Fracture Termination Rule
Definition
The principle that a propagating crack terminates when it encounters a free surface created by a pre-existing crack; at any T-junction, the crack forming the stem arrived after the crack forming the crossbar.
- Applies to
- Glass fracture sequencing
- Principle
- A crack stops at a pre-existing crack's free surface
- Reveals
- Which of two impacts happened first
- Also called
- Radial/concentric crack intersection rule
Common questions
How does the fracture termination rule help determine the sequence of two separate gunshots through the same window?+
At the T-junction where two crack systems meet, the crack that terminates against the other must have formed after it, since a propagating crack cannot cross a surface that no longer exists as continuous material, so examiners trace which cracks stop at which junctions to order multiple impacts.
Does the fracture termination rule work the same way for both radial and concentric cracks?+
Yes, the underlying physical principle is the same regardless of crack type: whichever crack was already present creates the free surface, so any later crack reaching that point will terminate against it, whether the intersecting cracks are radial, concentric, or a mix of both.
Can this rule be applied to fractured materials other than glass?+
The same free-surface termination logic applies to other brittle materials that fracture in a similarly predictable way, such as certain ceramics and ballistic-grade acrylics, though glass is the material most commonly encountered and studied in casework.
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...
- Cone Fracture
- A conical crack produced by concentrated contact loading (Hertzian contact), opening on the far (exit) face of the glass; the cone geometry...
- 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...
- 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...