bluuebunny/crossref_metadata_2025 huggingface dataset:
Progressive augmentation and ventilatory long‐term facilitation are enhanced in sleep apnoea patients and are mitigated by antioxidant administration
Authors: Lee Dorothy S. , Badr M. Safwan , Mateika Jason H.
Published: October 2009

Progressive augmentation (PA) and ventilatory long‐term facilitation (vLTF) of respiratory motor output are forms of respiratory plasticity that are initiated during exposure to intermittent hypoxia. The present study was designed to determine whether PA and vLTF are enhanced in obstructive sleep apnoea (OSA) participants compared to matched healthy controls. The study was also designed to determine whether administration of an antioxidant cocktail mitigates PA and vLTF. Thirteen participants with sleep apnoea and 13 controls completed two trials. During both trials participants were exposed to intermittent hypoxia which included twelve 4‐min episodes of hypoxia (, 50 mmHg; , 4 mmHg above baseline) followed by 30 min of recovery. Prior to exposure to intermittent hypoxia, participants were administered, in a randomized fashion, either an antioxidant or a placebo cocktail. Baseline measures of minute ventilation during the placebo and antioxidant trials were not different between or within groups. During the placebo trial, PA was evident in both groups; however it was enhanced in the OSA group compared to control (last hypoxic episode 36.9 ± 2.8 vs. 27.7 ± 2.2 l min−1; P≤ 0.01). Likewise, vLTF was evident during the recovery period in both groups; on the other hand vLTF was greater in the OSA group compared to control (29.3 ± 2.8 vs. 20.4 ± 1.3 l min−1; P≤ 0.01). PA and vLTF were reduced in the OSA group following antioxidant administration compared to the placebo (PA 30.6 ± 2.0 vs. 36.9 ± 2.8 l min−1, P≤ 0.01; vLTF 23.3 ± 1.4 vs. 29.3 ± 2.8 l min−1, P≤ 0.05). We conclude that PA and vLTF are enhanced in participants with OSA and that these forms of respiratory plasticity are mitigated after treatment with an antioxidant cocktail.
The response to paired motor cortical stimuli is abolished at a spinal level during human muscle fatigue
Authors: McNeil Chris J. , Martin Peter G. , Gandevia Simon C. , Taylor Janet L.
Published: October 2009

During maximal exercise, supraspinal fatigue contributes significantly to the decline in muscle performance but little is known about intracortical inhibition during such contractions. Long‐interval inhibition is produced by a conditioning motor cortical stimulus delivered via transcranial magnetic stimulation (TMS) 50–200 ms prior to a second test stimulus. We aimed to delineate changes in this inhibition during a sustained maximal voluntary contraction (MVC). Eight subjects performed a 2 min MVC of elbow flexors. Single test and paired (conditioning–test interval of 100 ms) stimuli were delivered via TMS over the motor cortex every 7–8 s throughout the effort and during intermittent MVCs in the recovery period. To determine the role of spinal mechanisms, the protocol was repeated but the TMS test stimulus was replaced by cervicomedullary stimulation which activates the corticospinal tract. TMS motor evoked potentials (MEPs) and cervicomedullary motor evoked potentials (CMEPs) were recorded from biceps brachii. Unconditioned MEPs increased progressively with fatigue, whereas CMEPs increased initially but returned to the control value in the final 40 s of contraction. In contrast, both conditioned MEPs and CMEPs decreased rapidly with fatigue and were virtually abolished within 30 s. In recovery, unconditioned responses required <30 s but conditioned MEPs and CMEPs required ∼90 s to return to control levels. Thus, long‐interval inhibition increased markedly as fatigue progressed. Contrary to expectations, subcortically evoked CMEPs were inhibited as much as MEPs. This new phenomenon was also observed in the first dorsal interosseous muscle. Tested with a high intensity conditioning stimulus during a fatiguing maximal effort, long‐interval inhibition of MEPs was increased primarily by spinal rather than motor cortical mechanisms. The spinal mechanisms exposed here may contribute to the development of central fatigue in human muscles.
Effect of Laser Surface Modification on the Crystallinity of Poly(L-Lactic Acid)
Authors: Bhatla Anubha , Yao Y. Lawrence
Published: October 2009

Crystallinity of semicrystalline polymers such as aliphatic homopolymer poly(L-lactic acid) (PLLA) affects their degradation and physical properties. In this paper, the effects of laser irradiation using the third harmonic of a Nd:YAG laser on the crystallinity, long-range order, and short-range conformations at the surface of PLLA films are investigated. The factors affecting the transformation are also studied. Detailed characterization of the effect of laser treatment is accomplished using microscopy, X-ray diffraction, and infrared spectroscopy. The cooling rates in the process and the spatial and temporal temperature profiles are numerically examined. The simulation results in conjunction with melting and crystallization kinetics of PLLA are used to understand the effect on sample crystallinity. The effects of laser fluence and annealing conditions on the crystallinity of the processed films are examined. Since degradation profiles depend on crystallinity, laser processing can potentially be used to achieve a modified spatially controlled polymer surface with promising applications such as controlled drug delivery.
Real-Time Estimation of Mean Remaining Life Using Sensor-Based Degradation Models
Authors: Elwany Alaa , Gebraeel Nagi
Published: October 2009

