bluuebunny/crossref_metadata_2025 huggingface dataset:
Study on the Grinding Mechanism of Glass Fiber Reinforced Plastics
Authors: Inoue H. , Kawaguchi I.
Published: April 2008

In order to clarify the grinding mechanism of polymer matrix composites, special test specimens were provided. The test specimen is such one that glass yarns are unidirectionally embedded at even interval on the middle plane of thick of a polymer matrix plate. The end face perpendicular to the plane on which glass yarns are lined up is ground in the direction at various angle from the direction of glass yarn. The aspects of the cut end of the glass yarn near the ground surface are observed microscopically, and relations between the angle of the direction of yarn and the topography of the ground surface are investigated. Following results are obtained. (1) The microscopically observed aspects of failure of the end of yarns near the ground surfaces are classified into two modes by the direction of yarn measured counterclockwise from the direction of grinding. In the range from 0 rad. to π/3 rad. of the angle, the failure of the end of yarn is comparatively deep, and spreads over the whole section of the yarn. In the range from π/2 rad. to π rad. of the angle, the failure of the end of the yarn is comparatively shallow, and random in the depth and the spread. (2) The topography is also classified into two types by the above angle. In the range from 0 rad. to π/3 rad. of the angle, the end of yarn forms a hollow pit, and in the range from π/2 rad. to π rad., the end of yarn forms a swollen proturberance. (3) The above facts are well understood by considering the digging up action of the grinding grain in the range from 0 rad. to π/3 rad., and the push down action of the grain in the range from π/2 rad. to π rad. in the grinding process.
Low Temperature Isothermal Strain in a Metastable Austenitic Stainless Steel Sheet
Authors: Oshida Y. , Deguchi A.
Published: April 2008

Low temperature stationary creep strain in a metastable austenitic stainless steel was studied at −162°C under various combinations of prestrain and stress ratio. It was found that the amount of transformed martensite during low temperature stressing increased with the number of thermal cycles as well as the degree of prestrain and stress ratio. When the applied stress exceeded 70 percent of the material yield strength at −162°C, the martensite volume increased significantly. At the same time, the stationary low temperature creep rate exceeded 1.8x10−10 (s−1), which would cause approximately 0.44 percent strain after continuous operation for a year.
An Ultrasonic Technique for Testing the Orthotropic Symmetry of Polymeric Sheets by Measuring Their Elastic Shear Coupling Coefficients
Authors: Habeger C. C.
Published: April 2008

An ultrasonic method, which allows the determination of the in-plane elastic stiffnesses of thin polymeric sheets, is described. The determination is complete, as it includes the shear coupling coefficients. Sheets are often assumed to display orthotropic symmetry, which means that the shear coupling coefficients are zero along the principal axes. With this technique, the shear coupling coefficients can be independently calculated, and the validity of the orthotropic assumption can be tested. A quantity called the nonorthotropic angle is presented as a coordinate-independent measure of the lack of orthotropic response. Results from a polyester sheet demonstrate that significant nonorthotropic behavior is encountered in commercial plastic sheets. Stiffnesses, calculated from tests conducted on laminated sheets, are shown to be in good agreement with stiffnesses predicted from measurements on individual plies. The technique is argued to be self-consistent and an attempt is made to convince the reader that this is a legitimate way to characterize all the in-plane elastic stiffnesses of thin sheets.
Machinability of High Temperature Composites by Abrasive Waterjet
Authors: Hamatani G. , Ramulu M.
Published: April 2008

An experimental investigation was conducted on the machinability of particulate reinforced ceramic TiB2/SiC and metal SiC/Al matrix composites by an abrasive water jet. Both piercing and slot cutting experiments were conducted to determine the influence abrasive waterjet machining has on the material. Machining performance was reported by both cut quality as measured by taper and machined surface characteristics. Based on these preliminary experiments, abrasive waterjet machining seems to be a satisfactory machining method for both metal and ceramic matrix composites.
Three-Dimensional Laser Machining of Composite Materials
Authors: Chryssolouris G. , Sheng P. , Choi W. C.
Published: April 2008

This paper presents a concept for performing three-dimensional laser machining on composite materials, using two intersecting laser beams to create grooves on a workpiece. A volume of material is removed when the two grooves converge. An analysis of the grooving process was conducted for carbon/teflon and glass/polyester materials. A model was developed to determine groove depth from process parameters and material properties. Close agreement was found between model predictions and experimental results for groove depths in carbon/teflon. Model predictions consistently overestimated depth values for continuous-beam glass/polyester results, and underestimated depth values for pulsed-beam glass/polyester at low power/high speed. Corrections for heat losses and high-temperature chemical interactions were added to the model to improve agreement with data. Groove width and damage width results were compared with surface quality standards for laser cutting of composites.
A Procedure for Low Cycle Fatigue Life Prediction for Various Temperatures and Strain Rates
Authors: Zhang Ange , Bui-Quoc T. , Gomuc R.
Published: April 2008

