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

An embedded formulation with conforming

Use of strong discontinuities with satisfaction of compatibilit

Efficiency of low versus high airline pressure in stunning cattle with a pneumatically powered penetrating captive bolt gun

The efficiency of stunning cattle was assessed in 443 animals (304 pure Zebu and 139 crossbred cattle), being mainly mature bulls and cows. Cattle were stunned using a Jarvis pneumatically powered penetrating captive bolt gun operating with low (160–175 psi, N = 82) and high (190 psi, N = 363) airline pressure, which was within the manufactures specifications. Signs of brain function and the position of the shots on the heads were recorded after stunning. Velocity of the captive bolt and its physical parameters were calculated. Cattle shot with low pressures showed more rhythmic respiration (27 vs. 8%, P < 0.001), less tongue protrusion (4 vs. 12%, P = 0.03) and less masseter relaxation (22 vs. 48%, P < 0.001). There was an increased frequency of shots in the ideal position when cattle were shot with the low compared to high airline pressures (15.3 vs. 3.1%). Bolt velocity and its physical parameters were significantly (P < 0.01) higher when using high pressure. Airline pressures below 190 psi are inappropriate when shooting adult Zebu beef cattle with pneumatically powered penetrating captive bolt guns

What are the Best Hierarchical Descriptors for Complex Networks?

This work reviews several hierarchical measurements of the topology of complex networks and then applies feature selection concepts and methods in order to quantify the relative importance of each measurement with respect to the discrimination between four representative theoretical network models, namely Erd\"{o}s-R\'enyi, Barab\'asi-Albert, Watts-Strogatz as well as a geographical type of network. The obtained results confirmed that the four models can be well-separated by using a combination of measurements. In addition, the relative contribution of each considered feature for the overall discrimination of the models was quantified in terms of the respective weights in the canonical projection into two dimensions, with the traditional clustering coefficient, hierarchical clustering coefficient and neighborhood clustering coefficient resulting particularly effective. Interestingly, the average shortest path length and hierarchical node degrees contributed little for the separation of the four network models.Comment: 9 pages, 4 figure

Crack propagation monitoring using an image deformation approach

An image deformation method is herein proposed to monitor the crack propagation in structures. The proposed approach is based on a computational algorithm that uses displacements measured by photogrammetry or image correlation to generate a virtual image of the surface, from an initial input to any given stage of analysis. This virtual image is then compared with the real image of the specimen to identify any discontinuities that appeared or evolved during the monitored period. The procedure was experimentally validated in the characterisation of crack propagation in concrete specimens. When compared with other image processing techniques, for instance based on edge detectors, the image deformation approach showed insensitiveness to any discontinuity previously existing on the surface, such as cracks, stains, voids or shadows, and did not require any specific surface treatments or lighting conditions. With this approach the global crack maps could be extracted from the surface of the structure and extremely small changes occurring within a given time interval could be characterised, such as the movement associated with the opening of cracks. It is highlighted that the proposed procedure is general and therefore applicable to detect and characterise surface discontinuities in different materials and test set-ups.FEDER FCOMP‐01‐0124‐FEDER‐020275, FCT PTDC/ECM/119214/2010, ARC DE150101703, FCT SFRH/BPD/102790/201

Modelling the behaviour of steel fibre reinforced concrete using a discrete strong discontinuity approach

The use of Fibre Reinforced Concrete (FRC) is gradually wide-spreading due to the significant advantages relatively to Normal Concrete (NC). In the case of steel fibres, the quasi-brittle behaviour of plain concrete structures can be modified into an enhanced ductile behaviour as a direct result of this addition. Since the mechanical properties of both FRC and NC can be significantly different, this work aims at developing a finite element formulation to specifically address the simulation of the behaviour of FRC members up to failure. For this purpose, the Conforming Generalised Strong Discontinuity Approach (CGSDA) is adopted with steel fibres explicitly introduced in the finite element mesh. The resulting formulation has the following main characteristics: i) variational consistency; ii) fibre elements automatically considered regardless of the presence of cracks; and iii) no additional degrees of freedom are required. The proposed formulation is validated using experimental results from tests conducted with different dosages of steel fibres.FCOMP-01-0124-FEDER-020275, FCT PTDC/ECM/119214/2010, FCT SFRH/BD/85922/2012, ARC DE150101703

Eficiência de fungicidas para o controle da mancha branca do milho.

A mancha branca é uma das principais doenças da cultura do milho no Brasil na atualidade. Dentre as medidas recomendadas para o controle da mancha branca, a resistência genética e o uso de fungicidas são as mais utilizadas pelos produtores. No entanto, relatos de baixa eficiência de controle com diferentes grupos químicos têm sido frequentes, o que tem gerado dúvidas quanto à sua eficiência no controle dessa doença em condição de campo. No presente trabalho, foram conduzidos quatro ensaios, em condição de campo, utilizando-se cultivares com diferentes níveis de resistência ou suscetibilidade à mancha branca do milho. Foi avaliada a eficiência de diferentes grupos químicos de fungicidas no manejo da mancha branca do milho em diferentes números de aplicações. Com os resultados obtidos, verificou-se que os fungicidas do grupo das estrobilurinas foram os que apresentaram maior eficiência no controle da doença. Os fungicidas triazóis, carbendazim, o tiofanato metílico e os antiobióticos oxitetraciclina e kasugamicina apresentaram baixa eficiência de controle

Influence of concrete strength and steel fibre geometry on the fibre/matrix interface

The main objective of the research described in this paper was to evaluate how the concrete compressive strength and the geometry of the steel fibres influence the behaviour of the fibre/matrix interface. With this aim, three different concrete matrices were designed with 20, 60 and 100 MPa, and two types of steel fibres were adopted (Dramix® 3D and Dramix® 5D). Specific pull-out specimens were produced and three sets of axial tensile tests were defined with different fibres (3D fibres, and 3D and 5D fibres with trimmed ends). A numerical model was calibrated and used to expand the scope of results obtained from the experimental tests. It can be concluded that the concrete compressive strength strongly influences the fibre/matrix strength. In the set with untrimmed 3D fibres, higher strengths are reached due to the hook shaped endings, for all concrete strengths, varying between 64% and 72% of the total load. For fibres with straight endings, increasing both diameter and length increases lead to higher adhesion and friction strengths.FCT PTDC/ECM/119214/2010, FCT SFRH/BD/84355/2012, FCT SFRH/BD/85922/2012 and FCT SFRH/BPD/102790/2014, ARC DE15010170