ISO/TS 6336-4-2019 pdf free.Calculation of load capacity of spur and helical gears – Part 4: Calculation of tooth flank fracture load capacity. Tooth flank fracture is characterized by a primary fatigue crack in the region of the active contact area. initiated below the surface due to shear stresses caused by the flank contact. Failures due to tooth flank fracture are reported from different industrial gear applications and have also been observed on specially designed test gears for gear running tests (images of tooth flank fractures can be found in Reference I9I) Tooth flank fracture is most often observed on case carburized gears but failures are also known for nitrided and induction hardened gears. Tooth flank fracture is sometimes also referred as subsurface-initiated bending fatigue crack, sub-surface fatigue or tooth flank breakage. The main failure characteristics are: — tooth fracture is due to a crack located in the active flank area, often at approximately half the height of the tooth; — primary crack initiation is at a considerable depth below the surface of the loaded gear flank, typically at or below the case-core interface; — the primary crack starter is often but not always associated with a small non-metallic inclusion; —…