Hackle Lines
Definition
Fine secondary cracks on the fracture surface that fan from the origin, perpendicular to the moving crack front. Used to track crack direction.
- Definition
- Fine secondary cracks fanning from the fracture origin
- Orientation
- Perpendicular to the moving crack front
- Use
- Tracks crack propagation direction
Common questions
How do hackle lines help reconstruct which side of a glass pane was struck?+
Hackle lines point back toward the origin of the crack as it fans outward, so by tracing their orientation on a fracture edge an examiner can determine which direction the crack was travelling and, combined with rib and conchoidal markings, infer the point and side of impact.
Are hackle lines visible on every type of fracture?+
They are most distinct on fractures that propagated at higher speed or under greater stress, since the fanning secondary cracks are a product of the energy released during rapid crack growth. Slow, low-stress cracks may show fewer or less-defined hackle lines.
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...
- Concentric Fracture
- An arc-shaped fracture encircling the impact zone, produced by outer-table bending tension at a distance from the focal impact; always post-dates the...
- GRIM-3
- Glass Refractive Index Measurement, third-generation instrument by Foster + Freeman (UK); an automated phase-contrast hot-stage system that identifies the RI match point...
- PDQ
- Paint Data Query database (RCMP-maintained). Cross-referenced from glass work when a vehicle is identified through paired glass and paint evidence.
- Radial Fracture
- Cracks that run outward from the point of impact like spokes on a wheel. Form first, on the side opposite the force.