Integrated structural analysis tool using linear matching method part 1 : Software development

A number of direct methods based upon the Linear Matching Method (LMM) framework have been developed to address structural integrity issues for components subjected to cyclic thermal and mechanical load conditions. This paper presents a new integrated structural analysis tool using the LMM framework for the assessment of load carrying capacity, shakedown limit, ratchet limit and steady state cyclic response of structures. First, the development of the LMM for the evaluation of design limits in plasticity is introduced. Second, preliminary considerations for the development of the LMM into a tool which can be used on a regular basis by engineers are discussed. After the re-structuring of the LMM subroutines for multiple CPU solution, the LMM software tool for the assessment of design limits in plasticity is implemented by developing an Abaqus CAE plug-­in with graphical user interfaces. Further demonstration of this new LMM analysis tool including practical application and verification is presented in an accompanying paper

Integrated structural analysis tool using linear matching method part 2 : Application and verification

In an accompanying paper, a new integrated structural analysis tool using the LMM framework for the assessment of design limits in plasticity including load carrying capacity, shakedown limit, ratchet limit and steady state cyclic response of structures was developed using Abaqus CAE plug-­‐ins with graphical user interfaces. In the present paper, a demonstration of the use of this new LMM analysis tool is provided. A header branch pipe in a typical AGR power plant is analysed as a worked example of the current demonstration and verification of the LMM tool within the context of an R5 assessment. The detailed shakedown analysis, steady state cycle and ratchet analysis are carried out for the chosen header branch pipe. The comparisons of the LMM solutions with the results based on the R5 procedure and the step-­‐by-­‐step elastic-­‐plastic FEA verify the accuracy, convenience and efficiency of this new integrated LMM structural analysis tool

Verification of the linear matching method for limit and shakedown analysis by comparison with experiments

The Linear Matching Method (LMM), a direct numerical method for determining shakedown and ratchet limits of components, has seen significant development in recent years. Previous verifications of these developments against cyclic nonlinear finite element analysis have shown favourable results, and now this verification process is being extended to include comparisons with experimental results. This paper presents a comparison of LMM analysis with experimental tests for limit loads and shakedown limits available in the literature. The limit load and shakedown limits were determined for pipe intersections and nozzle-sphere intersections respectively, thus testing the accuracy of the LMM when analysing real plant components. Details of the component geometries, materials and test procedures used in the experiments are given. Following this a description of the LMM analysis is given which includes a description of how these features have been interpreted for numerical analysis. A comparison of the results shows that the LMM is capable of predicting accurate yet conservative limit loads and shakedown limits

Calculation of a lower bound ratchet limit part 1 – Theory, numerical implementation and verification

It is important to be able to calculate the ratchet limit of a component when performing integrity assessments of plant components. This paper details the addition of a lower bound ratchet limit calculation to the Linear Matching Method. The extension of Melan's theorem into the alternating plasticity region is explained, followed by its implementation into the Linear Matching Method calculation procedure. Finally, the convergence properties of this method are analysed by the analysis of a plate with a central hole subject to cyclic thermal and mechanical loadin

Development and implementation of the Abaqus subroutines and plug-in for routine structural integrity assessment using the linear matching method

In recent years the Linear Matching Method (LMM) has been developed as a tool for structural integrity assessments of components subjected to cyclic loading conditions. Its capabilities include, among others, calculation of the shakedown limit, ratchet limit, plastic strain range for low cycle fatigue, creep rupture time and fatigue creep interaction. The LMM is now incorporated into EDF Energy’s R5 research program for the high temperature assessment of structural components. The purpose of this paper is to describe the development of the LMM framework, its incorporation into Abaqus and current plans to take the method from being primarily research based into wider use by industry for routine structural assessments. The LMM calculations are primarily carried out using the UMAT subroutine, and the first topic discussed in this paper is the implementation of this user subroutine. This includes details of the coding scheme to allow use of multi-processors for the calculations. A brief comparison of the LMM with full cyclic FEA is also included to validate the method and to demonstrate its advantages. The second topic of this paper discusses the development of an Abaqus/CAE plug-in to aid wider adoption of the LMM as an analysis tool for industry. The structure of the plug-in is described alongside the processes used for data collection from the user and automatic configuration of the model

Calculation of a lower bound ratchet limit part 2 : Application to a pipe intersection and dissimilar material join

