechanism is divided into three parts—initiation, development, and formation of the burr with appropriate assumptions. The mechanisms proposed are based on the observation of the behavior of workpiece material during orthogonal machining on commercial plasticine. To validate the model, orthogonal machining inside a scanning electron microscope at low speed was done with a copper workpiece and A16061-T6, A12024-T4 and A1390 were cut on a modified milling machine over a range of cutting speeds.
Optimal Design for Two-Dimensional Structures Made of Composite Materials
Authors: Sacchi Landriani G. , Rovati M.
Published: April 2008

The paper deals with the problem of finding the optimal orientation of orthotropic properties for an elastic body, subjected to a plane state of stress, in order to maximize the stiffness of the body itself. A variational formulation of the problem is presented and the computation of the necessary condition for an optimal solution is carried out. The physical meaning of such a condition is then outlined, and its generality pointed out with reference to the case of two-dimensional flexural systems. Finally, an extension of the plane stress problem is formulated, taking into account as design variables both the orientation of orthotropy axes and the mechanical properties of the material, according to a global constraint on the structural cost.
Buckling and Growth of Delamination in Thermoset and Thermoplastic Composites
Authors: Gillespie J. W. , Carlsson L. A.
Published: April 2008

Compression instability growth of through-width delaminations in composite laminates is investigated. A previously developed beam model that incorporates effects of elastic restraint at the ends of the delamination is combined with a finite element superposition model that yields the Mode I (GI) and Mode II (GII) components of the strain energy release rate. Experimental data were generated for near surface delaminations over a wide range of crack lengths in unidirectional graphite/epoxy and graphite/PEEK laminates. Good agreement between experimentally observed critical loads for crack propagation and analytical predictions was observed using a linear mixed-mode crack growth criterion.
Locating and Sizing Disbonds in Glassfibre-Reinforced Plastic Plates Using Shearography
Authors: Shang H. M. , Toh S. L. , Chau F. S. , Shim V. P. W. , Tay C. J.
Published: April 2008

Shearography is a double-exposure optical method which reveals defects in components from anomalies in interferometric fringe patterns. In this paper, disbonds of known shapes and sizes are deliberately created at different layers of glassfibre-reinforced plastic (GRP) laminates which are subsequently “vacuum-stressed” during the test. Experimental results show that both the shape and size of disbonds can be deduced easily from the boundaries of the anomalous fringe patterns; the depth of disbonds can also be estimated by counting the number of fringes appearing within these boundaries. The results also correlate well with those predicted from thin plate theory, suggesting that the response of disbonds in GRP plates during vacuum-stressing may be modelled with this theory.
Thermal Aspects of the Split-Beam Laser Welding Concept
Authors: Kannatey-Asibu Elijah
Published: April 2008

The high cooling rates normally encountered in the application of high intensity welding processes such as laser beam welding is often detrimental to the weldment, especially for high hardenability steels. To minimize this effect, the split-beam laser welding concept is proposed and analyzed. The analysis shows that even when the intensity of the single heat source is the same as the intensity of each of the dual heat sources, the resulting cooling rate at any specific temperature is lower for the dual source process than the single source process. For example, for mild steel, the cooling rate at a point 25 mm behind the heat source (where the temperature is 1364°C) was determined to be 382°C/s for the single source system, while that for a point 40 mm behind the major source (where the temperature is 1377°C) was determined to be 206°C/s for the dual heat source system. When the heat inputs for the dual system are reduced such that the total heat input is equal to that of the single source system, the resulting temperature rise is lower at all points of the weldment for the dual system. That also means a smaller weld pool size and heat affected zone. To maintain the same weld pool size and penetration as for the single heat source system then requires an increased total heat input for the dual heat source system, with the additional input depending on the spacing between the two heat sources.
A One-Dimensional, Two-Phase Flow Model for Taylor Impact Specimens
Authors: Jones S. E. , Gillis P. P. , Foster J. C. , Wilson L. L.
Published: April 2008

