bluuebunny/crossref_metadata_2025 huggingface dataset:
An Experimental Investigation of the Yield Loci of 1100-0 Aluminum, 70:30 Brass, and an Overaged 2024 Aluminum Alloy After Various Prestrains
Authors: Helling D. E. , Miller A. K. , Stout M. G.
Published: October 2009

The multiaxial yield behaviors of 1100-0 aluminum, 70:30 brass, and an overaged 2024 aluminum alloy (2024-T7) have been investigated for a variety of prestress histories involving combinations of normal and shear stresses. Von Mises effective prestrains were in the range of 1.2–32%. Prestress paths were chosen in order to investigate the roles of prestress and prestrain direction on the nature of small-strain offset (ε = 5 × 10−6) yield loci. Particular attention was paid to the directionality, i.e., translation and distortion, of the yield locus. A key result, which was observed in all three materials, was that the final direction of the prestrain path strongly influences the distortions of the yield loci. Differences in the yield locus behavior of the three materials were also observed: brass and the 2024-T7 alloy showed more severe distortions of the yield locus and a longer memory of their entire prestrain history than the 1100-0 aluminum. In addition, more “kinematic” translation of the subsequent yield loci was observed in brass and 2024-T7 than in 1100-0 aluminum. The 2024-T7 differed from the other materials, showing a yield locus which decreased in size subsequent to plastic straining. Finally, the implications of these observations for the constitutive modeling of multiaxial material behavior are discussed.
The Freely Expanding Ring Test—A Test to Determine Material Strength at High Strain Rates
Authors: Warnes R. H. , Karpp R. R. , Follansbee P. S.
Published: October 2009

The freely expanding ring test (ERT) is a conceptually simple test for determining the stress-strain behavior of materials at large strains and at high strain rates. This test is conducted by placing a thin ring of test material in a state of uniform radial expansion and then measuring its subsequent velocity-time history. The ring is usually propelled by a high explosive driving system. The test has not become popular in the materials property community, however, because there has been some concern about how the launching of the ring sample with an explosively generated shock wave might affect the properties to be measured. To determine the suitability of the ERT for these fundamental investigations, a series of experiments was performed on a carefully controlled material—oxygen-free electronic fully annealed copper. Recovered ring samples were analyzed and the change in hardness determined. Comparisons of the ERT data with that from Hopkinson bar tests at strain rates of about 5 × 103 s−1 indicate that the shock-induced hardness is approximately equivalent to a strain hardening of 5 percent. ERT data on this material at strain rates up to 2.3 × 104 s−1 are presented.
Strain Rate Sensitivity, Strain Hardening, and Yield Behavior of 304L Stainless Steel
Authors: Stout M. G. , Follansbee P. S.
Published: October 2009

Sheet and rod stock of 304L stainless steel were tested in uniaxial tension and compression at strain rates between 10−4 s−1 and 104 s−1. To evaluate the yield locus behavior of the sheet material, multiaxial experiments were performed at a strain rate of 10−3 s−1. We have analyzed these results in terms of existing strain-rate sensitivity, work hardening, and yield locus models. Strain-rate sensitivity was found to follow a thermal activation law over the entire range of strain rates used in this investigation. The best description of strain hardening did depend on the strain range to which the data were fit. The Voce law was the most accurate at large strains (ε > 0.40), whereas at small strains, in the vicinity of yield, the laws of either Swift or Ludwik were the most accurate. A simple power law description of work hardening was inadequate over all levels of strain. We examined a number of yield criteria, both isotropic and anisotropic, with respect to the biaxial yield behavior. Bassani’s yield criterion gave the best fit to our experimental results. However, the simple von Mises yield function also gave an acceptable prediction of yield strength and direction of current plastic strain rate. The yield criteria of Hill, both the quadratic and nonquadratic versions, did not match the experimental data. We feel that these results have direct application to the selection of the proper constitutive laws for the finite element modeling of the deformation of 304L stainless steel.
Progressive Failure in Carbon/Epoxy Laminates Under Biaxial Stress
Authors: Swanson S. R. , Christoforou A. P.
Published: October 2009

Despite a number of previous investigations, the question of what criterion to use to predict ultimate failure in fiber composite laminates is still open to question, and particulary so when the overall loading involves biaxial stresses. We have addressed this question by developing a progressive failure model, and comparing the model to experiments on biaxial loading of tubular specimens of quasi-isotropic AS4/3501-6 carbon/epoxy laminates. The progressive failure model uses a modified Tsai-Wu criterion for initial ply cracking, a rule for softening the ply stiffness coefficients with continued straining, and an ultimate failure criterion. It was found that a maximum fiber strain criterion agreed very well with the experiments.
Micromechanical Modeling of Damping in Discontinuous Fiber Composites Using a Strain Energy/Finite Element Approach
Authors: Hwang S. J. , Gibson R. F.
Published: October 2009

