bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of Carbon on Ion-Nitriding
Authors: Cho K. S. , Lee C. O.
Published: October 2009

This paper deals with ion-nitride processing and is primarily concerned with the effects of carbon content in the workpiece and of added carbon in the gas atmosphere on hardness, compound layer thickness, and diffusion layer thickness. Increased carbon content in the workpiece increases the compound layer thickness, but decreases the diffusion layer thickness. On the other hand, an optimal amount of added carbon in the gas atmosphere will increase the compound layer thickness as well as the diffusion layer thickness and hardness. It is found that the ion-nitriding temperature at which maximum hardness is attained is governed by the ion-nitriding time. When the treatment time is made sufficiently long, the maximum hardness is obtained at a temperature near 450°C.
Macroscopic Brittle Fracture Criterion Under Multiaxial Stresses
Authors: Awaji Hideo
Published: October 2009

On the basis of traditional fracture criteria and numerous data on the fracture under multiaxial stresses, we propose a new macroscopic criterion for brittle fracture in the state where in biaxial or triaxial stresses, compressive stress predominates. We base our theory on the concept of fracture mechanics, especially of mode II fracture. Our criterion is expressed as follows, τc=τ0+ζ1(σ1+σ3)+ζ2σ2 where τ0 = (KIIc/KIc). at is the imaginary pure shearing strength of the material, ζ1 = (KIIc/KIc) (at/ac) – 1/2 and ζ2 are the coefficients corresponding to the restraint for crack propagation. The criterion may be applicable to mode II fracture which occurs in the state where compressive stress is predominant.
The Fatigue and Toughness Properties of a C-Mn-Cb Plate Steel
Authors: Wilson A. D.
Published: October 2009

The fatigue and toughness properties of a C-Mn-Cb plate steel, described both by ASTM A633C and A737B, are presented and compared to the properties of A516-70. Production plate steels made by both conventional steelmaking techniques and low sulfur-calcium treatment are evaluated. The superiority of A633C over A516-70 in transition and upper shelf fracture toughness is demonstrated in both Charpy-V-notch and Dynamic Tear impact testing, as well as J-Integral fracture toughness at both a slow and fast loading rate. There was no substantial difference in fatigue behavior between the A633C and A516-70 steels, except that A633C was found more sensitive to inclusions, thus there was more of a pronounced improvement shown by using calcium treatment. The fatigue behavior was assessed using S-N axial fatigue testing, fatigue crack propagation testing and by determining the threshold for fatigue crack propagation. The residual stresses in A633C in the quenched and tempered condition influenced the fatigue crack propagation and near threshold behavior of this steel.
Reactor Surveillance Test and Fracture Mechanics Evaluation of Irradiation Embrittlement in Reactor Pressure Vessel Steels
Authors: Takahashi Hideaki , Saito Kiyoshi , Shoji Tetsuo , Date Kazuhiro , Suzuki Masahiko
Published: October 2009

With special reference to a nuclear reactor surveillance test, a new evaluation procedure for the fracture toughness from Charpy Vee-notch data is developed. This procedure utilizes a recrystallization-etch technique to determine the crack tip energy dissipation (Wp) within an intense strain region or the dissipation rate (dWp/da). These two parameters serve to characterize the crack tip resistance to cleavage-controlled fracture initiation. The effects of specimen geometry, strain rate, temperature and notch acuity on the cleavage-controlled fracture toughness transition are explained using a critical value of Wp or dWp/da and a modified rate parameter. A feasibility of the new surveillance test procedure for evaluating the irradiation embrittlement of reactor pressure vessel steel, such as SA533B-1, is here verified experimentally, utilizing the Charpy or small compact tension specimen irradiated in a test reactor.
Delayed Retardation of Overloading Effects in Impression Fatigue
Authors: Chu S. N. G. , Li J. C. M.
Published: October 2009

Delayed retardation of plastic zone propagation in impression fatigue caused by a single peak overload is reported together with the effects of overload amplitude and the number of cycles as well as the interaction between two single peak overloads.
Effect of Temperature on Creep Crack Growth
Authors: Radhakrishnan V. M. , McEvily A. J.
Published: October 2009

Investigations have been carried out to study the effect of temperature on crack growth under creep condition in 6061 Al alloy. A parameter approach, connecting the three variables - crack growth rate a˙, the load point deflection rate Δ˙ and the applied load P - given in the form a˙∝Δ/˙PPoα1/θ where α, θ, and Po are constants, has been found to give good correlation with the experimental data. The exponents, α and θ, are dependent on temperature. The activation energy for the crack growth process has been found to be around 24 Kcal/mole.
Small Crack Behavior and the Prediction of Fatigue Life
Authors: Hudak S. J.
Published: October 2009

It is becoming increasingly evident that an understanding of incipient microcracking and growth of small cracks is essential to the development of improved predictions of the fatigue life of structures. Information on the threshold and kinetic properties of small cracks is reviewed and critically discussed. It is shown that the use of conventional fracture mechanics concepts to characterize small cracks results in behavior which differs from that of large cracks—this difference is due to a breakdown of underlying continuum mechanics assumptions. Methods to incorporate small crack behavior in fatigue life predictions are also considered. In these predictions, the importance of separately treating crack initiation and crack growth and of accounting for small crack behavior and plasticity effects (particularly for notched members) is demonstrated.
Fatigue Crack Growth Behavior of Explosively-Bonded Clad Steel Plates
Authors: Takezono S. , Satoh M. , Takita K.
Published: October 2009

