TNO's Ballistic Laboratory is provided with a bunker in which up to 25kg of explosives can be detonated. This allows indoor trials on small vehicles against even AT mines. In addition, a test set-up for the testing of mines against bottom plates is available.
For experimental studies on the impact of blast waves on flat plates, two blast simulators, in which well-reproducible blast waves can be generated, are available at TNO-PML:
- Large blast simulator of 60m length and 2m end-diameter. This facility is driven by an explosive gaseous acetylene-oxygen mixture. This facility is particularly suited to test 2-D structures, like bottomplates, that can be mounted to the end-section. Blast waves with peak overpressures of up to 60kPa incident pressure and of 30ns duration can be generated.
- Small blast simulator of 22m length and with a test section of 40x40cm2. This shock tube is driven by compressed air. At the test section blast waves with peak overpressure levels of 120kPa incident pressure can be generated. The test section is provided with optical glass to allow access to the test section for visualisation of the shock-wave structure interaction.
Vehicle test rig
Together with DERA Chertsey, TNO PML is conducting a collaborative effort to develop both experimental and modelling tools which can be directly applied to the improvement of armoured fighting vehicle landmine protection and resistance. In particular, a better understanding of the prime local damage mechanisms and subsequent response of vehicle components during a mine attack is required. Within this project an experimental tool based on a versatile engineered test rig will be developed which provides a cost-effective method for gathering data. The test rig must be realistic in size and be capable of incorporating different geometrys (bottomplates, side-walls, wheel bay and welded joints) associated with both tracked and wheeled armoured fighting vehicles. It should also be robust so as to permit testing of components against realistic mine threats. In addition, modelling tools like the hydrocode LS DYNA will be used to accurately simulate tests performed using the experimental tool.
At TNO-PML standard measurement equipment is available, like:
- Pressure transducers; e.g. to measure the blast loading on structures and people;
- Strain gauges; e.g. to measure the deformation of structures;
- Laser displacement gauges; e.g. to measure the deformation and velocity of structures;
- Recording equipment (e.g. video, flash X-ray, Imacon High Speed Camera) to record the deformation and damage of structures.
Witness plates of various material and thickness are available to measure penetration by mine fragments to obtain an indication of human vulnerability. Also various human dummies, varying from simple wooden dummies to more sophisticated instrumented dummies, e.g. the Hybrid III crash dummy, are available.
Since 1997 at TNO-PML a new measuring device is being developed for measuring the combined blast and fragment loading close to a detonating warhead, e.g. a mine. Conventional measuring devices like pressure transducers are usually damaged as a result of the impacting fragments. The objective of the current study is to develop a more robust device to measure the combined blast/fragment impulse loading. The device should be small and easy transportable and must be versatile so it can be easily built into different set-ups.
It was decided to design the new device based on the principle of a so-called "Impulse Plug". This device consists of a plug, which is launched through a tube when it is hit by the combined impulse load of the blast wave and of the impacting fragments. The front of the plug is made out of a protecting material, which captures the fragments. The mass of these fragments can be measured afterwards. Based on the conservation of momentum law, with such an impulse plug, the impulse of the blast wave and the average velocity of the fragments can be determined. This requires the measurement of the mass of the plug prior to the test, the velocity of the plug during the movement through the tube, the cross surface of the plug and the mass of the impacting fragments. Validation tests are currently ongoing (van Wees, 1998).
In determining the effectiveness of clearing techniques, the characteristics of the ground in which the mine is buried will be of great importance. Therefore, it is important to report the characteristics of the ground in the test report. The ground parameters of importance for each individual clearing technique, like soil density, moisture, thermal conductivity, thermal capacity, sonic speed, will be identified.