The purpose of this paper is to describe the development and demonstrate the application of an efficient method for finite element modeling of damping and stiffness of discontinuous fiber reinforced composites. Dynamic stiffness and damping are defined in terms of the complex modulus, and composite damping is estimated by means of a strain energy method. This technique has the capability of predicting fiber interaction and fiber interface effects on composite damping. The resulting data from the analytical approaches, including the finite element method (FEM) and a “mechanics of materials” analysis, were compared with previous experimental results. These results showed that fiber interaction does affect the damping of discontinuous fiber composites, and that damping can be improved by increasing the fiber end gap size or by decreasing the fiber aspect ratio. It is also shown that the finite element implementation of the strain energy approach is a powerful tool for predicting the damping in composites.
Elastic-Plastic Analysis of Directionally Solidified Lamellar Eutectic Composites
Authors: Gerdeen J. C. , Predebon W. W. , Schwab P. M. , Shah A.
Published: October 2009

Yielding in a crystal structure occurs with plastic slip on preferential planes. It is similar to yielding on maximum shear planes in an isotropic continuum, but in this case the slip is anisotropic. The anisotropic slip is described by 24 piecewise, continuous yield functions, also known as the generalized Schmid’s law for FCC crystals. The plastic strain increment for any one slip mechanism is assumed given by the potential flow law of plasticity. However, there are combined slip situations where two or more slip mechanisms are activated simultaneously. In this paper, the plastic strains for all the possible intersections in FCC crystals are derived, i.e., for intersections of two, four, and eight yield surfaces of compatible stress states. A strain hardening modulus H′ is included by defining an equivalent shear stress τ and an equivalent plastic shear strain γp for each slip system. The analysis is programmed for finite-element solution on the computer, by defining a strain “vector” {dε}, a stress “vector” {dσ}, and an elastic-plastic compliance [C] for each element, relating the strain and stress vectors. The analysis is applied to the elastic-plastic yielding of directionally solidified eutectic systems of Co-CoAl which solidify into a lamellar structure. A plane strain analysis is compared with experiments and good correlation is found for the stress concentration effect when the lamellae have termination points.
Thermal Stress in a Coated Short Fiber Composite
Authors: Hatta Hiroshi , Taya Minoru
Published: October 2009

When a coated short fiber composite is subject to temperature change, thermal stresses in and around the coated fibers are induced due to the mismatch of thermal expansion coefficients of the constituents. The problem of the above thermal stresses in a coated short fiber composite is solved by using the Eshelby’s equivalent inclusion method under the assumption of thin coating. A parametric study is then conducted to examine the effect of thermo-mechanical properties of the coating on the stress field in an and around a coated short fiber. It is found in this study that critical parameters influencing the thermal stress field are the thermal expansion coefficients of the fiber and coating.
Effective Medium of Unidirectional Short-Fiber Composites by a Self-Consistent Method
Authors: Nomura Seiichi
Published: October 2009

A new self-consistent method is proposed to calculate the effective stiffness of unidirectional short-fiber composites where each transversely-isotropic short-fibers is embedded in an infinite homogeneous matrix phase. The equilibrium equation for the elastic field in short-fiber composite materials is converted into an integro-differential equation using the Green’s function for a homogeneous medium. The “effective medium” is chosen in such a way that the ensemble averaged strain field for the composite is equal to that of the homogeneous medium that exhibits the same overall response as the composite. The “effective stiffness” and the “effective mass density” are defined as those properties of the effective medium. The obtained expression for the effective stiffness is new and is not symmetrical with the matrix phase and the fiber phase, thus, reflecting the matrix role more properly than previous works which gave symmetrical results. The result is also favorably compared with experimental data.
An Experimental Comparison of Several Current Viscoplastic Constitutive Models at Elevated Temperature
Authors: James G. H. , Imbrie P. K. , Hill P. S. , Allen D. H. , Haisler W. E.
Published: October 2009

Four current viscoplastic models are compared experimentally for Inconel 718 at 593°C. This material system responds with apparent negative strain rate sensitivity, undergoes cyclic work softening, and is susceptible to low cycle fatigue. The models used include Bodner’s anisotropic model, Krieg, Swearengen, and Rhode’s model, Schmidt and Miller’s model, and Walker’s exponential model. Schmidt and Miller’s model and Walker’s model correct for negative strain rate sensitivity response. A correction similar to Schmidt’s is applied to the models of Bodner and Krieg et al. A series of tests has been performed to create a sufficient data base from which to evaluate material constants. A method to evaluate the constants is developed which draws on common assumptions for this type of material, recent advances by other researchers, and iterative techniques. A complex history test, not used in calculating the constants, is then used to compare the predictive capabilities of the models. The combination of exponentially based inelastic strain rate equations and dynamic recovery is shown to model this material system with the greatest success. The method of constant calculation developed in this work was successfully applied to the complex material response encountered. Backstress measuring tests were found to be invaluable and warrant further development.
Temper-Bead Weld Heat-Affected Zone Properties in A516-70 Steel
Authors: Kim Y. J. , Prince J. W.
Published: October 2009

