Evaluation of Steels Susceptibility to Hydrogen Embrittlement: A Thermal Desorption Spectroscopy-Based Approach Coupled with Artificial Neural Network.

A novel approach has been developed for quantitative evaluation of the susceptibility of steels and alloys to hydrogen embrittlement. The approach uses a combination of hydrogen thermal desorption spectroscopy (TDS) analysis with recent advances in machine learning technology to develop a regression artificial neural network (ANN) model predicting hydrogen-induced degradation of mechanical properties of steels. We describe the thermal desorption data processing, artificial neural network architecture development, and the learning process beneficial for the accuracy of the developed artificial neural network model. A data augmentation procedure was proposed to increase the diversity of the input data and improve the generalization of the model. The study of the relationship between thermal desorption spectroscopy data and the mechanical properties of steel evidences a strong correlation of their corresponding parameters. A prototype software application based on the developed model is introduced and is openly available. The developed prototype based on TDS analysis coupled with ANN is shown to be a valuable engineering tool for steel characterization and quantitative prediction of the degradation of steel properties caused by hydrogen.

Improved Accuracy of Thermal Desorption Spectroscopy by Specimen Cooling during Measurement of Hydrogen Concentration in a High-Strength Steel.

Thermal desorption spectroscopy (TDS) is a powerful method for the measurement of hydrogen concentration in metallic materials. However, hydrogen loss from metallic samples during the preparation of the measurement poses a challenge to the accuracy of the results, especially in materials with high diffusivity of hydrogen, like ferritic and ferritic-martensitic steels. In the present paper, the effect of specimen cooling during the experimental procedure, as a tentative to reduce the loss of hydrogen during air-lock vacuum pumping for one high-strength steel of 1400 MPa, is evaluated. The results show, at room temperature, the presence of a continuous outward hydrogen flux accompanied with the redistribution of hydrogen within the measured steel during its exposure to the air-lock vacuum chamber under continuous pumping. Cooling of the steel samples to 213 K during pumping in the air-lock vacuum chamber before TDS measurement results in an increase in the measured total hydrogen concentration at about 14%. A significant reduction in hydrogen loss and redistribution within the steel sample improves the accuracy of hydrogen concentration measurement and trapping analysis in ferritic and martensitic steels.

Environmental conditions and rodent infestation in Campo Limpo district, Sao Paulo municipality, Brazil.

Rodents are involved in the transmission to human beings of several diseases, including liptospirosis, which shows high lethality rates in Sao Paulo municipality. Despite this, few studies have assessed the relationship existing between urban environmental conditions and building rodent infestation. With the purpose of clarifying this relationship, an analysis has been conducted in order to quantify the influence of environmental factors upon rodent infestation on a low-income district. Diagnosis of the environmental situation has been performed to evaluate the frequency according to which harborage, food and access sources occur, and a survey on infestation rates in 2175 dwellings in the area studied. The logistic regression analysis showed that among the environmental variables, the one that showed the closest association with rodent infestation was access; followed by harborage, and food. It was concluded that poor socioeconomic and environmental conditions in the area propitiate the occurrence of high rodent infestation rates.

Evaluation on the effectiveness of actions for controlling infestation by rodents in Campo Limpo region, Sao Paulo Municipality, Brazil.

Rodents are responsible for the transmission of more than 60 diseases both to human beings and to domestic animals. The increase in rodent infestation in a given area brings several health problems to the nearby population. Thus, when infestation increases, it is time to take intervention measures. Although many countries have implemented programs aimed at controlling rodent infestation, literature on studies evaluating the effectiveness of intervention measures in urban areas is scarce. Aimed at contributing to the understanding of rodents' population dynamics in urban areas, the objective of this study was to evaluate the effectiveness of the control methods proposed by "Programa de Vigilancia e Controle de Roedores do Municipio de Sao Paulo" (Program for Rodents Surveillance and Control in Sao Paulo Municipality), conducted on Jardim Comercial District. As a first step, a survey to assess infestation rates was conducted in 1529 dwellings located in the area studied. After that, a chemical control upon rodents was accomplished in every dwelling infested. One week and six months after completion of control measures, a new evaluation on infestation rates was carried out, in order to verify the effectiveness of the procedures taken and to estimate the re-infestation capacity. Initial infestation rate was 40.0%, and the final infestation rate, 14.4%. Therefore, the effectiveness of the control methods utilized was 63.8%. It can thus be concluded that the control methods applied were quite effective.