This paper describes a procedure that permits the calculation of the fatigue life over a wide range of temperatures and strain rates. The isothermal fatigue life is expressed in terms of the total strain range by an equation previously obtained from a continuous damage concept. Additional new terms are introduced to take into account the effect of the temperature and of the strain rate. For a given material, a multiple regression analysis is carried out using some experimental results in order to evaluate the material constants involved. Once these constants are known, the life prediction can be made for other specified values of temperature and strain rate. The approach is applied to available data obtained from several stainless steels (AISI 304, 316, 348, and some SUS materials) under several combinations of temperatures and strain rates. The deviation of the calculated lives from the experimental values is reasonably acceptable. The extension of the proposed procedure to cases of cycling with a very low frequency, usually involving hold times, is examined and discussed.
Investigation of Creep/Fatigue Interaction on Crack Growth in a Titanium Aluminide Alloy
Authors: Mall S. , Staubs E. A. , Nicholas T.
Published: April 2008

Crack growth under sustained load and sustained load with superimposed fatigue cycles at elevated temperatures in a titanium-aluminide alloy (Ti3Al) was investigated. The objectives were to determine the creep crack growth characteristics and to evaluate the applicability of linear cumulative damage modeling to the Ti3Al alloy. The linear elastic stress intensity factor, K, was used as a correlating parameter for all the tests. Sustained load tests were used to characterize the time-dependent crack growth behavior at elevated temperatures. The test results showed that sustained load crack growth rate and fracture toughness were relatively insensitive to temperature between 700 and 800°C. Crack growth rates were only a factor of five apart between the slowest and fastest growth rates over this range of temperatures. Several sustained load tests with periodic fatigue cycles (hold-time tests) were used to test the applicability of linear cumulative damage modeling. The model was developed using data from the sustained load and a baseline fatigue test at 750°C. Crack growth rates calculated using the model were accurate for a fatigue cycle with a ten minute hold time, but were up to 2 times less than the growth rates for shorter hold-time tests based on summation of the sustained load and fatigue crack growth rates only. A mixed-mode correction factor added to the model produced more accurate results.
High Temperature Creep Damage Under Biaxial Loading—Part II: Model and Simulations
Authors: Trivaudey F. , Delobelle P.
Published: April 2008

The inadequacies, in describing the high temperature creep damage of two industrial alloys (Part I) with a model where the anisotropic damage variable D depends only on time have been pointed out. It is therefore proposed to introduce directly strain rate in the damage law. This rule is then integrated into a unified viscoplastic model, with internal variables, that has been developed elsewhere. Some numerical simulations obtained with the complete formulation are reported and, in general, yield acceptable results.
Numerical Analysis of a Strip With a Hole Subjected to Cyclic Loading
Authors: Ishikawa H. , Sasaki K.
Published: April 2008

This paper deals with the problem of a strip with a hole subjected to cyclic loading at the ends. For the numerical analysis, a constitutive model incorporating the motion of the center of the yield surface is implemented in a finite element method. The distributions of strain and stress during cyclic loading are discussed in detail both for the zero and nonzero mean values of cyclic load. To verify the results of the computer simulation, an experiment on a strip with a hole of type 304 stainless steel is carried out. Results of the experiment show that during cyclic loading with nonzero mean value of cyclic load, strain at the bottom of the circular hole is ratchetted with increase in number of cycles, and the stress approaches that due to the zero mean value of cyclic load.
Effect of Ripple Load on Stress-Corrosion Cracking in Structural Steels
Authors: Pao P. S. , Bayles R. A. , Yoder G. R.
Published: April 2008

The presence of small ripple loading can, under certain circumstances, significantly reduce time-to-failure and threshold stress intensity for stress-corrosion cracking (SCC) of steels. A predictive framework for such ripple-loading effects (RLE) is developed from concepts and descriptors used in SCC and corrosion fatigue characterization. The proposed framework is capable of defining critical conditions required for the occurrence of RLE and predicting the time-to-failure curves. The agreement between the predicted and laboratory data is excellent.
Experimental Micro Mechanics Methods for Conventional and Negative Poisson’s Ratio Cellular Solids as Cosserat Continua
Authors: Lakes R.
Published: April 2008

Continuum representations of micromechanical phenomena in structured materials are described, with emphasis on cellular solids. These phenomena are interpreted in light of Cosserat elasticity, a generalized continuum theory which admits degrees of freedom not present in classical elasticity. These are the rotation of points in the material, and a couple per unit area or couple stress. Experimental work in this area is reviewed, and other interpretation schemes are discussed. The applicability of Cosserat elasticity to cellular solids and fibrous composite materials is considered as is the application of related generalized continuum theories. New experimental results are presented for foam materials with negative Poisson’s ratios.
Tearing Modulus Analysis for Pipes Containing Constant Depth Internal Flaw
Authors: Rajab M. D. , Zahoor Akram
Published: April 2008

