Stress Intensity Range (ΔK)
Definition
The difference between the maximum and minimum stress intensity factor in one loading cycle, ΔK = K_max - K_min. The Paris law describes crack growth rate da/dN as proportional to ΔK to a power m, typically 2 to 4 for structural metals.
- Formula
- delta K = K max minus K min
- Governing law
- Paris law
- Typical exponent m
- 2 to 4 for structural metals
- Predicts
- Fatigue crack growth rate, da/dN
Common questions
How does delta K relate to beach marks seen on a fracture surface?+
Each loading cycle advances the crack by an increment governed by delta K, and variations in loading history over time leave the macroscopic beach marks visible to the eye, while individual cycles leave the finer striations seen under a microscope.
Why is the Paris law exponent m relevant to a forensic timeline?+
Because growth rate scales with delta K raised to the power m, small changes in operating stress produce large changes in how quickly a crack advances, which lets an analyst estimate how long a part had been cracking before final 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...
- Multi-Site Damage (MSD)
- The simultaneous presence of fatigue cracks at multiple adjacent fastener holes or structural features, characteristic of ageing aircraft fuselage and other riveted...
- Ratchet Marks
- Radial steps or ridges on a fatigue fracture surface separating adjacent regions that initiated from separate sites. They run from the component...