Component testing

Some possible applications include:

• Crack growth monitoring
• Cyclic / fatigue testing
• Profile of bending beam

The Video Gauge is able to measure:

• Position
• Displacement
• Rotation
• Bend angle
• Strain

Component testing often requires simultaneous measurement of both strain & displacements. That is something the Video Gauge is able to do with ease. It is possible to use multiple cameras, perhaps with one camera set up to measure the global deformation of a component while another camera is measuring local strains, for example at a joint.

Sometimes it is important to synchronise the video camera so that it captures images at specific moments such as when a cyclic test is at the peak of its loading. This can be achieved using the camera’s trigger input. The camera will capture an image whenever a voltage pulse is applied to the trigger input enabling synchronisation with external events.

The voltage input/output module can be used to feed signals from the test machine or other sensors into the Video Gauge. Any of the Video Gauge’s measurements can be fed out via the voltage output to other data-loggers or for feedback control of the test.

Case studies

	Residual stress measurement at the micro-scale The aim of this project was to measure residual stresses within metal samples at the micro-scale. This required measurement of surface deformations in the order of a few nanometers. Images produced with a Focused Ion Beam (similar to a scanning electron microscope) were analysed by the Video Gauge in order to make these measurements. (Image is Copyright 2008 Nicholas Daynes, Graeme Horne, Dept. of Mech. Eng., University of Bristol. Reproduced by permission.)
	Accuracy of Video Gauge for displacement measurement Precise measurement of displacement is traditionally achieved using devices such as a Dial Test Indicator (DTI) or a linear variable differential transformer (LVDT). The aim of this experiment is to validate the Video Gauge as a method for measuring displacement by comparing it directly with a calibrated DTI.
	Measuring changes in wing shape in a wind tunnel Tests on a compliant wing that changed shape depending on the air flow over it required that the changes in shape be determined as the wind tunnel testing progressed. The changes had to be measured without influencing the air flow. At the same time the strains within the special core material that supported the wing skins had to be measured to check that it was behaving in the expected way (negative Poisson's ratio).
	Tracking water level in the test of a tuned liquid damper A tuned liquid damper is a simple way of reducing the response of a building to dynamic loads such as earthquake shocks. It consists of a tank of water with the depth to length ratio set so that the natural frequency of the water sloshing in the tank matches that of the structure. The Video Gauge was used to monitor the depth of the water with time as well as the pendulum displacements of the plate and the displacements of the support frame.
	Measuring the shear component in three point bend testing of composite beams The beams were made by embedding carbon fibre composite rods in a soft, polyurethane elastomer, matrix. The aim was to produce a beam that was very compliant against twisting but very stiff in bending and tension. Beams with those properties could be used in helicopter rotor hubs. In order to understand how the samples deformed it was necessary to measure the shear deformation at the ends of the beam, as well as the overall bending of the beam.
	Measurement of the consolidation and shrinkage processes in composites manufacture It is very important in controlling the processing of advanced composites to develop an understanding of the consolidation and resin shrinkage processes throughout the cure cycle. For typical aerospace epoxies this requires the application of pressure up to a few Bar and temperatures up to about 180°C to a prescribed cycle. Equipment is available to do this such as Thermo Mechanical Analysers (TMA), but their sample sizes are very small and interpreting their outputs can be problematical.
	In-situ measurement of shear strains in bonded joints To understand the structural response of adhesive bonded joints requires that the shear strains in the adhesive to be measured at various points along the bond line. Specialised extensometry can be used to measure shear strains in adhesive joints, but measurement of these strains in real joints is difficult to achieve reliably. The adhesive is strain-rate sensitive so it is important to be able to capture the data in real time without having to stop the test and permit stress relaxation.