Fracture Behavior and Mechanical Characterization of Obsidian: Naturally Occurring Glass

Abstract

Obsidian is a natural glass of volcanic origin that is formed by the rapid cooling of viscous lava. Obsidian is commonly assumed to possess a fracture behavior identical to that of artificial glass. This study is specially concerned with mechanical properties and fracture behavior of obsidian. Nanoindentation techniques are used to study the hardness, modulus and fracture behavior of obsidian in comparison to some reference material samples. The indentation results indicated that obsidians mechanical properties are better than anecdotally accepted values for obsidian. When compared to artificial glasses, such as fused quartz and soda lime glass, the crack propagation threshold of obsidians are higher. Analytical methods such as XRD, SEM and EDS are used in order to discover distinctive structural features of obsidian. The strength of obsidian samples is measured by ring-on-ring(RoR) test. The RoR configuration is the most acceptable form associated with an ASTM standard that provides the maximum area under a constant maximum stress. One of the primary areas focus of this investigation is the determination of the fracture toughness of obsidian. Therefore, single edge V notched beam (SEVNB) method is used to find the fracture toughness value of obsidian. Specially made diamond slicing wheel is used to machine the V notch. The SEVNB specimens are loaded in three point bend flexure to the point of failure and the peak load is used to determine the fracture toughness. Further study on mechanical properties of obsidian may lead to new findings useful for various fields of material development. However, due to extreme complexity of mechanisms of formation and complicated obsidian structure, the further research needs cross-disciplinary efforts.