Development of an integrated multi-axis loading and strain mapping facility.

This Measurement Note details work carried out to demonstrate the capability and use of the NPL multi-axial strong floor test machine, in conjunction with a number of full-field strain mapping techniques. Two case studies were undertaken; (i) an open-hole tension (OHT) specimen loaded transversely via a pin fitted into the hole and (ii) an aluminium bolted T-joint loaded at 45°. For both case studies measured strain data was compared to strain maps predicted using finite element modelling and theoretical analyses. The strain mapping techniques used were; (i) strain gauges, (ii) electronic speckle pattern interferometry (ESPI) and (iii) digital image correlation (DIC). The results of the case studies have shown that the multi-axial strong floor has been used with some success in conjunction with DIC and strain gauge techniques. However, the balance between spatial and strain resolution when using the DIC technique, means that the technique is limited in its ability to measure strains near to the edges of a component or strain concentrators such as holes. It was not possible to use the ESPI technique on the strong floor due to the sensitivity of the equipment to vibration. However, results from tests undertaken on a uniaxial test machine have shown that the technique compares favourably with DIC and strain gauge measurements.