The Relation Between the Peak Stress for a Blunt Flaw and the Stress Intensity Factor for an Equivalent Crack

2010 ◽  
Author(s):  
Edwin Smith
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Effective Stress ◽  
Peak Stress ◽  
Fracture Initiation ◽  
Radius Of Curvature ◽  
Root Radius ◽  
Effective Stress Intensity Factor

The paper presents arguments to support the view that the often quoted relation σp = Lim[μKI/(πρ)1/2] as ρ (flaw root radius of curvature) tends to zero, with σp being the peak flaw-tip stress, KI, the effective stress intensity factor, and μ = 2, is strictly valid only for the case of an infinitely deep parabolic flaw. The importance of the parameter μ is highlighted with regards to the problem of fracture initiation at the root of a blunt flaw.

Effective Stress Intensity Factor in Mode III Crack Growth in Round Shafts

2003 ◽  
Author(s):  
A. Vaziri ◽  
H. Nayeb-Hashemi
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Fracture Surface ◽  
Crack Growth ◽  
Effective Stress ◽  
Mode Iii ◽  
Mode Iii Crack ◽  
Fracture Surfaces ◽  
Effective Stress Intensity Factor

Turbine-generator shafts are often subjected to a complex transient torsional loading. Such transient torques may initiate and propagate a circumferential crack in the shafts. Mode III crack growth in turbo-generator shafts often results in a fracture surface morphology resembling a factory roof. The interactions of the mutual fracture surfaces result in a pressure, and a frictional stress field between fracture surfaces when the shaft is subjected to torsion. This interaction reduces the effective Mode III stress intensity factor. The effective stress intensity factor in circumferentially cracked round shafts is evaluated for a wide range of applied torsional loadings by considering a pressure distribution in the mating fracture surfaces. The pressure between fracture surfaces results from climbing the rought surfaces respect to each other. The pressure profile not only depends on the fracture surface roughness (height and width (wavelength) of the peak and valleys), but also depends on the magnitude of the applied Mode III stress intensity factor. The results show that the asperity interactions significantly reduce the effective Mode III stress intensity factor. However, the crack surfaces interaction diminishes beyond a critical applied Mode III stress intensity factor. The critical stress intensity factor depends on the asperities height and wavelength. The results of these analyses are used to find the effective stress intensity factor in various Mode III fatigue crack growth experiments. The results show that Mode III crack growth rate is related to the effective stress intensity factor in a form of the Paris law.

3D Numerical Study on how the Local Effective Stress Intensity Factor Range Can Explain the Fatigue Crack Front Shape

2014 ◽  
Vol 891-892 ◽  
pp. 295-300
Author(s):  
Catherine Gardin ◽  
Saverio Fiordalisi ◽  
Christine Sarrazin-Baudoux ◽  
Jean Petit
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Effective Stress ◽  
Numerical Study ◽  
Stress Intensity Factor Range ◽  
Crack Advance ◽  
Effective Stress Intensity Factor ◽  
Curved Crack ◽  
Shaped Crack

The plasticity-induced crack closure of through-thickness cracks, artificially obtained from short cracks grown in CT specimens of 304L austenitic stainless steel, is numerically simulated using finite elements. Crack advance is incremented step by step, by applying constant ΔK amplitude so as to limit the loading history influence to that of crack length and crack wake. The calculation of the effective stress intensity factor range, ΔKeff, along curved shaped crack fronts simulating real crack fronts, are compared to calculation previously performed for through-thickness straight cracks. The results for the curved crack fronts support that the front curvature is associated to constant ΔKeffamplitude, thus assumed to be the propagation driving force of the crack all along its front.

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