Project underway

Dynamic fracture of rocks under high rate mechanical and electric breakdown induced loads

The project will be focused on studies of behavior and specifically fracture of rock materials subjected to dynamic high-rate loading conditions. The study will give a possibility for better understanding of mechanism underlying fracture and pre-fracture processes undergoing intensive dynamic deformation. One of the planned experiment types includes studies of rock materials fractured by electric discharges close to the interface between a rock and a dielectric liquid media. Theses study may have different important industry applications. One of possible practical examples is to start an oil well that is not producing oil due to a paraffin plug. In another experiments same rocks will be tested in dynamic tension experiments. The theoretical part will include development of a model predicting critical conditions leading to fracture in rock media with a single parameter responsible for “ temporal dependence of fracture” that can be measured in any of these experiments. This will give a possibility to predict the behavior of rock materials in rather complex loading conditions based on material parameters evaluated in much simpler experimental conditions.

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Construction materials under high strain rate

The mechanical behavior of the component materials of reinforced concrete (reinforcing steel and concrete) as well as fiber-reinforced cementitious composites when subjected to impact or blast still has many aspects requiring further investigation, with specific reference to large and socially-sensitive structures, as sheltering structures, high-rise buildings, bridges, off-shore platforms, pipelines, gasification reactors, secondary containment shells for nuclear power plants, and tunnels. The mechanical response of these structures exposed to blast and impact loading could only be predicted - and controlled - by formulating proper materials models for cementitious composites, including strain rate effects. This preliminary research permits the comparison of these new experimental results with some formulations proposed in literature which allow the definition of the variation of the mechanical characteristics in different strain-rate regimes. For these experiments will be used the facilities present in the two laboratories (Swiss and Russian). On the basis of the past experience of exchange in this project it is well identified the objective: to know to innovate.

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Split Hopkinson bar test on UHFRC/HPC

This project is part of the larger project funded by armasuisse named "Protection of Infrastructure Elements from the effects of IEDs and Blast Charges".

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Triaxially Compressed Hopkinson Bar (TriHB) for Geomaterial and Construction Material Testing

The project consists in the developing of Triaxially Compressed Hopkinson Bar (TriHB) for Geomaterial and Construction Material Testing. The main innovations to develop in the TriHB system can be summaries as below: (a) It can be used to test large and non-cylindrical samples under high strain rates, which can be used for testing not only intact rock, rock joint, composite rock, but also other civil engineering materials, such as concrete, cement, brick, timber, ceramics and even energy absorption foamed materials. (b) By applying impact loading from different driving source, the strain rate range can be extended. (c) Since 3 independent pairs of pressure bars will be used, the lateral confinement effect to the dynamic strength of rock and construction materials can be investigated. The confinement effect is very crucial to brittle material failure. The confinement effect in dynamic conditions at high strain rates has not been experimentally examined largely due to the limitation of the existing equipments.

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Rate and scale effects in fracture of concrete and rocks

High-rate dynamic fracture of concretes and rocks is of a great theoretical and practical interest. This is connected with a wide variety of applications where high-rate effects cannot be neglected if one wants to receive reasonable coincidence between theoretical prediction and reality. The applications include fracture mechanics of structures and geological objects that can (or should) be affected by intensive high-rate loads. Practical examples include antiterroristic protection, seismic safety of buildings, high-speed transport infrastructure, tunnel boring etc. In this connection the central problem consists in formulation of reliable and simple-to-use criterion being able to predict fracture of concrete and rocks under high-rate loads (impact, explosive, etc.). Planned joint research is concentrated on implementation of new experiments with concrete and rocks loaded using Swiss (Modified Hopkinson bar) and Russian (magnetic pulse installation) equipment able of creating intense short high-rate loads. The activities will also be aimed on studies of fracture on different scale levels, that will probably lead to improvement of high-rate fracture criteria for concrete and rocks.

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Teaching and Advanced Research on high strain rate behaviour of materials and testing

This Faculty Exchange Project is the first results of the Utilization of the Specific Infrastructure Project realized by the two proposers last year. This project continues in the dynamic behavior of materials field that is a basic requirement for numerous industrial applications and in many fields of the engineering which are interested in high qualify experimental skills. The basis of reciprocal collaboration developed in the previous project permit now to develop more stable interchange in the common field of interest including teaching activities. The relationship between the two research groups, coordinated by the proposers, will be strengthened by the mutual collaboration of the other Faculty members. The possibility given by the project, to work in a common experimental campaign, is a wonderful occasion to plane joint initiatives in important industrial fields as for example aerospace, automotive, nautical and construction. Modern advanced modelling tools, as FE codes, require information about the strain-rate behaviour of materials in terms of constitutive laws in a large range of strain-rate. These results are becoming essential for more optimized products.

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