Fatigue crack growth behavior of explosively-bonded clad steel plates was studied by making fatigue crack growth tests under a constant stress intensity factor range and carrying out a finite element elasto-plastic analysis of fatigue crack growth. Effects of an initial residual stress, a hardening layer and a yielding point of each original material on crack propagation were examined. It was concluded from the examination that for explosively clad materials which had a clad interface, residual stresses and a hardening layer near the interface, the fatigue crack growth rates were not related to the stress intensity factor range, but closely related to a maximum strain range at the crack-tip.
Ductile Tearing Instability of a Center-Cracked Panel of an Elastic-Plastic Strain Hardening Material
Authors: Zahoor Akram , Paris Paul C.
Published: October 2009

An analysis for crack instability in an elastic-plastic strain hardening material is presented which utilizes the J-integral and the tearing modulus parameter, T. A center-cracked panel of finite dimensions with Ramberg-Osgood material representation is analyzed for plane stress as well as plane strain. The analysis is applicable in the entire range of elastic-plastic loading from linear elastic to full yield. Crack instability is strongly influenced by the elastic compliance of the system, the conditions of plane stress or plane strain, and the hardening characteristics of the material. Numerical results indicate that if crack stability is ensured in a plane strain situation, then under the same circumstances a geometrically identical but plane stress panel will be stable.
Measuring the Actual Endurance Limit of One Specimen Using a Nondestructive Method
Authors: Harry R. , Joubert F. , Gomaa A.
Published: October 2009

The conventional endurance limit does not characterize one specimen but a set of virgin specimens. This present study deals with the determination of the present state of one specimen by its “actual” endurance limit. The connection between the state of a specimen and its thermal response, obtained by using the thermal test method, has already been shown. It is shown here the close correlation which exists between the transition stress value τl and the actual endurance limit of the specimen. Thus, the actual endurance limit of a specimen at any moment in its fatigue life, so, at any stage of treatment, could be determined by using a “nondamaging” method.
Threshold and Low-Rate Fatigue Crack Growth of a NiMoV Rotor Steel
Authors: Shih T. T. , Donald J. K.
Published: October 2009

An automated, computer-controlled K-decreasing technique was used to determine the threshold, ΔKth, and low-rate fatigue crack growth of a NiMoV rotor steel. A more conventional K-increasing technique was also used. Excellent agreement between results obtained from both techniques was observed. For the material and environment studied, no crack arrest was observed for crack growth rate down to 2.5 × 10−8 mm/cycle (10−9 in./cycle). As such, an operational definition of ΔKth was defined as the stress intensity factor range corresponding to a crack growth rate of 2.5 × 10−8 mm/cycle (10−9 in./cycle). In room temperature air environment, ΔKth was found to be 6.2 and 4.0 MPam (5.6 and 3.6 ksiin.) for R = 0.1 and R = 0.5, respectively. At the same ΔK level, crack growth rate was found to increase with increasing stress ratio. The influence of stress ratio on crack growth rate, however, decreases with increasing ΔK. By raising temperature to 93° C (200°F), ΔKth was found to be suppressed to 4.4 and 2.9 MPam (4.0 and 2.6 ksiin.) for R = 0.1 and R = 0.5, respectively. Stress ratio effect on crack growth rate is the same as at room temperature, but is less significant. Temperature was found to influence crack growth rate in the threshold region for both stress ratio studied, with higher crack growth rate at 93°C (200°F) than at room temperature. Temperature sensitivity was found to be less for R = 0.5 than R = 0.1. The existence of hydrogen was found to have little effect on ΔKth and low-rate fatigue crack growth behavior of this NiMoV rotor steel.
A Criterion for Plastic Failure of Notched High Strength Steel Structures
Authors: Margetson J.
Published: October 2009

A criterion of ductile failure for a high strength steel under a multiaxial state of stress is established. A family of multiaxial stress states at failure is generated from the fracture data of a number of notched tensile specimens with differing notch geometries. An elasto-plastic finite element analysis, for a work hardening material, is used to analyze each test. Several failure criteria are considered including maximum stress, maximum strain, and distortional energy. A Von Mises type criterion, suitably equated to the maximum tensile properties of the material, gives highly accurate predictions in all cases.
The Equivalence of the Final Stretch and Crack Tip Opening Angle Criteria for Plane Strain Crack Growth
Authors: Smith E.
Published: October 2009

The equivalence of the final stretch and crack tip opening angle criteria, as applied to the Dugdale-Bilby-Cottrell-Swinden type model for Mode I plane strain crack growth, is demonstrated. This equivalence is independent of the plastic zone size, geometrical parameters, and the stress distribution within the fracture process zone, if the yield stress is sufficiently low and the crack growth resistance is sufficiently high. The results therefore provide further support for the viability of crack tip opening angle as a crack growth characterizing parameter.
Fatigue Life Predictions of Smooth and Notched Specimens Based on Fracture Mechanics
Authors: El Haddad M. H. , Topper T. H. , Topper T. N.
Published: October 2009

