Cone Fracture
Definition
A conical crack produced by concentrated contact loading (Hertzian contact), opening on the far (exit) face of the glass; the cone geometry allows entry/exit determination in bullet-penetration and blunt-object impact cases.
- Cause
- Hertzian contact loading
- Shape
- Conical crack
- Opens on
- Far (exit) face
- Use
- Bullet-penetration and blunt-object entry/exit determination
Common questions
How does the cone geometry actually reveal which side a projectile entered from?+
The cone typically has its apex at the near (impact/entry) surface and widens as it opens outward on the far (exit) surface, so identifying the narrow versus wide face of the cone in a recovered fragment tells the examiner which side the force originated from, complementing radial and concentric crack analysis on the same pane.
Does a cone fracture form for any impact, or only under specific loading conditions?+
Cone fractures are characteristic of concentrated, localised contact loading such as a projectile or a sharp point, described by Hertzian contact mechanics. A broad, diffuse impact such as a hand or a flat object is more likely to produce the more familiar radial and concentric crack pattern without a distinct cone.
Related terms
- 3R Rule
- The fracture-analysis mnemonic: Radial cracks form at Right angles to the Reverse (far, non-impact) side of the glass. Applied to the fracture...
- Bayesian Likelihood Ratio (LR)
- The statistical framework that evaluates glass-fragment evidence by comparing the probability of the observed fragment population assuming contact with the source glass...
- Concentric Cracks
- Approximately circular cracks centred on the impact point; they form second, on the near (impact) face, and terminate when they encounter pre-existing...
- Entrance Bevelling
- The widening of a bullet-penetration hole toward the exit side, analogous to bevelling in bone wounds; the narrower opening is on the...
- Fracture Termination Rule
- The principle that a propagating crack terminates when it encounters a free surface created by a pre-existing crack; at any T-junction, the...
- Hackle Marks
- Ridges on the fracture surface oriented perpendicular to the crack propagation direction; they appear in the mist and hackle zones at higher...
- Mirror Region
- The smooth, flat area of a fracture surface nearest the crack origin, where the crack was propagating slowly and stably before accelerating...
- Mist Region
- The transitional fracture surface zone between the smooth mirror region and the rough hackle region, where the crack begins to bifurcate at...
- Radial Cracks
- Cracks extending outward from an impact point in approximately straight lines, like spokes on a wheel; they form first, on the rear...
- Secondary Transfer
- The movement of a glass fragment from a primary surface (which contacted the broken glass) to a secondary surface (which contacted the...
- Wallner Lines
- Rib-shaped features on a glass fracture surface produced by the interaction of the propagating crack front with reflected elastic stress waves; their...