Concentric Crack
Definition
A crack that runs in roughly circular arcs around the point of impact, joining radial cracks. The 4C rule applies: Concentric cracks have ridges on the same side as the Cause of force.
- Shape
- Roughly circular arcs around impact point
- Joins
- Radial cracks
- Governing rule
- 4C rule
- Ridge orientation
- Same side as the cause of force
Common questions
How does an examiner use the ridge orientation on a concentric crack to determine which side the force came from?+
The 4C rule links ridge direction on the crack edge to the side struck: ridges on a concentric crack face the side the force originated from. By examining the fracture edge under raking light or magnification, an examiner reads the ridge pattern to establish the direction of impact without needing to see the impact itself.
Do concentric cracks always form together with radial cracks, or can they occur alone?+
Concentric cracks typically form after radial cracks have already propagated outward from the impact point, and they terminate where they meet an existing radial crack rather than crossing it. A glass fracture showing only concentric cracks with no radial cracks is unusual and would prompt closer scrutiny of the loading conditions.
Related terms
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- Radial Crack
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- Wallner Lines and Hackle Marks
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