Modelling of the behaviour of a welded joint subjected to reverse bending moment at high temperature

The paper is concerned with the modeling of the behaviour of welds when subjected to severe thermal and mechanical loads where the maximum temperature during dwell periods lies in the creep range. The methodology of the life assessment method R5 is applied where the detailed calculations are carried out using the linear matching method (LMM), with the objective of generating an analytic model. The linear matching method has been developed to allow accurate predictions using the methodology of R5, the UK life assessment method. The method is here applied to a set of weld endurance tests, where reverse bending is interrupted by creep dwell periods. The weld and parent material are both Type 316L(N) material, and data were available for fatigue tests and tests with 1 and 5 h dwell periods to failure. The elastic, plastic, and creep behavior of the weld geometry is predicted with the LMM using the best available understanding of the properties of the weld and parent material. The numerical results are translated into a semi-analytic model. Using the R5 standard creep/fatigue model, the predicted life of the experimental welds specimens are compared with experimental data. The analysis shows that the most severe conditions occur at the weld/parent material interface, with fatigue damage concentrated predominantly in the parent material, whereas the creep damage occurs predominantly in the weld material. Hence, creep and fatigue damage proceed relatively independently. The predictions of the model are good, except that the reduction in fatigue life due to the presence of the weld is underestimated. This is attributed to the lack of separate fatigue date for the weld and parent material and the lack of information concerning the heat affected zone. With an adjustment of a single factor in the model, the predictions are very good. The analysis in this paper demonstrates that the primary properties of weld structures may be understood through a number of structural parameters, defined by cyclic analysis using the linear matching method and through the choice of appropriate material data. The physical assumptions adopted conform to those of the R5 life assessment procedure. The resulting semi-analytic model provides a more secure method for extrapolation of experimental data than previously available

Structural integrity assessment of superheater outlet penetration tubeplate

In recent years, the Linear Matching Method (LMM) has been well developed for the integrity assessment of the component subjected to cyclic thermal and mechanical loads. In this paper, the fatigue damage of a superheater outlet penetration tubeplate is assessed in detail using the LMM with an ABAQUS 3D finite element model. The significant thermal transients of the component are due to the out of phase steam temperature oscillations. The primary loading on the component is from pressure (steam and gas) and system moment on the penetration and tail pipes. A transient thermal analysis is performed in the first step to determine the component temperature history during the cycle. Then these temperature solutions are used as an input to the structural analysis to obtain the elastic stress history caused by these temperature loads. A shakedown analysis is thereafter carried out and the evaluation of the steady cyclic behaviour of tubeplate during the steady state cycle is then achieved using the LMM. The elastic, plastic and total strain ranges over the steady state cycle are evaluated for the fatigue damage assessment. Both the constant and changing residual stress solutions associated with the steady state cycle are obtained. The comparisons of stress and strain range calculations for out of phase temperature oscillations by the LMM and other methodologies are given in the paper. Finally, a LMM ratchet limit analysis is carried out to assess the capacity of the component subjected to the existing thermal transients to withstand an additional primary loads including both pressure and moment. The temperature dependent elastic-plastic properties are adopted throughout the LMM assessment

A simplified creep-reverse plasticity solution method for bodies subjected to cyclic loading

An extension of the upper bound shakedown theorem to load histories in excess of shakedown has been applied recently to the evaluation of a ratchet limit and the varying plastic strain magnitudes associated with a varying residual stress field. Solutions were obtained by the Linear Matching Method. In the present paper, this technique is extended to the evaluation of creep-reverse plasticity mechanism for bodies subjected to thermal cyclic loading including creep effects. The accumulated creep strain, the varying flow stress and the corresponding varying residual stress field during a creep dwell time are evaluated as well as the elastic follow-up factor. Three alternative computational strategies are discussed with differing but related assumptions. The problem of a plate with a central circular hole is discussed, subjected to cyclic thermal load. All three methods provide similar values for the elastic follow-up factor, indicating that the result is insensitive to the range of assumptions made. The simplest method, Method 1, is suggested as the basis of a general purpose method for use in life assessment

The linear matching method applied to the high temperature life integrity of structures. Part 1. Assessments involving constant residual stress fields

Design and life assessment procedures for high temperatures are based on 'expert knowledge' in structural mechanics and materials science, combined with simplified methods of structural analysis. Of these R5 is one of the most widely used life assessment methods internationally with procedures based on reference stress techniques and shakedown calculations using linear elastic solutions. These have been augmented by full finite element analysis and, recently, the development of a new programming method, the Linear Matching Method (LMM), that allows a range of direct solutions that include shakedown methods and simplified analysis in excess of shakedown. In this paper LMM procedures are compared with calculations typical of those employed in R5 for cyclic loading problems when the assumption of a constant residual stress field is appropriate including shakedown and limit analyses, creep rupture analysis and the evaluation of accumulated creep deformation. A typical example of a 3D holed plate subjected to a cyclic thermal load and a constant mechanical load is assessed in detail. These comparisons demonstrate the significant advantages of linear matching methods for a typical case. For a range of cyclic problems when the residual stress field varies during the cycle, which include the evaluation of plastic strain amplitude, ratchet limit and accumulated creep strains during a high temperature dwell periods, the corresponding LMM and R5 procedures are discussed in an accompanying paper

