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Ductilities generated after four types of creep test are compared: (i) constant load, (ii) constant stress (calculated); (iii) constant stress (from direct observation of the minimum section) and (...

We extend the analysis of Bok et al. (2020) in which the H I content of isolated galaxies from the AMIGA (Analysis of the interstellar Medium in Isolated GAlaxies) sample and selected paired galaxies from ALFALFA (Arecibo Legacy Fast ALFA) were examined as a potential driver of galaxy location on the WISE (Wide-field Infrared Survey Explorer) mid-infrared SFR–M⋆ sequence. By further characterizing the isolated and pair galaxy samples, i.e. in terms of optical galaxy morphology, a more detailed and quantitative description of local galaxy environment by way of the local number density (η) and tidal strength (Q) parameters, star formation efficiency (SFEH I⁠), and H I integrated profile asymmetries, we present plausible pathways for the broadening of the pair sample H I deficiency distribution towards both high and low deficiencies compared to the narrower isolated galaxy sample distribution (i.e. σPAIRS = 0.34 versus σAMIGA = 0.28). We associate the gas-rich tail of the pair deficiency distribution with the highest Q values, large profile asymmetries, and low SFEs. From this, we infer that merger activity is enhancing gas supplies, as well as disrupting the efficiency of star formation, via strong gravitational torques. The gas-poor wing of the deficiency distribution appears to be populated with galaxies in denser environments (with larger η values on average), more akin to groups. Despite our gas-rich selection criterion, there is a small population of early-type galaxies in the pair sample, which primarily fall in the positive deficiency wing of the distribution. These results suggest that a combination of a denser galaxy environment, early-type morphology, and higher stellar mass is contributing to the broadening of the deficiency distribution towards larger deficiencies. © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society., This work is based on the research supported in part by the National Research Foundation of South Africa (grant number UIDs: 101099 and 111745). JB additionally acknowledges support from the DST-NRF Professional Development Programme (PDP) and the University of Cape Town. MC is a recipient of an Australian Research Council Future Fellowship (project number FT170100273) funded by the Australian Government. THJ acknowledges funding from the National Research Foundation under the Research Career Advancement and South African Research Chair Initiative programmes, respectively. We acknowledge the work of the entire ALFALFA team for observing, flagging, and performing signal extraction. MGJ was supported by a Juan de la Cierva formación fellowship (FJCI-2016-29685) from the Spanish Ministerio de Ciencia, Innovacion y Universidades (MCIU). MGJ also acknowledges support from the grants AYA2015-65973-C3-1-R (MINECO/FEDER, UE) and RTI2018-096228-B-C31 (MCIU). This work has been supported by the State Agency for Research of the Spanish MCIU through the ‘Centro de Excelencia Severo Ochoa’ award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709). This publication makes use of data products from the WISE, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. This work also utilizes data from ALFALFA survey data set obtained with the Arecibo L-band Feed Array (ALFA) on the Arecibo 305 m telescope. Arecibo Observatory is part of the National Astronomy and Ionosphere Center, which is operated by Cornell University under Cooperative Agreement with the U.S. National Science Foundation. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS website is http://www.sdss.org/. In addition, we make use of data from the SDSS (SDSS DR7). The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions. The Participating Institutions are the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, University of Cambridge, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington. LVM acknowledges financial support from the grant IAA4SKA (Ref. R18-RT-3082) from the Economic Transformation, Industry, Knowledge and Universities Council of the Regional Government of Andalusia and the European Regional Development Fund from the European Union.

It is shown that the assumption of unit (negative) slope in the well known Monkman–Grant plot of time to failure against minimum creep rate is too restrictive. By acknowledging observed slopes in the range 0.8–1, a ductility–strain-rate relation is deduced where ductility decreases with reducing strain rate. This in turn has implications for the ductility exhaustion method as applied during stress relaxation in the dwell period of low cycle fatigue tests of austenitic steels at elevated temperature. The simple method is used to calculate the cyclic creep damage in typical tests on austenitic steels in the region 550–650 °C and is compared to other calculations as employed in the R5 high temperature assessment procedure. The assumption of a uniform nucleation rate of grain boundary voids with creep strain goes some way to predicting the slope of the ductility–strain-rate relation. Both the ‘unconstrained’ and ‘constrained’ (lower shelf) regions of void growth are discussed.

