Long Term Structural Changes in the EU Countries (1970-2000): Convergence or Divergence in the Agri-Food System?

The main objective of this paper is to analyse the structural changes in European Agri-food systems in the last 30 years in order to verify the presence of a convergence process towards a more homogeneous structure among EU countries. This analysis considers the relative importance of the main components of Agri-food systems (agriculture, food industry and food consumption) and how they change over time. The analysis of convergence utilise the European National Accounting Data (from the SEC2 Data Base of Eurostat) from 1970 to 2000 for twelve EU countries. We use tests of convergence on cross section data by countries, but also stochastic kernel methodologies to verify the dynamic evolution of groups of countries inside the EU. The results show there are important process of convergence among countries for the variables of the Agri-food system that are more linked to the economic development, such as the importance of agriculture and food consumption in GDP. On the other hand there are divergences on the variables more linked to the openness degree and to the competitiveness of the Agri-food system. The presence of polarisation process among groups of countries contribute to the permanence of long run structural changes among Northern and Southern countries in the EU.agro-food System, structural Changes, EU countries, convergence, Industrial Organization, A1, C23, O1, Q10, Q17,

Development of a Hopkinson bar apparatus for testing soft materials: application to a closed-cell aluminum foam

An increasing interest in lightweight metallic foams for automotive, aerospace and other applications has been observed in recent years. This is mainly due to the weight reduction that can be achieved using foams and for their mechanical energy absorption and acoustic damping capabilities. An accurate knowledge of the mechanical behavior of these materials, especially under dynamic loadings, is thus necessary. Unfortunately, metal foams and in general “soft” materials exhibit a series of peculiarities that make difficult the adoption of standard testing techniques for their high strain-rate characterization. This paper presents an innovative apparatus, where high strain-rate tests of metal foams or other soft materials can be performed by exploiting the operating principle of the Hopkinson bar methods. Using the pre-stress method to generate directly a long compression pulse (compared with traditional SHPB), a displacement of about 20 mm can be applied to the specimen with a single propagating wave, suitable for evaluating the whole stress-strain curve of medium-sized cell foams (pores of about 1-2 mm). The potential of this testing rig is shown in the characterization of a closed-cell aluminum foam, where all the above features are amply demonstrated.JRC.G.4-European laboratory for structural assessmen

BLAST Simulator Project: Performance assessment and preliminary tests. Administrative Arrangement No JRC 32253-2011 with DG HOME Activity A5 – Blast Simulation Technology Development

The Blast Simulator project involves the development of an apparatus able to reproduce the effects of a blast pressure wave on large scale structural components (such as columns, walls, etc.) with the objective to improve their strength in these severe loading situations. This technical report presents the setting up and the performance assessment of the prototype blast actuator developed at the JRC. The first preliminary tests performed have been described and evaluated. Satisfactory results have been obtained with respect to impacting masses and velocities and with the finally obtained pressure values.JRC.G.5-European laboratory for structural assessmen

Dynamic Behaviour of "Collapsible" Concrete

In this work a particular cement composite material for protection of structures and infrastructures against accidental actions, such as blast or impact, has been investigated. An experimental procedure has been developed in order to assess static and dynamic behaviour of energy absorbing cementitious composites. The granular cementitious composite has been studied focusing attention to compressive strength, high deformation and energy dissipation capacity which are important characteristics for an absorber material. An experimental characterization of the material behaviour under compressive static and dynamic loadings has been carried out. Different deformation velocities have been studied in order to define the material behaviour in a wide range of strain rates. The velocity range up to 0.1 m/s is investigated by means of a universal servo-hydraulic MTS 50 kN testing machine. Some preliminary results have been reported and discussed in the present work.JRC.G.4-European laboratory for structural assessmen

Compressive behaviour of dam concrete at higher strain rates

The mechanical behaviour of concrete when subjected to impact or blast has still many aspects requiring further study. Dam concrete is characterized by large coarse aggregates, hence large specimen sizes are needed in order to study a representative volume of the material. Exploiting an innovative equipment, based on Hopkinson bar techniques, the dynamic behaviour of concrete of 64~mm maximum aggregate size has been investigated. Direct dynamic compression tests have been performed on medium and large size cylindrical samples. Full stress-strain curves have been obtained, which have allowed the estimation of fracturing energies and of the relevant dynamic increase factor. The experimental campaign has also included a reference standard concrete in order to highlight the peculiarity of the dam concrete at high strain rates and to validate the transition of this type of testing to very large specimens.JRC.G.4-European laboratory for structural assessmen

Assessment of dynamic mechanical behaviour of reinforced concrete beams using a Blast Simulator

Critical infrastructures may become the target of terrorist bombing attacks or may have to withstand explosive loads due to accidents. The impulsive load connected to explosions is delivered to the structure in a few milliseconds forcing it to respond or fail in a peculiar mode. With reference to the above scientific framework this work presents an innovative apparatus designed and developed at the European Laboratory for Structural Assessment to reproduce a blast pressure history without using explosives. This apparatus is practically a hybrid nitrogen-spring-driven actuator that accelerates masses of up to 100 kg to a maximum velocity of about 25 m/s that impact against the tested structure. The pressure-load history applied to the structure is modulated and reshaped using appropriate layers of elastic soft materials (such as polymeric foams) placed between the specimen and the impacting masses. Specific instrumentation has extensively been utilised to investigate the blast simulator performance and to precisely measure the pressure loads applied to the specimen. A series of tests on real scale reinforced concrete beams/columns (250x250x2200 mm) has been performed to efficiently assess the performance and potentiality of the new blast simulator. Results are under evaluation. In addition to the experimental work, a series of numerical simulations by means of the explicit FEM code EUROPLEXUS have been carried out to support and improve the equipment design.JRC.G.4-European laboratory for structural assessmen

Dynamic response of Advanced Placed Ply composites

This work investigates the high strain rate behavior of AP-PLY composites. The large representative volume elements and brittle nature of this material necessitated the use of a bespoke Split-Hopkinson bar apparatus. AP-PLY and baseline laminates were subjected to tensile loading at strain rates of 30 s-1. Results were compared with quasi-static data to evaluate whether the laminate architecture introduced any strain rate dependency. In addition, the dynamic experiments were simulated using a multiscale modeling framework, providing further insights into the micromechanisms governing material behavior. The moduli of the AP-PLY composites were found to be strain rate independent, however, strengths were found to be marginally higher than those of their baseline counterparts. At high strain rates, the strain concentrations induced by the geometry of the individual tapes at through thickness undulations and tow boundaries were less significant due to reduced out-of-plane tow straightening and delamination. As a result, no reduction in AP-PLY strength in comparison to the baseline laminates was obtained. These differences in deformation micromechanisms led to an improvement of the damage tolerance when subjected to dynamic loading

Calibration procedure for force and displacement measurements at the HOPLAB

The report explains the calibration procedure of the HOPLAB facility. A short description of the facility is first included concerning the mechanical structure and its equipment in terms of sensors, transducers and relevant electronic instruments. A detailed explanation of the calibration procedure is next presented, which is principally centered at calibrating the force measurements along the input and output bars with a certified load cell. The main issues and problems connected to this particular testing rig are discussed. Finally an example of a typical elaboration, starting from raw experimental data to obtain the force-displacement curve of a specimen in tension, is provided.JRC.G.5-European laboratory for structural assessmen