The ESRF welcomes the shock community with a new access mode

12-12-2022

New set-ups designed and built by scientists at the University of Oxford, Imperial College London, and Nuclear Research Center Negev in collaboration with the ESRF will enable study of materials under rapid and extreme loading on ID19. The first experiments of this new Beamtime Allocation Group (BAG) have taken place recently.

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The bulk mechanical response of materials subjected to impact and shock loading has its origins in physical processes occurring at the underlying mesoscale. Until today, the standard time-resolved diagnostics are based almost exclusively upon visible radiation. This means that the knowledge of material behaviour under shock compression is based upon surface measurements, which are insufficient to reveal the early stages of a wide range of problems of acute technological relevance.

“Since many years, we tried to get the shock users in Europe and beyond to use the capabilities of the ESRF, but shock experiments are very complicated”, explains Alexander Rack, scientist in charge of ID19.

Over the last three years, a team from the University of Oxford, led by professor Daniel Eakins, developed the unique single stage gas-launcher necessary to carry out these kind of experiments. “The Shock BAG allows us to offer this platform to the wider user community, so they don’t have to build a gun, and to provide expertise in the operation of that system”, Eakins explains.  Specifically, the Shock-BAG builds-upon the dedicated single-stage gas-launcher, Hopkinson bar platforms, pulsed lasers and multi-MHz X-ray imaging scheme. The new access mode BAG will grow the high-rate and shock user community at ESRF and perfectly complement the recently developed laser-induced dynamic compression activities at the High Power Laser Facility on ID24 (XAS) and on ID09 (XRD) in terms of X-ray probe, attainable conditions and strain rate. In addition, the Shock-BAG would serve as a home for emergent techniques, such as pulsed power-, laser- and explosive-drive, which share similar challenges and diagnostic needs.

What research will benefit from shock experiments?

The shock community that will benefit from this new BAG covers several scientific disciplines in very different domains.

Earthquake triggers: When submitted to increasing stress, rocks in the Earth’s crust may break, creating shock waves, between 0.5 and 3 km per second. These shock waves damage the surrounding rock and fragment it, leading to earthquakes. Most dynamic rupture experiments in the past were carried out  under dry conditions and it was not possible to see through the rock. However, rocks may contain water and the evolution of this fluid when a shock wave propagates into a rock is not understood. With the new set-up, scientists will be able to image shock waves inside rock samples at micrometre spatial resolution and nanosecond time resolution, and characterise how the presence of water influences rock damage.

Internal damage in textured alloys: Dynamic compression and subsequent rapid unloading can initiate voids in metals and microcracks in brittle ceramics used in coatings or pressure vessels. It is well known that material microstructure plays a strong role in the evolution of tensile damage in metals or ceramics. However, the precise relationship between features like grain boundaries or texture and damage initiation sites and evolution is still unclear. With the new platform on ID19, scientists can now observe the formation and extent of subsurface tensile damage in different textures in alloys.

Void collapse and densification of porous systems: There are many systems that undergo compression of porous material, such as impacts of geologic materials or cavity collapse in fusion. The gas-gun set-up can reveal details of the mechanisms of collapse in spherical cavities.

High-pressure melting: The high pressures generating under shock loading can drive material into a liquid state. Scientists will now be able to measure the material behaviour during this transition, with the aim to understand the role of pressure on the kinetics of the melting process.

The new BAG will also grant access to industrial clients, such as aerospace or high-speed manufacturing, to the platform: “We will provide them with confidence in their modelling capabilities, so they can understand material behaviour under specific regimes. This will assist them in the design of new components or in understanding the rigor and reliability of material systems”, explains Eakins.