The pipe displacement and tearing modulus solutions are derived for pipes containing a uniform depth internal flaw under bending moment or axial loading. The tearing modulus solution is derived for both load control and displacement control conditions. These solutions are then used to construct critical stress curves for various flaw sizes for a carbon steel pipe. These curves are useful in predicting the onset of flaw growth instability. Critical stress curves can be similarly constructed for other materials and pipe geometries.
Characterization of Fatigue Crack Growth in Intermediate and Large Scale Yielding
Authors: McClung R. C. , Sehitoglu H.
Published: April 2008

Parameters previously proposed for the correlation of elastic-plastic fatigue crack growth data are critically reviewed and compared from a pragmatic engineering standpoint. Commonly employed estimates for the four most common parameters are shown to have essentially the same structure and to be numerically similar, despite their widely differing theoretical backgrounds. The significance of fatigue crack closure for crack growth under these conditions is considered. Elastic-plastic finite element analyses of crack closure are presented and compared with experimental data and simple analytical models. Normalized crack opening stresses are shown to change significantly between small scale and large scale yielding conditions, especially for R= − 1 loading. Different schemes for incorporating closure information into the crack growth parameters are examined, and the consequences of closure for the numerical structure of the parameter estimates are demonstrated. Experimental crack growth data from 1026 and 1070 steels are correlated with estimates of ΔK and ΔJ, both considering and neglecting the effects of crack closure. The data comprise wide ranges of maximum stress, plastic strain amplitude, and crack length, including conditions of small, intermediate, and large scale yielding. Correlations which include an explicit correction for crack closure are shown to be superior.
Single Crystal Modeling for Structural Calculations: Part 2—Finite Element Implementation
Authors: Me´ric L. , Cailletaud G.
Published: April 2008

This paper is devoted to the implementation in a finite element code of a micro-macro anisotropic viscoplastic model for F.C.C. single crystals derived from the slip theory. It shows elasto-viscoplastic structural calculations of two laboratory specimens: a tubular specimen loaded in torsion and a cylindrical one loaded in tension-compression: various crystallographic orientations are considered in the last case.
Discussion: “A Method for Dynamic Fracture Initiation Testing of Ceramics” (Duffy, J., Suresh, S., Cho, R., and Boff, E. R., 1988, ASME J. Eng. Mater. Technol., 110, pp. 326–331; Addendum, 1989, ASME J. Eng. Mater. Technol., 111, p. 86)
Authors: Baratta F. I. , Perrone P. J.
Published: April 2008

NOTE: The reference to the original article for the discussion “A Method for Dynamic Fracture Initiation Testing of Ceramics” (pp. 183–185) is incorrectly cited in the original PDF. The volume number should be 110, not 111. The Addendum is cited correctly. When searching for these articles, use the corrected citations in the HTML.
Application of Neutron Diffraction to Measure Residual Strains in Various Engineering Composite Materials
Authors: Majumdar S. , Singh J. P. , Kupperman D. , Krawitz A. D.
Published: April 2008

An experimental neutron diffraction technique was used to measure residual strains that developed in multiphase composite materials during postfabrication cooling as a result of thermal expansion mismatch or volume expansion due to change in crystal structure. The reinforcement geometries that were studied include unidirectional fibers, randomly oriented single crystal whiskers, and equiaxed particles. Both metal and ceramic matrices and reinforcements were considered. In some cases, the measured data compared fairly well with predictions based on simple elastic models. In other cases, either creep was shown to relax the residual strains during cooling, or the interpretation of the measured data contained uncertainties due to texture in the samples or lack of a clearly defined crystal structure for the reinforcement phase.
Deformation Heating During Cold Rolling of Aluminum Strips
Authors: Pietrzyk M. , Lenard J. G.
Published: April 2008

The temperature rise due to plastic work and interfacial frictional forces during cold rolling of aluminum and steel strips is investigated. The predictions of a two-dimensional thermal-mechanical model of the process, which includes convection in the direction of rolling, are compared to measurements. The comparison reveals the exceptional predictive capability of the model. While the temperature rise in commercial cold rolling is predicted to be significant, it would be expected to contribute little to the loss of strength. Breakdowns in lubricant delivery, however, would cause excessive roll wear and should be avoided.
Improvement of Fatigue Crack Growth Resistance by Serrated Grain Boundary at High Temperature
Authors: lizuka Hiroshi , Tanaka Manabu , Ashihara Fumio
Published: April 2008

Effects of serrated grain boundaries on the improvement of fatigue-crack growth resistance were investigated using austenitic 21Cr-4Ni-9Mn heat-resisting steel at 973K in air. Grain boundaries were serrated by grain-boundary reaction precipitates. The crack-growth rates were considerably decreased in the specimens with the serrated grain boundaries. The fatigue cracks were largely deflected by the serrated grain boundaries, and brittle intergranular fracture was retarded. The improvement of the crack-growth resistance was obtained especially under the conditions of low crack-growth rates of less than 30 μm/cycle. The widths and the heights of the deflected portions of the cracks were in the range from about a few μm to 30 μm.
An Experimental Study of the Evolution of Yield Loci for Anisotropic Materials Subjected to Finite Shear Deformation
Authors: Mallick K. , Samanta Shyam K. , Kumar A.
Published: April 2008

