European Laboratory for Structural Assessment: Large Hopkinson Bar Facility

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 tensile tests

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 high-strength steel
• maximum generated pulse: 1 MN force amplitude, 40 ms duration
• up to 15m/s induced impact speed with a maximum displacement of 30 cm
• conventional and semiconductor strain-gages for increased sensitivity
• pulse generation using the pre-tensioned bar method and explosive bolt release
• capability: maximum 4 tests / day

Large Hopkinson Bar for compression tests

Hopkinson Bar designed for the compressive characterisation of brittle and ductile materials (concrete, mortar, foams and polymers) using large size specimens. It features:

• aluminium or steel bars up to 120 mm diameter and 2.7 m length
• specimen up to 100 mm of diameter
• maximum generated pulse: 2 MN amplitude and about 5 ms duration (multiple reflections)
• conventional and semiconductor strain-gages for increased sensitivity
• pulse generation using the impactor bar
• capability: maximum 20 tests / day

Additional equipment

Conventional 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 20 tests / day

The ELSA HopLab is equipped with high-speed digital cameras (up to 200000 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). Since 2017 HopLab laboratory is involved in the Open Access to JRC infrastructures project (https://joint-research-centre.ec.europa.eu/open-access-jrc-research-infrastructures_en) granting access to external users to their facilities for testing and training.

Areas of research

• Dual-use (defence/security) applications;
• material/structural component testing at high loading-rate conditions (blast, impact) and high/low temperatures;
• security of buildings and protection of public spaces against explosion loads.

Recent projects

Dynamic properties of electron beam welded specimens. The  project focused on the tensile and compressive mechanical behaviour at high strain-rates of OFE copper and niobium subjected to electron beam welding.
User access report

Characterisation of automated tape composites at high strain rate. The project studied the tensile mechanical behaviour, at high strain-rates, of a series of advanced composite materials with a tape interlaced laminates structure.
User access report

Steel under severe high impact. The research concerned the investigation of the mechanical behaviour of high strength (S690QL) and very high strength (S960QL) steel tested in tension at high strain-rate.
User access report

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.
User access report

Energy absorption capability of CRUSHable CFRP structure with Additive Manufacturing Infill for lightweight vehicle design. The aim of the project is to verify the suitability of hybrid structures as energy absorbers for impacts, shocks and explosions scenarios. 

User access report

Contact: JRC-OPEN-ELSAec [dot] europa [dot] eu (JRC-OPEN-ELSA[at]ec[dot]europa[dot]eu)

Related media

Photos

Photo reportage: HopLab - European Commission Audiovisual Service

Video