Measurement of manufacturing-induced residual stresses in tungsten monoblock sub-assemblies for DEMO divertor designs.
The structural integrity assessment of multi-material systems requires a good understanding of both the operational loads expected in service and the pre-existing internal loads due to manufacturing. AMT staff have used a suite of complementary strain measurement techniques (contour method, plasma FIB DIC, neutron diffraction) to evaluate the as-manufactured stresses in a divertor monoblock, based on a candidate DEMO design. This sub-assembly comprises a tungsten block joined to a copper alloy pipe using a copper joint. Residual stress fields from this study have been shared with the EUROfusion community to improve divertor integrity assessments, including how often these components will need to be replaced and/or inspected.
Accurate measurement of strain localisation using Digital Image Correlation (DIC).
DIC is a very powerful tool for measuring strain in engineering materials andAMT has shown how accurate measurement of materials performance can be obtained post-localisation (“necking”) using the technique. These results are extremely important to design engineers because the data obtained using conventional strain measurement techniques (e.g., extensometers) cannot capture the post-necking behaviour that is commonly observed in lab-scale materials testing. Early results have revealed a previously unforeseen dependency – that of strain rate – on the observed post-necking material response. This work is highly relevant to anyone conducting lab-scale mechanical testing of engineering materials.
Towards a statistical treatment of microstructural data.
Materials engineers must demonstrate the data they produce is representative of bulk material performance. This process can be extremely challenging for high-value manufacturing, where access to large volumes of material may be limited. AMT has demonstrated how a statistical treatment of microscopy data can be used to determine the minimum statistically relevant volume of material required to represent bulk material properties. This approach is key to ensuring complementary numerical assessments (e.g., using crystal plasticity methods) consider a suitable amount of material.
Establishing synergistic irradiation testing at the Dalton Cumbria Facility (DCF).
The mechanical performance of irradiated materials is typically assessed ex situ - materials are irradiated before they are tested. AMT staff have developed a mechanical testing rig that will allow us to deform materials while they are being irradiated. The testing machine will be situated on one of the proton beamlines at the DCF, and will be the first machine in the UK capable of performing synergistic irradiation-mechanical testing. This capability is critical to provide assurance of materials intended for deployment in radioactive environments.
Investigation of size effects in miniature tensile testing.
Standard lab-scale mechanical testing requires a volume of material greater than can be produced in material irradiation campaigns. In AMT, we are working to reduce the size of test specimens, while retaining the key information produced in traditional testing. A systematic assessment of size effects has been carried out as part of EUROfusion activities. These results will aid the development of a new set of standards for miniaturised tensile testing, which will ensure test results are credible for through-life performance assessments.
Applied Materials Technology
The aim for Applied Materials Technology (AMT) is to become the leading UK authority on through-life performance of engineering materials that can be used in fusion machines and future fusion power plants.
The objectives for AMT are driven by a set of key challenges:
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Component-level material qualification in support of design assessment for fusion energy machines
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Technologies that provide material quality assurance within fusion timescales
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Integrity assessment methodologies for fusion systems
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Integrity assessment methodologies for fusion systems