This paper presents a set of experimental results concerning the evolution of yield loci for anisotropic materials in the course of finite shear deformation history. Thin walled tubes of SAE 1020 steel are tested under triaxial loading conditions – tension, torsion and internal pressure, at room temperature. The specimens were prepared from cold-drawn tubes which had a prominent fibrous grain structure. They showed considerable amount of in-plane anisotropy and orthotropic yield properties with respect to the longitudinal and circumferential axes. The as-received specimens were further pre-strained by imposing simple shear which causes the change in orientations of these elongated polycrystalline grains. Our previous experimental results [1] have verified that the principal directions of the total stretch of the current grain shape match with the directions of orthotropy, and in this work, the subsequent yield loci for the pre-strained material are determined with respect to the new reference frame fixed along these directions of orthotropic symmetry. By utilizing the unique triaxial loading scheme of our servo-hydraulic testing system it has been possible to create the principal directions of a biaxial state of stress in a specified direction. The changes in the size and shape of the yield loci in the stress space are critically analyzed in this paper.
Measurement of Residual Stresses Near the Surface Using the Crack Compliance Method
Authors: Cheng W. , Finnie I. , Vardar O¨.
Published: April 2008

The use of thin cuts for residual stress measurement is referred to as the crack compliance method. A computational model is presented for the determination of normal and shear residual stresses near the surface by introducing shallow cuts. The optimum regions for strain measurement are obtained. This method is shown to be considerably more sensitive than the conventional hole drilling method and is capable of measuring residual stresses which vary with depth below the surface.
On the Fatigue at High Frequency—Part II: Application to Some Materials
Authors: Xiangan Kong , Saanouni K. , Thanigaiyarasu G. , Bathias C.
Published: April 2008

This work deals with the experimental study of the so-called “ultrasonic fatigue” or fatigue at very high frequency (some kHz). After describing experimental facilities such as specimen shape, testing machine and measured parameters, we use the numerical method developed in Part I of this study to calculate thermo-mechanical fields in cracked and uncracked specimens. Prediction of S-N curves and thresholds for some different materials are also presented and discussed using mechanical fields obtained numerically.
A Physically Based Constitutive Description for Nonproportional Cyclic Plasticity
Authors: Jinghong Fan , Xianghe Peng
Published: April 2008

The hardening behavior of materials in nonproportional cyclic process is related to the internal changes of materials, such as dislocation cell for wary slip material and ladder or vein substructures for planar slip material. The multiplicatively separated form of hardening function f, in terms of nonhardening region proposed by Ohno [1], and the measure of nonproportionality A proposed by Banallal and Marquis in 1987 [2], is then explained on this physical foundation. The new contributions of this hardening function are: (a) two parameters (f2 and f3) dependent on A are used to differentiate between the influence of latent hardening realized by a sudden change of loading direction, and hereditary hardening associated with nonproportional loading, (b) a general differential form fi (i = 1,2,3) is proposed, and memorial parameters a1 and a3 are introduced to describe different deformation history effects for wary and planar slip materials, (c) different hardening mechanisms through fi are embedded into thermomechanically constitutive relation. The stress responses of 304 and 316 stainless steels subjected to biaxial nonproportional loadings at room temperature are analyzed and compared with the experimental results obtained by Chaboche [3], Tanaka [4, 5] and Ohno [1].
A Method for Estimation of the Fracture Toughness of CrMoV Rotor Steels Based on Composition
Authors: Viswanathan R. , Gehl S.
Published: April 2008

Assessment of the remaining life of steam turbine rotors in the presence of bore defects requires a knowledge of the fracture toughness (KIC) of the rotors. Current procedures for estimating the KIC involve two steps; as a first step, the fracture appearance transition temperature (FATT) at the critical location is determined; the FATT value is then used to estimate the KIC, based on published correlations between the excess temperature (T-FATT) and KIC. Some problems arise in implementing both of these steps. To determine the FATT of the material, large pieces of material have to be removed, machined into charpy specimens and tested; this procedure is often time consuming and expensive and sometimes not feasible. The excess temperatures versus the KIC correlation that is used to derive the KIC values from the FATT data is based on a variety of low alloy steels and is therefore characterized by a large scatter band, thus leading to considerable uncertainty in the estimated KIC. In this work, FATT and KIC data reported for a number of retired CrMoV rotors were gathered and analyzed and correlations specific to CrMoV rotors were developed. Based on these correlations, a method for estimating KIC with greater accuracy, based on a knowledge of the steel chemistry alone, is proposed. The method offers the advantage that very small samples removed from noncritical locations in the rotor would be sufficient to get the desired data.
Fatigue Crack Growth Behavior of Alloy 800H at Elevated Temperature
Authors: Hour K. Y. , Stubbins J. F.
Published: April 2008

