Finite element modelling of stresses and failure within plasma spray thermal barrier coating systems

Air plasma sprayed thermal barrier coating (APS TBC) systems are usually applied to engine components to reduce the temperature of the substrate and increase the efficiency of engines. However, failure of these coatings leads to oxidation and corrosion of the substrate. Therefore, a thorough understanding of the coating failure is necessary to predict the lifetime of coated components. This project has carried out stress analysis and prediction of subsequent failure of APS TBC systems associated with sintering of the TBC, oxidation of the bond coat (BC), substrate geometry, undulations at the coating interfaces and coating fracture toughness. Stress analysis is crucial for predicting TBC failure as stresses in the vicinity of the coating interfaces cause cracks and subsequent coating delamination. The Finite element (FE) method was used for stress analysis of TBC systems at high temperature stage and at cooling stage after operation. Initially, FE model of an axisymmetric unit cell representing the slice of a coated cylinder was used. Different radii for cylinders were used to investigate the significance of substrate curvature on coating stresses. The effect of asperities at the coating interface on residual stresses was observed using 3D models. The models were built based on the actual geometries of asperities, which were extracted from 3D SEM images of the coating interfaces. An Arrhenius approach was utilised to implement changes in mechanical and physical properties of TBC due to sintering. BC oxidation and related changes in its composition were also implemented. The accuracy of assumptions for FE models was validated by comparing the evaluated stresses against experimental results by project partners. Finally, the effects of stresses and fracture toughness of the coatings and coating interfaces on failure of the TBC system were studied, using cohesive surface modelling and extended finite element modelling (XFEM) methods

Finite element modelling of stresses and failure within plasma spray thermal barrier coating systems

Air plasma sprayed thermal barrier coating (APS TBC) systems are usually applied to engine components to reduce the temperature of the substrate and increase the efficiency of engines. However, failure of these coatings leads to oxidation and corrosion of the substrate. Therefore, a thorough understanding of the coating failure is necessary to predict the lifetime of coated components. This project has carried out stress analysis and prediction of subsequent failure of APS TBC systems associated with sintering of the TBC, oxidation of the bond coat (BC), substrate geometry, undulations at the coating interfaces and coating fracture toughness. Stress analysis is crucial for predicting TBC failure as stresses in the vicinity of the coating interfaces cause cracks and subsequent coating delamination. The Finite element (FE) method was used for stress analysis of TBC systems at high temperature stage and at cooling stage after operation. Initially, FE model of an axisymmetric unit cell representing the slice of a coated cylinder was used. Different radii for cylinders were used to investigate the significance of substrate curvature on coating stresses. The effect of asperities at the coating interface on residual stresses was observed using 3D models. The models were built based on the actual geometries of asperities, which were extracted from 3D SEM images of the coating interfaces. An Arrhenius approach was utilised to implement changes in mechanical and physical properties of TBC due to sintering. BC oxidation and related changes in its composition were also implemented. The accuracy of assumptions for FE models was validated by comparing the evaluated stresses against experimental results by project partners. Finally, the effects of stresses and fracture toughness of the coatings and coating interfaces on failure of the TBC system were studied, using cohesive surface modelling and extended finite element modelling (XFEM) methods

Modelling fracture of aged graphite bricks under radiation and temperature

The graphite bricks of the UK carbon dioxide gas cooled nuclear reactors are subjected to neutron irradiation and radiolytic oxidation during operation which will affect thermal and mechanical material properties and may lead to structural failure. In this paper, an empirical equation is obtained and used to represent the reduction in the thermal conductivity as a result of temperature and neutron dose. A 2D finite element thermal analysis was carried out using Abaqus to obtain temperature distribution across the graphite brick. Although thermal conductivity could be reduced by up to 75% under certain conditions of dose and temperature, analysis has shown that it has no significant effect on the temperature distribution. It was found that the temperature distribution within the graphite brick is non-radial, different from the steady state temperature distribution used in the previous studies [1, 2]. To investigate the significance of this non-radial temperature distribution on the failure of graphite bricks, a subsequent mechanical analysis was also carried out with the nodal temperature information obtained from the thermal analysis. To predict the formation of cracks within the brick and the subsequent propagation, a linear traction–separation cohesive model in conjunction with the extended finite element method (XFEM) is used. Compared to the analysis with steady state radial temperature distribution, the crack initiation time for the model with non-radial temperature distribution is delayed by almost one year in service, and the maximum crack length is also shorter by around 20%

