A technique for applying controlled test pressures to curved surfaces is based on a principle similar to that of a compartmented pilot's or astronaut's pressure suit. The technique involves the use of airbags that accommodate geometric complexity in both the surface under test and in the spatial variation of the pressure to be applied. This method also provides the enhanced capability to vary the pressure locally, refining the load distribution at the airbag interfaces.
Previous methods for applying pressure loads have involved the use of point-load actuators distributed over the test surface. In using this technique, especially with surfaces of complex curvature, the controllability of the actuators with respect to directions of the loads that they apply is limited and the concentrated load at the actuator locations is a poor approximation of the desired pressure distribution. In a technique similar to the present method, pressure is applied to the test surface via an airbag restrained by a negative mold of the surface. However, this technique requires the expense of constructing the mold and the mold leaves little flexibility to adapt to the variations in shape of the test surface.
In the present method, one or more airbags are restrained against the test surface by use of a custom-fitted net (see figure). The quantity, size, and inflation pressure of each of the airbags can be adjusted to obtain a sufficiently accurate approximation of the required pressure distribution. Airbag geometry is sized by the maximum deflection of the net and the deflections of the structure. The net system includes a means of adjustment to compensate for net stretching and control of net separation from the structure. Ratchet mechanisms secure the net to the ground or to a suitable framework and serve as means of adjusting preloads to control deflections of the airbags.
This work was done by Michael C. Eubanks, John J. Zipay, and Edgar O. Castro of Johnson Space Center. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Mechanics category, or circle no. 156 on the TSP Order card in this issue to receive a copy by mail ($5 charge). MSC-22352