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AbstractA high-level design study for a new experimental tokamak shows that advances in fusion science and engineering can be leveraged to narrow the gaps in energy confinement and exhaust power handling that remain between present devices and a future fusion pilot plant (FPP). This potential new U.S. facility, an Exhaust and Confinement Integration Tokamak Experiment (EXCITE), will access an operational space close to the projected FPP performance regime via a compact, high-field, high-power-density approach that utilizes advanced tokamak scenarios and high-temperature superconductor magnets. Full-device optimization via system code calculations, physics-based core-edge modeling, plasma control simulations, and finite element structural and thermal analysis has converged on a  T,  MA,  m, , D-D tokamak with strong plasma shaping, long-legged divertors, and 50 MW of auxiliary power. Such a device will match several absolute FPP parameters: plasma pressure, exhaust heat flux, and toroidal magnetic field. It will also narrow or close the gap in key dimensionless parameters: toroidal beta, bootstrap fraction, collisionality, and edge neutral opacity. Integrated neutron shielding preserves personnel access by limiting nuclear activation and maximizes experimental run time by reducing site radiation. In addition to design study results and optimization details, parameter sensitivities and uncertainties are also discussed.

AbstractOperating with hot tokamak plasma-facing components will be essential in fusion reactors to maximize the thermal efficiency of the blanket. The SOLPS-ITER edge plasma code package and the DIVIMP Monte Carlo impurity tracking code were used in tandem to simulate the effect of active wall heating on impurity sourcing and transport in a DIII-D–size tokamak. The SOLPS-ITER plasma background was generated based on a previous DIII-D discharge and includes the effect of particle drifts. DIVIMP simulations found that actively heating the lower divertor (versus the divertor shelf or the entire wall) was the most efficient way to minimize gross erosion and core impurity influx at temperatures above 1000 K. Replacing the graphite wall with a silicon carbide (SiC) wall yielded a 5 to 20× decrease in the estimated gross erosion rate of carbon, with a maximum decrease observed at a lower divertor temperature of 800 K. Gross erosion of Si from SiC was estimated to be almost 100× lower than that of C from SiC, due primarily to the low impact energy of incident D plasma on the divertor targets. The core impurity influx for SiC walls is predicted to be lower than that with graphite walls, but eroded Si ions appear to migrate preferentially (versus C) to the core due to a more peaked erosion profile closer to the strike points where the ion temperature gradient force drives particles upstream. These predictive simulations suggest that active heating of the plasma-facing wall may both lower wall erosion and improve core performance relative to the “warm” walls of current devices that are typically only heated via plasma contact. Relative reductions in gross erosion and upstream accumulation by using SiC instead of graphite as the wall material strengthen the argument for upgrades to current graphite-clad machines and continued development of SiC first-wall and blanket concepts.

Here we offer an approach for being reasonably sure that finite element determinations of stress concentration factors are accurate enough to be included in engineering handbooks. The approach has two contributors. The first consists of analyzing a stress concentration on a sequence of systematically refined meshes until the error estimates of ASME have that sufficient accuracy has been achieved. The second consists of constructing a test problem with an exact and somewhat higher value of its stress concentration factor, then analyzing this test problem with the same sequence of meshes and showing that, in fact, sufficient accuracy has been achieved. In combination, these two means of verification are applied to a series of U-notches in a plate under tension. Together they show that it is reasonable to regard finite element values of stress concentration factors on the finest meshes as being accurate to three significant figures. Given this level of accuracy, it is then also reasonable to use the approach to verify other existing stress concentration factors and resolve any discrepancies between them, as well as to verify new stress concentration factors.