Local magnetic flux density measurements for temperature control of transient and non-homogeneous processing of steels.

Measuring temperatures during high-temperature processing of steels is usually limited to surface measurements that cannot directly assess the internal temperature distribution. Here, we demonstrate the feasibility of using a magnetic flux density measurement system to assess transient and non-homogeneous temperature fields in a modern high-strength steel, within the intercritical temperature range where microstructural evolution defines their key mechanical properties. The system accurately detects the Curie temperature and distinguishes temperature change rates within the processed volume. The magnetic measurements are also sensitive to the volume above Curie temperature and its shape, as revealed when integrated with thermal computational simulations. The electromagnetic signal provides real-time qualitative and quantitative information relevant to the metallurgical conditions enabling future intelligent control systems for the production and processing of steels. Contactless measurements of temperature-dependent electromagnetic properties can enable through-thickness temperature monitoring solutions, opening up opportunities for non-destructive full-field imaging of steels during thermal and thermomechanical processing.

A Multiscale Modelling Approach for Estimating the Effect of Defects in Unidirectional Carbon Fiber Reinforced Polymer Composites.

A multiscale modelling approach was developed in order to estimate the effect of defects on the strength of unidirectional carbon fiber composites. The work encompasses a micromechanics approach, where the known reinforcement and matrix properties are experimentally verified and a 3D finite element model is meshed directly from micrographs. Boundary conditions for loading the micromechanical model are derived from macroscale finite element simulations of the component in question. Using a microscale model based on the actual microstructure, material parameters and load case allows realistic estimation of the effect of a defect. The modelling approach was tested with a unidirectional carbon fiber composite beam, from which the micromechanical model was created and experimentally validated. The effect of porosity was simulated using a resin-rich area in the microstructure and the results were compared to experimental work on samples containing pores.

Fundamentals of Force-Controlled Friction Riveting: Part II-Joint Global Mechanical Performance and Energy Efficiency.

The present work investigates the correlation between energy efficiency and global mechanical performance of hybrid aluminum alloy AA2024 (polyetherimide joints), produced by force-controlled friction riveting. The combinations of parameters followed a central composite design of experiments. Joint formation was correlated with mechanical performance via a volumetric ratio (0.28⁻0.66 a.u.), with a proposed improvement yielding higher accuracy. Global mechanical performance and ultimate tensile force varied considerably across the range of parameters (1096⁻9668 N). An energy efficiency threshold was established at 90 J, until which, energy input displayed good linear correlations with volumetric ratio and mechanical performance (R-sq of 0.87 and 0.86, respectively). Additional energy did not significantly contribute toward increasing mechanical performance. Friction parameters (i.e., force and time) displayed the most significant contributions to mechanical performance (32.0% and 21.4%, respectively), given their effects on heat development. For the investigated ranges, forging parameters did not have a significant contribution. A correlation between friction parameters was established to maximize mechanical response while minimizing energy usage. The knowledge from Parts I and II of this investigation allows the production of friction riveted connections in an energy efficient manner and control optimization approach, introduced for the first time in friction riveting.

Fundamentals of Force-Controlled Friction Riveting: Part I-Joint Formation and Heat Development.

This work presents a systematic study on the correlations between process parameters and rivet plastic deformation, produced by force-controlled friction riveting. The 5 mm diameter AA2024 rivets were joined to 13 mm, nominal thickness, polyetherimide plates. A wide range of joint formations was obtained, reflecting the variation in total energy input (24⁻208 J) and process temperature (319⁻501 °C). The influence of the process parameters on joint formation was determined, using a central composite design and response surface methodology. Friction time displayed the highest contribution on both rivet penetration (61.9%) and anchoring depth (34.7%), and friction force on the maximum width of the deformed rivet tip (46.5%). Quadratic effects and two-way interactions were significant on rivet anchoring depth (29.8 and 20.8%, respectively). Bell-shaped rivet plastic deformation-high mechanical interlocking-results from moderate energy inputs (~100 J). These geometries are characterized by: rivet penetration depth of 7 to 9 mm; maximum width of the deformed rivet tip of 9 to 12 mm; and anchoring depth higher than 6 mm. This knowledge allows the production of optimized friction-riveted connections and a deeper understanding of the joining mechanisms, further discussed in Part II of this work.