Advances in sensor technology have led to an increased interest in using degradation-based sensory information to predict the remaining lives of partially degraded components and systems. This paper presents a stochastic degradation modeling framework for computing and continuously updating remaining life distributions (RLDs) using in situ degradation signals acquired from individual components during their operational lives. Unfortunately, these sensory-updated RLDs cannot be characterized using parametric distributions and their moments do not exist. Such difficulties hinder the implementation of this sensor-based framework, especially from the standpoint of computational efficiency of embedded algorithms. In this paper, we identify an approximate procedure by which we can compute a conservative mean of the sensory-updated RLDs and express the mean and variance using closed-form expressions that are easy to evaluate. To accomplish this, we use the first passage time of Brownian motion with positive drift, which follows an inverse Gaussian distribution, as an approximation of the remaining life. We then show that the mean of the inverse Gaussian is a conservative lower bound of the mean remaining life using Jensen’s inequality. The results are validated using real-world vibration-based degradation information.
Quality and Inspection of Machining Operations: CMM Integration to the Machine Tool
Authors: Mears Laine , Roth John T. , Djurdjanovic Dragan , Yang Xiaoping , Kurfess Thomas
Published: October 2009

Dimensional measurement feedback in manufacturing systems is critical in order to consistently produce quality parts. Considering this, methods and techniques by which to accomplish this feedback have been the focus of numerous studies in recent years. Moreover, with the rapid advances in computing technology, the complexity and computational overhead that can be feasibly incorporated in any developed technique have dramatically improved. Thus, techniques that would have been impractical for implementation just a few years ago can now be realistically applied. This rapid growth has resulted in a wealth of new capabilities for improving part and process quality and reliability. In this paper, overviews of recent advances that apply to machining are presented. More specifically, research publications pertaining to the use of coordinate measurement machines to improve the machining process are discussed.
Taguchi Method Based Process Space for Optimal Surface Topography by Finish Hard Milling
Authors: Zhang Song , Guo Y. B.
Published: October 2009

Hard milling has a potential to replace finish grinding in manufacturing dies and molds. Surface finish is one key surface integrity parameter to justify the use of hard milling. In this study, a Taguchi design-of-experiment based finish milling hardened AISI H13 tool steel (50±1 HRc) with physical vapor deposition (PVD) (Ti, Al) N–TiN-coated end mill was conducted to investigate the optimal surface topography and roughness. A kinematic model of the cutting tool loci was developed to investigate the formation mechanism of the surface texture and correlate the simulated surface textures with the measured ones. The milled 3D surface topography and anisotropic roughness in the feed and step-over directions were thoroughly characterized and analyzed. The milled surface roughness Ra of less than 0.1 μm in the feed direction and 0.15 μm in the step-over direction has shown that hard milling is capable of replacing grinding as a finish or semifinish process. Furthermore, the process parameter spaces for the desired surface properties were indentified via the surface contour maps.
Reference Fracture Toughness Curves for Irradiated Pressure Vessel Steels
Authors: Wullaert R. A. , Oldfield W. , Server W. L.
Published: October 2009

Recently developed statistically-based fracture toughness reference curve procedures (Charpy V-notch and precracked Charpy methods) have been applied to unirradiated and irradiated plate and weld material from the HSST program and the Maine Yankee reactor surveillance program. The results have been compared to the reference procedure based upon the ASME Code and NRC regulations (KIR curve) and to actual measurements of fracture toughness. It was found that the fracture toughness measurements were closely grouped around the mean property curve predicted by the Charpy V-notch method. The bounds for each method were similar for HSST Plate 02, but differed considerably for the Maine Yankee material. It was found that the KIR approach overstated the shift in the temperature of the property transition for the Maine Yankee reactor material. However, the low temperature fracture toughness was predicted to be lower than predicted by the KIR approach. These conclusions are subject to some reservations because of the poor quality of some of the referencing data, and because the precracked Charpy and Charpy V-notch reference curve procedures are still being developed and tested. Reasons for the differences between the current KIR method as compared to the proposed new methods have been traced to shortcomings in current procedures.
Development of Fracture Toughness Reference Curves
Authors: Oldfield W.
Published: October 2009

A large base of KIC, KId and JIC (R-curve) fracture toughness data has been used to develop reference toughness curves. The most successful results were obtained when a sigmoidal function was fitted to data from which the heat-heat variation in both the temperature and fracture toughness had been reduced by referencing. Several referencing procedures have been studied, but the only one found to be ‘successful in this work was based upon the precracked instrumented Charpy V-notch test. The tanh function K=A+BtanhT−T0C (K = toughness, T = temperature, and A, B, T0 and C are coefficients which give the best fit between curve and data) fitted to precracked instrumented Charpy V-notch test data provided suitable referencing quantities. Using the coefficients A and B to reference fracture toughness, and T0 and C to reference temperature, lower bound reference curves were developed. Weighted, nonlinear regression procedures were used to define lower bound reference toughness curves for each of three stress intensification rates. The lower bound was the statistical global tolerance bound to the referenced data. The reference curves can be readily used to define a lower bound relationship between fracture toughness and temperature for nuclear pressure vessel steel on the basis of a set of precracked instrumented Charpy V-notch tests.
Finite Fatigue Life Distributions of SAE 1008 Subjected to Various Load-Time Histories
Authors: ElMaraghy H. A. , Siddall J. N.
Published: October 2009