An elastic plastic fracture mechanics solution for short fatigue cracks in smooth and notched specimens is presented which admits plasticity by replacing the conventional stress term with a strain term and accounts for the propagation of very short cracks by the introduction of an effective crack length which is equal to the actual length increased by length l0, the length constant l0 is characteristic of the material and material condition and is calculated from the smooth specimen endurance limit and the long crack threshold stress intensity. Crack growth results for cracks in both elastic and plastic strain fields of notched specimens when interpreted in terms of this strain based intensity factor showed excellent agreement with elastic long crack data. This intensity factor when combined with a propagation model that includes all stages of crack growth also successfully predicted the total fatigue life of the smooth and notched specimens studied here. The predicted propagation life of elliptical and circular notched specimens is in all cases within 50 percent of the actual fatigue lives.
A Plastic Fracture Instability Analysis of Wall Breakthrough in a Circumferentially Cracked Pipe Subjected to Bending Loads
Authors: Zahoor Akram , Kanninen M. F.
Published: October 2009

A method of analyzing internal surface circumferential cracks in ductile reactor piping is presented. The method utilizes an alternate but equivalent definition of the J-integral based on nonlinear structural compliance. The analysis is valid for situations where the cross section containing the crack is fully yielded. Results are obtained for radial and circumferential crack growth for pipes subjected to bending. The stability of radial crack growth (wall breakthrough) is assessed using the J-integral-based Tearing Modulus approach. The analysis is shown to be in good agreement with experimental results on the stability of surface crack growth in Type 304 stainless steel pipes. Example quantitative results for fracture instabiltiy assessments for nuclear piping are presented to demonstrate the practical application of the approach.
Dynamic Analysis of a Torsion Test Specimen Including Heat Conduction and Plastic Flow
Authors: Johnson G. R.
Published: October 2009

This paper presents an analysis of a copper torsion test specimen exhibiting a thermal softening instability at a high strain rate. A consititutive relationship derived from test data includes strain hardening, strain rate effects, and thermal softening. This relationship is used to numerically simulate the thermal softening instability. The results of the analysis are in good general agreement with the test data. The numerical technique is based on an explicit finite element formulation for axisymmetric solids. Elastic and plastic flow stresses are determined from strains, strain rates, and temperatures. Heat is generated by the plastic flow stresses and capability is provided to account for heat conduction. The general numerical technique can be used for a wide range of problems involving thermal-mechanical interaction.
Strong Tough HSLA Steels Via Processing and Heat Treating of Cu-Ni-Cb and Cu-Ti-B Compositions
Authors: Krishnadev M. R. , Sojka G. J. , Banerji S. K.
Published: October 2009

The paper deals with the development of control-rolled Cu-Ni-Cb HSLA steels with increased section capability for low-temperature environments and Cu-Ti-B HSLA steels for general structural applications as well as for specialized applications requiring quench and temper treatments. Results indicate that based on 2 percent copper additions it is possible to develop HSLA steels with strength level of over 690 MPa with sufficiently low transition temperatures (−40°C to lower than −70°C) and very upper shelf values (170 J to 270 J). In the boron-containing compositions, even in the absence of nickel, strength levels of 480 to 820 MPa with a T. T. of −20°C to lower than −60°C have been realized depending upon the rolling practice and the reheat and quench practice. The practical implications of the study are discussed.
A Statistically Based Investigation of the Environmental and Cyclic Stress Effects on Fretting Fatigue
Authors: Poon C. J. , Hoeppner D. W.
Published: October 2009

A completely randomized factorial experiment was conducted to investigate the environmental and cyclic stress effects on the fretting fatigue behavior of 7075-T6 aluminum alloy. Fretting fatigue tests were conducted in vacuum (10−5 Torr) and in laboratory air environment at two maximum cyclic stress levels. The fractographic features of the wear surface with respect to different environments were examined. The experimental results and statistical analysis showed that the environment, cyclic stress, and their interactions were significant factors in reducing the life of 7075-T6 aluminum alloy under fretting conditions. The fractographic analysis showed that fretting damage led to the development of cracks in the fretting areas in both environments. However, the mechanisms involved in crack development were different. The reduction in fatigue life under fretting condition was explained by a model utilizing fracture mechanics concepts.
An Analysis of Grain Size and Yield Stress Effects on Stress at Fatigue Limit and Threshold Stress Intensity Factor
Authors: Mutoh Y. , Radhakrishnan V. M.
Published: October 2009

Fatigue limits of smooth specimens and threshold stress instensity factors of specimens with large cracks depend on the microstructure of the material. A simple model in which it is assumed that the plastic zone size near the crack tip is of the order of the grain size at the threshold region has been presented in this analysis which explains the dependence of stress at the fatigue limit and the threshold stress intensity factor on yield stress and grain size.
The Effect of Product Form Upon Fatigue-Crack Growth Behavior in Alloy 718
Authors: James L. A.
Published: October 2009

