Multi-Site Damage (MSD)
Definition
The simultaneous presence of fatigue cracks at multiple adjacent fastener holes or structural features, characteristic of ageing aircraft fuselage and other riveted structures. MSD leads to rapid link-up and catastrophic failure once one crack bridges the gap between neighbours.
- Definition
- Simultaneous fatigue cracks at adjacent fastener holes
- Typical context
- Ageing riveted aircraft fuselage
- Failure mechanism
- Rapid crack link-up between neighbouring holes
- Outcome
- Catastrophic structural failure
Common questions
Why is MSD harder to catch than a single fatigue crack?+
Individually each crack may be below the size that standard inspection intervals are designed to detect, but once several small cracks at neighbouring holes link up their combined length can trigger failure well before any single crack would have.
How does MSD change how investigators interpret fracture surfaces?+
Investigators look for evidence of crack initiation at multiple, separate fastener holes rather than a single origin, since finding several independent origin sites is the physical signature that distinguishes MSD from an ordinary isolated fatigue failure.
Related terms
- Beach Marks
- Macroscopic curved bands on a fatigue fracture surface, visible without magnification, produced by changes in crack growth rate during service (load changes,...
- Fatigue Fracture
- Fracture resulting from repeated cyclic loading, typically at stresses below the static yield strength. The fracture surface has characteristic markings (beach marks,...
- Fatigue Striations
- Microscopic parallel marks on a fatigue fracture surface, formed during individual loading cycles in Stage II crack growth. Visible by SEM at...
- Ratchet Marks
- Radial steps or ridges on a fatigue fracture surface separating adjacent regions that initiated from separate sites. They run from the component...
- Stress Intensity Range (ΔK)
- The difference between the maximum and minimum stress intensity factor in one loading cycle, ΔK = K_max - K_min. The Paris law...