EU Science Hub

European Laboratory for Structural Assessment: Large Hopkinson Bar Facility (ELSA-HopLab)

The ELSA HopLab is a specialised laboratory (based on Hopkinson bar techniques) for the study of the behaviour of materials and structural components to very fast dynamic loads, such as those due to blast and impact, where knowledge of the material behaviour under high strain-rates is necessary. The laboratory has unique features with respect to the magnitude of the applied forces and the large size of the specimens to be tested.

The facility is operated by highly experienced scientific and technical staff and is supported by specialists in numerical simulation (see EUROPLEXUS).

The services offered by ELSA HopLab enable scientists to carry out high-quality research through unique experimental facilities for the characterisation of brittle or ductile materials and components at dynamic strain-rates and at high/low temperatures.

Large Hopkinson bar for ductile materials

This is the world’s largest Hopkinson Bar extending for a length of more than 200 meters. Thus, large material samples or structural components and sub-assemblies can be accurately tested under the required dynamic conditions. It features:

  • Bars of 72 mm diameter made of MSK steel
  • Maximum generated pulse: 1 MN force amplitude, 40 ms duration, 15m/s induced impact speed
  • Semiconductor strain-gages for increased sensitivity
  • Pulse generation using the pre-tensioned bar method and explosive bolt release
  • Ideal for tension tests; compression tests performed employing an ‘inversion frame’ developed according to specimen size and shape
  • Capability: maximum 2 tests / day

Medium-size Hopkinson bar for brittle materials

Modified Hopkinson bar designed for the compressive and tensile characterisation of brittle materials using large size specimens (concrete, glass, mortar, geo-materials etc.). It features:

  • Aluminium or steel bars of 100 mm diameter and 2.7 m length
  • Maximum generated pulse: 2 MN amplitude and about 0.8 ms duration
  • Semiconductor strain-gages for increased sensitivity
  • Pulse generation using the impactor bar
  • Capability: Maximum 4 tests / day

Additional equipment

Smaller Hopkinson bars of various bar diameters and lengths are also available for the testing of small material specimens under different dynamic loading types:

  • Apparatus for compressive testing of soft cellular materials
  • Apparatus for compressive testing of high-strength, brittle materials
  • Apparatus for tensile/compressive testing of metals
  • Capability: Maximum 5 tests / day

The ELSA HopLab is equipped with high-speed digital cameras (up to 50000 fps) and it has expertise for installing strain-gages and other sensors.

European and international collaboration

The laboratory has been involved in collaborative European competitive projects (SAFEWAY - Safety improvement of vehicle passengers through innovative on-road "bio-mechanics" safety features, ANCHR - Anchorages in normal and high performance concretes subjected to medium and high strain rates, LISSAC - Limit strains for severe accident conditions, REVISA - Reactor vessel integrity in severe accidents, etc.) as well as in international ones (DAM-CONCRETE for DHS, USA).

Areas of research

  • Security and safety of buildings and protection of public spaces against explosion loads
    • Materials for defence applications
    • Study of materials/structural components at high loading-rate conditions (blast, impact) and high/low temperatures

    Recent projects

    Dynamic performance of adobe masonry components. The project investigated the compressive strength of two different mixtures of adobe (in oven- and air-dried conditions) at three different strain-rates ranging from static to fast dynamic.

    Steel under severe high impact. The project focused on the dynamic testing of large specimens of high strength, innovative steels for concrete reinforcement with possible applications in the building and defence sectors.

    High strain rate behaviour of dam concrete. Experiments and multiscale modelling, sponsored by the US Department of Homeland Security S&T Infrastructure and Geophysical Division.