A temper-bead welding technique has been developed to provide an alternative weld repair method in which the application of a high temperature post-weld heat treatment (PWHT) can be avoided. In order to assess the integrity of temper-bead weld repairs, a series of experiments were carried out on a simulated temper-bead weld made on A516-70 steel plate. Metallographic examination of the weld repair shows that the temper-bead technique can produce a grain refined heat-affected zone (HAZ) microstructure with acceptable hardness values. The JIC fracture toughness test results show that the HAZ exhibited equivalent or greater fracture toughness than the base metal.
Detailed and Simplified Elastoplastic Analyses of a Cyclically Loaded Notched Bar
Authors: Ohno N. , Sˇatra M.
Published: October 2009

To find some features in the development of cyclic hardening in structural components with areas of strain concentration, detailed and simplified elastoplastic analyses are performed on an axisymmetric notched bar subjected to axial cyclic loading. For the detailed analysis, the constitutive model based on the cyclic nonhardening region is implemented in an incremental FEM. The model can describe an important feature in cyclic plasticity, i.e., the dependence of cyclic plastic behavior on cyclic stress and strain ranges. The simplified method which utilizes the cylic stress-strain curve as the constitutive relation is applied to the case of nonzero as well as zero mean values of the cyclic load, and its validity is discussed on the basis of the results of the detailed analysis. The detailed analysis with accelerated cyclic hardening and the methods of Neuber and Stowell-Hardrath-Ohman are examined, too.
Biaxial Creep-Fatigue Failure Characteristics in Two FCC Materials
Authors: Zamrik S. Y. , Zahiri F.
Published: October 2009

This paper describes the failure mode observed in two types of FCC structural materials: waspaloy and type 316 stainless steel as a result of biaxial low cycle fatigue at elevated temperatures. Torsional cycling was applied at high as well as low strain ranges. Creep effect was assessed by introducing hold periods of 90 seconds in the waspaloy tests and 30 minutes in the stainless steel tests. Data obtained from fatigue and creep-fatigue tests have shown that the failure process in the two materials was controlled by two failure mechanisms which depended, to different degrees, on the state of stress, dwell time, and temperature. The failure mechanisms were assessed by observing crack growth in each material under strain level and temperature. In the waspaloy, the mode of crack growth was more temperature than stress dependent, while in the stainless steel, it was stress dependent. The microstructure analysis showed that each type of crack growth was caused by variations in slip band formation, stages of crack initiation and propagation, secondary cracking and cracking of grain boundaries. Creep showed more interaction with fatigue in the stainless steel material than in the waspaloy.
The Characterization of Materials by Precision Strain Rate Sensitivity
Authors: Saimoto S.
Published: October 2009

Strain rate sensitivity is a measurement of the thermodynamic response of materials to changes in stress (τ). Correlations of the theoretical derivations to measured values are only valid if the strain rate (γ˙) is performed at constant structure (Σ). Thus transients during strain rate change obliterate the subtleties of the data especially since the strain rate sensitivity ∂lnτ∂lnγ˙T,Σisoftheorderof10−2. These transients, which are due to the inherent interactive nature of the testing frame of conventional tensile machines, can be nullified. This compensation results in a step-ramp in the displacement-time plot such that precision strain rate sensitivity can be measured. Moreover it is convincingly shown that the true elastic response of polyethylene including the unrelaxed modulus can be measured. Examples of evaluated material characteristics are: 1) the work to intersect dislocations at 0 K in dilute Al crystals. 2) the composition of interstitial solutes from which the solvus for NbCN in ferritic stainless steel can be determined. 3) the clustering in Al-4wt percent Cu during early GPI formation from which bond strength can be estimated.
Prediction of the In-Plane Electrical Conductivity of a Misoriented Short Fiber Composite: Fiber Percolation Model Versus Effective Medium Theory
Authors: Taya Minoru , Ueda Naoki
Published: October 2009

The in-plane electrical conductivity of a misoriented short fiber composite was studied both by fiber percolation model (FPM) and effective medium theory (EMT). A misoriented short fiber composite consists of insulating matrix and conductive short fibers, thus it exhibits a threshold behavior in the conductivity at a certain volume fraction of fibers. A comparison between FPM and EMT indicates that FPM can predict the threshold behavior well, while EPT fails, but it becomes valid at high volume fraction of fibers.
Effect of Shock and Elastic Waves on Dynamic Compaction Process of Two-Layer Powder Media
Authors: Miyagi K. , Sano Y.
Published: October 2009