The probabilistic fatigue properties of SAE 1008 steel were determined experimentally. A flexural bending fatigue testing program was carried out consisting of: (a) constant strain amplitude, (b) blocks of Hi-Lo and Lo-Hi-Lo strain amplitudes, and (c) narrow band random load history. Fatigue life of 30-45 specimens in each program were recorded and used to construct distributions of fatigue life. A computer simulation technique was used to predict these distributions. Experimental results and theoretical predictions are both presented for comparison.
On Effective Stress Range Factor in Fatigue
Authors: Lal K. M. , Garg S. B. L. , Le May I.
Published: October 2009

A detailed analysis of crack closure during fatigue crack propagation has been made using a simplified model. In addition, experimental work has been conducted using eddy current methods to determine crack closure. It was found that the effective stress range factor, U, depends on the applied stress range, stress ratio, yield strength and strain hardening exponent of the material, and that its value stabilizes in about 10 stress cycles for constant stress amplitude loading. Experimental and predicted results were seen to be in good agreement.
Design for Continuing Structural Integrity
Authors: Walker E. K. , Ekvall J. C. , Rhodes J. E.
Published: October 2009

This paper addresses the structural integrity planning that takes place during the design development process of commercial aircraft. Subjects discussed include the evolutionary nature of the process, the need for continued planning during service, the role of simplistic envelope criteria, and the basic concepts underlying analyses used in the planning process. Examples include in-service planning for older aircraft and design development for continued structural integrity of a modern wide-body transport. Concluding remarks discuss how the process will be applied to the next generation of aircraft.
Material Control and Fracture Control Planning for the Space Shuttle Orbiter Program
Authors: Ehret R. M.
Published: October 2009

Structural integrity of the Space Shuttle orbiter vehicle is assured primarily through analysis. The analysis is supplemented by tests intended to validate analysis methods or, in some cases, to provide direct demonstration of structural capability to withstand the design environments. The paper summarizes the Shuttle’s structural certification requirements and the major test efforts supporting this certification. A more detailed examination of the orbiter material control land fracture control programs is presented as efficient and constructive components of a viable structural integrity plane.
Low Cycle Fatigue Life Model for Gas Turbine Engine Disks
Authors: Meyer T. G. , Cruse T. A.
Published: October 2009

A low cycle fatigue (LCF) life exhaustion method is developed for gas turbine engine disks subjected to complex mission history loading. The method is incorporated into an algorithm for LCF life exhaustion prediction as a function of component, material, mission history, and mission ordering. Principal features in the LCF life model include a simple strain range-mean stress correlation model, a predictive model for the effects of strain-hardened surface layers due to machining and the effects of dwell (creep) due to elevated temperature exposure time, a fracture mechanics-based nonlinear, cumulative damage model, and full-scale component verification.
Correlations Between Advanced Nondestructive Evaluation Methods and Fracture Mechanics Parameters
Authors: Teller C. M. , Barton J. R. , Matzkanin G. A. , Kusenberger F. N. , Beissner R. E.
Published: October 2009

Investigations were conducted on surface entering fatigue cracks, 0.13 to 1.27 mm (0.005 to 0.05 in.) long, in rod-type tensile specimens of HY 180 and AISI 4340 steels using surface wave ultrasonics and magnetic perturbation. Pulse-echo, surface wave ultrasonic results indicate that at 10 MHz the minimum flaw size detectable in HY 180 specimens is two to three times larger than that in AISI 4340. Also, fatigue cracks as long as 0.76 mm (0.030 in.) in HY 180 specimens could not be reliably detected with 10 MHz surface waves unless load was applied to open the crack. Extensive magnetic perturbation measurements on AISI 4340 suggest a “hinge” model for the opening of small surface entering fatigue cracks.
Quantitative Decisions Relative to Structural Integrity
Authors: Rau C. A. , Besuner P. M.
Published: October 2009

The injury potential and increased cost of licensing, insurance premiums, product liability claims, and field repairs or recalls provide strong motivation to quantitatively evaluate and control the risk of various products. Risk analysis involves the definition of the probable failure modes and the assessment of failure probability, failure severity and the corresponding risks and costs. Basic concepts are reviewed and recent developments in methods to quantify the risk of structural failure when limited failure experience is available are presented. An example involving a turbine rotor is described which illustrates how the conventional and, new methods provide a quantitative basis for assessing structural integrity and risk and for making decisions regarding future operation, repair, or replacement.
Diffusion and Trapping of Hydrogen in a Bead-on-Plate Weld
Authors: Andersson B. A. B.
Published: October 2009