In this paper, a simple theoretical analysis of an old problem is presented. The analysis is more complete than earlier versions, but retains the mathematical simplicity of the earlier versions. The major thrust is to separate the material response into two phases. The first phase is dominated by strain rate effects and has a variable plastic wave speed. The second phase is dominated by strain hardening effects and has a constant plastic wave speed. Estimates for dynamic yield stress, strain, strainrate, and plastic wave speed during both phases are given. Comparisons with several experiments on OFHC copper are included.
Room Temperature Formability and Fracture Behavior of a High Strength AI-Zn-Mg Alloy
Authors: Swaminathan K. , Date P. P. , Padmanabhan K. A.
Published: April 2008

The formability and fracture behavior of a high strength, aluminum alloy made to (French) specification AFNOR 7020 is reported. The formability study included the evaluation of the room temperature forming limit diagram (FLD) of the material in the T4 temper and an analysis of the strain distribution profiles obtained in punch stretching that involved different stress states. The fracture surfaces were examined by scanning electron microscopy and a correlation between the forming and fracture behavior could be obtained.
On Compression of Rubber Elastic Sphere Over a Large Range of Displacements—Part 2: Comparison of Theory and Experiment
Authors: Tatara Y. , Shima S. , Lucero J. C.
Published: April 2008

This paper presents experimental results of simple compression of a soft rubber sphere in a very large range of forces attaining at 5000 N, presenting calculational results by a set of five equations presented in Part 1. The calculational values of approach, the radius of contact surface, and lateral expansion agree well with the experimental data in the large range of deformations. It is thus verified experimentally that the set of the equations (12), (13), (31), (40), and (43) in Part 1 is approximately valid in large deformations for rubber sphere. Program using a personal computer in calculating five quantities from the five nonlinear equations associated with the five quantities is noted.
The Overload Retardation Effect in Fatigue Crack Propagation of Worm-Like Graphite Cast Iron
Authors: Zhang Ange , Bui-Quoc Thang , Sun Xunfang
Published: April 2008

In this paper, single and multiple overloading tests under cyclic controlled stress were carried out on specimens of Worm-like Graphite Cast Iron (WGCI), a brittle material. The results showed that the overloading had a strong retardation effect on this material when the overload ratio r (ratio between the overload range and the baseline load range) is larger than 1.2. For example, the number of cycles of retardation due to overloading, N’, may be as high as ten times the cycles, N, required for the same crack length under baseline loading. In addition, for the testing conditions examined, there is no significant difference in the retardation effect under single or multiple overloading for this material. An analytical model based on the concept of crack closure and the effective stress intensity range was developed for evaluating the effect of the retardation. The development led to a correlation between the number of applied cycles and the crack size after overloading and permits to calculate the retardation cycles N’. Finally, the mechanisms attributed to the retardation effect for WGCI are discussed.
A Rate-Dependent Inelastic Constitutive Model—Part I: Elastic-Plastic Flow
Authors: Ellyin F. , Xia Z.
Published: April 2008

In this part a rate-dependent elastic-plastic constitutive model is presented which is an extension of our earlier rate-indpendent model. The effect of prior creep on the subsequent inelastic deformation is also included. The model can be used to predict inelastic processes with variable strain (stress) rates. It is shown, through comparison with the experimental results, that most of the rate-effect features of the material response can be simulated by the model. Despite the wide range of application, the model is relatively simple and incorporated a few material constants which could be easily determined from standard tests.
Computer-Aided Modeling of Polymer Processing: A Review
Authors: Tseng Ampere A. , Cheng Julius C.
Published: April 2008

Polymer processing is increasingly important ever since the rapid growth of polymer applications in the past decade. In this paper, the computational aspects of modeling the polymer behavior during its processing are reviewed. Following a discussion of the formulation of polymeric flow and heat transfer characteristics, the associated constitutive relationships are reported. The current status of the numerical techniques, as well as knowledge-based systems used in modeling of polymer processing, is then presented. Finally, a major polymer process called calendering is selected and simulated by a special finite difference technique to illustrate the procedure involved and the information revealed in modeling. Areas where further work is needed are also identified.
Analysis of Shear Banding in Plane Strain Compression of a Bimetallic Thermally Softening Viscoplastic Body Containing an Elliptical Void
Authors: Zhu Z. G. , Batra R. C.
Published: April 2008