The dynamic compaction processes of copper powder which was filled in two layers into a die and subjected to solid punch impaction were investigated experimentally in order to assess the effect of different initial density distributions of the powder on the compaction process. The compaction experiments were performed for two situations of layer arrangement: in the first situation the upper layer had a lower uniform initial density distribution than the lower layer and in the second this order was reversed. The processes were photographed for the two situations of layer arrangement using a high speed camera in order to analyze the movement of powder medium and punch, the propagation of shock and elastic waves in the powder medium and density distributions. The pressure on the plug supporting the medium in the die was also measured so that the analysis of the photograph would be facilitated. The two compaction processes observed and analyzed differed considerably, but the green density distributions had only a slight difference. The compaction process obtained for the first situation of layer arrangement agreed well with the theoretical prediction reported previously by the authors. The compaction process for the second situation also agreed with the theoretical result, indicating that the amounts of internal energy dissipation during the two processes differ only slight.
Redundant Deformation Factor Evaluation Through the Stress-Strain Curves Superposition Method in Round Section Bar Drawing—A Literature Analysis
Authors: Cetlin P. R.
Published: October 2009

An analysis of the stress-strain curves superposition method for the evaluation of the average deformation ε and redundant deformation factor φ is presented. This approach, originally proposed by Hill and Tupper, makes unrealistic suppositions, which led to some confusion in the literature concerning curve superposition criteria; the values of φ depend on the material, contrarily to Hill and Tupper’s original idea. If the technique is to be used, it is necessary to establish clear and objective superposition criteria.
Study of Affecting Parameters in Laser Hole Drilling of Sheet Metals
Authors: Yilbas Bekir Sami
Published: October 2009

In practical applications of laser drilling the quality of the drilled hole is the critical factor, and recently methods of studying the influence on quality of the main process variables have been developed, which seek to improve quality rather than explain the drilling mechanism. Hole quality can be judged by: internal form and taper and related geometrical features, and the extent of heat affected materials. The optimum performance in laser drilling depends very much upon the proper selection of laser parameters as well as the physical properties of the workpiece material. With so many variables, and incomplete knowledge of the relationships between them, statistical methods are needed to design experiments and analyze the results. In the present work five factors at four levels were considered. Four factors are given quantative; one, the material specification, is qualitative. The result is that the design has four blocks indentified with materials each of which can be treated as a complete factorial design. However, the materials can be described quantitatively by their physical properties, so the results were correlated with the groups generated by the dimensional analysis. It is observed that main effects of laser parameters as well as their interactions, have significant effects on all features of hole geometry. Drilling medium pressure was found to be very effective factor, since its interactions with the other parameters in any order are significant.
On the Mechanism of Fracture in Grey Cast Iron
Authors: Shawki G. S. A. , Naga S. A. R.
Published: October 2009

This paper presents the results of both experimental and analytical investigations into the conditions of failure for lamellar-graphite case iron under various modes of loading. The orientation of fracture planes is experimentally determined and surfaces of fracture zones are carefully examined with the help of a scanning electron microscope. While fracture for a tensile test takes place along its cross section, fracture in the compression test is herein shown to insist on developing along a plane inclined at some 55 to 65 deg to the cross section, irrespective of notches or grooves intentionally machined to persuade fracture to pursue certain preassigned paths. For the case of uniaxial compression, the present analysis correlates the ratio of compressive to tensile strengths to both rupture and friction angles. Relevant values are in conformity with earlier findings.
Multiaxial Fatigue Damage Models
Authors: Socie D.
Published: October 2009

Two multiaxial fatigue damage models are proposed: a shear strain model for failures that are primarily mode II crack growth and a tensile strain model for failures that are primarily mode I crack growth. The failure mode is shown to be dependent on material, strain range and hydrostatic stress state. Tests to support these models were conducted with Inconel 718, SAE 1045, and AISI Type 304 stainless steel tubular specimens in strain control. Both proportional and non-proportional loading histories were considered. It is shown that the additional cyclic hardening that accompanies out of phase loading cannot be neglected in the fatigue damage model.
The Fracture Toughness of Hardened Tool Steels
Authors: Watt D. F. , Nadin Pamela , Biner S. B.
Published: October 2009

This report details the development of a three-stage fracture toughness testing procedure used to study the effect of tempering temperature on toughness in 01 tool steel. Modified compact tension specimens were used in which the fatigue precracking stage in the ASTM E-399 Procedure was replaced by stable precracking, followed by a slow crack growth. The specimen geometry has been designed to provide a region where slow crack growth can be achieved in brittle materials. Three parameters, load, crack opening displacement, and time have been monitored during the testing procedure and a combination of heat tinting and a compliance equation have been used to identify the position of the crack front. Significant KIC results have been obtained using a modified ASTM fracture toughness equation. An inverse relationship between KIC and hardness has been measured.
An Advanced 12Cr Steel Rotor Applicable to Elevated Steam Temperature 593°C
Authors: Hizume A. , Takeda Y. , Yokota H. , Takano Y. , Suzuki A. , Kinoshita S. , Koono M. , Tsuchiyama T.
Published: October 2009

