Influence of fibres on the mechanical behaviour of fibre reinforced concrete matrixes

An experimental analysis focused on the mechanical behaviour of fibre reinforced concrete matrixes (FRCM) is presented using a total of three hundred and twelve specimens. A reference plain mixture was first defined and then three types of fibres were chosen to reinforce it (polypropylene, glass and steel fibres). Within each type of reinforcement, four volumetric proportions were adopted, ranging from 0.5% to 2% in 0.5% increments. The influence of each type of fibre and dosage on the properties of the FRCM, including compressive strength, bending behaviour, cracking and maximum loads and ductility was analysed. In summary, it was observed that the compressive strength generally grows with the reinforcement dosage, and that this growth is greatly affected by the properties of the fibre, namely by its tensile strength. The load-displacement curves are also highly affected by the type of reinforcement. Steel and polypropylene fibres provide the composite material a better capacity to withstand high deformations. Glass fibres have a reduced effect on this regard, due to their brittle behaviour. For each type of fibre, by increasing the fibres percentage, an increase in the load capacity is also observed, with a maximum of 160% for an addition of 2.0% of steel fibres. The cracking loads are consistently lower than that of the reference mixture, due to the loss of homogeneity and increased porosity caused by fibre addition, in spite of the favourable influence associated to the mechanical properties of the fibres. For polypropylene FRCM the cracking loads were approximately 35% lower than that of the reference mixture. For steel and polypropylene fibres the toughness indexes (I5, I10 and I20) were defined, being observed that for 1.5% volume fraction of steel fibres the I5 and I20 are respectively 6.80 and 35.08, whereas for the polypropylene fibres those indexes are respectively of 3.61 and 15.75 for the same fraction.FCT PTDC/ECM/119214/2010, FCT SFRH/BD/84355/2012, ARC DE15010170

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

The Spread of Opinions and Proportional Voting

Election results are determined by numerous social factors that affect the formation of opinion of the voters, including the network of interactions between them and the dynamics of opinion influence. In this work we study the result of proportional elections using an opinion dynamics model similar to simple opinion spreading over a complex network. Erdos-Renyi, Barabasi-Albert, regular lattices and randomly augmented lattices are considered as models of the underlying social networks. The model reproduces the power law behavior of number of candidates with a given number of votes found in real elections with the correct slope, a cutoff for larger number of votes and a plateau for small number of votes. It is found that the small world property of the underlying network is fundamental for the emergence of the power law regime.Comment: 10 pages, 7 figure

Element-wise fracture algorithm based on rotation of edges

We propose an alternative, simpler algorithm for FEM-based computational fracture in brittle, quasi-brittle and ductile materials based on edge rotations. Rotation axes are the crack front edges (respectively nodes in surface discretizations) and each rotated edge affects the position of only one or two nodes. Modified positions of the entities minimize the difference between the predicted crack path (which depends on the specific propagation theory in use) and the edge or face orientation. The construction of all many-to-many relations between geometrical entities in a finite element code motivates operations on existing entities retaining most of the relations, in contrast with remeshing (even tip remeshing) and enrichment which alter the structure of the relations and introduce additional entities to the relation graph (in the case of XFEM, enriched elements which can be significantly different than classical FEM elements and still pose challenges for ductile fracture or large amplitude sliding). In this sense, the proposed solution has algorithmic and generality advantages. The propagation algorithm is simpler than the aforementioned alternatives and the approach is independent of the underlying element used for discretization. For history-dependent materials, there are still some transfer of relevant quantities between meshes. However, diffusion of results is more limited than with tip or full remeshing. To illustrate the advantages of our approach, two prototype models are used: tip energy dissipation (LEFM) and cohesive-zone approaches. The Sutton crack path criterion is employed. Traditional fracture benchmarks and newly proposed verification tests are solved. These were found to be very good in terms of crack path and load/deflection accuracy