Technical report | Establishment of a VISAR Measurement System for Material Model Validation in DSTO

Abstract 

This report describes the establishment of a velocity interferometer measurement system, VISAR, capability in DSTO for recording high-temporal resolution velocity data in high-velocity impact experiments. This data is critical for model validation, material and warhead performance characterisation and effects studies. The present report describes preliminary plane impact tests used to establish the VISAR capability, and evaluates the methodological resolution issues relating to the experimental set-up. The set-up misalignment effects observed on the VISAR records have been numerically analysed using the CTH hydrocode and will be taken into consideration in future test programs.

Executive Summary

The Velocity Interferometer System for Any Reflector (VISAR) system is used extensively to provide a highly accurate measurement technique for recording the shock response of condensed materials. The system employs the well-known Doppler effect where the interference fringes of reflected light of a moving target are shifted in proportion to the target velocity. The system originates from the first advancements published in the works by L.M. Baker, E.R. Hollenbach and W.F. Hemsing [1-3] and results in the user-friendly interface and configuration of the VISAR system [4] used in the current work.

VISAR tests are among the mandatory instrumentation techniques when validating material models and establishing predictive capability using Finite-Element (FE) codes and hydrocodes. However, outsourced VISAR testing, where available, is prohibitively expensive due partly to the cost of the VISAR equipment but more so due to the cost of specially trained and experienced operators. Therefore, employment of an in-house VISAR system is beneficial and very economical.

Establishment of a VISAR capability in DSTO will allow the characterisation and analysis of material response to shock loads, including those loads due to warhead blast and fragmentation. This characterisation is of primary importance for the description of material response through constitutive material model refinement. Use of these models in hydrocodes advances the predictive capability. In addition, the VISAR test results can be used for the evaluation of target vulnerabilities and analysis of weapon efficiency.

The present work reports on preliminary tests using the recently commissioned DSTO VISAR system, providing an assessment of the experimental set-up and accuracy of the system installation. The effects associated with high strain rate material response and set-up projectile-target misalignment are analysed with the CTH code [5] using the rate sensitive model recently implemented in CTH [6]. Comparison of the simulation results with the test records from the VISAR system has demonstrated that the system is adequately capturing the material response with nanosecond resolution. These results indicate that the VISAR system is now ready for use in material and weapons effects studies.