Strain-controlled (low-cycle fatigue type) experiments were performed on 12 different high temperature alloys (ferritic, austenitic, superalloys, single-crystal material, a directionally solidified alloy and two titanium alloys) in the range 550–950°C. Symmetrical cycling conditions were suddenly changed to offset strain cycling at the same strain range, but in the tension or compression direction. Up to 50 cycles were allowed to determine the subsequent approach to symmetrical stress limits for each material (elastoplastic shakedown). Comparison is made with limited reported tests and related load-control tests involving strain ratchetting . Shakedown behaviour is shown to depend both on the path of approach, defined by stress–strain properties, but overall trends of stress versus cycle plots are best made by assuming an effective strain range which is less than the imposed experimental strain range.

Given total endurances of low cycle fatigue specimens, several empirical formulae enable an estimate to be made of ‘initiation’ cycles to a specific crack depth in a zone ranging from 20 to 400 μm from the surface. For greater depths, the cyclic growth behaviour of cracks can be calculated directly from relations using established constants (including the effects of creep dwell) for a wide range of alloys. However, below a critical depth of 200 μm or thereabouts, these empirical growth laws, expressed in terms of total strain range, break down. Early crack growth can take place discontinuously, as the crack tip encounters grain boundaries or other obstacles. Such information arises from replica takings, or in situ microscopic observations of surfaces during continuous cycling and creep–fatigue tests. Striation spacings on the fracture surface and the first observed striation spacing provide valuable indications of early crack growth. In this region, the cyclic rate of growth depends on (i) crack s...

Reversed-load (low-cycle-fatigue type) experiments were carried out on 13 different high temperature alloys (ferritic, austenitic and superalloys, single crystal materials, a directionally solidified alloy and two titanium alloys) in the range 400–1025°C. By means of interrupted tests in the steady state, the asymmetrical nature of the Bauschinger effect was examined, i.e., having regard to the magnitude and direction of the (prior) stress reversal during the course of the hysteresis loop. The cyclic stress–strain curve was characterised using the Ramberg–Osgood power deformation relation. The yield stress in a given direction during the course of a cycle could be made to vary according to the reversal point in the interrupted tests. A simple interpretation is provided in terms of the prevailing difference between the back stress and a friction stress. Comparison of the back-stress behaviour is made with that calculated from the widely used Chaboche relation. Predictions of yield stress behaviour ...

This paper attempts to link the energies to failure involved in low-cycle fatigue at elevated temperature with those involved in forward creep. These energy levels are connected by a suitable sliding strain-rate scale. The principle is then applied to (i) dwell tests on 1CrMoV, 304 and 20Cr25Ni/Nb steels at 550, 650 and 750°C respectively and (ii) service failure of a thick-walled ferritic steam vessel at 570°C. Calculated creep-fatigue endurance using the linear damage summation rule is then plotted on Damage Diagrams. Sensitivity analyses are carried out as regards the linking of energy levels in fatigue (upper-shelf) with those in creep (lower-shelf). These involve knowledge of creep laws or stress relaxation relations and the methods of connecting energy levels (power law or those giving an S-shaped curve). Within this paper, sufficient information has been provided for investigators to undertake their own analyses on relevant laboratory tests or service assessments.

This paper considers the likely strain concentration effects generated in the shoulder/gauge intersection region of typical specimens employed in low cycle fatigue tests at high temperatures. The starting point is taken as the well known elastic stress concentration factor curves of Peterson which are extrapolated using data in the literature and other supporting (finite-element) calculations. Elastic–plastic values of strain concentration factors are then derived using the relations due to (a) Neuber, (b) Stowell–Hardrath–Ohman and (c) an energy method. It is shown in each case that these factors decrease with evolutionary cyclic hardening and increase with cyclic softening in a systematic way, as the material behaves according to the Ramberg–Osgood deformation law. A sensitivity study is carried out for each method, both for a ‘model material’ and real alloys and the implications of the shoulder radius/gauge diameter ratio is considered against the recommendations of various Testing Standards an...

