Parameter for Correspondence Between Notched and Unnotched Specimens' Fatigue Data : (Part 6) Interpretation of Notch Effect Based on the Equivalent Stress Ratio

2004 ◽  
Vol 2004 (0) ◽  
pp. 15-16
Author(s):  
Hiroshi MATSUNO ◽  
Yoshihiko MUKAI
Keyword(s):  
Stress Ratio ◽  
Equivalent Stress ◽  
Notch Effect ◽  
Fatigue Data

Modeling of Fatigue Slip Bands and Application to Notch Fatigue Problems

2008 ◽  
Author(s):  
Hiroshi Matsuno
Keyword(s):  
Fatigue Strength ◽  
Slip Band ◽  
Equivalent Stress ◽  
Cyclic Stress ◽  
Empirical Equations ◽  
Fundamental Idea ◽  
Slip Bands ◽  
Heat Treated ◽  
Fatigue Data ◽  
Stress Ratios

In the present paper, equivalent stress ratios (REQ-ratios), which have been proposed as parameters for correspondence between cyclic stress conditions of notched and unnotched specimens, are reviewed. The REQ-ratios are formulated based on a concept of plastic adaptation hypothesized for a fatigue slip band from a viewpoint of macro-mechanics. A method for diagramming fatigue strength of metals based on the parameter of the REQ-ratios is newly proposed. The method diagramming together the fatigue strength of notched and unnotched specimens is applied not only to fatigue problems of usually annealed, normalized and heat-treated materials but also to those of severely heat-treated and surface-treated ones. Fatigue strength diagrams are characterized with two types of fatigue strength: σw1 and σw2. The character of σw2 appears not only in specimens with sharp notches but also in unnotched specimens fatigue-tested at lower RN-ratios. Criteria on fatigue strength σw1 and σw2 are derived from the fatigue strength diagrams and formulated as empirical equations. Characteristics of fatigue slip bands are reviewed and two types of fatigue mechanisms are proposed related with fatigue strength σw1 and σw2 from a viewpoint of micro-mechanics. Consequently, it is found that the hypothesis of plastic adaptation is a very useful and fundamental idea for modeling a fatigue slip band and also for analyzing fatigue data of practical metals and alloys.

A Master S-N Curve Representation of Subsea Umbilical Tube Weld Fatigue Data

2010 ◽  
Author(s):  
Pingsha Dong ◽  
Xinhua Yang
Keyword(s):  
Stress Ratio ◽  
Correction Term ◽  
Fatigue Loading ◽  
Nominal Stress ◽  
Stress Range ◽  
Fatigue Data ◽  
Range Parameter ◽  
Weld Fatigue ◽  
Curve Representation ◽  
The One

In this paper, some of the available duplex and super-duplex stainless steel umbilical tube fatigue data are analyzed using an equivalent nominal stress range parameter, which shares a great deal of similarity to the one used in the 2007 ASME Div 2 Code. The proposed fatigue parameter consists of nominal stress range, a size correction term RTt with RT being the tube radius and t being tube wall thickness, and a stress ratio term (1 − R) with R being applied stress ratio. With it, the available girth weld fatigue test data are shown to collapse into a narrow band. The equivalent nominal stress range parameter is also shown to be effective in correlating seam weld data collected from seam-welded umbilicals, but with a different slope in log-log based S-N plot. Coiling/uncoiling low-cycle effects can be addressed by introducing a pseudo elastic nominal stress definition. Miner’s rule can be used to combine both coiling/uncoiling effects with subsequent high-cycle fatigue loading.

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