High temperature crack growth behavior is investigated over a wide range of R-ratios, frequencies, and temperatures in Alloy 800H. It is found that high R-ratio, low frequency, or high temperature can enhance creep damage and thus induce an intergranular crack growth mode. At low frequencies, the nonlinear fracture mechanics parameter, C*, is found to correlate time-dependent fatigue crack growth rate well if the applied mean stress is used in calculating C*. On the other hand, the Paris crack growth law using Keff is proven to be an adequate expression to use when fatigue (time-independent) damage dominates. These conclusions correlate well with damage mechanisms observed from sample fracture surfaces.
On Compression of Rubber Elastic Sphere Over a Large Range of Displacements—Part 1: Theoretical Study
Authors: Tatara Y.
Published: April 2008

This paper presents one general theory of large elastic deformations of a rubber sphere in simple compression, as the removal of restrictions of the constant Young modulus and small deformation in the prevailing Hertzian theory in contact of elastic bodies. It derives a set of five equations associated with approach, radii of contact surface without and with lateral extension of free surface, the lateral extensive displacement on the contact surface and the position of the contact surface in a very large range of applied forces, on the basis of the Hertz theory (half-space elastic body model) with an extensive term, in consideration of the rubber-elastic nonlinear elasticity, the lateral extension and the symmetry of the deformed shape of the rubber sphere. In Part 2 it is shown that results calculated by the set of the equations fit experimental data for a rubber sphere.
Analysis of Flow Patterns and Solidification Phenomena in the Die Casting Process
Authors: Minaie B. , Stelson K. A. , Voller V. R.
Published: April 2008

An analysis of the flow patterns and associated solidification phenomena during the die casting process is presented. In the filling stage of the die cavity, the flow patterns are predicted using the volume of fluid method. These predictions are compared with experiments using water for a variety of geometries including an obstacle within the die cavity and multiple gates. In the solidification analysis, an enthalpy technique on a fixed grid is used to model the phase change with convection and diffusion occurring after the cavity is filled with liquid aluminum. A feature of this model is the prediction of the shape of the liquid-solid interface. Emphasis is placed on the effect of velocities from the residual flow field on this interface.
Life Estimation of Cracked Stainless Steel Components Under Creep Conditions
Authors: Radhakrishnan V. M. , Kamaraj M. , Balasubramaniam V. V.
Published: April 2008

Experimental investigations have been carried out to study the creep crack growth in types 316, 308 Cb, and 304 L stainless steel in the temperature range of 873–1073 K under plane stress condition. Testings have been carried out with both the base metal and the welded composite joints, because such joints are commonly used in nuclear power industries. Among the various parameters tried to correlate the creep crack growth, the energy rate line integral has been found to give the best description of the crack growth rate. The steady-state energy rate line integral has been found to correlate well with the rupture time. Based on this observation, life estimations are presented for thin components containing various initial defect sizes.
Temper Embrittlement in 2-1/4 Cr-1 Mo Steels After 75,000-Hour Isothermal Aging
Authors: Buscemi C. D. , Jack B. L. , Skogsberg J. W. , Erwin W. E.
Published: April 2008

A long-term laboratory study has confirmed that temper embrittlement (TE) in 2-1/4 Cr-1 Mo plate, forgings, and weldmetals levels off over time. Fifty-five heats of 2-1/4 Cr-1 Mo steel from several vendors were aged for up to 75,000 hours at 427 to 482°C (800 to 900°F), and extent of embrittlement was determined from shifts in 54 J (40 ft-lb) transition temperature for each heat. Embrittlement levelled off within 35,000 hours at 427°C (800°F) and 454°C (850°F), and within 10,000 hours at 482°C (900°F). Plate material embrittled least, while submerged arc and shielded metal arc weldments embrittled most. Although steel chemistry has previously been used to predict TE susceptibility, our analysis of these 55 heats, and of 23 heats of 2-1/4 Cr-1 Mo in a 1982 API study, shows that a step-cool treatment simulating long-term exposure is a more reliable way to screen susceptible materials.
An Appraisal of a Recent Analysis for Estimating the Plastic Component of the Deformation J Integral for a Stationary Crack
Authors: Smith E.
Published: April 2008

This paper provides an appraisal of a recent analysis for estimating the plastic component of the deformation J integral for a stationary crack. Such an estimation is a prerequisite when describing ductile crack extension in nuclear reactor pressure vessel materials. The assumptions in the analysis are emphasized, and the approximations arising as a consequence of introducing these assumptions are demonstrated.
Evaluation of a Modified Cyclic Neuber Relation
Authors: Wang K. C. , Sharpe W. N.
Published: April 2008

A preceding paper reported the results of biaxial strain measurements at the roots of notched aluminum specimen subjected to monotonic tension loading. The specimens had different amounts of constraints at the notch root, and it was shown that a modified version of the Neuber relation gave some improvement in its predictive capability. Several of those specimens were also subjected to fully reversed cyclic loading until microcracks formed at the notch roots, and the results of those biaxial strain measurements are reported here. The modified Neuber relation in the cyclic form was used to predict the strains at the notch roots. Reasonably close agreement between the predicted and the measured load-strain loops was found for all three levels of constraint.
Experimental and Numerical Investigation of Rotating Bladed Disk Forced Response Using Underplatform Friction Dampers
Authors: Sever Ibrahim A. , Petrov Evgeny P. , Ewins David J.
Published: April 2008