Dectin-1 is the primary pattern recognition receptor for fungal glucans. Dectin-1 mediates the internalization and biological response to glucans. We examined the effect of i.v. or i.p. glucan phosphate (GP) administration on Dectin-1 membrane expression in murine peripheral blood leukocytes, splenocytes, bone marrow, and peritoneal cells from 3 h to 10 days after injection. Circulating leukocytes were also examined for uptake and internalization of glucans from the blood. Fluorescent-labeled GP was taken up from the systemic circulation by circulating peripheral leukocytes, splenocytes, and peritoneal cells. Following internalization, glucan colocalized with Dectin-1 in an intracellular vesicle. A single parenteral injection of GP resulted in a significant reduction (approximately 33-85%) in peripheral leukocyte membrane-associated Dectin-1 positivity that lasted for up to 7 days. The loss of leukocyte membrane-associated Dectin-1 after GP administration was primarily due to decreased levels of Dectin-1 on neutrophil and monocyte membranes with no significant changes in the percentage of neutrophils or monocytes circulating in the blood. Administration of control carbohydrate polymers, i.e., mannan or pullulan, which are not ligands for Dectin-1, did not decrease Dectin-1 leukocyte positivity, indicating that the effect on Dectin-1 is specific to glucans. In fact, mannan administration increased leukocyte Dectin-1 positivity, thus demonstrating a differential effect on leukocyte Dectin-1, compared with GP. We conclude that systemic administration of GP has a specific and prolonged effect on loss of leukocyte membrane Dectin-1 positivity. These data may have important implications for developing dosing regimens for immunomodulatory carbohydrates.

Lipopolysaccharide (LPS) has been implicated in sepsis-mediated heart failure and chronic cardiac myopathies. We determined that LPS directly and reversibly affects cardiac myocyte function by altering regulation of intracellular Ca2+concentration ([Ca2+]i) in immortalized cardiomyocytes, HL-1 cells. [Ca2+]ioscillated (2+oscillations and decreased basal [Ca2+]iby 30–40 nM. HL-1 cells expressed Toll-like receptors, i.e., TLR-2 and TLR-4. Thus, we differentiated effects of LPS on [Ca2+]iand Ca2+oscillations by addition of utlrapure LPS, a TLR-4 ligand. Ultrapure LPS had no effect on basal [Ca2+]i, but it reduced the rate of Ca2+oscillations. Interestingly, Pam3CSK4, a TLR-2 ligand, affected neither Ca2+parameter, and the effect of ultrapure LPS and Pam3CSK4 combined was similar to that of utlrapure LPS alone. Thus, unpurified LPS directly inhibits HL-1 calcium metabolism via TLR-4 and non-TLR-4-dependent mechanisms. Since others have shown that endotoxin impairs the hyperpolarization-activated, nonselective cationic pacemaker current ( If), which is expressed in HL-1 cells, we utilized whole cell voltage-clamp techniques to demonstrate that LPS (1 μg/ml) reduced Ifin HL-1 cells. This inhibition was marginal at physiologic membrane potentials and significant at very negative potentials ( P < 0.05 at −140, −150, and −160 mV). So, we also evaluated effects of LPS on tail currents of fully activated If. LPS reduced the slope conductance of the tail currents from 498 ± 140 pS/pF to 223 ± 65 pS/pF ( P < 0.05) without affecting reversal potential of −11 mV. Ultrapure LPS had similar effect on If, whereas Pam3CSK4 had no effect on If. We conclude that LPS inhibits activation of If, enhances its deactivation, and impairs regulation of [Ca2+]iin HL-1 cardiomyocytes via TLR-4 and other mechanisms.

Cyclic stress-strain tests were undertaken at 550 °C on plain specimens and notched specimens of different notch acuities in several low- and high-alloy ferritic steels (1Cr-Mo-V, NF616, TB12M, and HCM12A). Integrated axial strains were measured between the minimum sections of the notches using a longitudinal extensometer, while surface hoop strains were measured by means of a diametral extensometer with probes located across the notch root. The same extensometry was employed in plain specimens. Over a period of 100 cycles, softening occurred in all plain specimens. These effects were also demonstrated in notched specimens in both axial and diametral directions, although to a lesser degree. From hysteresis loops determined in the notch tests, the cyclic deformation response of the notched regions was expressed in terms of an ‘equivalent gauge length’. Deviations from elastic-plastic behaviour in plain specimens were noted in that the commonly used ‘effective Poisson's ratiO' was greater than calculated. The effect was investigated further by exploring the characteristics of a very shallow notch, induced by straining a plain specimen to the onset of necking and beyond. The implications of observed behaviour in strain-control low-cycle fatigue tests is discussed.