An analytical model for diffusion of hydrogen in presence of reversible and irreversible traps in the metal is given. A numerical model for solution of the resulting system of nonlinear partial differential equations is developed. The temperature dependence of the material parameters is estimated. The transient distributions of temperature, stress and hydrogen are numerically found for a bead-on-plate weld. The effects of trapping, stress, thermotransport and plastic strain on the hydrogen distribution are discussed. Calculated amounts of residual and diffusible hydrogen are compared with existing experimental data. It is concluded that an increased knowledge of the mechanisms behind formation of residual hydrogen is needed for practical welding situations with large amounts of residual hydrogen.
Mechanical Properties of Al-Mica Particulate Composite Material
Authors: Nath Deo , Bhatt R. T. , Biswas S. K. , Rohatgi P. K.
Published: October 2009

Cast aluminium alloy mica particle composites of varying mica content were tested in tension, compression, and impact. With 2.2 percent mica (size range 40μm – 120μm) the tensile and compression strengths of aluminium alloy decreased by 56 and 22 percent, respectively. The corresponding decreases in percent elongation and percent reduction are 49 and 39 percent. Previous work [2] shows that despite this decrease in strength the composite with 2.5 percent mica and having an UTS of 15 kg/mm2 and compression strength of 28 kg/mm2 performs well as a bearing material under severe running conditions. The differences in strength characteristics of cast aluminium-mica particle composites between tension and compression suggests that, as in cast iron, expansion of voids at the matrix particle interface may be the guiding mechanism of the deformation. SEM studies show that on the tensile fractured specimen surface, there are large voids at the particle matrix interface.
Structural Integrity Procedures for Naval Ships
Authors: Palermo P. M.
Published: October 2009

The application of both light and heavy sections of high strength metals in weight sensitive ships demands that structural integrity principles be followed during all stages of design, fabrication and life-cycle support of ship structures. The integration of the interfacing disciplines of material sciences, fracture mechanics, structural design, welding engineering, production engineering and nondestructive testing are necessary ingredients of the Navy’s structural integrity plan. The relationships of these groups in the past, and envisioned in the future, are discussed. Results of early structural integrity efforts for present day ships as well as structural integrity aspects of ongoing designs are also discussed.
Numerical Integration of Some Stiff Constitutive Models of Inelastic Deformation
Authors: Kumar Virendra , Morjaria Mahesh , Mukherjee Subrata
Published: October 2009

Several strategies for numerical time-integration of some stiff constitutive models of inelastic deformation are presented in this paper. Numerical results and comparisons are presented for the integration of one such model for the case of uniaxial deformation under various prescribed histories of stress or strain. A simple one step Euler type integration scheme with automatic time-step control, which can be easily adapted to the solution of multiaxial boundary value problems, appears promising.
Radiation Effects in Boiling Water Reactor Pressure Vessel Steels
Authors: Kass J. N. , Giannuzzi A. J. , Hughes D. A.
Published: October 2009

Effect of neutron irradiation on notch toughness properties of Boiling Water Reactor pressure vessel steels was determined. Samples from several heats of plate, weld metal, and forgings were irradiated to three different fluence levels and tested. A statistical evaluation of the data was conducted to determine regression analysis mean decreases in upper shelf energy and increases in transition temperature versus fluence.
A Critical Analysis of Crack Growth in Creep
Authors: Radhakrishnan V. M. , McEvily A. J.
Published: October 2009

Experimental investigations have been carried out to study the crack growth behavior in creep in a 6061 Al alloy. The crack growth rate is analyzed by the stress intensity factor, reference stress, energy rate line integral C* and modified J integral method and a critical examination is made of the applicability of different procedures. Based on the experimental observations near the crack zone, a new parameter in the form [Δ˙ / (P/P0)α], where Δ˙ is the deflection rate, P the applied load and the exponent α and P0 are constants, is proposed to describe the crack growth behavior in ductile materials.
Deformation Modeling Applied to Stress Relaxation of Four Solder Alloys
Authors: Rohde R. W. , Swearengen J. C.
Published: October 2009

Stress relaxation of four solder alloys, 50 percent Pb-50 percent In; 37.5 percent Sn-37.5 percent Pb-25 percent In; 63 percent Sn-37 percent Pb; and 62.5 percent Sn-37 percent Pb-0.5 percent Ag, has been examined at 222 K, 298 K, and 344 K. A model previously utilized to describe inelastic deformation of aluminum and stainless steels is applied and found to provide an excellent description of the experimental data. This model is based upon the general concept of stress assisted thermally activated dislocation glide in a microstructure evolving by the process of strain hardening and recovery. Model parameters useful for calculations of time dependent behavior of these solders are presented and their significance is discussed.
Modelling of Cyclic Plasticity With Unified Constitutive Equations: Improvements in Simulating Normal and Anomalous Bauschinger Effects
Authors: Miller A. K.
Published: October 2009