The sensitivity of the Greenland ice sheet to climate forcing is of key importance in assessing its contribution to past and future sea level rise. Surface mass loss occurs during summer, and accounting for temperature seasonality is critical in simulating ice sheet evolution and in interpreting glacial landforms and chronologies. Ice core records constrain the timing and magnitude of climate change but are largely limited to annual mean estimates from the ice sheet interior. Here we merge ice core reconstructions with transient climate model simulations to generate Greenland‐wide and seasonally resolved surface air temperature fields during the last deglaciation. Greenland summer temperatures peak in the early Holocene, consistent with records of ice core melt layers. We perform deglacial Greenland ice sheet model simulations to demonstrate that accounting for realistic temperature seasonality decreases simulated glacial ice volume, expedites the deglacial margin retreat, mutes the impact of abrupt climate warming, and gives rise to a clear Holocene ice volume minimum. The Greenland ice sheet could contribute 7 m (23 feet) of sea level rise if it were to melt completely. For future sea level rise predictions we need to know how the Greenland ice sheet will respond to rising temperatures. We can figure out how sensitive Greenland is by studying a natural period of warming (called the last deglaciation) that happened at the end of the last Ice Age 18,000 years ago. During the last Ice Age the Greenland ice sheet was much larger than it is today, and as the climate warmed it shrunk to its present size. We combine ice core data and climate models to reconstruct Greenland‐wide temperatures for all seasons over the last 22,000 years. This reconstruction makes it possible to simulate Greenland ice loss during the last deglaciation in ice sheet models. The model output can be compared to data on past ice sheet volume, for example, from moraines left behind in the landscape as the ice melted. Our reconstruction provides a critical step in learning from the past behavior of the Greenland ice sheet in order to predict its future. Merging climate models and ice core data gives seasonality and spatial pattern of deglacial warmingTemperature fields are useful for forcing ice sheet models and interpreting local ice retreatTemperature seasonality expedites deglacial ice loss and mutes the impact of abrupt climate change

Conflicts between indigenous people and mining companies have occurred in many countries and over many years, with the pressure for mining companies to improve their performance leading to a growth of corporate social responsibility concepts. Energy Resources of Australia and the Gundjeihmi Aboriginal Corporation (representing the Mirarr people) sought to resolve a number of long-standing issues relating to surface water management and monitoring associated with the Ranger Uranium Mine. This article summarises the process adopted and discusses the main factors that underpinned the success of the project.

When stress concentration factors are not available in handbooks, finite element analysis has become the predominant method for determining their values. For such determinations, there is a need to know if they have sufficient accuracy. Tuned Test Problems can provide a way of assessing the accuracy of stress concentration factors found with finite elements. Here we offer a means of constructing such test problems for stress concentrations within boundaries that have local constant radii of curvature. These problems are tuned to their originating applications by sharing the same global geometries and having slightly higher peak stresses and stress gradients. Consequently, they are incrementally more challenging to solve with finite elements than their originating applications. They also have exact solutions. Thus, a precise determination can be made of the errors incurred in their finite element analysis.

For some finite element analyses of stresses in engineering components, low-order elements can be preferred. This choice, however, results in slow convergence, especially at key stress concentrations. To overcome this difficulty, submodelling of stress concentrators can be employed. With submodelling, a subregion within the original global configuration and centred on the stress concentrator of interest is analysed by itself, with a consequent reduction in computation. The more aggressive the submodelling, the smaller the subregion and the greater the computational savings. To realize such savings in actuality, it is necessary that appropriate boundary conditions be applied to the subregion. Some of these boundary conditions must be drawn from a global analysis of the original configuration: then it is essential to ensure that such boundary conditions are determined sufficiently accurately. This paper describes a procedure for being reasonably certain that such is the case. The procedure is evaluated on a series of test problems and demonstrated on a contact application. Results show that good engineering estimates of peak stresses can be obtained even in regions of unusually high stress gradients. Furthermore, these estimates can be obtained in return for quite moderate levels of computational effort. Copyright © 1999 John Wiley & Sons, Ltd.

Road recycling in Perth and Kinross G. Sinclair, BSc, CEng, MICE and J. Valentine, CEng, MICE & Proc. Instn Civ. Engrs Mun. Engr, 1999, 133, Dec., 165171 Paper 11965 Road maintenance presents councils and local authorities with the challenge of maintaining road surfaces to the highest possible standards but with the least disruption to the road user. Any maintenance process that can successfully realize both of these aims and at the same time oer cost and waste savings is clearly desirable...

Energy arguments remain, even today, as probably the most fundamental physically-reasoned justification for the application of linear elastic fracture mechanics to brittle materials. Accordingly, they have attracted and continue to attract quite a number of investigations. Not all of these studies employ the same approach. Unfortunately, nor do they all lead to the same conclusions regarding the implications of elastic fracture mechanics. Here, by examining the energy balance of fracture mechanics from a classical physics viewpoint, equivalent valid approaches are identified. This in turn enables the various contributions over the years to be placed in perspective with respect to whether or not they are correct.