This paper investigates the importance of multiaxial stress states by considering several distinct testing techniques used in assessing both creep deformation and creep damage accumulation. The requirements of testing programmes to determine the necessary data are discussed in respect of sensitivity and interdependence of the principal and hydrostatic stress ratios.

This paper is concerned with the laboratory isothermal (low cycle) fatigue crack growth properties (generally at 550°C) of eleven ferritic steel samples taken from power station components which have seen between 63,000 h and 175,000 h service exposure to high temperatures. Full chemical analyses and abbreviated service histories of the materials are presented. Both the short crack (LCF) and deep crack (LEFM) regimes are examined. In some cases it was possible to continue the growth of actual service cracks under laboratory conditions, by suitable machining of samples into specimens; in other cases it was necessary to start the crack artificially. It is intended that the results can be used in direct application to remanent life assessments. In many tests the creep-fatigue interaction was simulated by the addition of a 0.5 h tensile dwell, it being assumed that major damage was already present in the extracted samples. The short crack growth tests at 550°C with dwell have demonstrated that even wh...

Reheat cracking in the heat affected zones of austenitic stainless steels can occur during high temperature service and is thought to arise from the relaxation of welding residual stresses, resulting in creep damage. Key features of reheat cracking are the magnitude of the residual stresses, degree of triaxiality, extent of stress relaxation behaviour and the influence of triaxial stress on creep ductility. A thermo-mechanical pre-conditioning technique has been developed for testing specimens to represent the welding cycles experienced between 200 and 1100 °C by the ‘strain affected zone’ of a weldment in a steam header during manufacture. Subsequent creep tests have been carried out at 550 °C on pre-conditioned plain and notched specimens to identify the behaviour as regards creep rate and ductility in both the uniaxial and triaxial stress states. The results have been compared with data in the literature and with models of the influence of multiaxial stress on creep ductility. It has been found that certain types of pre-conditioning give a marked reduction in creep ductility as strain rate is reduced, which helps to explain the reheat cracking process.

There are no procedural standards for the determination of stress-strain properties where a reversal of stress is involved. The purpose of this Code of Practice is to detail the requirements for cyclic stress-strain (CSS) testing on uniaxial testpieces. CSS testing may entail the use of a single testpiece to produce data over several strain ranges. Alternatively, data from a number of constant strain range tests may be obtained, for example as the by-product of a series of low cycle fatigue (LCF) endurance tests. Procedures for LCF testing are covered by a number of existing Codes of Practice and Standards [1–6], and this document does not recommend any alteration to these. This Code of Practice has been prepared by the CSS Working Party of the ESIS TC11 High Temperature Mechanical Testing Committee.Historically, CSS results have been reported in terms of a relatively simple power law. However, engineers involved in design and assessment activities are now increasingly tending to use more advanced...

This paper is concerned with the laboratory isothermal (low cycle) fatigue response of sixteen ferritic steel samples taken from power station components which have seen between 70,000 h and 170,000 h service exposure to high temperatures. After suitable machining into specimens the cyclic stress-strain properties between 300 and 600°C at strain rates between 6 × 10−4/s and 5 × 10−6/s were established using the multiple step technique (which is discussed in some detail). Ferritic steels generally cyclically soften, and by evolutionary tests undertaken at 550°C it is demonstrated that start/up and shut/down procedures in service have accelerated this process in material subjected to temperature transients. The steady-state cyclic stress-strain response has shown a marked loss in strength compared with data on a selection of unexposed steels e.g. material trepanned from turbine casings at the manufacturing stage or from specially cast test blocks. The data have been fitted to the Ramberg–Osgood law ...

Cyclic stress–strain tests were undertaken at temperatures between 550°C and 820°C on plain and doubly-notched specimens of three alloy steels: 20Cr/25Ni/Nb, 316 and 1CrMoV respectively. Integrated axial ‘strains’ were measured between the minimum sections of the (semi-circular) notches using a longitudinal extensometer, while surface hoop strains were measured on one notch by means of a diametral extensometer. Cyclic hardening occurred in plain specimens of 316 steel, cyclic softening occurred in the 1CrMoV steel and the 20Cr/25Ni/Nb alloy showed stable behaviour. These effects were also demonstrated in notched specimens, although to a lesser degree. From hysteresis loops determined during multiple step tests, the cyclic deformation response of the notched regions was expressed in terms of an ‘equivalent gauge length’. Comparison was also made between the equivalent (von Mises) stress–strain curves deduced at a representative (skeletal) point in the minimum section with stress–strain data obtaine...

