Phase-field modeling of fracture in variably saturated porous media

We propose a mechanical and computational model to describe the coupled problem fuid flow, deformation and cracking in variably saturated porous media. A classical poromechanical formulation is adopted and coupled with a phase-field formulation for the fracture problem. The latter has the advantage of being able to reproduce arbitrarily complex crack paths without introducing discontinuities on a fixed mesh. The obtained simulation results show good qualitative agreement with desiccation experiments on soils from the literature

Phase-field modeling of fracture in partially saturated porous media

Porous media such as soil, rocks and concrete are of great importance in the context of civil engineering and environmental geomechanics. They consist of a solid skeleton and pores \ufb01lled with \ufb02uids, e.g. air and water. Complex mechanisms of \ufb02ow and transport take place within the pore network and can lead to deformation of the solid skeleton and eventually to fracture phenomena [1]. Phase-\ufb01eld modeling of fracture has recently emerged as an alternative to conventional approaches such as remeshing, extended \ufb01nite element methods or cohesive zone modeling. The phase-\ufb01eld framework can be considered a special type of gradient damage modeling approach, where a di\ufb00usive approximation of the crack is taken into account and the continuous phase-\ufb01eld parameter is used to describe the material integrity. The essential advantages are the possibility to describe arbitrarily complicated fracture patterns such as nucleation, branching and merging, without ad-hoc criteria on a \ufb01xed mesh, through the solution of partial di\ufb00erential equations derived from variational principles [2, 3, 4, 5]. Phase-\ufb01eld modeling of fracture in porous media has been addressed in some recent publications [6, 7], which however have only focused on the fully saturated case. Objective of this contribution is to describe fracture in partially saturated porous media using a phase-\ufb01eld approach. In this study, the material is described by its linear-elastic properties. The overall balance of linear momentum, the continuity equation and the phase-\ufb01eld evolution equation constitute a nonlinear coupled and time-dependent system of equations, which needs to be discretized and linearized. We formulate the coupled non-linear system of partial di\ufb00erential equations governing the problem with displacements, capillary pressure and crack phase-\ufb01eld as unknowns. The spatial discretization is carried out with \ufb01nite elements of appropriate order for the di\ufb00erent unknowns. We discuss its solution and present some relevant examples

Phase-field modeling of fracture in partially saturated porous media

Porous media such as soil, rocks and concrete are of great importance in the context of civil engineering and environmental geomechanics. They consist of a solid skeleton and pores filled with fluids, e.g. air and water. Complex mechanisms of flow and transport take place within the pore network and can lead to deformation of the solid skeleton and eventually to fracture phenomena [1]. Phase-field modeling of fracture has recently emerged as an alternative to conventional approaches such as remeshing, extended finite element methods or cohesive zone modeling. The phase-field framework can be considered a special type of gradient damage modeling approach, where a diffusive approximation of the crack is taken into account and the continuous phase-field parameter is used to describe the material integrity. The essential advantages are the possibility to describe arbitrarily complicated fracture patterns such as nucleation, branching and merging, without ad-hoc criteria on a fixed mesh, through the solution of partial differential equations derived from variational principles [2, 3, 4, 5]. Phase-field modeling of fracture in porous media has been addressed in some recent publications [6, 7], which however have only focused on the fully saturated case. Objective of this contribution is to describe fracture in partially saturated porous media using a phase-field approach. In this study, the material is described by its linear-elastic properties. The overall balance of linear momentum, the continuity equation and the phase-field evolution equation constitute a nonlinear coupled and time-dependent system of equations, which needs to be discretized and linearized. We formulate the coupled non-linear system of partial differential equations governing the problem with displacements, capillary pressure and crack phase-field as unknowns. The spatial discretization is carried out with finite elements of appropriate order for the different unknowns. We discuss its solution and present some relevant examples

Seleção de produtos alternativos para o controle do oídio (Oidium sp.) em feijão-caupi (Vigna unguiculata).

O objetivo deste trabalho foi avaliar a eficácia de produtos alternativos para a aplicação no manejo integrado do oídio em feijão-caupi para a redução dos riscos de intoxicação e dos custos com o controle. Foram avaliadas 13 formulações alternativas de fungicidas disponíveis no mercado regional com eficiência de controle desconhecida. Os produtos foram aplicados em feijãocaupi da cultivar BRS Carijó cultivado em experimento em blocos ao acaso com seis repetições. Ao longo de 10 dias após o início da exposição ao inóculo, as plantas foram avaliadas diariamente quanto à incidência e severidade da doença. Foi medido o percentual da área foliar infectada por meio de escala diagramática e construiu-se a curva de progresso da doença. Verificou-se que as formulações à base de enxofre, etilfosfonato de potássio e enxofre granulado, apresentaram média de 98,2% de eficiência de controle. Entre os produtos à base de derivados cítricos, flavonoides apresentou 95,3% de eficiência. Entre os produtos biológicos, o produto à base de Bacillus subtilis se destacou com 94,6% de eficiência relativa. Entre os produtos inorgânicos, o fosfito de potássio apresentou 94,8%, enquanto o bicarbonato de sódio apresentou elevada fitotoxidez à cultura

Atividade microbiana em áreas com diferentes usos do solo em agricultura dependente de chuva no Semiárido do Submédio São Francisco.

As diferentes formas de uso do solo apresentam forte impacto sobre a atividade microbiana, principalmente nas condições edafoclimáticas do Bioma Caatinga. Nessas condições, os baixos teores de nutrientes, água e matéria orgânica estabelecem um frágil equilíbrio, facilmente alterado. Neste trabalho, avaliaram-se as formas de agricultura mais tradicionais no Semiárido. Sejam elas: o cultivo anual, o cultivo de pastagem e o uso pastoril da Caatinga. As áreas apresentam o mesmo uso por um período superior a 25 anos e tomou-se uma área preservada de vegetação natural como área de referência para o estudo. Os resultados indicaram que a maior atividade biológica se concentrou nas profundidades até 30 cm, provavelmente por causa da existência de uma camada de adensamento pedogenético a partir de 40 cm. O teor de carbono da biomassa microbiana (C-BMS) foi mais elevado nas amostras oriundas de vegetação natural, contudo, a respiração foi mais elevada nas amostras tomadas em áreas de cultivo anual. Os resultados indicam que as operações de cultivo anual promovem a maior emissão de CO2 nas camadas superficiais do solo