Hackle Marks
Definition
Ridges on the fracture surface oriented perpendicular to the crack propagation direction; they appear in the mist and hackle zones at higher crack velocities and provide a local direction-of-propagation vector.
- Definition
- Ridges perpendicular to crack propagation direction
- Zone
- Appear in mist and hackle zones at higher crack velocities
- Use
- Local direction-of-propagation vector
Common questions
How do hackle marks differ from hackle lines?+
Hackle marks and hackle lines describe closely related ridge features on a fracture surface, both perpendicular to crack travel, but hackle marks specifically appear at the higher-velocity mist and hackle zones of the break, distinguishing the terminal, fast-fracturing region from the slower initial crack path.
Why does crack velocity change the appearance of the fracture surface?+
As a crack accelerates it branches and interacts with more microscopic stress variations in the glass, producing progressively rougher texture, from a smooth mirror zone near the origin through a hazy mist zone to a coarse hackle zone, which lets examiners estimate how far along the crack's path a given point lies.
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...
- 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...
- 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...