Using the powerful Earth-occultation technique, long-term, nearly continuous monitoring of the entire low-energy gamma-ray sky is now possible with the advent of BATSE, the Burst and Transient Source Experiment on board the Compton Gamma Ray Observatory (CGRO). In this paper, we present a catalog of 34 moderately strong gamma-ray sources measured by BATSE. It consists of 0.03-1.8 MeV photon spectra averaged over weeks and months, and light curves of the 35-200 keV flux, with 1 day resolution, covering the first three phases of the CGRO mission (1991 May through 1994 October). These results have been obtained using the JPL Enhanced BATSE Occultation Package (EBOP) developed under the CGRO Guest Investigator Program. The EBOP concept and approach are also described in some depth. This paper presents highlights extracted from a large EBOP database which has now been archived at the Compton Observatory Science Support Center (COSSC). This database contains a complete record of ~1200 daily source count rates in 14 energy channels along with the corresponding Poisson and systematic errors for 64 sources, including 30 not described here. An interface to XSPEC is included in the archive allowing conversion from count rates to photon fluxes. This paper therefore serves also as a reference and entree into the archive and provides an index and guide for those investigators using the EBOP system and database for their respective scientific investigations.

BACKGROUND McClintock1,2 was one of the first to model continuous-cycling fatigue crack growth by assuming a succession of miniature low-cycle-fatigue (LCF) specimens at the crack tip. Elements ahead of the crack amass damage until the arrival of the tip itself. Such models had been summarized by Majumdar and Morrow,3 but the author was unaware of these papers at the time. The ideas were pursued further by Chakrabortty4 whose paper, again unknown to the author, was published in the same issue (1979, Vol. 2) of FEMS. In the original paper5 crack propagation is represented by successive regeneration at the crack tip, the process becoming progressively easier as the crack grows owing to an increase in strain concentration. These ‘initiation’ cycles were related to the ‘Coffin’ expression for crack initiation, thereby introducing two empirical constants k and α. The paper is of the class ‘ρ/N’ where ρ is the assumed size of a crack-tip process zone and N is the cycles required to traverse that zone. Expressions had been previously derived linking LCF with linear-elastic fracture-mechanics (LEFM) crack growth, using the parameter ΔJ.6 (It was later shown that this was identical to using an equivalent stress intensity parameter.7) It has been shown that the approach does not apply for crack depths < 180 μm.6 At elevated temperature the ΔJ approach was successful for describing crack growth in the range 0.2–1.2 mm for the cobalt-based alloy MAR-M509 at 600 °C.8 Other studies have in fact shown9 that crack growth rates are approximately constant below a depth of 200 μm. Even to this day short crack growth relations in LCF and their practical use are not as familiar as those in LEFM. It may justifiably be argued that for every paper published on LCF short crack growth, several hundred have appeared dealing with LEFM crack growth in terms of the ‘Paris’ law. One of the original referees' comments was that the paper5 should have been presented in terms of LEFM. The author nevertheless defended his approach because for small cracks it was thought useful to retain the crack depth explicitly. It will be shown that LCF crack growth data have a definite part to play in the assessment of components and structures.

Comparisons have been made on evolutionary and stabilised cyclic stress-strain behaviour following different prior ageing treatments in a 316 steel. Prior stress-free ageing at a temperature higher than the test temperature reduces the ability of this steel to cyclically harden and consequently the material does not achieve maximum strength. An apparent saturation of cyclic hardening at room temperature can however, be continued by further cyclic hardening at 625°C. The rate of precipitation during low cycle fatigue can be two orders of magnitude greater than that occurring during stress-free ageing at 625°C. Quantitative measurements based on an extraction technique are presented and compared with particle size measurements in the literature. Prior high temperature low cycle fatigue exposure has been shown to reduce subsequent creep rates with a concomitant reduction in ductility: the same effect is found by prestrain at room temperature. Neither cyclic stress-strain properties nor creep behaviou...