In simulating cyclic plasticity with several existing “unified” constitutive equations, the predicted hysteresis loops are “oversquare” with respect to experimentally-observed behavior. To eliminate this shortcoming in the constitutive equations developed by the present author, the work-hardening coefficient in the equation controlling the back stress (R) has been made a function of the back stress itself and the sign of the effective modulus-compensated stress σ/E – R. This improvement results in simulated hysteresis loops whose curvature closely resembles that in experimental tests. The improvement preserves all of the previously demonstrated capabilities such as cyclic hardening, cyclic hardening, cyclic softening, etc. The same equations can also simulate some unusual experimentally-observed Bauschinger effects involving local reversals in curvature. The curvature reversals in the simulations result from strain softening of the isotropic work-hardening variable in the equations. The physical significance of the behavior of the constitutive equations is discussed in terms of annihilation of previously-generated dislocation loops by reversing dislocations and experimentally-observed decreases in dislocation density and dissolution of cell walls upon stress reversal.
An Analysis of Wrinkling in the Swift Cup Test
Authors: Triantafyllidis N. , Needleman A.
Published: October 2009

The onset of flange wrinkling in the Swift cup test is analyzed as a plastic bifurcation problem. The flange is modelled as an annular plate made of an orthotropic elastic-plastic material that is isotropic in the plane of the plate. The critical drawing stress and displacement obtained employing a deformation theory of plasticity and a flow theory of plasticity are compared. The effects of flange geometry and material properties on wrinkling are investigated. Employing a simple linear elastic spring model of the blankholder, the effect of blankholder stiffness on wrinkling is studied. The present results for the critical stress at the onset of wrinkling and for the number of wrinkles are compared with those obtained previously employing a beam model of the flange.
Fatigue Crack Growth Response Following a High-Load Excursion in 2219-T851 Aluminum Alloy
Authors: Wei R. P. , Fenelli N. E. , Unangst K. D. , Shih T. T.
Published: October 2009

To develop further phenomenological understanding of load interaction effects in fatigue, examinations of the influences of stress intensity (K) level, plate thickness and chemical environment on fatigue crack growth response following a single high-load excursion (overload) were carried out on a 2219-T851 aluminum alloy. An overload ratio (that is, the ratio between the magnitude of the overload and the maximum in the subsequent constant-amplitude fatigue loading) of 2.0 was used. Experiments were carried out in dehumidified argon, air (30 to 70 percent relative humidity), and3.5percent NaCl solution at room temperature. The results showed that delay (as measured by the duration of overload affected crack growth) increased with increasing K level and with decreasing plate thickness, and decreased with increasing aggressiveness of the chemical environment. The high-load excursion (overload) affected crack growth through a region of material ahead of the crack tip. Within this overload affected zone, crack growth rate first increased (sometimes), followed by fairly rapid decrease to a minimum value (delayed retardation), and then increased gradually to its steady-state value. The overload affected zone size was found to depend on K-level, and on crack-tip constraint, and to be independent of chemical environment, and was found to be equal to the appropriate (plane-strain or plane-stress) plastic zone size for the overload. Identification of a delayed retardation zone was made, and identification of this zone with the cyclic plastic zone size for the preceding fatigue loading was suggested. The effects of K level, plate thickness and chemical environment on delay were considered in relation to their respective influences on the overload-affected-zone and delayed-retardation-zone sizes, and on the rate of fatigue crack growth. A residual stress intensity concept for describing fatigue crack growth response within the overload affected zone was considered. With suitable modifications, reasonable estimates of crack growth response could be obtained. Further need for verification and understanding of these modifications are discussed.
Fracture Mechanics Aspects of the Structural Integrity Technology of Spherical Aluminum Containment Vessels for LNG Tankers
Authors: Kaufman J. G. , Bucci R. J. , Kelsey R. A.
Published: October 2009

The Kvaerner-Moss spherical tank design offers significant economic advantage for the shipboard transport of liquefied natural gas. An analytical and experimental approach based on fracture mechanics concepts was used to assist the designer in providing answers to the following basic questions: (1) Might a discontinuity smaller than detectable by nondestructive inspection lead to catastrophic fracture; (2) How fast would such a discontinuity grow under fatigue loading likely to occur during the lifetime of the tank; (3) Could a fatigue crack growing part way through the tank wall precipitate catastrophic fracture before it grows through the wall and is detected as a leak; and (4) If leakage develops, how much time is available to get the ship safely to port for discharge and repair? Both “critical” locations in the tank, i.e., the highest stressed region of the membrane and the equatorial ring, are examined. Available data indicating the safety of spherical tanks fabricated of aluminum alloy 5083-0 is documented.
The Role of Three-Dimensional Effects in Constant Amplitude Fatigue Crack Growth Testing
Authors: McGowan J. J. , Liu H. W.
Published: October 2009