In an accompanying paper in this issue a lower bound method based on Melan's theorem was derived and implemented into the Linear Matching Method ratchet analysis procedure. This paper presents a ratchet analysis of a pipe intersection subject to cyclic thermo-mechanical loading using the proposed numerical technique. This work is intended to demonstrate the applicability of the lower bound method to a structure commonly seen in industry and also to better understand the behaviour of this component when subjected to cyclic loading. The pipe intersection considered here has multiple materials with temperature dependent properties. Verification of the results is given via full elastic-plastic analysis in Abaqus

A direct method for the evaluation of lower and upper bound ratchet limits

The calculation of the ratchet limit is often vital for the assessment of the design and integrity of components which are subject to cyclic loading. This work describes the addition of a lower bound calculation to the existing Linear Matching Method upper bound ratchet analysis method. This lower bound calculation is based on Melan's theorem, and makes use of the residual and elastic stress fields calculated by the upper bound technique to calculate the lower bound ratchet limit multiplier. By doing this, the method combines the stable convergence of the upper bound method but retains the conservatism offered by the lower bound. These advantages are complemented by the ability of the Linear Matching Method to consider real 3D geometries subject to complex load histories including the effect of temperature dependent yield stress. The convergence properties of this lower bound ratchet limit are investigated through a benchmark problem of a plate with a central hole subject to cyclic thermal and mechanical loads. To demonstrate the effectiveness of the method, the ratchet limit of a thick walled pipe intersection, also subject to cyclic thermal and mechanical loads, is considered. Validation of these results is provided by full elastic-plastic FEA in Abaqus

Inter-comparison of quantitative imaging of lutetium-177 (177Lu) in European hospitals

Background: This inter-comparison exercise was performed to demonstrate the variability of quantitative SPECT/CT imaging for lutetium-177 (177Lu) in current clinical practice. Our aim was to assess the feasibility of using international inter-comparison exercises as a means to ensure consistency between clinical sites whilst enabling the sites to use their own choice of quantitative imaging protocols, specific to their systems. Dual-compartment concentric spherical sources of accurately known activity concentrations were prepared and sent to seven European clinical sites. The site staff were not aware of the true volumes or activity within the sources—they performed SPECT/CT imaging of the source, positioned within a water-filled phantom, using their own choice of parameters and reported their estimate of the activities within the source. Results: The volumes reported by the participants for the inner section of the source were all within 29% of the true value and within 60% of the true value for the outer section. The activities reported by the participants for the inner section of the source were all within 20% of the true value, whilst those reported for the outer section were up to 83% different to the true value. Conclusions: A variety of calibration and segmentation methods were used by the participants for this exercise which demonstrated the variability of quantitative imaging across clinical sites. This paper presents a method to assess consistency between sites using different calibration and segmentation methods

International differences in self-reported health measures in 33 major metropolitan areas in Europe.

The increasing concentration of populations into large conurbations in recent decades has not been matched by international health assessments, which remain largely focused at the country level. We aimed to demonstrate the use of routine survey data to compare the health of large metropolitan centres across Europe and determine the extent to which differences are due to socio-economic factors

Plasmacytoid dendritic cells appear inactive during sub-microscopic Plasmodium falciparum blood-stage infection, yet retain their ability to respond to TLR stimulation

Plasmacytoid dendritic cells (pDC) are activators of innate and adaptive immune responses that express HLA-DR, toll-like receptor (TLR) 7, TLR9 and produce type I interferons. The role of human pDC in malaria remains poorly characterised. pDC activation and cytokine production were assessed in 59 malaria-naive volunteers during experimental infection with 150 or 1,800 P. falciparum-parasitized red blood cells. Using RNA sequencing, longitudinal changes in pDC gene expression were examined in five adults before and at peak-infection. pDC responsiveness to TLR7 and TLR9 stimulation was assessed in-vitro. Circulating pDC remained transcriptionally stable with gene expression altered for 8 genes (FDR < 0.07). There was no upregulation of co-stimulatory molecules CD86, CD80, CD40, and reduced surface expression of HLA-DR and CD123 (IL-3R-α). pDC loss from the circulation was associated with active caspase-3, suggesting pDC apoptosis during primary infection. pDC remained responsive to TLR stimulation, producing IFN-α and upregulating HLA-DR, CD86, CD123 at peak-infection. In clinical malaria, pDC retained HLA-DR but reduced CD123 expression compared to convalescence. These data demonstrate pDC retain function during a first blood-stage P. falciparum exposure despite sub-microscopic parasitaemia downregulating HLA-DR. The lack of evident pDC activation in both early infection and malaria suggests little response of circulating pDC to infection