Test Devices has developed a strain survey technique for high-speed rotating parts designed to overcome the problem of high g-loads affecting instrumentation.

Strain surveys enable engineers to understand how their designs can be modified for increased life and improved performance while reducing material costs, and are commonly used for static and linearly moving parts. Strain surveys for rotating parts are much more difficult.

Finite element analysis can be used to identify high stress points - including bolt holes, blades and attachment points - but critical parts must be tested to determine the actual stresses.

Hudson, Massachusetts-based Test Devices mounts small strain sensors on to the test article at the areas of concern with special adhesives. Wires are then dressed and fixed along the part, to the arbor on which it is held, and run up through the centre of the arbor drive spindle and to a slip ring that transfers the sensor data to a computer.

A profile of the strain readings over the designer's chosen range of speeds is created from the resulting data. Test Devices says its equipment allows speeds all the way up to and including burst speeds. Unlike one-time brittle coatings sometimes used, Test Devices strain surveys can cycle a part multiple times and be done at various temperatures giving a more accurate representation of design performance, the company says.

Source: Flight International