Characterization of bovine MHC DRB3 diversity in global cattle breeds, with a focus on cattle in Myanmar

Background: Myanmar cattle populations predominantly consist of native cattle breeds (Pyer Sein and Shwe), characterized by their geographical location and coat color, and the Holstein-Friesian crossbreed, which is highly adapted to the harsh tropical climates of this region. Here, we analyzed the diversity and genetic structure of the BoLA-DRB3 gene, a genetic locus that has been linked to the immune response, in Myanmar cattle populations. Methods: Blood samples (n = 294) were taken from two native breeds (Pyer Sein, n = 163 and Shwe Ni, n = 69) and a cattle crossbreed (Holstein-Friesian, n = 62) distributed across six regions of Myanmar (Bago, n = 38; Sagaing, n = 77; Mandalay, n = 46; Magway, n = 46; Kayin, n = 43; Yangon, n = 44). In addition, a database that included 2428 BoLA-DRB3 genotypes from European (Angus, Hereford, Holstein, Shorthorn, Overo Negro, Overo Colorado, and Jersey), Zebuine (Nellore, Brahman and Gir), Asian Native from Japan and Philippine and Latin-American Creole breeds was also included. Furthermore, the information from the IPD-MHC database was also used in the present analysis. DNA was genotyped using the sequence-based typing method. DNA electropherograms were analyzed using the Assign 400ATF software. Results: We detected 71 distinct alleles, including three new variants for the BoLA-DRB3 gene. Venn analysis showed that 11 of these alleles were only detected in Myanmar native breeds and 26 were only shared with Asian native and/or Zebu groups. The number of alleles ranged from 33 in Holstein-Friesians to 58 in Pyer Seins, and the observed versus unbiased expected heterozygosity were higher than 0.84 in all the three the populations analyzed. The FST analysis showed a low level of genetic differentiation between the two Myanmar native breeds (FST = 0.003), and between these native breeds and the Holstein-Friesians (FST < 0.021). The average F ST value for all the Myanmar Holstein-Friesian crossbred and Myanmar native populations was 0.0136 and 0.0121, respectively. Principal component analysis (PCA) and tree analysis showed that Myanmar native populations grouped in a narrow cluster that diverged clearly from the Holstein-Friesian populations. Furthermore, the BoLA-DRB3 allele frequencies suggested that while some Myanmar native populations from Bago, Mandalay and Yangon regions were more closely related to Zebu breeds (Gir and Brahman), populations from Kayin, Magway and Sagaing regions were more related to the Philippines native breeds. On the contrary, PCA showed that the Holstein-Friesian populations demonstrated a high degree of dispersion, which is likely the result of the different degrees of native admixture in these populations. Conclusion: This study is the first to report the genetic diversity of the BoLA-DRB3 gene in two native breeds and one exotic cattle crossbreed from Myanmar. The results obtained contribute to our understanding of the genetic diversity and distribution of BoLA-DRB3 gene alleles in Myanmar, and increases our knowledge of the worldwide variability of cattle BoLA-DRB3 genes, an important locus for immune response and protection against pathogens.Fil: Giovambattista, Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico CONICET- La Plata. Instituto de Genética Veterinaria "Ing. Fernando Noel Dulout". Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias. Instituto de Genética Veterinaria; ArgentinaFil: Moe, Kyaw Kyaw. University of Veterinary Science; BirmaniaFil: Polat, Meripet. No especifíca;Fil: Borjigin, Liushiqi. No especifíca;Fil: Hein, Si Thu. University Of Veterinary Science; BirmaniaFil: Moe, Hla Hla. University Of Veterinary Science; BirmaniaFil: Takeshima, Shin Nosuke. No especifíca;Fil: Aida, Yoko. No especifíca

Modelling the coefficient of thermal expansion in Ni-based superalloys and bond coatings

