Impact fractures

Foragers occupying Dzombo Shelter, eastern Botswana, and producing a Later Stone Age technology came into
contact with incoming Iron Age food-producers at approximately AD 350. From the onset of their interactions
the Later Stone Age record began to change. One such change was in stone tool preference; over much of southern
Africa scraper frequencies increased whereas backed tools declined. However, between c. AD 900 and 1200 at
Dzombo, backed tools inexplicably dominate the formal tool assemblage. This paper seeks to understand the role
of backed tools at Dzombo from before the arrival of farmers until the establishment of the Mapungubwe state, c.
AD 1220, in order to explain shifts in use and preference patterns. By performing a macro-fracture analysis it was
possible to demonstrate an increased occurrence of fractures consistent with impact-related damage between
approximately AD 350 and 1200, and it is suggested here that during this time hunting activities were intensified.
The factors possibly driving this intensification are discussed and could relate to forager–farmer interactions or a
shift in the site's function. As is shown, the former is more likely. The macro-analysis of backed tools provides
greater clarity when viewing Dzombo's archaeological sequence and to some extent confirms earlier suggestions
that in order to augment growing mercantile opportunities spurred on by the arrival of farmers, forager hunting
activities increased.

Understanding the mechanism for brittle material removal via solid particle impact is important for various areas such as energy and aerospace industries. The existing analytical formulation of erosion damage, consistent with indentation fracture theory, overestimates actual erosion by over 200%. This study complements an existing analysis by prescribing a realistic shape and mechanical properties to the impinging particle. We quantitatively show that a lateral crack in glass does not nucleate at the indenter's tip or the theoretical plastic depth, but at an intermediate depth. This depth can be found by implementing the actual particle penetration depth into Hill's ratio. Several new geometries of the particle's impacting tip are proposed as ways to achieve adequate particle penetration depth instead of an expanding hemispherical cavity. The crater depth, surface roughness, and erosion efficiency of borosilicate glass are predicted with 10%, 24%, and 23% error, respectively, using a simple analytical routine.

In the last few decades, zooarchaeological studies have demonstrated beyond doubt that the hunting abilities of hominins were quite formidable from quite early on. Unfortunately, direct evidence for the use of weapons in hunting is quite rare and depends heavily on the preservation of organic elements. In particular, in the absence of such evidence, it is notoriously difficult to pinpoint the first appearance of complex, mechanically-assisted projectiles (such as darts and arrows) in the archaeological record. In this chapter, we present data from a controlled ballistic experiment with the aim of establishing patterns in the formation of impact fractures that would allow for the discrimination of thrusting spears, (hand-thrown) javelins, and spearthrower darts and arrows. By controlling for the weapon tip shape, weight, and raw material, impact angle (IA), as well as target composition, we are able to focus on the key elements that separate the different launching systems: velocity and kinetic energy output. The results show that fracture scar length is proportional to kinetic energy at impact, but only if the impact is perpendicular, as acute IAs reduce the energy requirements for the production of large, typical impact fractures. We also confirm previous results of Hutchings (JAS 38:1737–1746, 2011) regarding the relationship between precursory loading rate and fracture propagation speed, documenting a weak linear relationship between the two in our sample. We conclude by discussing the implications of this study for identifying different weapon armatures in the archaeological record.