Recent instances of the destruction of cultural assets in conflict zones have demonstrated the need to develop methods which will allow for the assessment of damage to heritage stone in the field. In particular, non-destructive methods would be invaluable when working on sites damaged by contemporary ballistics. Permeability (TinyPerm 3) and surface hardness (Equotip) surveys of stone damaged by 7.62 × 39 mm (AK-47) projectiles were undertaken to determine the ability of these methods to identify the spatial distribution of damage patterns such as shear faces and surface fractures. Results demonstrate the ability of surface hardness surveys to distinguish between non-impacted surfaces of the target stone and surfaces which shattered/sheared upon impact. Whilst spatial distribution analysis (“heat mapping”) of Equotip data did not correlate directly with surface fractures, permeability data heat maps were found to be indicative of surface fracture distribution. The data suggests that compaction of the stone matrix at the impact crater results in a lesser reduction of hardness in this area relative to the wider damaged surface. Surveys of impacted stone using the methods outlined here can identify damage patterns that are not visible to the naked eye, thus aiding in damage identification on fragile sites.

The shift of armed conflicts to more urbanised environments has increased the risk to cultural heritage sites. Small arms impacts are ubiquitous in these circumstances, yet the effects and mechanisms of damage caused are not well known. A sandstone target was shot under controlled conditions to investigate surface and subsurface damage. A 3D model of the damaged block, created by structure from motion photogrammetry, shows that internal fracturing was at least as extensive as the visible surface fractures. Backscatter electron imaging of the damaged surface shows a shift from intragranular fracturing and grain size reduction at < 5 mm from the impact point to primarily circumgranular fracturing and grain ‘plucking’ at 20 mm from the impact point. Internal fracture intensity decreased with distance from the centre of the crater. Volumes around the impact point are therefore at greater risk of subsequent weathering deterioration, but significant damage extends to the periphery of the target, rendering whole blocks vulnerable. The surface crater, despite being one of the most conspicuous aspects of conflict damage, has many times less area than internal and surface fractures.

Bullet impacts are a ubiquitous form of damage to the built environment resulting from armed conflicts. Bullet impacts into stone buildings result in surficial cratering, fracturing, and changes to material properties, such as permeability and surface hardness. Controlled experiments into two different sedimentary stones were conducted to characterise surface damage and to investigate the relationship between the impact energy (a function of engagement distance) and crater volumes. Simplified geometries of crater volume using only depth and diameter measurements showed that the volume of a simple cone provides the best approximation (within 5%) to crater volume measured from photogrammetry models. This result suggests a quick and efficient method of estimating crater volumes during field assessments of damage. Impact energy has little consistent effect on crater volume over the engagement distances studied (100–400 m), but different target materials result in an order of magnitude variation in measured crater volumes. Bullet impacts in the experiments are similar in appearance to damage caused by hypervelocity experiments, but crater excavation is driven by momentum transfer to the target rather than a hemispherical shock wave. Therefore in contrast to predictions of impact scaling relationships for hypervelocity experiments, target material plays the dominant role in controlling damage, not projectile energy.

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 3 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 intermediate cartridge (ammunition) were compared: the steel-tipped 5.56 × 45 mm NATO projectile generally produced larger and deeper craters than the 7.62 × 39 mm projectile that is commonly fired from AK-47 rifles, despite having approximately half the mass of the latter. These results characterize 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: for example building stone with low tensile strength is likely to sustain more damage and be at risk of greater deterioration.

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.