The coefficient of thermal expansion (CTE) of nickel-based superalloys and bond coat layers was modelled by considering contributions from their constituent phases. The equilibrium phase composition of the examined materials was determined using thermodynamic equilibrium software with an appropriate database for Ni-based alloys, whereas the CTE and elastic properties of the principal phases were modelled using published data. The CTEs of individual phases were combined using a number of approaches to determine the CTE of the phase aggregate. As part of this work, the expansion coefficients of the superalloy IN-738LC and bond coat Amdry-995 were measured as a function of temperature and compared with the model predictions. The predicted values were also validated with the published data for the single-crystal superalloy CMSX-4 and a number of other Ni-based alloy compositions at 1000 K. A very good agreement between experiment and model output was found, especially up to 800  $$^\circ$$ � C. The modelling approaches discussed in this paper have the potential to be an extremely useful tool for the industry and for the designers of new coating systems

Modelling the coefficient of thermal expansion in Ni based superalloys and bond coatings

The coefficient of thermal expansion (CTE) of nickel based superalloys and bond coat layers was modelled by considering contributions from their constituent phases. The equilibrium phase composition of the examined materials was determined using thermodynamic equilibrium software with an appropriate database for Ni-based alloys, whereas the CTE and elastic properties of the principal phases were modelled using published data. The CTEs of individual phases were combined using a number of approaches to determine the CTE of the phase aggregate. As part of this work, the expansion coefficients of the superalloy IN-738LC and bond coat Amdry-995 were measured as a function of temperature and compared with the model predictions. The predicted values were also validated with the published data for the single-crystal superalloy CMSX-4 and a number of other Ni based alloy compositions at 1000 K. Very good agreement between experiment and model output was found, especially up to 800°C. The modelling approaches discussed in this paper have the potential to be an extremely useful tool for the industry and for the designers of new coating systems

Effects of three-dimensional coating interfaces on thermo-mechanical stresses within plasma spray thermal barrier coatings

It has been acknowledged that stresses within a thermal barrier coating (TBC) and its durability are significantly affected by the coating interfaces. This paper presents a finite element approach for stress analysis of the plasma sprayed TBC system, using three-dimensional (3D) coating interfaces. 3D co-ordinates of the coating surfaces were measured through 3D reconstruction of scanning electron microscope (SEM) images. These co-ordinates were post processed to reconstruct finite element models for use in stress analyses. A surface profile unit cell approach with appropriate boundary conditions was applied to reduce the problem size and hence computation time. It has been shown that for an identical aspect ratio of the coating interface, interfacial out-of-plane stresses for 3D models are around twice the values predicted using 2D models. Based on predicted stress development within the systems, possible crack development and failure mechanisms of the TBC systems can be predicted

Malaria incidence in Myanmar 2005–2014: steady but fragile progress towards elimination

Abstract Background There has been an impressive recent reduction in the global incidence of malaria, but the development of artemisinin resistance in the Greater Mekong Region threatens this progress. Increasing artemisinin resistance is particularly important in Myanmar, as it is the country in the Greater Mekong Region with the greatest malaria burden. If malaria is to be eliminated in the region, it is essential to define the spatial and temporal epidemiology of the disease in Myanmar to inform control strategies optimally. Results Between the years 2005 and 2014 there was an 81.1 % decline in the reported annual incidence of malaria in Myanmar (1341.8 cases per 100,000 population to 253.3 cases per 100,000 population). In the same period, there was a 93.5 % decline in reported annual mortality from malaria (3.79 deaths per 100,000 population to 0.25 deaths per 100,000 population) and a 87.2 % decline in the proportion of hospitalizations due to malaria (7.8 to 1.0 %). Chin State had the highest reported malaria incidence and mortality at the end of the study period, although socio-economic and geographical factors appear a more likely explanation for this finding than artemisinin resistance. The reduced malaria burden coincided with significant upscaling of disease control measures by the national government with support from international partners. These programmes included the training and deployment of over 40,000 community health care workers, the coverage of over 60 % of the at-risk population with insecticide-treated bed nets and significant efforts to improve access to artemesinin-based combination treatment. Beyond these malaria-specific programmes, increased general investment in the health sector, changing population demographics and deforestation are also likely to have contributed to the decline in malaria incidence seen over this time. Conclusions There has been a dramatic fall in the burden of malaria in Myanmar since 2005. However, with the rise of artemisinin resistance, continued political, financial and scientific commitment is required if the ambitious goal of malaria elimination in the country is to be realized

Anti-malarial landscape in Myanmar: results from a nationally representative survey among community health workers and the private sector outlets in 2015/2016