We study plane strain thermomechanical deformations of a prismatic viscoplastic body of square cross-section and deformed at a nominal strain-rate of 5000 s−1. The body has two thin layers placed symmetrically about the horizontal centroidal axis and an elliptical void at the center. The major axis of the void coincides with the vertical centroidal axis and also with the direction of loading. The layer material differs from that of the body in only the value of the yield stress in a quasistatic simple compression test. The yield stress for the layer material is taken to be either one-fifth or five times that of the matrix material. The deformations are assumed to be symmetrical about the vertical and horizontal centroidal axes. It is found that in each case shear bands initiate from points on the traction free edges where the matrix/layer interfaces intersect them and propagate into the softer material. For the soft layer these bands initially merge into one and propagate horizontally. Subsequently, each of these bands bifurcates into two which propagate into the matrix material along the direction of the maximum shear stress. There is minimal interaction between these bands and those initiating from points slightly away from the void tips. These latter bands pass through the soft layer rather easily. When the layer material is harder than the matrix material, the material in the first quadrant is eventually divided into five subregions each of which is deforming virtually rigidly and the velocity suffers a sharp jump across the boundaries between these regions.
Elastic Buckling of Infinitely Long Specially Orthotropic Plates on Tensionless Foundations
Authors: Shahwan K. W. , Waas A. M.
Published: April 2008

The results of an analytical study on the elastic buckling of long narrow orthotropic plates resting on a tensionless foundation are reported. The motivation for the present study stems from the importance of delamination buckling as a viable mode of failure in fibrous laminated composites. When near surface delaminations undergo buckling, the buckled displacements are of one sign, because the remainder of the laminate (parent sublaminate) essentially acts like a rigid foundation. The results of the present study can be incorporated into developing delamination growth models for various loading conditions. Example results are presented for five different types of plates where one is of the isotropic type and the remaining four are of the laminated orthotropic type. Example results for two types of Graphite/Epoxy material systems (IM7/8551-7 and T300/BP907) are reported. In the laminates considered, the stacking is sequenced so that the bending constitutive constants D16 and D26 vanish. Extensive parametric analysis was performed and it was found that for the case of a simply supported plate and in the limiting case of a rigid foundation, conforming to buckled displacements of one sign, the increase in the buckling load over that of a simply supported plate but with no foundation varies between 22 and 33 percent, depending on the plate stacking sequence. On the other hand, for the clamped-free case this number was found to vary between 24 and 36 percent for all types of materials used in this study. Previous studies that addressed similar issues did not pay particular attention to the one sided buckling constraint that is placed due to physical considerations.
A Yield Criterion of Porous Materials With Anisotropy Caused by Geometry or Distribution of Pores
Authors: Hisatsune T. , Tabata T. , Masaki S.
Published: April 2008

Axisymmetric deformation of anisotropic porous materials caused by geometry of pores or by distribution of pores is analyzed. Two models of the materials are proposed: one consists of spherical cells each of which has a concentric ellipsoidal pore; and the other consists of ellipsoidal cells each of which has a concentric spherical pore. The velocity field in the matrix is assumed and the upper bound approach is attempted. Yield criteria are expressed as ellipses on the σm σ3 plane which are longer in longitudinal direction with increasing anisotropy and smaller with increasing volume fraction of the pore. Furthermore, the axes rotate about the origin at an angle α from the σm-axis, while the axis for isotropic porous materials is on the σm-axis.
EDM Surface Characterization of a Ceramic Composite TiB2/SiC
Authors: Ramulu M. , Garbini J. L.
Published: April 2008

Electrical Discharge Machined (EDM) hole surface characteristics of 20 percent Titanium diboride (TiB2) particulate and Silicon carbide (SiC) matrix composite material were investigated. The EDM hole surfaces produced by using brass, copper and graphite were examined by scanning electron microscopy (SEM) and surface profilometry to determine the surface characteristics. As-machined surfaces showed the microcracks in the recast layer, and the individual TiB2 grains were exposed on the surface. The depth of the recast structure on the surface has varied from 8 μm to less than a micrometer and was approximately proportional to the amount of impinging energy or power input. The EDM process appears to be a promising method of producing an excellent surface in electrically conductive TiB2/SiC composite under slow cutting conditions.
Acoustic Emission Monitoring of the Cutting Process—Negating the Influence of Varying Conditions
Authors: Emel E. , Kannatey-Asibu E.
Published: April 2008

