On notch fracture mechanics

2021 ◽  
Vol 87 (2) ◽  
pp. 56-64
Author(s):  
G. Pluvinage
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Plastic Zone ◽  
Fracture Resistance ◽  
Notch Radius ◽  
Notch Stress Intensity Factor ◽  
Blunt Notch ◽  
Notch Stress

Different stress distributions for an elastic behavior are presented as analytical expressions for an ideal crack, a sharp notch and a blunt notch. The elastic plastic distribution at a blunt notch tip is analyzed. The concept of the notch stress intensity factor is deduced from the definition of the effective stress and the effective distance. The impacts of the notch radius and constraint on the critical notch stress intensity factor are presented. The paper ends with the presentation of the crack driving force Jρ for a notch in the elastic case and the impact of the notch radius on the notch fracture toughness Jρ,c. The notch fracture toughness Jρ,c is a measure of the fracture resistance which increases linearly with the notch radius due to the plastic work in the notch plastic zone. If this notch plastic zone does not invade totally the ligament, the notch fracture toughness Jρ,c is constant. This occurs when the notch radius is less than a critical one and there is no need to use the cracked specimen to measure a lower bound of the fracture resistance.

scholarly journals Notch Stress Intensity Factor (NSIF)-Based Fatigue Design to Assess Cast Steel Porosity and Related Artificially Generated Imperfections

Metals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1097
Author(s):  
Manuel Schuscha ◽  
Michael Horvath ◽  
Martin Leitner ◽  
Michael Stoschka
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fatigue Strength ◽  
Intensity Factor ◽  
Cast Steel ◽  
Experimental Investigations ◽  
Fatigue Assessment ◽  
Notch Stress Intensity Factor ◽  
Fatigue Design ◽  
Notch Stress

Shrinkage porosities and non-metallic inclusions are common manufacturing process based defects that are present within cast materials. Conventional fatigue design recommendations, such as the FKM guideline (“Forschungskuratorium Maschinenbau”), therefore propose general safety factors for the fatigue assessment of cast structures. In fact, these factors mostly lead to oversized components and do not facilitate a lightweight design process. In this work, the effect of shrinkage porosities on the fatigue strength of defect-afflicted large-scale specimens manufactured from the cast steel G21Mn5 is studied by means of a notch stress intensity factor-based (NSIF-based) generalized Kitagawa diagram. Additionally, the mean stress sensitivity of the material is taken into account and establishes a load stress ratio enhanced diagram. Thereby, the fatigue assessment approach is performed by utilizing the defects sizes taken either from the fracture surface of the tested specimens or from non-destructive X-ray investigations. Additionally, a numerical algorithm invoking cellular automata, which enables the generation of artificial defects, is presented. Conclusively, a comparison to the results of the experimental investigations reveals a sound agreement to the generated spatial pore geometries. To sum up, the generalized Kitagawa diagram, as well as a concept utilizing artificially generated defects, is capable of assessing the local fatigue limit of cast steel G21Mn5 components and features the mapping of imperfection grades to their corresponding fatigue strength limit.

The Use of the Singular Elastic Peak Stress Evaluated by FE Analyses for Fatigue Strength Assessment of Welded Joints

2007 ◽  
Vol 348-349 ◽  
pp. 253-256
Author(s):  
Bruno Atzori ◽  
Paolo Lazzarin ◽  
Giovanni Meneghetti
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fatigue Strength ◽  
Intensity Factor ◽  
Welded Joints ◽  
Peak Stress ◽  
Elastic Peak ◽  
Strength Assessment ◽  
Notch Stress Intensity Factor ◽  
Notch Stress

The paper presents a simplified version of the Notch Stress Intensity Factor (NSIF) approach useful for fatigue strength assessments of welded joints. The evaluation of the NSIF from a numerical analysis of the local stress field usually needs very refined meshes and then large computational effort. A relationship is proposed here to estimate the Notch Stress Intensity Factor from finite element analyses carried out by using a mesh pattern with a constant element size. The main advantage of the presented relationship is that only the elastic peak stress numerically evaluated at the V-notch tip is necessary to estimate the NSIF instead of the whole stress-distance set of data (that is why the method has been called Peak Stress Method, i.e. PSM). An application of the PSM to fatigue strength assessment of fillet welded joints made of structural steels and aluminium alloys under tensile or bending loads is presented. In those joints, only mode I stress distribution is singular at the weld toe due to the presence of a V-notch angle equal to 135 degrees.

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