Abstract
To travel safely behind screens that can protect us from stones and hail, we must understand the response of glass to impact. However, without a means to observe the mechanisms that fail different silicate architectures, engineering has relied on external sensors, post-impact examination and best-guess to glaze our vehicles. We have used single and multi-bunch, X-ray imaging to differentiate distinct phases of failure in two silicates. We identified distinct micromechanisms, operating in tandem and leading to failure in borosilicate glass and Z-cut quartz. A surface zone in the amorphous glass densifies before bulk fracture occurs and then fails the block, whilst in quartz, fast cracks, driven down cleavage planes, fails the bulk. Varying the rate at which ejecta escapes by using different indenter tip geometries controls the failed target’s bulk strength. This opens the way to more physically based constitutive descriptions for the glasses allowing design of safer, composite panels by controlling the impulses felt by protective screens.
Highlights
To travel safely behind screens that can protect us from stones and hail, we must understand the response of glass to impact
When forces acting on an amorphous material exceed its strength, fracture generally initiates at a flaw to define the end of elastic behaviour[6]
An interesting result is that the failure initiation is further retarded in borosilicate glass in these experiments[19]
Summary
To travel safely behind screens that can protect us from stones and hail, we must understand the response of glass to impact. Inelastic processes start when failure is initiated on the loaded surface of the material where residual stress concentrations are typically concentrated[7] At this time, cracks propagate at a speed determined by the stress level, and these may accelerate to a limit which peaks at the Rayleigh wave speed in the material[8,9,10]. Using monochromatic X rays allows the density of www.nature.com/scientificreports structure within failing zones to be resolved These processes are typically simulated with empirical descriptions within finite element codes that degrade the macroscopic strength in their constitutive models for brittle solids[28,29]. Kolsky bar loading, and an adapted three-point bend test, were used to drive cracks into silicates and boron carbide These results relate single fractures to bulk stress intensity factors, illustrating the limitations of applying a macroscopic engineering parameter to local failures. X rays allow observation of operating mechanisms in the critical first moments of compression before penetration begins
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