At the rear of Thrust SSC there are titanium body panels adjacent to the efflux from the Rolls-Royce Spey jet engines.
The effiux stream from the jets causes these panels to resonate, particularly on re-heat, raising some concern about
the strength of the panels and their fixings, and that the panels may part company during these extreme conditions.
Measurements Group UK Limited agreed to sponsor testing the panels. At a technical meeting it was decided that a visual indication of the highly stressed points would be a good starting point, and MG UK were asked to provide and fit 'PhotoStress" photoelastic coatings to the panels in the areas of suspected high stresses.
The installation was carried out at MG UK's premises in Basingstoke, and three 10"x10" sheets of PhotoStress PS-l were bonded to a titanium panel, which was then taken for testing to Assessment Services at Titchfield. The panel was vibrated on a Ling Dynamics shaker, one of the largest in the country, and MG UK provided a Model 031 polariscope with a stroboscopic light source and an operator. When viewed through the polariscope, the PhotoStress coatings show coloured fringes giving the magnitudes of the local strains and directions of principal strains under static loading. With the stroboscopic light source, dynamic conditions can be stopped" and examined or moved slowly through a vibration cycle to measure the variations.
The complete test was filmed. When analysed the tests showed clearly how the stress concentrations and the directions of principal stresses changed at the various frequency inputs. This information was used to decide the locations for strain gauges for the next tests.
At the next technical meeting it was decided that 10 off 3-element rosette strain gauges, type CEA-Ob-250UR-3b0, should be installed by MG UK and the tests on the shaker repeated at the various frequencies. Successful tests were carried out in August 1995 providing vital information on the strength requirements.
For more information, please contact:
Measurements Group UK Ltd Stroudley Road Basingstoke Hampshire RG24 8FW Tel: +44 (0)1256 462131 Fax: +44 (0)1256 471441 WWW: http://measurementsgroup.com
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