Artificial Current Component A lightning strike tests were performed on three different types of composite panels. Panels of type A were not equipped with lightning strike protection; panels of types B and C were protected against lightning strike with two different types of copper mesh. The measured back surface velocity of the panels seems to be proportional to the peak current normalized with the panel weight. Post-test inspections revealed extended delamination inside panels of type A. For panels of types B and C no delamination was found. Panels of type B and C showed characteristic circular smuts on the impacted surface as well as diamond shaped evaporation of the copper mesh. For panels of type B, the dimensions of the copper evaporation were significantly larger than for panels of type C. it was also found that the orientation of the evaporation zone seems to be related to the geometry of the copper mesh. Multi-physical simulations considering the electro-explosion of the copper mesh were carried out in order to assess if the shape and extent of the evaporation zone could be traced back to electro-explosion of the copper mesh. The predicted damage correlates well with the inner damage zone, but is not able to reproduce the full amount of copper evaporation.

In the present study we introduce an innovative method for the measurement of impact-induced pressure waves within geological materials. Impact experiments on dry and water-saturated sandstone targets were conducted at a velocity of 4600 m/s using 12 mm steel projectiles to investigate amplitudes, decay behavior, and speed of the waves propagating through the target material. For this purpose a special kind of piezoresistive sensor capable of recording transient stress pulses within solid brittle materials was developed and calibrated using a Split-Hopkinson pressure bar. Experimental impact parameters (projectile size and speed) were kept constant and yielded reproducible signal curves in terms of rise time and peak amplitudes. Pressure amplitudes decreased by 3 orders of magnitude within the first 250 mm (i.e., 42 projectile radii). The attenuation for water-saturated sandstone is higher compared to dry sandstone which is attributed to dissipation effects caused by relative motion between bulk material and interstitial water. The proportion of the impact energy radiated as seismic energy (seismic efficiency) is in the order of 10 À3 . The present study shows the feasibility of real-time measurements of waves caused by hypervelocity impacts on geological materials. Experiments of this kind lead to a better understanding of the processes in the crater subsurface during a hypervelocity impact.

No abstract

No abstract

This paper reports on a new gauge for blast impulse determination close to explosive charges. The gauge is based on the autonomous data recorder g-rec developed at the Ernst-Mach-Institute for data acquisition in harsh environments. Combined with an acceleration sensor these data recorders allow for the direct determination of the momentum transferred to an object by a blast wave even in the immediate vicinity of the explosive charge. From this the blast impulse can be determined. Using autonomous electronics distinct advantages are gained compared to classical passive momentum traps. The paper summarizes the properties of the g-rec recorder and describes the setup of the autonomous momentum trap in detail. Numerical simulations are presented which illustrate the gauge performance and its limitations. Tests with 1 kg charges demonstrate the feasibility of the approach. Good agreement was found between simulations and tests. The application range of the gauges is determined by the measurement range of the built-in acceleration sensor and its overall dimensions and weight. The present configuration is designed for distances between ∼0.3 and 1 m from charges between several 100 g and several kilograms. Data were successfully collected down to reduced distances of 0.25 m/kg1/3. Minor changes in gauge dimensions, weight, or measurement range enable the gauges to be deployed at even closer distances