Five different product forms (sheet, plate, bar, forging, and weldments) all taken from the same heat of Alloy 718 were tested at five different temperatures in each of two different heat-treated conditions. In general, no consistent effect of product form was noted for any of the wrought forms (sheet, plate, bar, or forgings). However, the crack growth rates were higher in weldment specimens than in wrought specimens for some test temperature/heat-treatment combinations. The present results suggest that product form did not influence the heat-to-heat variations noted previously in crack growth studies on wrought Alloy 718.
Multispecimen Fatigue Crack Propagation Testing
Authors: Ermi A. M. , Bauer R. E. , Chin B. A. , Straalsund J. L.
Published: October 2009

Chains of miniature center-cracked-tension specimens were tested on a conventional testing machine and on a prototypic in-reactor fatigue machine as part of the fusion reactor materials alloy development program. Annealed and 20 percent cold-worked 316 stainless steel specimens were cycled under various conditions of temperature, frequency, stress ratio and chain length. Crack growth rates determined from multispecimen visual measurements and from an electrical potential technique were consistent with those obtained by conventional test methods. Results demonstrate that multispecimen chain testing is a valid method of obtaining fatigue crack propagation information for alloy development.
A Design Approach for Correlating High Temperature Fatigue Crack Growth Over a Wide Range of Parameters
Authors: McGowan J. J. , Liu H. W.
Published: October 2009

High temperature fatigue crack growth was studied in several materials under various environmental conditions. At temperatures less than one-half of the melting point, creep effects were found to be negligible in comparison to environmental effects. The general fatigue behavior is a result of both time dependent and cycle dependent processes. A model is formulated which combines linearly the separate time and cycle dependent behaviors to correlate the general fatigue behavior. The cycle dependent behavior in the model is based upon the premise that the relative corrosion rate controls the crack growth rate. The few constants in the cycle dependent portion of the model are based upon the fatigue crack growth in the environment with zero load ratio and no dwell. The time dependent behavior is determined from static crack growth data in the environment. The resulting Kinetic Model correlates with good success the effects of temperature, frequency, dwell time and load ratio on the high temperature air fatigue crack growth of IN-100.
Evaluation of Radiation Damage in Reactor Pressure Vessel Steel by Elastic-Plastic Fracture Mechanics
Authors: Khan M. A. , Shoji T. , Takahashi H. , Suzuki M.
Published: October 2009

Elastic-plastic toughness characterization of SA533B nuclear pressure vessel steel is described in terms of the J integral approach. A simple test procedure has been proposed from which the JIC value at crack extension can be estimated for both unirradiated and irradiated steels using a single compact tension specimen. The values of JIC determined by the proposed method are compared with those determined by the single specimen compliance method. The JIC fracture toughness of the pressure vessel steel irradiated at 200°C to a neutron flux density ranging from 6.2 × 1017 to 2.34 × 1019 n/cm2 (E>1 MeV) has been explored for different test temperatures. It is shown that irradiation significantly reduces the JIC fracture toughness of this material. These results are compared with the data available in the literature.
A New Parameter for Characterizing Corrosion Fatigue Crack Growth
Authors: Shoji T. , Takahashi H. , Suzuki M. , Kondo T.
Published: October 2009

The role of mechanical factors, such as ΔK, R, and K˙ (loading rate), and its significance on corrosion fatigue crack growth acceleration were discussed in terms of crack tip strain rate and/or nucleation rate of fresh metal surface. A new parameter for characterizing corrosion fatigue crack growth was proposed, paying attention to rates of crack tip mechanochemical reactions, i.e., oxide film rupture rate, passivation rate, and solution renewal rate, which are influenced by the crack tip mechanical condition, microstructure of material, and environment. Hence a new parameter da/dt]air, the time base pure fatigue crack growth rate which was related closely to crack tip deformation rate, was introduced as a measure of actual crack tip strain rate. In various combinations of materials and environments, it was shown that the value of da/dt]air determines a crack growth rate in the environment, irrespective of mechanical factors such as ΔK, Kmax, R, and K˙, or frequency.
A State Variable Analysis of Inelastic Deformation of Thin Walled Tubes
Authors: Wire G. L. , Duncan D. R. , Cannon N. S. , Johnson G. D. , Alexopoulos P. S. , Mukherjee S. , Li Che-Yu
Published: October 2009

This paper presents the results of inelastic analysis performed to calculate the deformation of a thin-walled tube subjected to a variety of loadings at elevated temperatures. A state variable constitutive model is used to describe material behavior. The material parameters for a particular material—Type 316 austenitic stainless steel—are determined from uniaxial load relaxation and tensile tests, and internally pressurized tube tests. The simulated results are compared with experimental data. The significance of the comparisons is discussed in terms of the validity of the state variable approach used here.
Constitutive Equations for the Rate-Dependent Deformation of Metals at Elevated Temperatures
Authors: Anand L.
Published: October 2009