Earlier work has shown tool failure monitoring using frequency-based pattern recognition analysis of acoustic emission signals to be feasible while machining under fixed cutting conditions. However, cutting conditions change quite frequently in industrial production, and since AE signals are affected by varying conditions, a model is developed based on Taylor’s expansion using experimental data obtained for various process variables and their output AE spectra, and is used to filter the influence of varying conditions on signal classification. The experimental study involved a fractional factorial experimental design which delineated effects of variables on AE generation during machining. Normalized AE spectra within the 100 to 1000 kHz range were used as system output along with the AE power. While the normalized spectra were found unaffected by changes in the depth of cut, the total AE power was also little affected by the mixed flank and crater wear, and feed rate changes. Using the model and filter designed, performance of the tool wear, chip noise and tool breakage classifier improved to 83, 99, and 97 percent classification, respectively.
Stress-Strain Equations for Some Near-Eutectic Tin-Lead Solders
Authors: Jen K. P. , Majerus J. N.
Published: April 2008

This paper presents the evaluation of the stress-strain behavior, as a function of strain-rate, for three tin-lead solders at room temperature. This behavior is critically needed for reliability analysis of printed circuit boards (PCB) since handbooks list minimal mechanical properties for the eutectic solder used in PCBs. Furthermore, most handbook data are for stable eutectic microstructure whereas PCB solder has a metastable microstructure. All three materials were purchased as “eutectics.” However, chemical analysis, volume fraction determination, and microhardness tests show some major variations between the three materials. Two of the materials have a eutectic composition, and one does not. The true stress-strain equations of one eutectic and the one noneutectic material are determined from compressive tests at engineering strain-rates between 0.0002/s and 0.2/s. The second eutectic material is evaluated using tensile tests with strain-rates between 0.00017/s and 0.042/s. The materials appear to exhibit linear elastic behavior only at extremely small strains, i.e., less than 0.0005. However, this “elastic” behavior showed considerable variation, and depended upon the strain rate. In both tension and compression the eutectic alloy exhibits nonlinear plastic behavior, i.e., strain-softening followed by strain-hardening, which depends upon the strain rate. A quadratic equation σy = σy(ε˚/ε˚0) + A(ε˚/ε˚0)ε + B(ε˚/ε˚0)ε2 fit to the data gives correlation coefficients R2 > 0.91. The coefficients σy(ε˚/ε˚0), A(ε˚/ε˚0), B(ε˚/ε˚0) are fitted functions of the normalized engineering strain rate ε˚/ε˚0. Replicated experiments are used at each strain-rate so that a measure of the statistical variation could be estimated. Measures of error associated with the regression analysis are also obtained so that an estimate of the total error in the stress-strain relations can be made.
Constitutive Modeling of High-Elongation Solid Propellants
Authors: O¨zu¨pek S¸. , Becker E. B.
Published: April 2008

A phenomenological approach is used to represent the nonlinear viscoelastic behavior of solid propellants. A three-dimensional finite strain viscoelastic model, modified by a strain softening function that accounts for damage effects, is considered in the research. Some of the significant aspects of high-elongation propellants are incorporated into the constitutive model. The resulting stress-strain relation is applied to a particular high-elongation propellant by means of the related material characterization. The response predicted by the model is compared with the experimental data for different loading conditions. The model predicts the propellant behavior quite well at uniaxial strain magnitudes up to 50 percent. Numerical analysis of very general geometries and loadings are possible, since a fully general model is calibrated.
Integration of Microstructural Development and Properties Design Into the CAD/CAM Environment
Authors: Fragomeni J. M. , Hillberry B. M. , Sanders T. H. , Gaitatzes A. G.
Published: April 2008