An accurate knowledge of the dependence of the fatigue crack growth rate (da/dN) on the stress intensity factor range (ΔK) is necessary to perform a safety analysis of any structure. Fatigue crack growth tests are normally performed on simple, two-dimensional finite thickness specimens to determine this dependence. Certain anomalies in this dependence have been observed when specimen thickness and mean stress have been varied. The thickness effect and the mean stress effect on the fatigue crack growth rate are related to the variation in crack closure and the local stress intensity factor along the crack front. A simple model incorporating both of these two effects is proposed. The model is applied to fatigue crack growth data for a nickel-base super alloy (IN-100) with very good success.
Cyclic Behavior of Turbine Disk Alloys at 650°C
Authors: Cowles B. A. , Sims D. L. , Warren J. R. , Miner R. V.
Published: October 2009

Five gas turbine disk alloys representing a range of strengths and processing methods were tested for resistance to both cyclic crack initiation and propagation at 650° C using a 0.33 Hz fatigue cycle and a cycle incorporating a 900 s tensile dwell. At the low strain ranges pertinent to disks, resistance to crack initiation increased with increasing tensile yield strength among the alloys, though the advantage was somewhat smaller for the creep fatigue cycle. Cyclic crack growth resistance, however, decreased with increasing strength and very markedly so for the dwell cycle.
Effect of Prestrain at Elevated Temperature on Ductile Fracture of High Strength Steel
Authors: Mutoh Y. , Toyoda M. , Satoh K.
Published: October 2009

The processes of ductile fracture of KD32 steel specimens subjected to prestrain at elevated temperature are observed. Although several large voids are observed at a relatively small strain level, they have no important role in fracture processes. As soon as micro-voids nucleate at some strain level, which is the stage just before final fracture, they rapidly grow and coalesce. It is proposed that ductile fracture of KD32 steel specimens occurs when the value of equivalent stress reaches a critical value. It seems that the most important reason for the decrease in fracture strain with prestraining at elevated temperature is the strain hardening according to amount of prestrain and prestraining temperature.
The Effects of Composition and Microstructure on Temper Embrittlement in 2 1/4 Cr-1 Mo Steel
Authors: Murza J. C. , McMahon C. J.
Published: October 2009

Temper embrittlement was studied using laboratory heats of 2 1/4 Cr-1 Mo steel of a specified hardness and grain size. Particular amounts of P, Sn, Sb, Mn, and Si were added in various combinations. Charpy impact and hardness tests were performed and scanning electron microscopy, and Auger microprobe investigations were conducted. Specimens with both martensitic and bainitic microstructures were embrittled by step cooling and by long time ageing at 480 and 520°C prior to study. Only steels which contained added P showed any consistent and significant embrittlement. While neither Mn nor Si themselves acted as embrittling elements, they both strongly promoted P segregation and thus acted to raise the embrittlement susceptibility markedly. Evidence of the previously discovered [reference [7]] thermal history effect (due to reduction of the free-Mo content by carbide formation) on the embrittlement kinetics was obtained. The results on the bainitic and martensitic steels were essentially similar, the only difference being that the bainitic steels had higher transition temperatures in the unembrittled conditions. The 2 1/4 Cr-1 Mo steel can have a very low susceptibility to temper embrittlement if the P, Mn, and Si contents are kept sufficiently low.
Large Strain, High Strain Rate Testing of Copper
Authors: Lindholm U. S. , Nagy A. , Johnson G. R. , Hoegfeldt J. M.
Published: October 2009

This paper describes the development of a high-speed torsional testing machine and results obtained on the strain-rate dependent strength of copper at large shear strains. Test techniques and data obtained are intended to be useful in applications such as ballistics and machining. For copper, the results indicate positive strain hardening behavior to very large strains under low rate, isothermal conditions and the transition to adiabatic thermal softening, shear instability and localization (shear banding) at high rates.
Low Cycle Fatigue of Commercial Piping Steels in a BWR Primary Water Environment
Authors: Hale D. A. , Wilson S. A. , Kass J. W. , Kiss E.
Published: October 2009

This report summarizes results of a comprehensive experimental program on the low cycle fatigue behavior of commercial grade piping steels in a high-pressure, high-temperature, oxygenated water environment. A total of 110 specimens of special design were tested in a boiling water reactor (BWR) primary water environment (500°F, 1040 psig (or 260° C, ∼ 7 MPa). Four piping steels, in several different metallurgical conditions, were involved (Types-304 and –304L stainless steels, Inconel-600 and A-516 carbon steel). Companion tests, employing the same types of specimens, were conducted in 500° F (260° C) air. The results of this work confirm the adequacy of the current ASME Section III fatigue design curves to account for the effect of a BWR primary water environment on the low cycle fatigue behavior of the four materials tested.
Fracture Toughness of 4130 Quenched and Tempered Steel
Authors: Nguyen-Duy Phuc , Bayard Serge
Published: October 2009

