Surface damage from perpendicular and oblique bullet impacts in stone

Abstract

Controlled experiments were conducted to investigate the surface damage caused by perpendicular and oblique impacts of bullets into sandstone and limestone targets. Individual bullets fired in conditions simulating modern rifles at typical combat distances excavated craters with diameters from 22 to 74 mm and depths from 4 to 24 mm. Limestone target craters were up to twice as large and deep as those in sandstone. These craters have a complex shape consisting of a central excavation surrounded by a shallow dish, compared to the simple bowl shape of most sandstone impacts. Radial fractures extending to the edge of the target block were common in limestone targets. Impacts at an angle of 45° to the surface in both rock types result in asymmetric craters. Two common types of ammunition were compared: the steel-tipped NATO projectile generally produced larger and deeper craters than the projectile that is commonly fired from AK-47 rifles, despite having approximately half the mass of the latter. These results characterise the sort of damage that can be expected at many sites of cultural significance involved in contemporary conflict zones, and have important implications for their conservation.

Measuring crater volumes from bullet impacts: implications for field methods and cratering mechanics

“…Kenkmann et al 43 Target lithology is a bigger determining factor of final crater volume than impact energy, despite the scatter observed here (see Fig. 6) 15 . This could be used in conjunction with knowledge of heritage construction materials to prioritise post-conflict efforts on weaker materials.…”

“…Measurements of depth and diameter are possible with simple analogue tools such as calipers and depth gauges. Although this study took a digital approach to these measurements, it is unlikely the substitution with analogue values will affect the overall conclusions, as Campbell et al 15 show reasonable agreement between analogue crater profiles obtained using a Barton comb and profiles measured from photogrammetry models. Volumes can be estimated in the field with the simplified geometry, providing an overview of crater volume distribution while investigators are on site, supporting first-response assessments of conflict damage to heritage.…”

“…Therefore care should therefore be taken when estimating the volume of craters with higher depth/diameter ratios. This method has been developed for impact craters with good rotational symmetry (created by perpendicular impacts), and it is uncertain whether it can be applied to asymmetric craters generated by some impacts at oblique trajectories 15 .…”

“…For heritage affected by armed conflict, the capture of adequate digital imagery for representative 3D models may not be possible in all situations, so alternative methods must be used. Campbell et al 15 compared crater profiles measured manually using a Barton comb with profiles extracted from a 3D model. This study investigates a simpler approach: can crater volumes be estimated using just depth and diameter measurements and simplified volume geometries?…”

Subsurface fracturing of sedimentary stones caused by bullet impacts

“…The sandstone sample (SRS_09) has a shallow, bowl shaped crater with an area equivalent diameter of 40 mm and a maximum depth of 5.1 mm (24). 20 mm directly below the crater floor is an open (<1.5 mm) fracture that is 16 mm in length, but does not reach the edge of the section (Figure 3a).…”