In this paper, we present a methodology and results from an experimental investigation of forced vibration response for a bladed disk with fitted underplatform “cottage-roof” friction dampers, together with the corresponding numerical predictions. A carefully designed and constructed rotating test rig is used to make precise measurements, which involve only the phenomena of interest. For this purpose, the measurement rig is operated under vacuum to eliminate aerodynamic effects on the rotating blisk and noncontact excitation and measurement techniques are employed so as not to modify the bladed disk dynamics. The experimental data measured are used for validation of multiharmonic balance-based prediction tools developed at the Imperial College. Predictions are carried out both with and without taking inherent mechanical mistuning into account, which is identified from measured data. Measured and predicted response curves are compared with each other and the degree of correlation is discussed.
Multishock Compactions of Powder Media Influenced by Elastic Waves in Punch and Plug
Authors: Sano Yukio , Tokushima Koji , Miyagi Kiyohiro
Published: April 2008

The previous theoretical predictions of the compaction of a copper powder medium, based on the assumption that the punch and plug were both a rigid body, did not satisfactorily agree with the experimental results obtained for short initial powder lengths and long plug lengths. This type of compaction amounts to cases when the plug length exceeds the second critical length which will be described below. Shock waves in a powder medium and elastic waves in the elastic punch and plug, schematically shown in space coordinate-time diagrams, suggest that the elastic wave in the plug is the probable cause of the inconsistency between the theoretical and experimental data of the previous investigation. In fact, the diagrams indicate that the shock wave transmitted in the medium across the medium-plug interface exerts an effect on the compaction process when the plug length does not exceed what is termed the first critical length. In cases when the effect of die wall friction is neglected, the mean green density-initial powder length relation of the copper medium is obtained from a theoretical approximation based on energy of the medium for the compaction with the sum of the initial powder length and the plug length being constant. This relation indicates that the effect of elasticity of the plug is large as the plug length becomes large. The second critical plug length at which the effect of elasticity becomes balanced with the effect of die wall friction is established by this relation and by the previously computed density-length relation with the effect of die wall friction taken into account. More specifically, these two relations provide a relation involving the first and second critical-plug lengths. The relation inferred as such agrees qualitatively with the previous experimental data in the examined region of the initial powder length. This qualitative agreement suggests that if the effects of elasticity and die wall friction are considered, a satisfactory theoretical and experimental agreement could be obtained. Therefore, the mean green density-initial powder length relation is computed taking into account both the effects. The computed relation agrees quantitatively with the previous experimental data even for short initial powder lengths and long plug lengths.
An Application of Incremental Plasticity Theory to Fatigue Life Prediction of Steels
Authors: Chen W. R. , Keer L. M.
Published: April 2008

An incremental plasticity model is proposed based on the von-Mises yield condition, associated flow rule, and nonlinear kinematic hardening rule. In the present model, fatigue life prediction requires only the uniaxial cycle stress-strain curve and the uniaxial fatigue test results on smooth specimens. Experimental data of 304 stainless steel and 1045 carbon steel were used to validate this analytical model. It is shown that a reasonable description of steady-state hysteresis stress-strain loops and prediction of fatigue lives under various combined axial-torsional loadings are given by this model
Nonlinear Response of Resin Matrix Laminates Using Endochronic Theory
Authors: Mathison S. R. , Pindera M. J. , Herakovich C. T.
Published: April 2008

The nonlinear response of laminated, resin matrix fibrous composites is modeled using orthotropic endochronic theory. The theory is formulated in terms of elastic constants and endochronic parameters characterizing the linear and nonlinear response, respectively, of unidirectional composites. All constants and parameters can be determined from normal (tension and/or compression) and shear tests on unidirectional and off-axis specimens. The nonlinear constitutive response relations for the unidirectional lamina are presented and the procedure for determining constants and parameters from test is described. The results are then used to predict the nonlinear response of unidirectional laminae and angle-ply laminates. Comparison between theory and experiment for compression loading of AS4/3502 graphite-epoxy, angle-ply laminates shows excellent correlation.
Particle-Level Investigation of Densification During Uniaxial Hot Pressing: Continuum Modeling and Experiments
Authors: Williamson R. L. , Knibloe J. R. , Wright R. N.
Published: April 2008

A combination of continuum models and experiments is used to investigate the deformation of individual particles during hot pressing. Results are described for both monosized and bimodal particle distributions, including a simple bimodal composite system. The effects of pressure and temperature on the densification rate, particle shape, and stress and strain fields are described. The detailed strain fields calculated by the model are useful for predicting microstructural development during the pressing process and thus can aid in the design of optimal pressing cycles.
Development of Constitutive Relationships Using Compression Testing of a Medium Carbon Steel
Authors: Rao K. P. , Hawbolt E. B.
Published: April 2008