Approximate constitutive equations are proposed for use in the analysis of the rate-dependent deformation of metals at temperatures in excess of a homologous temperature of 0.5. The constitutive equations are formulated within the scope of some recent theories of elastoviscoplasticity with internal variables, but employ only a single scalar internal variable representing an isotropic resistance to plastic flow offered by the internal microstructural state of the material. The special constitutive euqations incorporate strain hardening of the Voce type, and account for the effects of the prior histories of strain rate and temperature undergone by the material. These equations, however, do not represent the important effects of static recovery or of static and dynamic recrystallization.
Steady and Transient Creep Behavior Based on Unified Constitutive Equations
Authors: Merzer A. M.
Published: October 2009

A set of constitutive equations, which has been used to describe a variety of quasi-static and dynamic viscoplastic phenomena, are applied to creep problems. Simulations of steady and transient creep at constant stress are obtained which compare well with experimental results both qualitatively and quantitatively. Simulations of creep resulting from rapid changes in the applied stress also compare well with observations. The constitutive equations can be used to describe logarithmic creep. These latter predictions are compatible with experimental results in considerable detail.
Constitutive Equations Study in Biaxial Stress Experiments
Authors: Oytana C. , Delobelle P. , Mermet A.
Published: October 2009

An experimental study of high temperature creep constitutive equations is reported. The experiments are performed in uniaxial and biaxial (tension-torsion) state of stress. Stress drop experiments starting from a given plastic state (i.e., fixed creep rates, stresses and temperature) lead to the flow rules. It is so pointed out: that hardening is essentially kinematical (as well as creep induced anisotropy), that in steady creep the components of this hardening are proportional to those of applied stress. Then, constitutive equations can be derived from that, the identification of which is reduced to the determination of three hardening and recovery scalar functions and to the knowledge, easily open to measure, of the relationship between the equivalent strain rate and the effective equivalent stress. In the case of our experiments, this relationship is a power law.
A Nonlinear Elastic Model for Isotropic Materials With Different Behavior in Tension and Compression
Authors: Medri Gianluca
Published: October 2009

This note presents a model suitable for the mechanical characterization of isotropic materials with different behavior in tension and compression. The model has been derived from the nonlinear elastic theory and elaborated to adapt it to the small deformation field; the constitutive relation may reliably correlate stress and strain fields even in three-dimensional elastic problems.
A Simplified Approach to the Effect of Specimen Size on the Creep Rupture of Cross Weld Samples
Authors: Williams J. A.
Published: October 2009

Various methods are available to assess the performance of welded joints under creep conditions. One approach uses the creep rupture testing of cross weld geometries in uniaxial tension. This paper examines an idealized model of a cross weld specimen where the weld metal is weaker than the parent material. The analysis, which is developed from published work on brazed and soldered joints, characterizes the limit load of the specimen as a function of the weld thickness:specimen diameter ratio and the yield strengths of both materials. The limit load is then used to define a creep reference stress which may be applied to uniaxial data. The predictions of the failure location and failure time are compared with cross weld creep data generated within the CEGB as no suitable data were found in the general literature. Finally, the model is used to postulate a size or weld thickness:specimen diameter effect on stress rupture testing of cross weld geometries.
The Rolling of Very Thin Sheets
Authors: Scrutton R. F. , Lenard J. G.
Published: October 2009

Thin strip specimens were reduced to foil by passing them repeatedly between the rolls of a two-high mill at low speeds. Narrow specimens were tested to avoid complications caused by roll bending. Factors governing the rate of reduction were examined, these being roll preload value and roll surface finish for low carbon strips as well as material strength, hardness, and anisotropy for aluminum and copper. No minimum thickness was found for the steel specimens; for aluminum and copper limiting thickness values were obtained based on the onset of edge cracking and longitudinal fracture. Thickness values and total number of passes were found to be inversely related. Roll surface finish and preload value affected the rate of reduction in a significant manner; hardness and developing anisotropy did not.
The Effect of Strain Rate on the Strain to Fracture of a Sheet Steel Under Biaxial Tensile Stress Conditions
Authors: Broomhead P. , Grieve R. J.
Published: October 2009

The present investigation was undertaken as a preliminary study into the influence of strain rate on the forming limit diagram for low carbon steel. For a variation in strain rate from 10−3 s−1 to 70 s−1 experiments have shown that, in the positive quadrant of the forming limit diagram, the position of the forming limit curve is lowered with increasing strain rate. Further, it is suggested that a degree of correlation exists between strain rate and the work hardening exponent “n,” and as such the influence of strain rate on the forming limit diagram manifests itself through the change in n value. Slow speed forming was carried out under oil pressure using a bulge test with elliptical dies. To attain higher strain rate a water-hammer forming technique was employed together with the same die sets as those used for bulge forming.
Growth of Corner Cracks at a Hole
Authors: Liu A. F. , Kan H. P.
Published: October 2009

