Modelling size effects for static strength of brittle materials

The paper proposes a new model for the assessment of size effects affecting the fracture strength of brittle materials. The proposed model permits to accurately estimate the relation between the specimen strength, the initial defect size and to take into account the strength variation with respect to the tested volume. The proposed methodology is analytically defined and thereafter validated with the literature data obtained through tests on different types of brittle materials, and on specimens with increasing volume. A simple procedure for parameter estimation is also defined in the paper. The literature validation proves the effectiveness of the proposed methodology, with the resulting fitting models in well agreement with the experimental dataset and characterized by high values of coefficients of correlation, similar or larger than those obtained in the literature with different approaches

Modeling the Population Dynamics and Management of Italian Ryegrass under Two Climatic Scenarios in Brazil

This article belongs to the Special Issue 2019 Feature Papers by Plants’ Editorial Board Members.Italian ryegrass (Lolium multiflorum L.) is an annual grass widely distributed in cultivated crops around the world. This weed causes significant yield reduction in many crops and has developed herbicide resistance. The aim of this study was to develop a cohort-based stochastic population dynamics model that integrates both emergence (thermal time) and dynamic population models as a tool to simulate the population dynamics of susceptible and resistant populations of L. multiflorum under the effects of climate change. The current climate scenario and the increase in the average air temperature by 2.5 °C were considered. Chemical and cultural management strategies commonly used in the South Region of Brazil during the winter and summer seasons were incorporated into the model. In the absence of control and under the current climate conditions, the seed bank population grew until reaching an equilibrium density of 19,121 ± 371 seeds m−2 for the susceptible and 20463 ± 363 seeds m−2 for the resistant populations. Considering the second climate scenario, the seed bank reaches an equilibrium density of 24,182 ± 253 seeds m−2 (+26% in relation to the current scenario) for the susceptible population and 24,299 ± 254 seeds m−2 (+18% in relation to the current scenario) for the resistant one. The results showed that the effect of the rise in temperature implies an increase in population in all the management strategies in relation to the current climate scenario. In both climate scenarios, the strategies based on herbicides application controlling cohorts 1 and 2 were the most efficient, and cropping systems including winter oat-soybeans rotation had a smaller impact on the L. multiflorum seed bank than crop rotations including winter wheat or summer corn. Crop rotations including wheat and corn for L. multiflorum management as an adaptive strategy under the future climate change are suggested.This research was funded by HRAC-BR (Associação Brasileira de Ação a Resistência de Plantas Daninhas aos Herbicida). FBP acknowledges economic support from the CAPES (Coordenação de Aperfeiçoamento de Pessoal de Ensino Superior). JLG-A was partially funded by the Spanish Ministry of Science, Innovation and Universities (grant AGL2015- 64130-R)

Static strength of brittle materials under multiaxial nonuniform stress states: A novel statistical model for assessing size effects

In this paper, a model for the assessment of size effects on quasi-static strength of brittle materials subjected to applied load inducing a nonuniform stress distribution within the material volume is proposed. An equivalent stress computed through finite element analysis is introduced in the model to account for the effect of the stress gradient within the loaded volume. The defect size distribution is modelled, differently from the literature, with the largest extreme value distribution. The proposed model has been validated with datasets available in the literature and obtained through bending tests on concrete specimens. For each type of test, the model permits to properly assess size effects. Due to its general formulation, a model for the strength variation with respect to the loaded volume, regardless of the testing type, was also obtained, further proving its effectiveness

A pedagogia histórico-crítica na trajetória histórica e nos fundamentos teóricos do currículo para a rede pública municipal de ensino de Cascavel/PR

A finalidade deste artigo é a de primeiramente relatar a trajetória histórica do processo deelaboração do Currículo para a Rede Pública Municipal de Ensino de Cascavel, naseqüência, expor os principais pressupostos que fundamentam este documento que seconstitui em três volumes (Educação Infantil, Ensino Fundamental (Anos Iniciais) eEducação de Jovens e Adultos - Fase I) concluído em 2007 e implementado a partir de2008. O documento tem como referencial teórico a epistemologia materialista históricodialética(MARX), a proposições da psicologia histórico-cultural (VIGOTSKY) e apedagogia histórico-crítica (SAVIANI). Intenta-se também apresentar os pressupostossobre a educação das pessoas com deficiências, afirmados nesse Currículo. À vista daimplementação do referido documento, é exposto o processo de formação continuadadesencadeado no município nos anos de 2008 a 2010, que buscou instrumentalizar osprofessores da Rede Municipal de Ensino para a compreensão e aplicação efetiva egradativa do documento, que foi pela primeira vez na história, elaborado pela própria Redee com discussões envolvendo os professores das escolas municipais