The upper limit of steam temperature which 12Cr steel rotors can withstand has been considered to be 566°C, but the recent projects on the advanced steam turbine of large capacity demand to raise it. The key factor in upgrading the creep rupture strength of the existing 12Cr steel rotors is to adjust “Equivalent Molybdenum Content” to the optimum, which is 1.5 percent in case no tungsten is contained. A HP-IP rotor, of 11 tons in final machined weight, for EPDC’s Wakamatsu high-temperature turbine to be operated with 593/593°C steam, has been manufactured with the chemical composition of C 0.14, Si 0.08, Mn 0.51, P 0.013, S 0.001, Ni 0.60, Cr 10.23, Mo 1.48, V 0.17, Nb 0.056, N 0.045, and Al 0.002 percent, respectively, through ESR process, Its creep rupture strength after heat treatment is 122 MPa for 593°C and 105 hr. The paper reports the concept of this material and the actual achievement in Wakamatsu rotor forging, referring to the working condition expected on the rotors for 1000 MW-class advanced steam turbine.
Constitutive Equations for Nonproportional Cyclic Elasto-Viscoplasticity
Authors: Benallal A. , Marquis D.
Published: October 2009

This paper is concerned with the behavior of metallic materials under general complex loadings. A complete experimental investigation is carried out to exhibit the main features of this behavior. Nonproportional loadings are characterized by an additional hardening when compared to proportional loadings. This hardening is observed to be strongly dependent on the loading path and can be recovered when the nonproportionality decreases. It is shown that a classical model of elasto-viscoplasticity fails when applied to the prediction of responses under complex loadings. The examination of the assumptions on which the model is built allows to understand its deficiencies and, on the basis of an experimental program, a simple constitituve model is derived for cyclic elastoviscoplasticity under nonproportional loadings. This model is shown to give good results for the prediction of very complex tests.
The Role of Constitutive Formulation in the Analysis of Hot Rolling
Authors: Lenard J. G. , Wang F. , Nadkarni G.
Published: October 2009

The effect of constitutive modelling of material behavior on the predictive abilities of two models of flat rolling is studied. Comparison of calculated roll forces and powers to those measured on a commerical steel mill indicates that the Orowan model is sufficiently accurate when supplied with carefully determined flow strength data. The manner of representation of that data is found to be significant. The results show that a multidimensional databank, which stores values of strength for specific strains, rates of strain and temperatures is very useful in modelling the process.
Phenomenological Modeling of Hardening and Thermal Recovery in Metals
Authors: Chan K. S. , Bodner S. R. , Lindholm U. S.
Published: October 2009

Modeling of hardening and thermal recovery in metals is considered within the context of unified elastic-viscoplastic theories. Specifically, the choices of internal variables and hardening measures, and the resulting hardening response obtained by incorporating saturation-type evolution equations into two general forms of the flow law are examined. Based on the analytical considerations, a procedure for delineating directional and isotropic hardening from uniaxial hardening data has been developed for the Bodner-Partom model and applied to a nickel-base superalloy, B1900 + Hf. Predictions based on the directional hardening properties deduced from the monotonic loading data are shown to be a good agreement with results of cyclic tests.
An Analysis Method for the Dynamic Compaction Processes of Powder Media Within a Die
Authors: Sano Yukio
Published: October 2009

A method of analysis for the multishock compaction process of die-contained powder media with a plug at one end and an impacting punch at the other end is presented. In the method assumptions are made that the media are of a simple rigid-plastic type, and compressed only at the fronts of the shock waves passing through, and furthermore the punch and plug are rigid bodies. Based on the assumptions, particle velocities of elements between the punch surface and a shock wave front are the same and equal to the punch velocity, while velocities of elements between the front and the plug surface are equal to a velocity of the plug surface, i.e., zero. Therefore, it is possible to use jump conditions at the front and equations of motion for the punch and medium moving with the same velocity as it, instead of partial differential equations, i.e., conservation equations which were used in other methods. The equations of motion, together with the jump conditions and rigid-plastic constitutive relation equations provide two sets of equations governing the process. It is shown that there exist unique solutions of the equations of motion, and the equations are analyzed for a copper powder medium. Exact solutions obtained are compared with approximate solutions analyzed previously by the von Neumann and Richtmyer method. A fairly good agreement of the solutions by both the methods indicates that the approximate solutions are effective.
Development of Wear Sensor for Tool Management System
Authors: Rutelli G. , Cuppini D.
Published: October 2009

In automatic metalworking systems, in-process tool-life monitoring and quality control of the parts produced play a crucial role. This paper is on the architecture and performance of an opto-electronic sensor designed for automatic tool-wear monitoring in Computer Numerical Controlled (CNC) lathe applications. Tool wear is sensed by detecting the wear land image, which is captured by an analogic camera, digitized and processed using a computer system. The computer system, linked to the lathe control module, implements a real-time procedure supporting an optimal tool replacement strategy.
Multiaxial Fatigue Damage Criterion
Authors: Ellyin F. , Golos K.
Published: October 2009