The two-dimensional growth characteristics of corner cracks emanating from an open hole were demonstrated by conducting constant amplitude cyclic crack growth tests on a set of 51 specimens. The specimens were machined from 2024-T851 aluminum alloy in three thicknesses (6.35, 12.7, and 19.30 mm) and three hole diameters (6.35, 12.7, and 19.05 mm). The precrack sizes are very small (typically 0.5 to 1.0 mm in either length or depth dimensions) having many arbitrary initiated length-to-depth ratios. Empirical stress intensity factors for various crack size, crack shape, and specimen geometry combinations were calibrated by back-tracking of the crack growth rate behavior in these specimens and the material baseline crack growth rate data (also in three thicknesses of the same heat) developed from compact specimens. Superposition principles were applied to separate the lumped stress intensity factors into a parametric functional form. It has been demonstrated that these empirically derived stress intensity expressions are capable of predicting the crack growth behavior in both the length (on specimen surface) and depth (on the hole wall) directions.
Biaxial Fatigue of Fiber-Reinforced Composites at Cryogenic Temperatures. Part I: Fatigue Fracture Life and Mechanisms
Authors: Wang S. S. , Chim E. S.-M. , Socie D. F.
Published: October 2009

A study of biaxial fatigue of glass fiber-reinforced composites subjected to in-phase, cyclic tensile and torsional loading at cryogenic temperatures is presented. Fatigue failure of the composite is investigated in terms of cyclic fracture, stiffness degradation, and energy dissipation. Fatigue fracture lives of the cryogenic composite are obtained for the cases of various combinations of cyclic tensile and torsional stresses. A power-law relationship is established between the range of cyclic octahedral shear stress and the number of cycles to fracture. Influences of hydrostatic mean stress and stress biaxiality ratio on fatigue fracture of the fiber composite are determined. Fracture mechanisms in the material during the cryogenic biaxial fatigue are examined by using optical and scanning electron microscopes.
Long-Life Fatigue of Type 316 Stainless Steel at Temperatures up to 593°C
Authors: Jaske C. E. , Frey N. D.
Published: October 2009

Some energy-system structural components may be subjected to 107 or more cycles of small-amplitude, strain-controlled vibrations. In such cases, information on the elevated-temperature, long-life (>106 cycles to failure) fatigue resistance of the austenitic steels often used in these components is needed. Present design guidelines provide fatigue curves for these steels only up to 106 cycles to failure. The objective of the present study was to evaluate the long-life fatigue resistance of one such steel, namely Type 316 stainless steel. Strain-controlled long-life (> 106 cycles to failure) fatigue experiments were conducted on solution-annealed Type 316 stainless steel in air at temperatures from 21 to 593° C. These were all for continuous cycling of smooth specimens under fully reversed straining (no mean stress). Results of this work provided a major advance in understanding the fatigue behavior of this steel. Tentative best-fit fatigue curves have been developed, but more data are needed to establish needed statistical confidence in them. At 21°C, strain and load-controlled experiments gave similar fatigue-resistance values at 108 cycles when inelastic straining was taken into account. However, at 427°C and above, strain-controlled cycling yielded fatigue-resistance levels at 108 cycles about 15 to 25 percent above those for load-controlled cycling. This difference is related to the continually increasing stress levels observed under strain cycling at the higher temperatures. That is, cyclic hardening continues to occur for 105 or more cycles of straining with accompanying two- to threefold increases in strength. This increased strength gives the increased fatigue resistance at long lives. Under load-controlled conditions, such cyclic hardening cannot occur, and the fatigue resistance is lower. Results of this work emphasize the need for considering the intended service conditions in carrying out laboratory experiments. The impact of these results on recommended experimental procedures for long-life fatigue testing of such alloys is discussed. Finally, considerations for application of these data in fatigue design are addressed.
A Review of the Abrasive Wear of Metals
Authors: Misra Ambrish , Finnie Iain
Published: October 2009

A survey is presented of the experimental work which has been carried out on the abrasive wear of metals. The effect of variables such as surface hardness, abrasive hardness, abrasive particle size, and velocity are discussed for several types of abrasive wear. The similarities between different types of wear are described with the viewpoint of using one type of wear test to rank materials for another application.
Fatigue of Thick Tubes: Effect of Mean Pressure, Honing, Plating, Burnishing, and Peening
Authors: Findley W. N. , Reed R. M.
Published: October 2009

Experimental results are presented for fatigue of closed-ended thick-walled tubes of 2.5 wall ratio and 32.3 mm (1.27 in.) ID for SAE 4333 steel subjected to pulsating internal pressure. Results are given for the following conditions: as-received-polished bore, stress relieved, honed with a 207 MPa (30 ksi) mean pressure, honed with a 276 MPa (40 ksi) mean pressure, nickel plated bore, roller burnished bore, and shot peened bore.
Stress-Strain Behavior of Inconel 718 During Low Cycle Fatigue
Authors: Cook T. S.
Published: October 2009

In the development of better methods of assessing damage accumulation, one of the requirements is an understanding of the cyclic constitutive behavior of the material. It is known that the cyclic stress-strain behavior is affected by temperature and possibly Rε ratio (εmin/εmax) and that the properties change as cycles are accumulated. This report presents some results, particularly the development of a mean stress in the material, obtained during low cycle fatigue tests of Inconel 718. The tests varied temperature and Rε ratio to determine their effects on the cyclic constitutive relation. Changes in the cyclic stress-strain behavior as a function of cycles were also examined. It was possible to relate the mean stress to either the total or plastic strain ranges for all temperatures. There was sufficient scatter in the data to prevent an unambiguous interpretation of the effect of Rε ratio on the mean stress, however.
Fatigue Crack Propagation Beyond General Yield
Authors: Vardar O¨ktem
Published: October 2009