Empirical or semi-empirical stress-strain relationships are of limited applicability because (i) they require a large number of constants to represent the effect of process variables, (ii) they are not able to adequately describe the typical hot deformation characteristics i.e., strain hardening at lower strains and steady state flow stress at higher strains, and (iii) they are not able to provide reliable extrapolation. In the present study, flow curves for hot deformation of a medium carbon steel in compression were obtained using a computer controlled thermo-mechanical simulator. The flow stress data were analyzed using three Arrhenius-type equations, each representing the flow stress in terms of strain rate and temperature at different strain levels. It was found that the hyperbolic-sine equation represented the data very well; each of the different activation parameters of this equation varied systematically with strain, and could be satisfactorily described using a power relationship. Using these proposed relationships the flow stress can be described in terms of the process variables—strain, strain rate and temperature—in an explicit fashion of use in finite-element analysis of hot deformation processes.
An Experimental Study of Interfacial Friction-Hot Ring Compression
Authors: Wang F. , Lenard J. G.
Published: April 2008

Ring compression tests were conducted at constant true strain rates in the temperature range of 900–975°C. The constant friction shear factor, m, was determined using a calibration chart. Scaling was permitted during the experiments in which a glass based lubricant was also used. Frictional conditions were affected most by the rate of strain; increasing it led to lower values of m.
A Viscoplastic Model for Single Crystals
Authors: Jordan E. H. , Walker K. P.
Published: April 2008

A viscoplastic constitutive model is described in which deformation behavior is postulated on representative slip systems and the behavior of the entire crystal is determined by summing the slip on the active slip systems. By building in the slip geometry known from the metallurgical literature, it is possible to predict the anisotropic deformation behavior and to model in a straightforward manner other phenomena which have been described by metallurgists in crystallographic terms. Elevated temperature tension-torsion tests were run and used to verify the model’s predictive abilities. Ratchetting behavior under thermomechanical loading conditions is specifically addressed.
Closure and Growth of Fatigue Cracks at Notches
Authors: McClung R. C. , Sehitoglu H.
Published: April 2008

The closure behavior of fatigue cracks growing out of notches is studied with an elastic-plastic finite element model. Crack opening stresses are shown to change significantly as the crack extends. Opening stresses are low at first and then gradually rise to stable values as the crack tip moves away from the notch field. These transient changes are not limited to the region of the original inelastic notch field. The rate of change of opening stresses with increasing crack length is a function of both nominal maximum stress and nominal stress ratio. Stable levels are reached more quickly at higher stress ratios and lower maximum stresses. These transient changes in Sopen have been emulated with a simple model which considers only changes in Sopen due to changes in the local stress field. The numerical results are quantitatively consistent with observed trends in experimental crack growth data, which show that accelerated crack growth can occur beyond the original notch plastic boundary. Finite element results and experimental data also both suggest that the accelerated short crack growth effect for cracks near notches is much less pronounced at higher stress ratios.
Stress Versus Temperature Dependence of Activation Energies for Creep
Authors: Freed A. D. , Raj S. V. , Walker K. P.
Published: April 2008

The activation energy for creep at low stresses and elevated temperatures is associated with lattice diffusion, where the rate controlling mechanism for deformation is dislocation climb. At higher stresses and intermediate temperatures, the rate controlling mechanism changes from dislocation climb to obstacle-controlled dislocation glide. Along with this change in deformation mechanism occurs a change in the activation energy. When the rate controlling mechanism for deformation is obstacle-controlled dislocation glide, it is shown that a temperature-dependent Gibbs free energy does better than a stress-dependent Gibbs free energy in correlating steady-state creep data for both copper and LiF-22mol percent CaF2 hypereutectic salt.
Modeling of Ratchetting in Biaxial Experiments
Authors: Guionnet C.
Published: April 2008

A new unified viscoplastic constitutive equation has been developed for interpreting ratchetting experiments. The model is based essentially on a generalized Armstrong-Frederick equation for the kinematic variable; the coefficient of the dynamic recovery term in this equation is a function of both instantaneous and accumulated inelastic strain which is allowed to vary in an appropriate manner in order to reproduce the experimental ratchetting rate. The validity of the model is verified by comparing predictions with experimental results for austenitic stainless steel (17-12 SPH) tubular specimens subjected to cyclic torsional loading under constant tensile stress at 600°C.
Application of a Unified Viscoplastic Model to Simulation of Autoclave Age Forming
Authors: Foroudastan S. , Peddieson John , Holman M. C.
Published: April 2008

A unified viscoplastic constitutive equation is combined with Bernoulli/Euler beam equations to create a model of autoclave age forming of beam specimens. Predictions based on the model are obtained numerically and compared with experimental data. Encouraging agreement is found between simulations and observations. Issues related to extensions of the methodology to more complicated geometries are discussed.
A Combined Theoretical/Experimental Approach to the Dynamic Characterization of Viscoelastic Materials
Authors: Greif R. , Johnson M. S.
Published: April 2008

This research combines theoretical and experimental approaches to the dynamic mechanical characterization of viscoelastic materials. A detailed derivation is presented for the dynamic response of a typical viscoelastic rod sample. Particular attention is given to the effect of inertia on experimental results for storage modulus and loss factor. The limitations of the testing equipment are examined in comparison to the theoretical formulation.
A Method for the Experimental Determination of Residual Stresses in Axisymmetric Composite Cylinders
Authors: Rammerstorfer F. G. , Fischer F. D.
Published: April 2008