Abstract Background In 2015/2016, an ACTwatch outlet survey was implemented to assess the anti-malarial and malaria testing landscape in Myanmar across four domains (Eastern, Central, Coastal, Western regions). Indicators provide an important benchmark to guide Myanmar’s new National Strategic Plan to eliminate malaria by 2030. Methods This was a cross-sectional survey, which employed stratified cluster-random sampling across four regions in Myanmar. A census of community health workers (CHWs) and private outlets with potential to distribute malaria testing and/or treatment was conducted. An audit was completed for all anti-malarials, malaria rapid diagnostic tests. Results A total of 28,664 outlets were approached and 4416 met the screening criteria. The anti-malarial market composition comprised CHWs (41.5%), general retailers (27.9%), itinerant drug vendors (11.8%), pharmacies (10.9%), and private for-profit facilities (7.9%). Availability of different anti-malarials and diagnostic testing among anti-malarial-stocking CHWs was as follows: artemisinin-based combination therapy (ACT) (81.3%), chloroquine (67.0%), confirmatory malaria test (77.7%). Less than half of the anti-malarial-stocking private sector had first-line treatment in stock: ACT (41.7%) chloroquine (41.8%), and malaria diagnostic testing was rare (15.4%). Oral artemisinin monotherapy (AMT) was available in 27.7% of private sector outlets (Western, 54.1%; Central, 31.4%; Eastern; 25.0%, Coastal; 15.4%). The private-sector anti-malarial market share comprised ACT (44.0%), chloroquine (26.6%), and oral AMT (19.6%). Among CHW the market share was ACT (71.6%), chloroquine (22.3%); oral AMT (3.8%). More than half of CHWs could correctly state the national first-line treatment for uncomplicated falciparum and vivax malaria (59.2 and 56.9%, respectively) compared to the private sector (15.8 and 13.2%, respectively). Indicators on support and engagement were as follows for CHWs: reportedly received training on malaria diagnosis (60.7%) or national malaria treatment guidelines (59.6%), received a supervisory or regulatory visit within 12 months (39.1%), kept records on number of patients tested or treated for malaria (77.3%). These indicators were less than 20% across the private sector. Conclusion CHWs have a strong foundation for achieving malaria goals and their scale-up is merited, however gaps in malaria commodities and supplies must be addressed. Intensified private sector strategies are urgently needed and must be scaled up to improve access and coverage of first-line treatments and malaria diagnosis, and remove oral AMT from the market place. Future policies and interventions on malaria control and elimination in Myanmar should take these findings into consideration across all phases of implementation

Do pneumococcal conjugate vaccines provide any cross-protection against serotype 19A?

<p>Abstract</p> <p>Background</p> <p>Introduction of the 7-valent pneumococcal conjugate vaccine (7vCRM) in several countries has led to a rapid, significant drop in vaccine-type invasive pneumococcal disease (IPD) in immunized children. In the United States and some other countries with high antibiotic use, a subsequent rise in serotype 19A IPD has been taken to indicate that the 19F conjugate in the vaccine provides no cross-protection against the immunologically related 19A.</p> <p>Discussion</p> <p>We systematically assessed the clinical efficacy and effectiveness of 19F-containing vaccines against 19A disease or nasopharyngeal carriage by searching English-language articles in the electronic databases PubMed, Current contents, Scopus, and Embase from 1985 to 2008. The vaccine efficacy and effectiveness point estimates were consistently positive for modest protection against 19A IPD and acute otitis media (AOM). However, statistical significance was not reached in any individual study. No consistent impact of 7vCRM on 19A nasopharyngeal colonization could be detected. These findings are discussed in context of immunogenicity analyses indicating that 7vCRM induces functionally active anti-19A antibodies after the booster dose, and that other 19F-containing vaccine formulations may elicit higher levels of such antibodies after both primary and booster doses.</p> <p>Summary</p> <p>Taken together, these results suggest that 19F-conjugates can provide some protection against 19A disease. The magnitude of this protection in a given setting will likely depend on several factors. These include the anti-19A immunogenicity of the specific vaccine formulation, the number of doses of that formulation needed to elicit the response, and the burden of 19A disease that occurs after those doses. It is possible that a modest protective effect may be obscured by the presence of countervailing selection pressures (such as high antibiotic use) that favor an increase in colonization with antibiotic-non-susceptible strains of 19A.</p