Mean Stress Effects on the High Cycle Fatigue Limit Stress in Ti-6Al-4V

2008 ◽  
pp. 476-476-17 ◽  
Author(s):  
T Nicholas ◽  
DC Maxwell
Keyword(s):  
Fatigue Limit ◽  
High Cycle Fatigue ◽  
Mean Stress ◽  
Cycle Fatigue ◽  
Stress Effects ◽  
Limit Stress

Influence of Mean Stress on the Fatigue Behavior of 304L SS in Air and PWR Water

2005 ◽  
Author(s):  
H. D. Solomon ◽  
C. Amzallag ◽  
A. J. Vallee ◽  
R. E. De Lair
Keyword(s):  
Fatigue Limit ◽  
Fatigue Behavior ◽  
Secondary Hardening ◽  
304L Stainless Steel ◽  
Mean Stress ◽  
Cycle Fatigue ◽  
Different Temperatures ◽  
Limit Stress ◽  
Conventional Models ◽  
Stress Models

Load-controlled experiments on 304L stainless steel were run in Air and PWR water, at 150°C and 300°C, with and without a mean stress of 100MPa. These experiments were run to determine the influence of temperature, environment, and mean stress on the 107 Cycle Fatigue Limit stress amplitude. A 100MPa mean stress was found to have different effects at the different temperatures and environments. In contrast to all the conventional models used to describe the effects of mean stress, when the testing was done at 300°C (for both air and PWR water), a 100MPa mean stress was found to raise the 107 Cycle Fatigue Limit relative to that observed without a mean stress. This was ascribed to the effect of the hardening due to the initial straining and to secondary hardening, both of which are more pronounced at 300°C than at 150°C. The increased initial and secondary hardening resulted in the development of less non-elastic strain, thereby improving the fatigue behavior. In PWR water at 150°C, a 100MPa mean stress reduced the 107 Cycle Fatigue Limit by more than that predicted by conventional mean stress models, but in air at 150°C, the decrease in the endurance limit was more in keeping with the predictions of these models. This difference was ascribed to the effect of the PWR water, in the absence of significant initial straining and secondary hardening.

scholarly journals High-Cycle Fatigue Behaviour of Pure Tantalum under Multiaxial and Variable Amplitude Loadings

2014 ◽  
Vol 891-892 ◽  
pp. 1341-1346
Author(s):  
David Marechal ◽  
Nicolas Saintier ◽  
Thierry Palin-Luc ◽  
François Nadal
Keyword(s):  
High Cycle Fatigue ◽  
Fatigue Behaviour ◽  
Fracture Mechanisms ◽  
Mean Stress ◽  
Cycle Fatigue ◽  
Stress Effects ◽  
Military Applications ◽  
Stress Damage ◽  
Damage Rule ◽  
Pure Tantalum

Due to its specific mechanical properties, tantalum is often used in strength-demanding military applications. High-cycle fatigue (HCF) behaviour of pure tantalum, however, has been rarely reported and the mechanisms at stake to account for deformation under cyclic loadings are still badly understood. This paper aims at better understanding the fatigue behaviour of tantalum and at clarifying the mechanisms of damage formation encountered under such loadings. HCF experiments performed at room temperature on commercially-pure tantalum are presented. Mean stress effects were investigated in the aim of clarifying the interaction between fatigue and creep. Fracture mechanisms were observed to vary from intergranular to transgranular depending on applied stress amplitude and mean stress. Damage mechanisms were investigated under tension and torsion. Results are analyzed in the light of existing fatigue criteria, the limitations of which are discussed. Finally, complex sequential loadings, representative of in-service loadings, were applied to tantalum smooth specimens. The contribution of each loading sequence to the overall damage was quantified and analyzed in terms of linear or non-linear cumulative damage rule.

Safety Factor in Fatigue Under Fluctuating Stresses

1987 ◽  
Vol 109 (4) ◽  
pp. 397-401 ◽  
Author(s):  
V. A. Avakov
Keyword(s):  
Safety Factor ◽  
High Cycle Fatigue ◽  
Stress Amplitude ◽  
Static Strength ◽  
Mean Stress ◽  
Cycle Fatigue ◽  
Safety Factors ◽  
Generalize Expression ◽  
Allowable Stresses ◽  
Number Of Cycles

It is common to assume identical allowable safety factors in static strength [m], defined by mean stress (Sm), and in fatigue [a], defined by stress amplitude (Sa), in order to find the full safety factor (F) under asymmetrical cycles, or to plot any type of the Sm–Sa diagram of allowable stresses. Here additional modification is considered to generalize expression of the full factor of safety in fatigue under asymmetrical stresses, utilizing unequal allowable safety factors in static strength (by mean stress) and in fatigue (by stress amplitude): ([a] ≠ [m]). We assume that loading is stationary, and cumulated number of cycles is large enough to consider high cycle fatigue.

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