Several elastic configurations containing cracks under transverse tension which intersect a free surface are investigated. In order to ensure reliable results two independent numerical methods are employed on a comparison problem, each method being tuned to handle the special features involved. The comparison provides confidence in other results which focus on the key quantity in linear elastic fracture mechanics, the energy release rate. These findings may be summarized as follows: that the decays in the energy release rates found as the free surface is approached in the various problems treated are probably not significant from a fracture toughness testing point of view and not of major consequence in cyclic life calculations, although there are some indications that this may not be the case if near-surface residual stress fields are present; and that these variations in energy release rate can be compensated for by relatively minor perturbations in crack-front profiles.

This paper is concerned with the singular behavior of harmonic functions at the vertex of a plane, composite, wedge region. Separable harmonic functions which include logarithmic terms are investigated for their possible existence in the vicinity of the vertex. The eigenequations governing existence are examined and explicit determination of the singular eigenvalues made for several combinations of boundary and interface conditions. The results enable an appreciation of the possible singular nature in such problems which aids any complete (numerical) analysis.

Information on the singular behavior at the vertex of a bi-material wedge is the objective of this paper. A summary of the necessary conditions, which depend heavily on the associated eigenvalue equation, for stress singularities of O(r-? 1n r) as r?0 or O(r-?) as r?0 is stated. The eigenvalue equations arising from a wide range of boundary and interface conditions are then provided. Bi-material wedge problems that have been subjected to singularity analyses of some generality in the literature are briefly reviewed.

This paper examines the composite, two-dimensional, linear elastic wedge for singular stresses at its vertex. A full range of wedge boundary and matching conditions is considered. Using separation of variables on the Airy stress function, the usual determinant conditions for singularities of the formO(r-?) asr ? 0 are established and further conditions are derived for singularities of the formO(r-? lnr) asr ? 0. The order of the determinant involved in these conditions depends upon the number of materials comprising the wedge. Two systematic methods of expanding the determinant for theN-material wedge are presented.

The plane elastostatic stress field near an interface crack is considered and a model developed for the interface crack tip which is free from the inter-penetration of the crack flanks present in some earlier investigations, yet permits propagation in a crack opening mode along or near the interface. The basis of the model lies in taking, as the configuration to which the loads are applied, a crack tip which subtends an opening angle. By means of an asymptotic eigen-analysis, the main features of this departure from the norm in LEFM are identified and some examples presented which demonstrates its potential usefulness.

Abstract not available.

Alterations in the structure and molecular composition of avian hepatocyte nuclei were compared following administration in vivo of lethal and sub-lethal doses of α-amanitin. This toxin interferes with extranucleolar transcription by direct inhibition of RNA polymerase II activity. The resultant effects include: extensive condensation of chromatin, displacement of nucleoplasmic contents and fragmentation of nucleoli. Changes in nuclear morphology were quantitated by stereometry and related to variations in RNA and residual, non-histone proteins (NHP). Gross alterations in nuclear structure and depletion of RNA and NHP levels were of similar magnitude with both doses of amanitin. The effects were fully reversible, however, with a minimal dose but terminal with a lethal dose. DNA and histone protein levels remained unchanged at all stages.

Predicting crack growth under cyclic loading in applications usually requires the efficient extraction of stress intensity factors from finite element analyses of mixed mode situations. Two approaches to this end are examined: one, a competitive fitting procedure using crack-flank displacement data, the other, a path independent integral which can readily distinguish between modes. A protocol is established for comparing the two on a set of about forty test problems which have exact solutions. Analysis is via quarter point elements on a common sequence of three successively refined meshes for each problem. Results show that the path independent integral is more consistently accurate and reliably convergent, yet comparable in implementation effort.

A number of current practices in fracture mechanics which use quantities near a crack tip to make conclusions about response at the crack tip itself are examined. Specifically these include: stress and displacement matching to estimate stress intensity factors, monitoring local stress and strain values to predict fracture, and both crack opening angle and crack opening displacement as fracture criteria. By means of a pair of counter applications, all of these procedures are demonstrated to have the potential of leading to completely incorrect conclusions. An understanding of what causes this inadequate performance then indicates that such procedures may be unreliable in general and prompts suggestions as to alternatives.

