Arbitrary bi-dimensional finite strain crack propagation

In the past two decades numerous numerical procedures for crack propagation have been developed. Lately, enrichment methods (either local, such as SDA or global, such as XFEM) have been applied with success to simple problems, typically involving some intersections. For arbitrary finite strain propagation, numerous difficulties are encountered: modeling of intersection and coalescence, step size dependence and the presence of distorted finite elements. In order to overcome these difficulties, an approach fully capable of dealing with multiple advancing cracks and self-contact is presented (see Fig.1). This approach makes use of a coupled Arbitrary Lagrangian-Eulerian method (ALE) and local tip remeshing. This is substantially less costly than a full remeshing while retaining its full versatility. Compared to full remeshing, angle measures and crack paths are superior. A consistent continuationbased linear control is used to force the critical tip to be exactly critical, while moving around the candidate set. The critical crack front is identified and propagated when one of the following criteria reaches a material limiting value: (i) the stress intensity factor; or (ii) the element-ahead tip stress. These are the control equations. The ability to solve crack intersection and coalescence problems is shown. Additionally, the independence from crack tip and step size and the absence of blade and dagger-shaped finite elements is observed. Classic benchmarks are computed leading to excellent crack path and load-deflection results, where convergence rate is quadratic

Efeito da umidade do solo sobre o dano da lagarta Elasmo, Elasmopalpus lignosellus (Zeller) na cultura do milho.

O objetivo deste trabalho foi estudar o efeito da umidade do solo sobre o ataque da lagarta elasmo, Elasmopalpus lignosellus (Zeller), na cultura do milho. Avaliou-se o efeito de seis laminas de agua sobre o dano causado pela lagarta, com idade de quatro, 10 e 15 dias. Atraves de irrigacao por aspersao, aplicaram-se diariamente as laminas de agua no solo, coletando-se amostras de solo antes e apos a irrigacao, para determinar a umidade. Os resultados mostraram uma relacao quadratica entre o conteudo de umidade do solo e a porcentagem de plantas de milho atacadas pela praga. Concluiu-se que o dano causado por lagartas com ate 10 dias de idade pode ser reduzido com o manejo da umidade do solo em sistema irrigados