A multiaxial fatigue failure criterion is proposed based on the strain energy density damage law. The proposed criterion is hydrostatic pressure sensitive; includes the effect of the mean stress, and applies to materials which do not obey the idealized Masing type description. The material constants can be evaluated from two simple test results, e.g., uniaxial tension, and torsion fatigue tests. The predicted results are compared with biaxial tests and the agreement is found to be fairly good. A desirable feature of this criterion is its unifying nature for both short and long cyclic lives. It is also consistent with the crack initiation and propagation phases of the fatigue life, in the sense that both of these phases can be related to the strain energy density either locally or globally.
Surface Small Crack Growth Behavior of Type 304 Stainless Steel in Low-Cycle Fatigue at Elevated Temperature
Authors: Okazaki Masakazu , Endoh Tomohiro , Koizumi Takashi
Published: October 2009

Surface small crack growth behavior of Type 304 stainless steel during low cycle fatigue under fast-fast and slow-fast cyclings was investigated at a temperature of 873 K by using the smooth specimens which had the different grain sizes. It was shown that the crack, which had already grown up to a few grain size, predominantly propagated with strain cycling, and that it was very important for the safety assessment of the components in service to detect the crack of a few grain sizes. It was also shown that small crack growth rate showed the minimum when they arrived at the grain boundaries. Above behavior resulted from that the grain boundaries temporarily impeded the small crack growth. The crack length below which the grain boundaries notably affected the small crack growth rate was also given as the function of relative length to the average grain size. Furthermore, the small crack growth rate was compared with the macroscopic crack growth one. In fast-fast cycling, the small crack growth rate was about ten times as large as the macroscopic crack growth one, where its length was comparable to the grain size. Based on the results thus obtained, the application limit of macroscopic crack growth law to the surface small crack growth was discussed. The application limit proportionally increased with the grain size, and it was about ten times average grain size in both fast-fast and slow-fast cyclings.
Computer Simulation of the Uniaxial Elastic-Plastic Behavior of Paper
Authors: Ramasubramanian M. K. , Perkins R. W.
Published: October 2009

The elastic properties of paper materials have been predicted by a micromechanics model of a ribbon-like nonwoven structure. The present model extends the previous linear elastic theory to incorporate nonlinear elastic and deformation theory plastic behavior. The theory incorporates different nonlinear or plastic parameters of fibers that are loaded in tension and compression. The theory is used to develop a computer simulation of the uniaxial straining of a strip of paper. Theoretical results are compared with experiments conducted on two classes of paper materials.
Nonlinear Elastic Properties of Organic Matrix Composites at Elevated Temperatures
Authors: Ha Sung Kyu , Springer George S.
Published: October 2009

A model is presented for describing the nonlinear, elastic behavior of unidirectional organic matrix composites at elevated temperatures. The model describes the longitudinal and transverse tensile, longitudinal and transverse compressive, and shear stress-strain relationships, as well as the Poisson ratios. Tests were performed in the temperature range 75 to 350°F using unidirectional laminates made of Fiberite T300/976 graphite epoxy tape. The constants required in the model for this material were deduced from the data.
Nondestructive Evaluation of Composite Structures Using System Identification Technique
Authors: Tsai W. H. , Yang J. C. S.
Published: October 2009

A system identification technique is presented for nondestructive test to detect and to characterize the existence and location of cracks and other damages in composite structures. Various composite structures, including Kevlar-epoxy plate, graphite epoxy ring, and graphite-epoxy coupon have been tested for different damages such as crack, delamination, impact damage, fatigue damage, etc. In addition, the correlation between severity of any type of the damages mentioned above and changes in identified system parameters has also been systematically studied.
Strength Loss in Composite Cylinders Under Impact
Authors: Christoforou A. P. , Swanson S. R.
Published: October 2009

The problem of strength loss in composite structures due to impact appears to be important due to the sensitivity of advanced composites to these loadings. Although a number of studies have been carried out on impact of flat composite plates, relatively little work has been done on tubular geometries such as pressure vessels despite the usage in applications. We have addressed the problem of calculating strength loss due to low velocity, lateral impact of composite cylinders. In our model we use an existing Fourier Series expansion procedure to calculate ply stresses and strains, compare these values with allowables to predict fiber breakage during the impact, and finally use fracture mechanics to predict the strength loss due to the impact. Although the model is quite simplified, the general trends of experiments appear to be represented.
Microdynamics of Crushing in Cellular Solids
Authors: Stronge W. J. , Shim V. P.-W.
Published: October 2009

Lightweight, open-celled foams and honeycombs can exhibit deformation localization during static crushing as a result of buckling and plastic collapse of cell walls. Localization of deformation is a manifestation of strain-softening behavior that limits transmitted forces through these shock mitigating materials. Collision tests on two-dimensional cellular solids with strain-softening behavior reveal that with some microstructures, strain-rate effects can stabilize less compliant modes of deformation. When stabilization occurs, it amplifies the intensity of transmitted shocks.
The Relationship Between Tensile Strength and Shear Strength in Composite Materials Subjected to High Strain Rates
Authors: Chiem Chi-Yuen , Liu Zeng-Gang
Published: October 2009