Policy-Oriented Impact Assessment of Climatic Variations

IIASA organized a Task Force Meeting (held in late June 1986) to undertake a policy-oriented assessment of various climatic impacts. Among the questions addressed were: What are the main policy questions and research needs of this field? Is there a niche for IIASA to fill meaningfully over the next several years? If so, should the work be an independent entity within the current Environment Program or should it be absorbed within the framework of other projects? This report of the Task Force Meeting provides a focus not only for IIASA, but also for many other national and international bodies engaged in climate impact research. In particular, the idea of integrated regional assessments seems to have caught on, and this Research Report is likely to become a basic reference

Normalized Ricci flow on Riemann surfaces and determinants of Laplacian

In this note we give a simple proof of the fact that the determinant of Laplace operator in smooth metric over compact Riemann surfaces of arbitrary genus $g$ monotonously grows under the normalized Ricci flow. Together with results of Hamilton that under the action of the normalized Ricci flow the smooth metric tends asymptotically to metric of constant curvature for $g\geq 1$, this leads to a simple proof of Osgood-Phillips-Sarnak theorem stating that that within the class of smooth metrics with fixed conformal class and fixed volume the determinant of Laplace operator is maximal on metric of constant curvatute.Comment: a reference to paper math.DG/9904048 by W.Mueller and K.Wendland where the main theorem of this paper was proved a few years earlier is adde

A Scanning Electron Microscope for Ultracold Atoms

We propose a new technique for the detection of single atoms in ultracold quantum gases. The technique is based on scanning electron microscopy and employs the electron impact ionization of trapped atoms with a focussed electron probe. Subsequent detection of the resulting ions allows for the reconstruction of the atoms position. This technique is expected to achieve a much better spatial resolution compared to any optical detection method. In combination with the sensitivity to single atoms, it makes new in situ measurements of atomic correlations possible. The detection principle is also well suited for the addressing of individual sites in optical lattices.Comment: 5 pages, 2 figure

Censored Glauber Dynamics for the mean field Ising Model

We study Glauber dynamics for the Ising model on the complete graph on $n$ vertices, known as the Curie-Weiss Model. It is well known that at high temperature ($\beta < 1$) the mixing time is $\Theta(n\log n)$, whereas at low temperature ($\beta > 1$) it is $\exp(\Theta(n))$. Recently, Levin, Luczak and Peres considered a censored version of this dynamics, which is restricted to non-negative magnetization. They proved that for fixed $\beta > 1$, the mixing-time of this model is $\Theta(n\log n)$, analogous to the high-temperature regime of the original dynamics. Furthermore, they showed \emph{cutoff} for the original dynamics for fixed $\beta<1$. The question whether the censored dynamics also exhibits cutoff remained unsettled. In a companion paper, we extended the results of Levin et al. into a complete characterization of the mixing-time for the Currie-Weiss model. Namely, we found a scaling window of order $1/\sqrt{n}$ around the critical temperature $\beta_c=1$, beyond which there is cutoff at high temperature. However, determining the behavior of the censored dynamics outside this critical window seemed significantly more challenging. In this work we answer the above question in the affirmative, and establish the cutoff point and its window for the censored dynamics beyond the critical window, thus completing its analogy to the original dynamics at high temperature. Namely, if $\beta = 1 + \delta$ for some $\delta > 0$ with $\delta^2 n \to \infty$, then the mixing-time has order $(n / \delta)\log(\delta^2 n)$. The cutoff constant is $(1/2+[2(\zeta^2 \beta / \delta - 1)]^{-1})$, where $\zeta$ is the unique positive root of $g(x)=\tanh(\beta x)-x$, and the cutoff window has order $n / \delta$.Comment: 55 pages, 4 figure

A method for the evaluation of a ratchet limit and the amplitude of plastic strain for bodies subjected to cyclic loading

An extension of the upper bound shakedown theorem to load histories in excess of shakedown has been presented elsewhere in this issue. Here the minimisation process described therein is applied to the solutions of the ratchet limit as well as shakedown and limit load for a range of simple problems. The solutions provide an estimate of the maxima of the varying plastic strain magnitudes, which is compared with the Neuber approximate values. The position of the ratchet boundary is confirmed by comparison step-by-step analysis