It is shown in this study that two different types of spectral emission are generally produced in gamma-ray bursts. A subset of bursts is identified that exhibits a marked lack of fluence above 300 keV, and these bursts are shown to have luminosities about an order of magnitude lower than bursts with significant fluence above 300 keV. The bursts lacking emission above 300 keV exhibit an effectively homogeneous intensity distribution. In addition, it is shown that both types of emission are common in many bursts, demonstrating that a single source object is capable of generating both of them. These results strongly favor a gamma-ray burst source object that produces two different types of emission with varying degrees of superposition. The impact of this behavior is strong enough that it affects the properties of the burst intensity distribution, as well as the burst spectral characteristics.

Data from a previous round robin low cycle fatigue exercise on 316L steel, 9Cr1Mo steel and IN718 alloy at 550°C and Nimonic 101 at 850°C are re-examined, emphasis being placed on material stress-s...

We analyze time-averaged spectra from 86 bright gamma-ray bursts from the first 5 years of the Burst And Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory to determine whether the lowest energy data are consistent with a standard spectra form fit to the data at all energies. The BATSE Spectroscopy Detectors have the capability to observe photons as low at 5 keV. Using the gamma-ray burst locations obtained with the BATSE Large Area Detectors, the Spectroscopy Detectors' low-energy response can be modeled accurately. This, together with a postlaunch calibration of the lowest energy Spectroscopy Detector discriminator channel, which can lie in the range 5-20 keV, allows spectral deconvolution over a broad energy range, ~5 keV to 2 MeV. The additional coverage allows us to search for evidence of excess emission, or for a deficit, below 20 keV. While no burst has a significant (≥3 σ) deficit relative to a standard spectra model, we find that 12 bursts have excess low-energy emission, ranging between 1.2 and 5.8 times the model flux, that exceeds 5 σ in significance. This is evidence for an additional low-energy spectral component in at least some bursts, or for deviations from the power-law spectral form typically used to model gamma-ray bursts at energies below 100 keV.

Strain-controlled total endurance tests have been carried out on smooth specimens of 2 1/4Cr-1Mo steel at 550°C in continuous cycling, and also using interspersed blocks of major and minor cycling. Similar low-cycle fatigue crack growth tests were also carried out on cylindrical specimens of 1/2CrMoV steel containing a 0.2 mm deep starter defect using interspersed blocks of major, intermediate and minor cycling, their order being changed in separate tests. Damage summation in the smooth specimen tests at failure was found to be less than unity (irrespective of the failure criterion) when Miner's rule was employed, and the results are compared with limited previous data. Damage was also summed on an energy-expended basis and this was found to be (i) independent of strain range, and (ii) independent of cycle type (i.e. continuous loading or block loading). The nearer the chosen failure criterion to crack initiation, the closer was the agreement in accumulated energies. Similarly, in the crack growth tests, the number of complete loops to failure (10% load drop) was independent of block order over a wide range of applied strain ranges, but was affected by the number of cycles in each block. However, the energy criterion was again able to rationalise all the data.

Fully two-dimensional gamma-ray imaging with simultaneous high-resolution spectroscopy using an externally segmented germanium sensor has been demonstrated in the laboratory with a calibrated radioactive source. The system employs a single high-purity coaxial detector with its outer electrode segmented into five distinct charge collection regions and a lead coded aperture, with a uniformly redundant array (URA) pattern. A series of one-dimensional responses was collected around 511 keV while the system was rotated in steps through 180/spl deg/. A nonnegative, linear least-squares algorithm was then employed to reconstruct a two-dimensional image. Corrections for multiple scattering in the detector, and the finite distance of source and detector are made in the reconstruction process. >

Isothermal uniaxial cyclic loading experiments have been conducted on specimens of the nickel-based superalloy IN100 at selected temperatures in the range 600–1000°C. Power-law stress—strain relations based on plastic strain (Ramberg-Osgood), total strain and their bilinear equivalents have been used to describe the behaviour. In addition, uniaxial thermomechanical fatigue (TMF) tests have been performed on tubular specimens of the material over the temperature range 650–1050°C. The aim of these tests was to model the response during thermal shock experiments involving rapid heating and cooling cycles between 200°C and 1100°C. Some transient tests have also been carried out on blade-shaped single-wedge specimens of IN 100 to simulate the type of thermal fatigue (TF) cycle experienced by turbine blades during service. A finite element sensitivity analysis has been undertaken to predict the results of both the TMF and TF tests using the two different bilinear descriptions of the isothermal cyclic stress-str...

