Blast Quantification Using Hopkinson Pressure Bars

Near-field blast load measurement presents an issue to many sensor types as they must endure very aggressive environments and be able to measure pressures up to many hundreds of megapascals. In this respect the simplicity of the Hopkinson pressure bar has a major advantage in that while the measurement end of the Hopkinson bar can endure and be exposed to harsh conditions, the strain gauge mounted to the bar can be affixed some distance away. This allows protective housings to be utilized which protect the strain gauge but do not interfere with the measurement acquisition. The use of an array of pressure bars allows the pressure-time histories at discrete known points to be measured. This article also describes the interpolation routine used to derive pressure-time histories at un-instrumented locations on the plane of interest. Currently the technique has been used to measure loading from high explosives in free air and buried shallowly in various soils

Deformation of Armox 440T plates subject to buried explosive charge detonations: A benchmark for appliqué systems

Loading of vehicle undercarriages from the detonation of shallow-buried explosives remains a serious threat to life in conflict and post-conflict zones. One method to protect lightly-armoured vehicles is to retrofit them with appliqué armour, which must be strong enough to provide adequate protection, but light enough to maintain vehicle manoeuvrability. A key performance metric of this armour is its deformation under loading, which must be limited to avoid impact upon vehicle occupants. The high-strength steel Armox 440T is commonly used due to its high load capacity, strength-to-weight ratio, ductility and low cost: as other protection systems are developed, it would be of great benefit to compare their deformation against an Armox 440T benchmark. However, no definitive benchmarking study has been published to date, mainly due to the difficulties in ensuring repeatable loading from complex buried detonations. This paper presents experiments which underpin such a benchmarking study, building on the authors’ previous work to establish a methodology which produces very consistent loading from shallow-buried detonations. Tests were conducted with a range of explosive masses and plate thicknesses, with target plates secured in a purpose-designed frame to produce simple, consistent boundary conditions. Plate deformations captured by stereo high-speed digital image correlation were compared to a commonly-used low-cost peak deflection method. High-speed digital image correlation was found to make highly reproducible displacement measurements with a standard deviation of 2% of the mean. The low-cost method provided slightly higher variability up to 5% of the mean value, and measurements of peak deformation were systematically 20% higher, but in a consistent manner, with a low unit cost and without risk to expensive test equipment. The low-cost method therefore allowed the development of a multivariate regression relationship between deformation, charge size and plate thickness, which provides a benchmark for the assessment of future protection solutions