The temperature field and mode I stress intensity caused by resistance heating are calculated for a model problem. The results indicate that, for a constant far-field electric current, the stress intensity is proportional to the crack length to the power 5/2. Consequently, the effect of localized heating becomes especially important as the crack length increases and may, if ignored, cause significant errors during the more severe thermal fatigue tests that utilize direct resistance heating.

When numerical methods are applied in engineering, verification is essential. Test problems can help in meeting this requirement. This is especially so when these problems are tuned to the application at hand. Unfortunately, in practice such tuned test problems are not always directly available. For these cases, this paper describes an approach for constructing tuned test problems. The approach may be used on ordinary or partial differential equations, be they linear or non-linear. This is demonstrated on a number of applications drawn from dynamics, solid mechanics, and fluid mechanics. © 1997 John Wiley & Sons, Ltd.

To study the effect of immunologic stimuli on renal expression of Ia antigens (the class II products of the major histocompatibility complex), we induced acute graft-vs-host disease (GVHD) in mice and assessed Ia expression in the host kidney. Serologic absorption analyses showed that the amount of host Ia antigen increased up to tenfold in kidney, and immunofluorescence demonstrated that this increase occurred predominantly in renal tubule epithelial cells. To determine whether these alterations reflected changes in Ia gene transcription, we hybridized DNA probes for mRNAs encoding either Ia Ea or Aß chains to total RNA extracted from the kidneys of normal mice and mice with acute GVHD. Northern hybridization blots revealed that the level of Ia mRNA expression in GVHD kidney is enhanced about sevenfold when compared with that found in normal kidney. Using the Ea probe, this result was shown to reflect increased expression of C3H host EakmRNA, since the Eabgene is not transcribed by the C57BL/6 donor strain used. We conclude that the increase in expression of Ia in renal tubule epithelium during GVHD probably reflects increased I-region gene transcription in host kidney cells. These findings may have implications for the pathogenesis of renal allograft rejection and immunologic renal disease.

The nature of the stress field occurring at the vertex of an angular elastic plate under in-plane loading is reconsidered. An additional boundary condition is introduced. This boundary condition reflects the action of cohesive stress-separation laws. Companion asymptotic analysis proceeds routinely on employing coupled eigenfunction expansions. Results show that a number of configurations that had previously contained stress singularities become singularity free.

Recent studies indicate that most of the “scatter” observed in finite fatigue-life-testing of metals is an inherent characteristic of the material and does not necessarily indicate poorly adjusted machines or improper testing techniques. In the present study, groups of 17 to 57 specimens of 75S-T6 aluminum alloy were tested in rotating bending at six different stress levels. The smallest stress used was 30,000 psi and the greatest was 62,500 psi. A statistical analysis was made of fatigue-life data obtained at each of the six stresses. The distribution of the fatigue lifetimes, for each stress, was found to be approximately logarithmic-normal. The standard deviation (which is a measure of scatter in the fatigue life) was related to the stress amplitude and could be represented within the stress range investigated, by a simple exponential function. Constants of an S-N relation recently proposed by W. Weibull were evaluated for a probability of failure P = 0.50. Results of the study are summarized in two equations and in a composite S-N diagram showing lines of equal probability of failure.

In this study, a set of two parameters was used to describe the state of dynamic equilibrium for hardening and softening behavior in a variety of metallic materials, subjected to cyclic and static loading conditions, temperatures, and strain rates in the range of practical interest. The parameters consisted of a time-temperature parameter and a cyclic stress-strain parameter. Stable or near-stable values of cyclic stress and strain and of creep rate were extracted from numerous sources in the literature. Values for each parameter were calculated from that data and their functional relationship was studied. Results suggest a single relationship between the two parameters for pure FCC metals for both creep and fatigue.

In the low-temperature range, the engineering yield strength of polycrystalline bcc metals can change by a factor of 10 or more with serious consequences appearing in the form of catastrophic brittle fracture. Engineering variables known to have an important effect on the yield behavior are state of stress, temperature, loading or strain rate, composition, and microstructure. For iron, chromium, molybdenum, and tungsten, it is shown that yield behavior can be represented by a single-valued relation between two dimensionless parameters.

