User:FuzzyMagma/Cold dwell fatigue

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Cold dwell fatigue is a phenomenon that occurs in certain materials, particularly titanium-based alloys, under cyclic loading where the maximum tensile load is maintained for a given duration, resulting in a reduction in fatigue life by a decade or more compared to conventional fatigue without the hold period. This reduction in fatigue life is referred to as the "dwell debit". The formation of facets, which are always associated with the failure initiation site, is considered fundamental to cold dwell fatigue. A commonly utilized model for facet nucleation is an adaptation of the classical Stroh model for crack initiation due to dislocation pile-up.

French investigators traced the serious engine failure involving an Air France Airbus A380 over Greenland to a phenomenon known as "cold dwell" fatigue. The failure was caused by a fan hub disintegration, which had resulted from cold dwell fatigue. The stress holds at moderate temperatures led to substantial reductions in cyclic life and were implicated in the service failures.

It has been about 50 years since the discovery that titanium alloys were susceptible to cold dwell fatigue, following two in-service failures of the Rolls Royce RB211 engine. Since then, a plethora of academic, industrial, and government research has been performed to understand the major factors influencing cold dwell fatigue.

Facets formation is considered fundamental to cold dwell fatigue, and it is always associated with the failure initiation site. The commonly utilized model for facet nucleation is an adaptation of the classical Stroh model for crack initiation due to dislocation pile-up introduced by Evans and Bache.

In the linear cumulative damage rule, when D C was calculated using the time exhaustion rule, the creep-fatigue damage was organized by the inequality D Total = (D F, D C) ≤ (0.1, 10 −6). The phenomenon of cold dwell fatigue can occur under cyclic loading at room temperature and remains pronounced at 120°C but fades out above 200°C.

In summary, cold dwell fatigue is a phenomenon that occurs in certain materials, particularly titanium-based alloys, under cyclic loading, resulting in a reduction in fatigue life by a decade or more compared to conventional fatigue without the hold period. The phenomenon was implicated in the service failures of the Rolls Royce RB211 engine and the Air France Airbus A380 over Greenland. Research has been conducted to understand the major factors influencing cold dwell fatigue. The commonly utilized model for facet nucleation is an adaptation of the classical Stroh model for crack initiation due to dislocation pile-up. The stress sensitivity of the cold dwell fatigue test was higher than that of the low cycle fatigue test. The phenomenon is called "cold" dwell fatigue as it is prevalent at room temperature and remains pronounced at 120°C but fades out above 200°C.