The paper analyses the fracture behaviour of several rocks, namely a sandstone, a limestone and two marbles, one of them being a Carrara marble. The experimental program comprises in total 216 fracture specimens, tested in 4-point bending conditions and including specimens with notch radii varying from 0.15 mm up to 15 mm. The notch effect is analysed through the evolution of the apparent fracture toughness and the application of the Theory of Critical Distances.The present study aims to generalize a previous study on a granite and a limestone to a broader range of rocks. The point and line methods of the Theory of the Critical Distances successfully explain the notch effect on the fracture specimens. The value of the critical distance of these rocks is of the order of mm. Finally, the results show a correlation between the microstructural features of the rocks, specifically the grain size, and their critical distances.

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This work presents an energetic continuum approach for the fracture assessment of rocks containing U-shaped notches and subjected to Mode I loading conditions. Three different methodologies are proposed in this article, all of them based on the premise that brittle failure will occur when the average strain energy density over a certain control area reaches a critical value that only depends on the material, as stated by the Strain Energy Density (SED) criterion.The first method proposed (A) deals with the application of the SED criterion through an expression with a series of already tabulated parameters, which are particularised for the analysed rocks by rational extrapolation. Therefore, this first method avoids the use of numerical analysis. By contrast, the second method (B) aims to obtain numerically the previously extrapolated parameters, and the third method (C) directly relates the strain energy density with the applied load, without the use of those parameters.The research is based on the results obtained from an exhaustive experimental programme comprising 300 fracture specimens tested in four-point bending conditions. These tests combine parallelepiped samples made of 6 different types of rocks (two marbles, two limestones, a sandstone and a granite) and containing 8 different notch radii (varying from 0.15 mm up to 15 mm).Thus, this work aims to show the potential, capacity and limitations of the SED criterion in rock fracture analyses, comparing with this purpose the experimentally obtained fracture loads and those predicted by the three proposed methodologies.

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A mediados de 2018 el ministro de Hacienda de Argentina y el presidente del Banco Central de ese país enviaron una carta a la directora del Fondo Monetario Internacional solicitando un préstamo de 50 000 millones de dólares. En unos pocos días, menos de una semana hábil, ese pedido fue aceptado por el FMI y luego ampliado en 7100 millones de dólares más, desembolsándose finalmente un total de 45 000 millones. De acuerdo a lo que surge de constancias judiciales y administrativas, la decisión de contraer el préstamo fue adoptada por los precitados funcionarios argentinos sin ley especial habilitante, sin acto administrativo autorizatorio, sin expediente y sin recabar previamente los dictámenes jurídicos y técnicos exigidos por la legislación nacional. Esas omisiones determinaron que la operatoria presentara severas falencias en materia de competencia y procedimientos de formación de la voluntad estatal. En este trabajo se plantea que esa sumatoria de fallas en los procesos decisorios domésticos implicó una transgresión por parte del Estado a sus obligaciones bajo la Convención Americana sobre Derechos Humanos en materia de derechos civiles y políticos –gobierno democrático, participación ciudadana y acceso a la información pública– y derechos económicos, sociales, culturales y ambientales, todo lo cual compromete la validez del acuerdo celebrado con el organismo financiero.

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This work aims to assess the fracture of U-notched limestone samples subjected to mixed mode I+II loading conditions with a predominant mode I influence, both at room temperature and at 250ºC. This analysis is based on the use of the Theory of the Critical Distances, and more specifically on the use of the Line Method, considering both an analytical and a numerical approach for the definition of the stress fields. An experimental campaign of almost 400 three-point bending tests has been performed as a basis for the fracture assessment of the limestone, using Single Edge Notched Bend (SENB) specimens with notch radii varying from 0.15 mm up to 15 mm, different temperature conditions and variable loading positions. The Theory of Critical Distances has successfully been applied to study the experimental results. The analytical and numerical stress fields for pure mode I fracture assessments provide similar accurate results both at 23ºC and 250ºC. Similarly, the mixed mode (I+II) fracture assessments allow the critical distance (𝐿𝐿) to be characterised for different mode mixities (𝑀𝑀 𝑒𝑒 ), using the stress field around the notch tip obtained from the numerical models. Comparing the values of the critical distance against the mode mixity in isolation, a slight decrease of 𝐿𝐿 is observed as it approaches pure mode I conditions (𝑀𝑀 𝑒𝑒 = 1). However, if the results are analysed separately for each notch radius, 𝐿𝐿 seems to be relatively constant with 𝑀𝑀 𝑒𝑒 . In parallel, a certain influence of the notch radius on the critical distance is appreciated, which shows an increment both at 23ºC and 250ºC.