Force traceability within the meganewton range

Large-scale structures, from high-rise buildings to bridges and wind turbines, must often withstand considerable loads. EU directives require that structures remain safe under all conditions and that construction materials are tested to confirm safety margins. Large material testing machines able to produce the high loads experienced by structures rely on transfer standards – called build-up systems – to transfer traceability from precise lab-based calibrations to material testing facilities.

Multiple transducers, devices that convert force into an electrical signal, are commonly used to measure the loads experienced by build-up systems in such tests, but understanding their performance beyond their normal operating range requires further investigation.

This project investigated the performance of different types of build-up system components using high loads to develop new calibration procedures for complete systems to 50 MN with robust links to the SI units.

The project:

• Investigated differences between single transducer calibrations and their use in build-up systems in order to enable reliable performance extrapolation to loads beyond their normal operating limits
• Developed a calibration correction database for transducers and build-up systems based on determining the effects of environmental conditions to improve measurement accuracy
• Established new calibration procedures for build-up systems to 50 MN, enabling their use as transfer devices for material testing machines in material testing facilities
• Developed and validated a novel hexapod build-up system with six load monitoring ‘legs’. This enables test machine alignment, a major source of measurement error, to be reliably assessed for the first time.

This project investigated the performance of individual transducers and also when these are assembled into different types of build-up systems in order to generate improved calibrations with robust links to the SI units. As a result, operators of high load material testing machines can now have greater confidence in the reliability of their measurements. Improved calibrations support greater testing accuracy and help building material manufacturers to demonstrate the strength of their products which aids compliance with the European Directives that underpin public safety.

The hexapod system enables the accurate assessment of test machine alignment by identifying any forces exerted outside of the main test loading direction. For the first time it is now possible to reliably determine test machine alignment, and any changes to the load’s direction induced during the testing of complex components such as rail carriage springs. Improving testing accuracy will increase confidence in spring performance testing that must meet the standards required by EU Directives.

Building on the outcomes of this project, the EMPIR project Torque measurement in the MN•m range is developing traceability for rotational force measurements above 1 meganewton metres.