This investigation incorporates the development and control of microstructure and properties into a computer aided design/computer aided manufacturing (CAD/CAM) environment for materials design. An integrated computer model has been developed which predicts the microstructure and properties based on the material processing and the material composition. The material processing includes the extrusion parameters and the aging conditions employed during heat treatment. The material being utilized as a demonstration medium is a special precipitation hardenable aluminum-lithium-zirconium (Al-Li-Zr) alloy which has been direct-chill (D.C.) cast and direct extruded. A model has been developed based on a series of quantitative transmission electron microscopy (TEM) investigations to predict microstructure from the composition and material processing. This model, referred to as the microstructural model, provides the basis for the overall CAD/CAM model for materials design. Also included is an analysis of the microstructural mechanisms that contribute to the strengthening of precipitation hardened alloys that contain shearable precipitates. A number of existing models regarding particle shearing and looping mechanisms in precipitation hardened systems were evaluated regarding their suitability in describing the Al-Li aging and strengthening behavior. These analytical models are incorporated with the microstructural model to make theoretical predictions for the critical resolved shear strength.
Evaluation of the Mechanical Properties and Corrosion Resistance of Al-2.5Mg-Cr Alloys
Authors: Shuaib A. N. , Ahmad Z.
Published: April 2008

The results of this paper relate to a development program designed to improve the corrosion resistance and mechanical properties of Al-2.5Mg alloys, by the addition of chromium and silicon, for desalination applications. The effect of 0.1 wt to 0.3 wt percent chromium addition on the mechanical properties and corrosion resistance of Al-2.5Mg in the Arabian Gulf water has been investigated. The results show that chromium addition has beneficial effects on the mechanical properties and corrosion resistance of the Al-2.5Mg alloys. A near optimum combination of mechanical properties and corrosion resistance is obtained by 0.2 wt and 0.3 wt percent chromium addition.
Analytical Solutions of Shock Fitting Equations for the Multishock Compaction of Die-Contained Powder Media
Authors: Sano Yukio , Tokushima Koji , Inoue Yuji , Tomita Yoshihito
Published: April 2008

In an earlier paper [4], two sets of equations which governed the processes of propagation of shock waves reflected from the punch and plug surfaces in a die-contained copper powder medium were presented. The pressure-specific volume relation included in the sets of equations was composed of three partial relations having different material constants. In the present paper the sets of equations are simplified by assuming that the pressure and specific volume at the front and back sides of the shock front are always related by the same material constants, and linear equations are obtained by introducing a further minor assumption into the simplified nonlinear equations included in the sets of equations. Two sorts of analytical solutions of the linear equations are obtained. One is a general-form solution, while the other is a closed-form solution. The general-form solution calculated is compared satisfactorily with the difference solution computed in the previous study, confirming that the assumption introduced into the simplified equations is minor. Furthermore, calculated characteristics of the general-form solution are revealed by the consideration of the simplified equations and the linear equations, giving greater insight into the compaction processes. The closed-form solution, which is obtained only for the propagation of the shock wave starting from the punch surface and returning from the plug surface, agrees well with the general-form solution.
A New Test Method for the Determination of the Flexural Modulus of Spirally Wound Paper Tubes
Authors: Bank L. C. , Cofie E. , Gerhardt T. D.
Published: April 2008

A new static test method to determine the flexural modulus of spirally wound paper tubes is described. The experimental method is based on the standard three-point-bend procedure. The method requires testing the tube at multiple (two or more) span lengths. The testing can be performed on either a rigid frame fixture under constant static load or in a universal testing machine under monotonically increasing quasi-static load. The test data are analyzed with a modified form of a classical Euler-Bernoulli beam theory. The modified theory accounts for nonbending deflection components that are obtained with the three-point-bend test. The effect of time-dependent creep deflection on the modulus prediction is also discussed. Extensive testing of a variety of paper tubes was conducted to verify the proposed test method. The accuracy of the method was determined by comparison with dynamic bending modulus predictions obtained from modal tests on the tubes. The dynamic modulus predictions were based on Euler-Bernoulli beam theory. Results of tests performed on a specially designed static frame fixture and tests performed on a universal testing machine are compared. It is found that the bending modulus predictions using the new analysis method are considerably closer to the dynamic bending modulus than those predictions obtained by classical beam theory.
Estimation of Size and Depth of Debonds in Laminates From Holographic Interferometry
Authors: Shang H. M. , Lim E. M. , Lim K. B.
Published: April 2008