The fracture-energy criterion JIc was determined by the single specimen method on quenched and tempered 4130 steel used for tower anchor bars of high voltage transmission lines. A thermodynamic approach was used to rationalize JIc as a stable crack initiation criterion. Slow-bend testing was performed on three-point bend specimens of different dimensions. The effect of microstructure (martensite and bainite + ferrite) on the value of JIc is not significant. Specimen dimensions (1.5 × 3 × 15 cm; 2 × 4 × 20 cm) seem not to affect JIc values. Critical stretch zone width, WSZc, was evaluated on broken specimen halves using scanning electron microscopy. With some assumptions, relationships between WSZc, CTOD and JIc were established. Values of JIc calculated via WSZc compare favorably with JIc determined from a single specimen.
Age Softening Characteristics of Annealed 2-1/4Cr-1Mo Steel in the Temperature Range 424 to 704°C
Authors: Pizzo P. P. , Mandurrago G. L.
Published: October 2009

The short-term age softening characteristics of isothermal annealed and post weld heat treated 2-1/4Cr-1Mo steel have been investigated over the temperature range 454 to 727°C (850 to 1340°F). Significant degradation in flow strength is observed for times and temperatures within the current service regime of the commercial alloy. Age softening is atypical: flow strength degradation is most rapid at some intermediate temperature. The reduction in flow strength is greatest, and occurs most rapidly, at 575°C (1067°F). The strength degradation is attributed to time-dependent redistribution of molybdenum within the proeutectoid ferrite. It is predicted that thermal aging in the temperature range 427 to 593°C (800 to 1000°F) will result in similar strength decrements for annealed 2-1/4Cr-1Mo steel regardless of prior thermal history above 704°C (1300°F).
An Explanation for the Effects of Hold Periods on the Elevated Temperature Fatigue Behavior of 2 1/4 Cr-1 Mo Steel
Authors: Challenger K. D. , Miller A. K. , Brinkman C. R.
Published: October 2009

An analysis of previously reported elevated-temperature fatigue with hold time data supplemented by a metallographic examination of the 2 1/4 Cr-1Mo alloy steel specimens is reported. The tests were conducted in air over the temperature range of 427 to 593° C. Hold periods were introduced at various points of the hysteresis loop during each cycle. An explanation for the previously reported effects of these hold periods on the fatigue life is presented. The explanation attributes the reduction in fatigue life to the combination of reduced interaction solid solution hardening and accelerated fatigue crack initiation due to oxide cracking. The effect of hold periods is primarily due to an environmental interaction (rather than to a creep interaction) with the fatigue damage processes.
A Statistical Simulation Model of Miner’s Rule
Authors: Johnsen S. E. J. , Doner M.
Published: October 2009

A Monte Carlo simulation model of the classical Miner’s rule for cumulative fatigue damage is devised and implemented for an example of three summands. Results from the simulation are compared with Miner’s rule. The concept of damage-sum-to-failure is developed and applied to measured values of INCO 901 at room temperature.
A New Approach to the Evaluation of Fatigue Under Multiaxial Loadings
Authors: Garud Y. S.
Published: October 2009

A critical review of the methods for evaluating fatigue of metals under simple (proportional) and complex (nonproportional) loadings indicates that most of the criteria are expressed in terms of either stresses or strains. In this paper a new approach to the evaluation of fatigue under these loadings is proposed. This approach is based upon the idea of relating fatigue life to the plastic work during a cycle of the loading. A procedure is outlined for the calculation of plastic work which involves explicit considerations of the material constitutive relations. It is based on the structure of modern plasticity theories and a new “hardening rule.” Validity of the constitutive relations to predict the cyclic stress-strain response is demonstrated for out-of-phase multiaxial loadings. Available experimental results of fatigue tests under out-of-phase loadings are shown to be in good agreement with the predictions using the new approach.
Long-Life Fatigue Test Results for Two Nickel-Base Structural Alloys
Authors: Mowbray D. F. , Giaquinto E. V. , Mehringer F. J.
Published: October 2009

This paper reports the results of fatigue tests on two nickel-base alloys, hot-cold-worked and stress-relieved nickel-chrome-iron Alloy 600 and mill-annealed nickel-chrome-moly-iron Alloy 625 in which S-N data were obtained in the life range of 106 to 1010 cycles. The tests were conducted in air at 600°F, in the reversed membrane loading mode, at a frequency of ~ 1850 Hz. An electromagnetic, closed loop servo-controlled machine was built to perform the tests. A description of the machine is given.
The Effect of a Higher Loading Rate on the JIc Fracture Toughness Transition Temperature of HY Steels
Authors: Hasson D. F. , Joyce J. A.
Published: October 2009

The objectives of the study were to extend the JIc transition temperature analysis of earlier work for HY130 to HY80 steel and also to determine the effect of a higher strain rate on the JIc fracture toughness of both HY80 and HY130 steels. The fracture parameter JIc in both low and high strain rate tests demonstrated a ductile to brittle transition in HY80 and HY130 steels analogous to Charpy V notch transition behavior. The JIc transition temperature from slow rate tests was less conservative than that from fast rate tests. The JIc transition temperatures from slow and fast rate tests gave less conservative transition temperatures than those from Charpy tests. SEM stereo pair fractography showed that the transition from ductile to brittle behavior was not as gradual for the fast rate testing as previously reported for slow rate tests.
Efficiency of Wire Rope Terminations
Authors: Matanzo F. , Metcalf J. T.
Published: October 2009