This paper contributes to understand the dynamic behavior of a woven carbon/epoxy composite subjected to tensile and shear impact loading in the orthogonal direction by using the tensile and torsional split-Hopkinson bars, respectively. The influences of the equivalent strain rates on the tensile and shear yield stress and strength are found. The yield stress ratio and strength ratio between tensile and shear loading on this composite are compared at a range of the equivalent strain rates from 500 s−1 to 3000 s−1. The relationship between the strain rates and these ratios are established. The failure mechanism is analyzed by microscope observation on the rupture surface of the specimens.
Second Stage Creep of SiC Whisker/6061 Aluminum Composite at 573K
Authors: Morimoto T. , Yamaoka T. , Lilholt H. , Taya M.
Published: October 2009

The second stage creep behavior of 6061 aluminum alloy and 15 percent Vf SiC Whisker/6061 aluminum composite was studied both experimentally and analytically. In order to obtain the accurate input data for the creep analysis, we have also conducted the experiment to measure various microstructure parameters. Based on these data and the Taya-Lilholt creep model, the second stage creep rates are calculated. A good agreement between the analytical and experimental results is obtained if the debonding at the matrix-fiber interface is considered in the analysis.
NONSS: A New Method for Integrating Unified Constitutive Equations Under Complex Histories
Authors: Miller A. K. , Tanaka T. G.
Published: October 2009

A new numerical method has been developed to facilitate the use of unified constitutive equations in finite-element codes. The method has high stability, permits large time increments, and generally is noniterative. The method has been embedded in a subroutine package called NONSS which can readily link to finite element codes. This paper summarizes the method’s development and gives examples of its behavior for a variety of cases.
Subcritical Crack Growth of Glass Under Combined Modes I and II Loading
Authors: Yoda M.
Published: October 2009

The glass plate specimens with inclined cracks introduced by Vickers microhardness indentation were subjected to sustained bend stress in water. Subcritical crack growth behaviors were investigated under combined Modes I and II loading. The crack velocity dc/dt can be described as a function of coplanar energy release rate G. The experimental results show that the dc/dt which is initially high decreases and thereafter increases with G. The crack velocity data are found to be influenced by the residual stress and the presence of a lateral crack. Inclined cracks in the increasing region tend to show the crack velocity higher than would be expected from the Mode I results of β = 90 deg on the basis of G as the β between the loading axis and the crack plane decreases. The dc/dt-G curves in this region have a steeper portion at low velocities and thereafter tend to a shallower portion.
The Influence of Small Defects on Tensile Specimen Ductility and Symmetry of Deformation
Authors: Matic P. , Jolles M. I.
Published: October 2009

The quantitative translation of physical weld quality into structural integrity prediction depends on accurate characterization of weld material behavior in the presence of fabrication defects. The presence of such defects will, however, significantly influence the response of common material test specimens. If the influence of such defects is fully understood, test specimen data may be interpreted in a more meaningful way. The role of a physically relevant geometric imperfection, in the form of a spherical void defect, on cylindrical tensile specimen response is computationally simulated for HY-100 weld metal. Defect radius and location along the specimen axis are treated as independent parameters. Asymmetry of specimen deformation (in terms of specimen neck location) and specimen ductility (in terms of the reduction of area at failure) are computationally predicted. Results suggest that the neck location does not necessarily coincide with the defect location. Therefore, geometric defects are a sufficient condition for asymmetry of neck location but not a necessary condition for neck formation. In addition, coincidence of the defect and the neck reduces the specimen ductility at failure to a minimum value which depends on defect size. When the defect and neck are separated, the defect free specimen ductility at failure, i.e., the maximum ductility value, is recovered as an upper bound. The transition between these two ductility values is abrupt, despite the continuous nature of the physical problem. Preliminary implications of these results on the assessment of defect criticality are discussed.
Low-Cycle Corrosion Fatigue of Three Engineering Alloys in Salt Water
Authors: Bernstein H. , Loeby C.
Published: October 2009

Low-cycle fatigue tests were conducted under strain control in salt water on 2024 aluminum, 304 stainless steel, and 1045 steel. All three materials showed a significant reduction in life due to corrosion fatigue in the low-cycle fatigue regime. The corrosion fatigue life of the aluminum and steel was time dependent, with significantly shorter lives at lower frequencies or at longer strain hold times. The corrosion fatigue life of the stainless steel was not time dependent for the conditions studied. Elastic and plastic strain-range versus life equations were modified by a frequency term to predict the corrosion fatigue life. This model correlated the fatigue data to within a factor of 1.28. A modification of this model correlated some corrosion fatigue data in the literature to within a factor of 1.19.
Rubber Elasticity and Fracture
Authors: Shaw M. C. , Young E.
Published: October 2009

Rubber is an amorphous elastomer of high entropy that is normally treated by statistical thermodynamics instead of molecular modeling. A pseudo-amorphous model is introduced that is useful in extending true stress-true strain uniaxial tensile results to other more complex states of stressing. While the statistical thermodynamic approach is still needed to deal with thermal aspects of rubber elasticity, the new approach represents a simpler, more accurate method of dealing with mechanical properties. Fracture of rubber follows a criterion of constant engineering strain (or constant extension ratio) in the resultant principal stress direction which is consistent with the proposed model and the experimental results presented.
The Performance of Titanium-Nitride Coated HSS Tools
Authors: Bruno M. , Bugliosi S. , Chiara R.
Published: October 2009

