Earth Penetration and Detecting Unexploded Ordnance
Buried unexploded ordnance (UXO) in civilian and military sites is a problem worldwide. In particular, buried UXO hampers the handover of formerly used defense sites (FUDS) for civilian use. SERDP has funded the development of sensors for UXO, but depending on the ordnance and environment, some items have been difficult to detect. A partnership between New York University (NYU), Manhattan College (MC), and Southwest Research Institute (SwRI) intends to develop new procedures for predicting depth of burial (DoB) based on site-specific geotechnical data and fundamental physical principles ( Project Overview). The project team is achieving this goal through the development of new experimental, analytical, and probabilistic numerical capabilities.
Interactions between penetrating projectiles and the ground are quite complex, owed in part to aspects of soil behavior including porous multi-phase composition, spatial heterogeneity and history-dependent elastoplastic response, among other factors. The project team captures the salient features of these complex behaviors by (1) incorporating in situ soil behavior from geotechnical site characterization into their analytical models, and (2) visualizing soil-projectile interactions by transparent soil techniques that have been pioneered at NYU. This video, for example, illustrates movement of a projectile through a clay-like material. Detailed data for the motion induced in the soil particles helps to understand the connections between conventional geotechnical behavior, both in situ and in the lab, and resistance to high speed ordnance penetration.
An important feature of the ballistic experiments in this project is the use of unique vertical-firing guns. The largest one is 3-inch diameter and set up in the SwRI facilities in San Antonio, TX. This gun will be taken to FUDS locations in the later stages of the project. Two other vertical guns are used at smaller scales at NYU and MC. Coupled with photon-Doppler-velocimeters (PDV), these guns enable direct measurement of penetration resistance.
The results of these experimental efforts will be used to calibrate deterministic and probabilistic numerical simulations capable of describing the response of geomaterials to impact loading. Inputs are soil parameters from standard geotechnical experiments and in situ tests including the cone penetrometer test. Outputs are stochastic predictions for DoB for standard ordnance striking particular sites. The figure shows vertical stresses during cone penetrometer embedment in a sandy soil captured using the coupled Eulerian-Lagrangian approach employed in the large deformation finite element simulations.
Drs. Stephan Bless and Magued Iskander are leading these efforts at NYU. The team also consists of Dr. Bless, one of the country’s leading experts in impact mechanics, and Dr. Iskander, who is internationally known for his work in experimental soil mechanics. They are joined by Dr. Mehdi Omidvar and Dr. Anirban De at MC. Dr. Omidvar is a well-known researcher in high strain rate response of granular media, rapid soil penetration, and numerical and analytical modeling. Dr. De is an expert on site characterization. The SwRI effort takes place in their ballistics and explosive range, the most extensive such contractor facility in the country, led by Mr. Donald Grosch.