Nine wire rope terminations were evaluated with respect to true efficiency, service life, and sensitivity to poor workmanship in a comprehensive laboratory test program. The portion of the program concerned with true efficiency, as determined by pull tests to destruction, is reported here. Five diameter values of Lang and Regular construction ropes of the 6 × 19 and 6 × 37 class were used on the following wire rope terminations: Flemish Loop with Steel Sleeve and Thimble, Flemish Loop with Steel Sleeve, Wedge Socket, Swaged Socket, Turn Back Loop with Aluminum Sleeve and Thimble, Thimble Splice with Four Tucks, U-Bolt Clips with Thimble, Zinc Poured Socket, and Resin Poured Socket. The true efficiency was shown to be affected by termination type, rope type, and the interaction of these factors. The efficiency values measured in this test program are less than those reported in the literature which are based on the catalog breaking load rather than on the true breaking load. From a graphic and statistical analysis of the data it was possible to present a selection procedure for optimizing the efficiency.
Crack Arrest Modes of a Transverse Crack Going Through a Longitudinal Crack or a Hole
Authors: Theocaris P. S. , Milios J.
Published: October 2009

The process of a transverse crack intersecting a longitudinal central crack, a longitudinal eccentric crack, or a central hole was investigated by means of high-speed photography and caustics. The results show that the crack momentarily arrests when arriving at the discontinuity, then reinitiates later, usually with a different velocity. Although the geometrical characteristics of the discontinuities had an effect, all crack arrest processes show fundamental similarities, since they are all related to the destruction and reconstruction of the singular stress field of the moving crack at the discontinuity. These results are in accordance with previous work of the authors for crack arrest at the interface of biphase plates.
Fatigue Criteria Under Combined Stresses or Strains
Authors: Sines George , Ohgi George
Published: October 2009

A brief presentation is given of a previously proposed criterion for long-life fatigue under combined alternating and combined static stress. A new criterion is proposed for long-life fatigue under high static stress. Generalizations are made on criteria for low-cycle fatigue under combined stress and the form that these criteria take in principal stress space. Speculations are made on a possible criterion for fatigue under variable phasing between the principal stress amplitudes.
Flow Stresses of Prestrained Annealed OFHC Copper and SAE 1018 Steel
Authors: Thomsen E. G. , Holthuis J. T. , Thomsen H. H.
Published: October 2009

The tensile properties of annealed OFHC copper and SAE 1018 steel drawn to various prestrains up to ln A0/A ≅ 1.5 were evaluated. It was found that the resulting Bridgman corrected curves could not be matched at the calculated prestrains. However, a match could be achieved by ignoring the calculated or theoretical prestrains. This method of obtaining a unified curve leads to the belief that the two materials under investigation soften at the higher prestrains. For the moment there appears to be no method to predict the softening effects. It was found that the yield strengths fall below the unified true stress-true strain or flow stress curves and that necking appears to be in agreement with the theory. Consequently, necking strains in tension drop to nearly zero after the first drawing pass.
Materials for Generator Retaining Rings
Authors: Viswanathan R.
Published: October 2009

Retaining rings are among the highest stressed components of electricial generators, whose integrity is critical to the reliable and safe operation of the generators. The steel currently used for this application is susceptible to stress corrosion cracking and is also limited by yield strength to about 1200 MPa. The use of alternate materials with improved mechanical properties can enhance the reliability, efficiency, size capability and availability of generators. This paper is a state-of-the-art review of the materials technology pertaining to retaining rings.
A Damage Accumulation Model for Fatigue Crack Propagation
Authors: Ihara C. , Igarashi A.
Published: October 2009

The fatigue crack propagation rate is investigated on the basis of a dislocation multiplication model which was used previously in evaluation of the fatigue life up to crack initiation. The expression for fatigue crack propagation rate is derived from a two-dimensional version of a stochastic model proposed by Tsurui and one of the authors (A.I.), and a distribution function of the life of material elements in this expression is calculated on the dislocation multiplication model. On these theoretical bases, it is shown that the fatigue crack propagation rate is proportional to some power of the stress intensity range. Our results are compared with the experimental data.
A Phenomenological Model for Transient Deformation Based on State Variables
Authors: Jackson M. S. , Cho C. W. , Alexopoulos P. , Li Che-Yu
Published: October 2009

The state variable theory of Hart, while providing a unified description of plasticity-dominated deformation, exhibits deficiencies when it is applied to transient deformation phenomena at stresses below macroplastic yielding. It appears that the description of stored anelastic strain is oversimplified. Consideration of a simple physical picture based on continuum dislocation pileups suggests that the neglect of weak barriers to dislocation motion is the source of these inadequacies. An appropriately modified description incorporating such barriers allows the construction of a modified phenomenological model including transient effects. The applicability of the modified model to aluminum has been investigated at room temperature. A consistent set of parameters describing the mechanical properties of the material has been determined experimentally. Agreement between experiment and model predictions for fairly complex loading histories is good. Although the constitutive equations for microplastic flow could not be established unambiguously, the results indicate that the general structure of the transient deformation model represents the deformation properties well.