This paper presents the technological and economic feasibility of HSS coated tools for application in flexible manufacturing systems.
Constitutive Modeling of Anisothermal Cyclic Plasticity of 304 Stainless Steel
Authors: Ohno N. , Takahashi Y. , Kuwabara K.
Published: October 2009

Temperature-history dependence in anisothermal cyclic plasticity of 304 stainless steel is studied for the constitutive modeling within the temperature range from room temperature to 600°C. Cyclic plastic behavior under in-phase and out-of-phase changes of temperature and athermal strain is analyzed first by use of an elaborate constitutive model with its material constants determined from isothermal experiments; good agreement is obtained between the predictions and experiments, if we assume that the internal change proper to higher temperature prevails under such thermomechanical cycling. This finding leads us to extend the evolution equation of isotropic hardening so that it can be valid for more complex variations of temperature. The extended model simulates well the recent experiments of Niitsu and Ikegami under multi-step changes of temperature.
The Structure and Mechanical Properties of Palm Timber as a Fibre Composite
Authors: Anagbo P. E. , Oguocha N. A.
Published: October 2009

A study has been made of wood extracted from the oil palm (Elaeis guineensis), coconut palm (Cocos nucifera), and fan palm (Borassus flabe) which are common species of tropical palms. The wood from the palms is a natural composite material and measurements show that between 1/3 and 1/2 of the volume consists of fibre. However, the properties of both fibre and matrix vary with the species of palm. Mechanical testing of the wood as used in local constructions has shown that palm timber can indeed withstand tensile and compressive loads parallel to the grain better than the common nonfibrous tropical woods. The elastic moduli of palm timbers in tension parallel to the grain and in static bending are higher than those of obeche and mahogany and vary approximately linearly with the density of the material. The elastic modulus in compression parallel to the grain is related to the volume fraction of fibre, suggesting a shear-mode type of deformation. The intrinsic high hardness and strength of palm timber recommends it as a structural material, suitable for trusses. The fibrous structure also leads to an attractive surface appearance on polishing and the aesthetic consideration suggests that the material could also be utilized for such items as furniture and tiles.
The Use of Spheroidal Graphite Cast Irons to Develop Forgeability Criteria Based on Local Strain Measurements
Authors: Shi J. , Ghoreshy M. , Smith R. W. , Too J. J. M.
Published: October 2009

An attempt has been made to develop forgeability criteria based on data obtained from local strain measurements. Nodular case iron has been used as the modelling material because its microstructure may be manipulated to contain near-spherical graphite nodules which are suitable for the study of deformation, foregeability, etc. Cracking will occur under certain deformation conditions which may be determined by following the changes in spherulite/nodule shape and habit. Local strain in any area of interest may be determined by measuring the shape change of the previously spherical nodules in terms of an aspect ratio b/a (a = major axis, b = minor axis of the deformed nodules) from specimens sectioned after deformation. A wide variety of forgeabilities can be obtained by changing the microstructure and composition of the matrix.
Temperature-Dependence of Multiaxial Non-Proportional Cyclic Behavior of Type 316 Stainless Steel
Authors: Murakami S. , Kawai M. , Aoki K. , Ohmi Y.
Published: October 2009

Temperature dependence of multiaxial cyclic behavior of type 316 stainless steel was elucidated experimentally. Cyclic tests under constant total-strain amplitudes were performed for uniaxial tension-compression and circular (non-proportional) strain paths at several temperatures; room temperature, 200°C, 400°C, 500°C, 600°C, and 700°C. The strain amplitudes of the cycles were specified to be 0.2, 0.3, and 0.4 percent under constant strain rate of 0.2 percent per min. A quantitative discussion was made with special emphasis on the difference between material behavior under uniaxial tension-compression strain cycles and multiaxial non-proportional circular ones at these temperatures. The most significant cyclic hardening was observed in the temperature range between 400°C and 600°C for both the proportional and the non-proportional strain cycles. At these particular temperatures, much larger inelastic strain was accumulated until a cyclic stabilization was obtained. Though the effect of non-proportionality in the cyclic strain paths on the cyclic hardening was significant particularly at the temperature below 450°C, it rapdily decreased at higher temperatures.
Improving the Toughness of 3-1/2NiCrMoV Steam Turbine Disk Forgings
Authors: Bodnar R. L. , Taylor K. A. , Albano K. S. , Heim S. A.
Published: October 2009

Due to the in-service stress corrosion cracking of some 3-1/2NiCrMoV steam turbine disks, the Charpy V-notch toughness requirements for replacement forgings have dramatically increased in recent years. In response to the new requirements, several avenues for improving the toughness of 3-1/2NiCrMoV steel have been explored and are discussed in this paper. Improvements in forging practice, preliminary heat treatment, final heat treatment and composition are recommended which allow the new requirements to be met.