Double-exposure holography has been shown to be a useful nondestructive testing technique for the detection of debonds in laminates when subjected to vacuum stressing. The size of a debond is estimated from the boundary containing anomalous fringes and subsequently, its depth is estimated from these fringes using a thin-plate model. Rigid-body motion is frequently present during testing, causing ambiguity in the identification of the shape of the debond and hence difficulty in the estimation of its size and depth. In this paper, a simple method is presented which isolates the effects of rigid-body motion so that accurate assessment of the detected debonds can be achieved. Also, the use of a circle to outline the ambiguous boundary is found suitable for square debonds.
Application of a Unified Constitutive Theory to the Nonproportional Multiaxial Strain Deformation of 1045 Steel
Authors: Sherwood J. A. , Fay E. M.
Published: April 2008

An automated procedure for the determination of the material constants in a constitutive equation which is used to model the multiaxial nonlinear material behavior of isotropic materials is discussed. The material model used in this research is a unified theory where the time-dependent strain (creep) and time-independent strain (plasticity) are treated as one (unified) inelastic strain. The flow equation considers the inelastic rate of strain and it is assumed that inelastic strain is present at all levels of stress. Application of the model to proportional and nonproportional biaxial loadings is presented.
Fatigue Behavior of Chromium Steel Surface Deposits
Authors: Barbangelo A.
Published: April 2008

A study of fatigue behavior has been carried out using a set of commercial surfacing chromium steels in the state of deposits postheated at 350°C. The set consisted of various filler metals with different contents of chromium, nickel, carbon, and carbide-forming elements. It has been found that all the deposits examined are characterized by very close values of their fatigue crack growth threshold, ΔKth. In each material, as the stress intensity factor range is varied, three different propagation kinetics are observed, probably triggered by the presence of trapped hydrogen. Fracture toughness and, even though less strictly, subcritical growth by fatigue depended on the vanadium or columbium contents of each material, rather than on the other alloying elements. By adding vanadium or columbium and increasing the columbium content, one obtains a sharp decrease in plane-strain fracture toughness. No interdependence has been found between the values of the fracture toughness and the impact toughness of each material. This apparent discrepancy between the two kinds of toughness can be explained by using a distance criterion for failure at the tips of sharp cracks.
Analysis of Part-Throughwall Crack in a Pipe Under Combined Tension and Bending
Authors: Zahoor A.
Published: April 2008

J-resistance curve solution is developed for a circumferential part-throughwall crack in a pipe under combined tension and bending. The J solution can be applied with load-displacement-crack extension data from one pipe test. Material resistance curves are developed for part-throughwall cracks in Type-304 stainless steel base material and SAW weld, and SA333 Gr6 and A106 GrB carbon steel base materials. Posttest tearing instability analyses are performed to predict the load carrying capacity of pipes containing part-throughwall cracks and to assess the accuracy of a Jestimation scheme solution.
Estimation of Cutting Temperature in High Speed Machining
Authors: Lin Jehnming , Lee Shinn-Liang , Weng Cheng-I
Published: April 2008

This paper presents a study of the inverse heat conduction problem for high speed machining. A finite element method with an inverse scheme and an experimental measurement using infrared (IR) pyrometer with fiber optic are applied to predict the tool-chip interface temperature and the total heat dissipating to both tungsten carbide and ceramic inserts. A one-dimensional ellipsoidal mapping model of the cutting temperature distribution is adopted here and the average transient cutting temperature is calculated by the inverse finite element method with measured surface temperatures adjacent to the tool edge. Also the analysis of the errors coming from the sensor location and mapping model is studied. The results show the estimated cutting temperature is well convergent and agrees to other previous investigations. It is found that the thermal conductivity of the tool material has significant effect on the heat dissipation but little effect on the tool-chip interface temperature in high speed machining.