High strain fatigue experiments were carried out on thirteen different high temperature alloys at 550°C. By means of multiple step tests and interrupted tests in the steady state, the asymmetrical nature of the Bauschinger effect was examined, i.e. having regard to the magnitude and direction of the stress reversal point during the course of the hysteresis loop. The cyclic stress–strain curve was characterised using the well known Ramberg—Osgood deformation relationship, and distinction was made between actual curve shape and the locus approximation. The yield stress during the course of a cycle could be made to vary according to the reversal point in the interrupted tests, but even in steady state cycling, the cyclic yield point was found to decrease as the total strain range was increased. Limited investigations were also performed during evolutionary (hardening or softening) cycling and all results were interpreted in terms of the prevailing back stress and friction stress. A formula to predic...

— Thermo-mechanical fatigue stress-strain data on ferritic/austenitic steels and superalloys from a variety of sources are analysed with regard to hysteresis loop stress asymmetry. This arises from a decoupling of the thermal and mechanical strain signals in the test technique so that many tension-compression load combinations are possible. Data from simplified isothermal and bithermal tests are also examined. Taking a typical example of an “out-of-phase” thermo-mechanical loop on a 1/2 CrMoV steel cycled between 200 and 550°C, isothermal stress-strain data were generated at 50°C intervals on material from the same cast and, used in conjunction with the elastic characteristics of the apparatus, an attempt was made to re-create this loop. The methods employed were (i) a graphical construction between appropriate isothermal yield contours (ii) a tangent modulus calculation (iii) a secant modulus calculation. Method (i) appeared to give the closest agreement in the present case.

An earlier modification of the Paris law for the growth of deep cracks in the linear elastic fracture mechanics regime is extended to include a term enabling the prediction of cyclic crack growth rates at low frequencies. The relation requires (i) a reference growth law under continuous cycling at the appropriate elevated temperature and (ii) a specified, dimensionless degradation term, defined as Dc, the creep/oxidation damage per cycle, which increases as the applied frequency decreases or as the dwell time at peak load is prolonged. The relationship is validated against data from the previous analysis on low alloy ferritic and austenitic steels in the range 538–650°C and against further published results on Ni-based alloys at temperatures up to 700°C. It appears that for the former series oxidation is the dominant damaging mode, whereas a linear creep damaging mechanism is manifest in the Ni-based alloys. Moreover, levels of cyclic damage in terms of Dc are higher in the latter, ranging between 10−3 an...

High temperature total endurance tests were conducted on two alloys (316L steel and 9Cr–1Mo (wt-%) steel) at 550°C in high strain fatigue under continuous cycling at total strains in the range 0·6–2·0%. The austenitic steel cyclically hardened, whereas the ferritic steel cyclically softened. From striation spacing measurements on fracture surfaces (and to a lesser extent from observations of tensile load drop), it has been possible to correlate progress of the major crack with strategic points on the hardening/softening curves at each strain range. The minimum depth at which striations were measured with confidence was ~0·04 mm and by establishing growth laws it is demonstrated that this depth was typically achieved by the ‘plateau’ regions for both alloys. By extrapolation of the growth relationships it is concluded that cracking ~4–20 μm deep has occurred by the end of the earlier rapid hardening and softening phases.MST/1813

High temperature total endurance tests were conducted on three alloys (316L steel at 550°C; 9Cr–1Mo steel at 550°C; Nimonic 101 at 850°C) in low cycle fatigue under continuous cycling. The austenitic steel was observed to cyclically harden, whereas the ferritic steel and the superalloy both cyclically softened. Methods for rationalising evolutionary behaviour were variation of percentage hardening/softening with strain range, cumulative ductility criterion, variation of secant modulus in the hysteresis loops, and cumulative energy criterion. The energy expended per cycle appears to be the most attractive. For a given strain range this was approximately constant at any stage of evolution. More significantly, the cumulative energy at saturation was constant, approximately independent of total strain range, and about 0·5–3·0 J mm−3 according to the material used. The Palmgren–Miner hypothesis (which is widely used in summing fatigue damage) was originally derived on an energy argument and it is propo...