Strain gaging Earth penetrators to provide dynamic force data

During Earth entry of high speed projectiles large, time-dependent forces are applied to the structure. In order to accurately model the response of these penetrators using both finite element methods and lumped mass-spring models, this force-time relationship must be quantified and used as an input for the analytical models. Two Earth penetrators were internally strain gaged to obtain strains in the penetrator body which could be used to calculate the applied forces. The installation techniques used to install the gages 0.46 m (18 in) from the end of the 127 mm (5 in) inside diameter penetrator case are presented. Gage and adhesive selection as well as wiring and data acquisition techniques designed to survive the high inertial loads encountered during Earth entry are discussed and preliminary results from the first test are shown.