Publications

Cavity expansion is a method for modeling the penetration of an axisymmetric or wedge-shaped solid body--a penetrator--into a target by using analytic expressions to capture the effects of the target on the body. Cavity expansion has been implemented as a third-party library (CavityExpansion) that can be used with explicit, transient dynamics codes. This document describes the mechanics of the cavity expansion model implemented as a third-party library. This document also describes the applications interface to CavityExpansion. A set of regression tests has been developed that can be used to test the implementation of CavityExpansion in a transient dynamics code. The mechanics of these tests and the expected results from the tests are described in detail.

A procedure has been developed to represent the loading on a penetrator and its motion during oblique penetration into geologic media. The penetrator is modeled with the explicit dynamics, finite element computer program PRONTO 3D and the coupled pressure on the penetrator is given in a new loading option based on a separate cavity expansion (CE) solution that accounts for the pressure-reduction from a nearby target free surface. The free-surface influ- ence distance is selected in a predictive manner by considering the pressure to expand a spherical cavity in a finite radius sphere of the target material. The CE/PRONTO 3D procedure allows a detailed description of the penetrator for predicting shock environments or structural failure dur- ing the entire penetration event and is sufficiently rapid to be used in design optimization. It has been evaluated by comparing its results with data from two field tests of a full-scale penetrator into frozen soil at an impact angles of 49.6 and 52.5 degrees from the horizontal. The measured penetrator rotations were 24 and 22 degrees, respectively. In the simulation, the rotation was21 degrees and predominately resulted from the pressure reduction of the free surface. Good agree- ment was also found for the penetration depth and axial and lateral acceleration at two locations in the penetrator.

An oblique penetration modeling procedure is evaluated by correlation with onboard acceleration data from a series of six penetration tests into Antelope Dry Lake soil at Tonopah Test Range, Nevada. The modeling represents both the loading which is coupled to the penetrator bending and the penetrator structure including connections between the major subsections. Model results show reasonable agreement with the data which validates the modeling procedure within a modest uncertainty related to accelerometer clipping and rattling of the telemetry package. The experimental and analytical results provide design guidance for the location and lateral restraint of components to reduce their shock environment.