Comparative analysis of severe pediatric and adult leptospirosis in Sao Paulo, Brazil.

Although leptospirosis may be fatal in childhood, the experience of many clinicians working in disease-endemic areas is that classic Weil's disease and death are less common among pediatric patients. The aim of the study was to ascertain disease spectrum and outcome differences in severe pediatric and adult leptospirosis in a large at-risk population. Epidemiologic, clinical, and laboratory data were obtained on hospitalized cases from São Paulo during 2004-2006. A total of 42 case-patients < 18 years of age and 328 case-patients ≥ 18 years of age were tested during the study. Compared with children, adults had higher rates of jaundice (P = 0.01), elevated serum bilirubin levels (P < 0.01), oliguria (P = 0.02), and elevated creatinine levels (P = 0.01) but not for thrombocytopenia or pulmonary involvement. The overall case-fatality rate was 27% (adult) versus 5% (pediatric) (P < 0.01). Severe pediatric leptospirosis may be less likely to show all classic features of Weil's disease and may be less fatal than in adults.

Predictors of lethality in severe leptospirosis in urban Brazil.

To ascertain prognostic factors associated with fatal outcomes in severe leptospirosis, a retrospective case-control study was done using population-based surveillance data. Centralized death certificate reporting of leptospirosis mortality was combined with details of patients' hospitalizations, which were obtained from hospitals representing all sectors of São Paulo city. Among identified leptospirosis cases, 89 lethal cases and 281 survivor cases were analyzed. Predictors of death included age>40 years, development of oliguria, platelet count<70,000/microL, creatinine>3 mg/dL, and pulmonary involvement. The latter was the strongest risk factor with an estimated odds ratio of 6.0 (95% confidence interval: 3.0-12.0). Serologic findings with highest titer against Leptospira interrogans serovar Copenhageni did not show significant differences between survivors and non-survivors. Lung involvement was an important predictor of death in leptospirosis in São Paulo, of relevance in leptospirosis-endemic regions where this complication is common.

Dengue no município de São Paulo: uma análise por Geoprocessamento / Dengue in the city of Sao Paulo: an analysis by Geoprocessing

A dengue tornou-se um grande problema em muitos centros urbanos modernos, uma vez que tais locais fornecem os contextos propícios à ocorrência desta endemia. As características inerentes aos processos de urbanização vivenciadas pelas metrópoles brasileiras, como o município de São Paulo, criaram condições favoráveis à disseminação do vetor e à instalação de epidemias através da introdução do vírus via casos importados. A cidade de São Paulo, contudo, sempre registrara uma preponderância de casos importados sobre os autóctones até o ano de 2003, quando o município experimentou uma epidemia marcada pela transmissão local do agravo (incidência de 7,2 casos/100.000 habitantes, sendo confirmados 787 casos autóctones e 779 casos importados). A identificação dos locais que albergaram aglomerados de casos, bem como sua caracterização do ponto de vista demográfico e socioeconômico, forneceriam informações relevantes acerca do comportamento espacial dessa enfermidade, especialmente em ambientes urbanos complexos como a cidade de São Paulo. Nesse sentido, as técnicas de geoprocessamento e, em especial, o Sistema de Informação Geográfica (SIG) fornecem uma estratégia de abordagem do espaço no contexto dos estudos epidemiológicos. A estimação de densidade de Kernel, uma das ferramentas de análise espacial encerradas no SIG, permite a identificação e delimitação de aglomerados espaciais de casos, bem como de características demográficas e socioeconômicas que compõem os diferentes recortes do ambiente urbano. Os casos importados apresentaram um padrão de dispersão maior, sendo registrado na maioria dos distritos administrativos e formando um grande aglomerado espacial abrangendo distritos da região central, de melhor perfil socioeconômico, maior densidade populacional e de maior densidade de domicílios. Os autóctones demonstraram uma menor dispersão espacial, poupando vários distritos e formando quatro grandes aglomerados disjuntos espacialmente e abrangendo áreas mais peri...