An analytical procedure applicable for the experimental determination of initially existing residual stresses in long composite circular cylinders is derived within the framework of the drilling and turning technique. The method is demonstrated for a long cylinder composed of two different materials. An extension to cylinders composed of an arbitrary number of circular cylindrical layers can easily be derived in analogy to the described procedures.
A Viscoplastic Theory for Anisotropic Materials
Authors: Nouailhas D. , Freed A. D.
Published: April 2008

The purpose of this work is the development of a unified, cyclic, viscoplastic model for anisotropic materials. The first part of the paper presents the foundations of the model in the framework of thermodynamics with internal variables. The second part considers the particular case of cubic symmetry, and addresses the cyclic behavior of a nickel-base single-crystal superalloy, CMSX-2, at high temperature (950°C).
Estimation of Axisymmetric Residual Stresses in a Long Cylinder
Authors: Cheng W. , Finnie I. , Vardar O¨.
Published: April 2008

An approach based on linear elastic equations is developed to predict axisymmetric axial and radial residual stresses in a long cylinder in plane strain from hoop stresses measured in both plane strain and plane stress. This approach, when combined with the authors’ crack compliance method for residual stress measurement, leads to a simplified experimental procedure for measurement of axisymmetric residual stresses in cylinders.
Thermal Cycling Response of Quasi-Isotropic Metal Matrix Composites
Authors: Newaz G. M. , Majumdar B. S. , Brust F. W.
Published: April 2008

In this study, thermal cycling response of quasi-isotropic metal-matrix composite (MMC) with a stacking sequence of [0/ ± 45/90]s was investigated. The thermal cycles were imposed between temperatures of 316–649° C. Metallography of the samples at the edge has shown the presence of fiber-matrix debonding and ply-to-ply separation (delamination) in the 45 and 90 deg plies. The propensity for debonding was found to be greater when fibers are too close in any of these plies. Both closed form elastic analysis and linear finite element analysis using temperature dependent material properties were undertaken to evaluate the criticality of local stresses and strains in the constituent materials. Inelastic deformation around fiber-matrix interface leading to cracking in the 90 deg ply was best simulated by higher local variation in fiber volume fraction in the composite and the presence of initial process induced defect.
High Temperature Low Cycle Fatigue and Cyclic Constitutive Relation of MAR-M247 Directionally Solidified Superalloy
Authors: Hasebe Tadashi , Sakane Masao , Ohnami Masateru
Published: April 2008

This paper investigates the effect of solidification direction on cyclic constitutive relation and low cycle fatigue life for a directionally solidified (DS) superalloy Mar-M247LC at 1173 K in air. Strain controlled push-pull low cycle fatigue tests were carried out for three kinds of specimens of which loading direction was 0, 45 and 90 deg to DS axis. The 0 deg specimen exhibited the largest fatigue strength, the 45 deg specimen the smallest and the 90 deg specimen the intermediate. The difference in the fatigue strength due to the loading direction was discussed in detail from the viewpoint of the anisotropy of Young’s modulus. A life prediction method for DS specimens, considering the anisotropy of the Young’s modulus, was proposed and successfully applied to the low cycle fatigue data.
Use of Subsized Specimen for Evaluating the Strength and Fracture Toughness of Irradiated 2 1/4 Cr-1 M0 Steel
Authors: Mao X. , Takahashi H. , Kodaira T.
Published: April 2008

The procedure of the determination of yield and ultimate strengths of irradiated 2 1/4 Cr-1 M0 steel using small punch specimen (10 mm by 10 mm by 0.5 mm) has been demonstrated. The result was compared with the result obtained from conventional tensile test. Fracture toughness of irradiated 2 1/4 Cr-1 M0 steel was measured by use of subsized CT specimen and D. C. electrical potential method. Owing to irradiation hardening of 2 1/4 Cr-1 M0 steel, yield and ultimate strength increase substantially and fracture toughness decreases 37 percent when the steel is irradiated to a fluence of 3.2 x 1023 n/m2. The small punch and subsized CT specimen can be used for irradiation test so that considerable irradiation space will be saved.
Application of the Hybrid Constitutive Model for Cyclic Plasticity to Sinusoidal Loading
Authors: Ishikawa H. , Sasaki K.
Published: April 2008

In order to study the applicability of the proposed hybrid constitutive model for cyclic plasticity to nonproportional loading, type 304 stainless-steel specimens subjected to sinusoidal loading that could change the degree of nonproportionality of the strain path were examined in detail. The subsequent yield surface during the loading was discussed in advance because the plastic deformation induced anisotropy coefficient tensor in the yield function had to be determined from the yield surface obtained by the experiment. From the experimental results, the subsequent yield surfaces during the loading could be assumed to be of the quadratic form of stress. The simulations based on the model gave a good description of the sinusoidal loading, irrespective of the degree of nonproportionality of the strain path.