Intrinsic Fatigue Limit and the Minimum Fatigue Crack Growth Threshold

Abstract

In the field of long-life fatigue, predicting fatigue lives and limits for mechanical components is crucial for ensuring reliability and safety. Fracture mechanics tools have enabled the estimation of fatigue lives for components with small cracks or defects. However, when dealing with defects larger than the microstructural characteristic size, estimating the fatigue resistance of a material requires determining the cyclic resistance curve for the defect-free matrix, which depends on knowledge of the material’s intrinsic fatigue limit. This study focuses on the experimental evidence regarding the intrinsic fatigue limit and its correlation with naturally nucleated non-propagating cracks. Fracture mechanics models for small crack propagation are introduced, and their disparities and limitations are analyzed. The concept of intrinsic fatigue limit is then introduced and applied to reanalyze a recent publication. Methods for estimating the intrinsic fatigue limit are explored and applied to experimental results reported in the literature. The need to clarify and accurately predict the intrinsic fatigue limit is highlighted in alloys where the processing generates defects larger than the microstructural size of the matrix, as often observed in materials and components produced using additive manufacturing.

Structural Design and Analysis of Large-Diameter D30 Conical Polycrystal Diamond Compact (PDC) Teeth under Engineering Rotary Mining Conditions

“…In the process of rotary excavation, conical tooth cracking, chipping, and crushing are the main forms of conical PDC tooth failure; the cause of workpiece cracking is largely determined by its material properties and is closely related to the microstructure of the material. Due to the microstructure of polycrystalline diamond being face-centered cubic stacking, the structure is stable, and the PDC layer has a high level of hardness and brittleness, which is prone to brittle fracture under a large impact load [30][31][32]. Figure 11 shows the load-deformation relationship graphs for different fracture modes; brittle fractures occurs when the load reaches the maximum value that the material can withstand to reach the destabilizing fracture point, followed by the instantaneous fracture and failure of the workpiece.…”

“…stacking, the structure is stable, and the PDC layer has a high level of hardness and brittleness, which is prone to brittle fracture under a large impact load [30][31][32]. Figure 11 shows the load-deformation relationship graphs for different fracture modes; brittle fractures occurs when the load reaches the maximum value that the material can withstand to reach the destabilizing fracture point, followed by the instantaneous fracture and failure of the workpiece.…”