Tests are carried out on compact tension specimens of AISI 1020 hot-rolled steel at nominal stress levels beyond yield. The results show that crack propagation rates can be correlated successfully using an operational definition of the range ΔJ of the J-integral. The rate of crack growth per cycle da/dN is shown to be related to ΔJ by da/dN=A (ΔJ)α for conditions ranging from linear elastic to limit load. The exponent α agrees well with other published data on low strength steels and the quantity A is found to have a weak dependence on frequency. Examination of the fracture surface reveals that static failure modes are operating at the high crack propagation rates.
The Use of Notched Beams to Establish a Multiaxial Stress-Fracture Criterion for Beryllium
Authors: Mayville R. A. , Finnie I.
Published: October 2009

Fracture of beryllium under biaxial states of stress has been studied in the past using thin-walled tubes loaded by combinations of axial load, torsion, and internal pressure. In the present investigation to obtain a triaxial state of stress, notched beams of beryllium with varying dimensions were tested in plane strain four-point bending. The conditions necessary to ensure plane strain are discussed in detail and plane strain finite element analyses are used to determine the stresses and strains at fracture in the notched specimens. Based on the test results a strain dependent, maximum tensile stress fracture criterion is proposed for parts without macroscopic cracks. In addition, the plane strain fracture toughness of beryllium is estimated from the notched bar tests using the RKR model.
The Minimum Elastic Energy Density Criterion in Dynamic Problems of Propagating Cracks
Authors: Theocaris P. S. , Papadopoulos G.
Published: October 2009

In a previous paper by the authors the minimum elastic strain energy density criterion was studied by considering the general case where both KI and KII-components of the stress intensity factor are operative when the crack is stationary, and static elastic fracture theory is valid. In this paper the dynamic case was considered. The influence of the velocity of a propagating slant crack in a homogeneous and elastic plate was taken into account. The dynamic stress intensity factors KId and KIId were accurately determined by using the method of reflected caustics and the dynamic initial curve was defined to delineate the boundary of the core region, which is assumed to be the limiting curve, along which the energy density should be evaluated. It was shown that, in particular cases, important corrections to the position of this minimum and its size should be introduced in order to take care of the dynamic influence.
Tensile Property Improvements of Spinodal Cu-15Ni-8Sn by Two-Phase Heat Treatment
Authors: Louzon T. J.
Published: October 2009

A heat treatment has been developed which produces significant improvements in the tensile properties of Cu-15Ni-8Sn spinodal alloy. The treatment involves solution heat treatment in the two-phase region rather than the single-phase region normally used. After quenching and aging, increased strength and ductility of the alloy over single phase solution heat-treated and aged values were found. The mechanical properties obtained were superior to any previously observed for material of the compositions studied in the solution treated, quenched, and aged condition. Also, the alloys’ transformation kinetics were greatly slowed by the two phase heat-treatment. It is suggested that the increase in strength and slow kinetics of transformation observed are caused by grain size effects and by grain boundary modifications. Resistivity data and etching response corroborate these arguments.
Further Compositional Effects on the Temper Embrittlement of 2 1/4 Cr-1 Mo Steels
Authors: McMahon C. J. , Murza J. C. , Gentner D. H.
Published: October 2009

As an extension of a previous study (reference [1]), the effects of a 0.3 pct nickel content, of tin in combination with several other elements, and of a 0.1 pct vs a 0.2 pct carbon content, were examined in 2 1/4 Cr-1 Mo steel having a bainitic microstructure, a hardness of Rc 15, and a grain size in the range ASTM no. 5 to 7. The main effect of the nickel was reduction in the FATT of steels in the unembrittled condition. The only deleterious effect was a small contribution to temper embrittlement in the steel containing high manganese and silicon concentrations. Tin was found not to be an embrittling element in this class of steel in the sense that it segregates and lowers intergranular cohesion. However, it strongly promotes phosphorus-induced temper embrittlement, apparently in a manner similar to silicon. A modified type of plot relating composition to temper embrittlement susceptibility is proposed. It was found that the 0.1 pct and 0.2 pct carbon steels had equivalent temper embrittlement behavior when the hardness and grain size were held constant.
Microstructural and Macrostructural Modeling of the Fracture Behavior of Pearlitic Gray Irons
Authors: Verma D. K. , Berry J. T.
Published: October 2009

An attempt is made to rationalize the fracture behavior of pearlitic gray irons on both the microstructural and macrostructural levels. Along with the effects of inoculation, those of as-cast section size and carbon equivalent may be rationalized on the basis of coarseness and volume fraction of the weak graphite flakes present in the structure based upon Hornbogen and Motz microstructural model. On the macrostructural level, however, the eutectic cell size is the single most important parameter controlling fracture behavior of gray irons. An analytical model is developed to predict the fracture toughness as a function of notched tensile strength and eutectic cell size. Analytical predictions on both the microstructural and macrostructural levels compare well with experimental results.
The Effects of Induction Heating Conditions on Controlling Residual Stresses in Welded Pipes
Authors: Rybicki E. F. , McGuire P. A.
Published: October 2009