Corrosion fatigue crack growth rates for SAE 4340 steel in distilled water environments were investigated utilizing fracture mechanics techniques. Crack growth rates, resulting from various forms of repeated loading, were compared to those induced by static load using small sample statistical theory. These comparisons indicate that corrosion fatigue crack growth may be either time or cycle dependent depending on the load profile, loading frequency, and temperature. Data are presented suggesting that whenever the maximum cyclic stress intensity in the fatigue cycle is below the static threshold stress intensity (KIscc), the environment no longer plays a major part in assisting the crack growth rate.

The yield behavior of niobium (columbium) has been studied under conditions of different states of stress, temperatures and strain rates, material compositions, and microstructures. Using data gathered in the present investigation as well as that obtained from ten other sources, it is shown that a relationship including the foregoing variables is given by γ˙G=Ae−[ΔH*−V(τG−τiG)]/RT While details of the frequency factor A remain unclear, it appears that it may be treated as a constant over a wide range of temperatures and strain rates. The analysis included in this paper shows that a simple parameter representation of yield behavior of niobium is feasible in terms of pertinent engineering variables.

It is pointed out that numerical solutions of electromagnetic boundary-value problems deserve to receive greater emphasis, particularly those arising in practical applications. Numerical methods of solution can also be of great help in theoretical studies where suitable analytical solutions are difficult to obtain. By using a certain fundamental integral equation for the electromagnetic field, it is shown that many problems can be reduced to the solution of standard types of integral equations for which numerical techniques of solution already exist.

Plastic deformation that accumulates with running time may constitute a mode of failure in some rolling element applications, particularly at elevated temperature. This phenomenon is studied in a simple room temperature investigation involving annealed brass toroids and cylinders mated with hard steel rollers. Evidence of sizable accumulation of plastic strain with cycles of rolling, despite subsequent contact stress reduction, leads to a consideration of the effect of a complex combined stress history, such as that induced by the rolling action, on plastic flow in metals.

The influence of temperature and strain rate on the upper yield point of ingot iron was studied. Torsion tests were conducted using strain rates of 12.5/sec, 0.25/sec, and 0.0001/sec over the temperature range 77 to 525 deg K. The upper yield point showed a rapid increase as the temperature was lowered. An increase in the strain rate also caused an increase in the yield point. An apparent activation energy can be associated with the strain rate and temperature dependence of the yield point. This energy is influenced by stress level, and it appears from the present study that the relationship can be described by an equation of the form ΔH=ΔH¯τ¯−ττ¯b. If this relationship is substituted for ΔH in a modification of the Boltzmann relation, the following result is obtained: logγ˙γ˙1=MΔH¯RT1τ¯−τ1τ¯b1−T1Tτ¯−ττ¯−τ1b. This equation describes the experimental data within ± 3000 psi. The results of this investigation compared with tensile test data from other investigators confirm that state of stress is an important factor in determining whether a material will behave in a ductile or brittle fashion.

An investigation was made of the effect of various surface-finishing operations on the fatigue strength of two titanium alloys, RC 130B and Ti 140A. The types of finish studied included rough-machined, machined and mechanically polished, cold-rolled electropolished, and ground surfaces. Through the use of microhardness measuring techniques it was found that the different finishing methods introduced varying degrees and varying depths of cold work in the surface layers of the metal. Cold-rolling produced the highest hardness in the surface layer while grinding gave the lowest value; in one case the ground surface appeared to be slightly softer than the inner core metal. In general, the fatigue strength for lifetimes exceeding 2 × 107 cycles was found to vary according to the hardness of the surface layer with the highest hardness corresponding to the greatest fatigue strength. Roughness of the surface was also found to influence fatigue strength but to a much lesser degree than hardness. As a first approximation the relationship between surface hardness, surface roughness, and fatigue strength could be expressed by an equation of the form Z = KX−a Yb where Z is fatigue limit, X is surface roughness, Y is hardness, and K, a, and b are constants of the material. Data from the present study were evaluated in terms of this equation and the results are presented in the form of a nomograph. Results of tests made on notched specimens appear to indicate that titanium is less notch-sensitive in fatigue than was previously reported. Early reports of extreme notch sensitivity may have resulted from comparisons made between notched and smooth specimens having quite different surface preparations in the test section.