Induction heating for stress improvement (IHSI) is a method for reducing the tensile weld induced stresses on the inner surfaces of the girth welded pipes. The process entails inductively heating the outside of a welded pipe while cooling the inner surface with flowing water. A 10-in. Schedule 80 Type 304 stainless steel pipe was selected for this study. Residual stresses due to welding were first determined using a finite element computational model. Several IHSI treatments subsequent to welding are then examined computationally to determine the effect of induction coil length and maximum outer surface temperatures on the final residual stress state. All IHSI treatments gave reduced inside surface tensile weld induced stresses on the inner surface. Longer coils and higher outer surface temperatures led to inner surface stresses that were more compressive.
The Effect of Specimen Size on Stress-Strain Behavior in Compression
Authors: Gunasekera J. S. , Havranek J. , Littlejohn M. H.
Published: October 2009

Compressions tests on right, cylindrical steel specimens were performed in order to determine the stress-strain behavior. Lubrication was achieved by using a thin PTFE (Hostaflon) sheet on either side of the specimen. Preliminary testing with geometrically similar specimens (aspect ratio of 1.5) showed that the stress-strain relations were affected by the size of the specimen. This paper deals with the theoretical investigation and the experimental verification of this phenomenon (termed the “size effect”). It is concluded that homogeneous deformations up to large strains can be maintained by proper selection of the PTFE sheet thickness.
The Effect of Test System Misalignment in the Dynamic Tension Test
Authors: Wu Han C. , Wang T. P. , Yip M. C.
Published: October 2009

An analysis of test system misalignment is presented for dynamic tension test. Sheet type rectangular 1100-0 aluminum specimens are used for discussion. For a constant strain rate tension test, the strain rate is constant only on the neutral axis of the specimen. The lower the strain rate is, the more significant the misalignment errors become. The neutral axis will shift away from the centerline of the specimen as the plastic strain increases. But, it will reach a limit and will not completely move back to the centerline.
Multiaxial Stress Rupture Testing and Compendium of Data for Creep Resisting Steels
Authors: Browne R. J. , Lonsdale D. , Flewitt P. E. J.
Published: October 2009

Recently, there has been an increasing need for more accurate methods of predicting the life of components operating in the creep range. Although many such components are invariably subject to multiaxial stress systems, present life estimation methods utilize available uniaxial creep rupture data via a representative stress for the component. This stress is usually empirically derived and in many cases leads to undue conservatism in life estimates because no account is taken of the creep and rupture response of the material to multiaxial stresses. This paper reviews the various multiaxial stress rupture test techniques which have been employed to determine the multiaxial stress rupture criterion. The multiaxial stress rupture data available in the literature for some commonly used creep resisting steels are compiled and discussed.
Effect of Prestrain at Elevated Temperature on the Fracture Behavior of High Strength Steels
Authors: Satoh K. , Toyoda M. , Mutoh Y.
Published: October 2009

It is well known that fracture initiation behavior is influenced by weld thermal straining. In the present report, attention is focused on the influence of weld thermal straining on the fracture mechanism. The influence of prestrain at elevated temperature or strain-aging on the initiation and propagation behaviors of ductile and cleavage fracture in KD32 and HT80 steels is investigated. A relationship between the increase in the lowest temperature at which a tear dimple region can be observed (Ti) or the decrease in stretched zone width and the increase in hardness at the notch tip is found.
Wave Propagation in the Split Hopkinson Pressure Bar
Authors: Follansbee P. S. , Frantz C.
Published: October 2009

Elastic wave propagation in the split Hopkinson pressure bar (SHPB) is discussed with an emphasis on the origin and nature of the oscillations that often trail the leading edge of the pressure wave. We show that in the conditions of the SHPB test the pressure bars vibrate in the fundamental mode and that elastic wave propagation can be fully described mathematically. Excellent agreement is found between experimental results and predictions of the mathematical treatment. This suggests that dispersion effects in the pressure bars can be removed from the strain gage records, which reduces the magnitude of the oscillations in the resulting stress strain curve.
Evaluation of Fracture Toughness (JIC) Using Single Specimen Fracture Test Augmented by Finite Element Analysis
Authors: Streit R. D.
Published: October 2009

Fracture toughness is evaluated using the combination of results from a single compact tension fracture test and computationally developed key-curves. The key-curves—a family of load-deflection curves for the test specimen with different length cracks—were developed using the tensile flow properties of the material. By overlaying the experimental test results on these curves the crack length and crack growth during the test can be deduced. The value of J for each crack length is then evaluated from the experimental load-deflection data. The J versus crack extension curve is plotted and JIC evaluated. The method is applied to the evaluation of the toughness of depleted uranium and is shown to substantially reduce the scatter often observed in the J versus Δa data.
Application of a Theory of Viscoplasticity to Uniaxial Cyclic Loading
Authors: Eisenberg M. A. , Yen C.-F.
Published: October 2009

The uniaxial specialization of a theory of cyclic viscoplasticity is described. The theory incorporates a realistic description of nonlinear stress-strain curves and of transient cyclic hardening and softening in both rate-dependent and rate-independent approximations. The applications to constant strain amplitude, incremental step tests, and random inputs are demonstrated.