Significance of Ms and Validation of Reference Stress Solutions for Crack Like Flaws Part 2

This paper presents a non-linear numerical investigation of surface cracks in round bars under bending moment by using ANSYS finite element analysis (FEA). Due to the symmetrical analysis, only quarter finite element (FE) model was constructed and special attention was given at the crack tip of the cracks. The surface cracks were characterized by the dimensionless crack aspect ratio, a/b = 0.6, 0.8, 1.0 and 1.2, while the dimensionless relative crack depth, a/D = 0.1, 0.2 and 0.3. The square-root singularity of stresses and strains was modeled by shifting the mid-point nodes to the quarter-point locations close to the crack tip. The proposed model was validated with the existing model before any further analysis. The elastic-plastic analysis under remotely applied bending moment was assumed to follow the Ramberg-Osgood relation with n = 5 and 10. J values were determined for all positions along the crack front and then, the limit load was predicted using the J values obtained from FEA through the reference stress method.

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Simplified Analysis Methods for Primary Load Designs at Elevated Temperatures

ASME 2011 Pressure Vessels and Piping Conference: Volume 1 ◽

10.1115/pvp2011-57074 ◽

2011 ◽

Author(s):

Peter Carter ◽

T.-L. Sam Sham ◽

R. I. Jetter

Keyword(s):

Elevated Temperatures ◽

Design Procedure ◽

Inelastic Strain ◽

Temperature Dependent ◽

Perfectly Plastic ◽

Reference Stress ◽

Analysis Methods ◽

Elastic Perfectly Plastic ◽

Further Development ◽

Primary Load

The use of “simplified” (reference stress) analysis methods is discussed and illustrated for primary load high temperature design. Elastic methods are the basis of the ASME Section III, Subsection NH primary load design procedure. There are practical drawbacks with this current NH approach, particularly for complex geometries and temperature gradients. The paper describes an approach which addresses these difficulties through the use of temperature-dependent elastic, perfectly-plastic analysis. Traditionally difficulties associated with discontinuity stresses, inelastic strain concentrations and multiaxiality are addressed. A procedure is identified to provide insight into how this approach could be implemented. Though preliminary in nature, it is intended to provide a basis for further development and eventual Code adaptation.

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Reference Stress Approach for Fracture Assessment of Extrados Circumferential Through-Wall Crack at the Interface between Elbow and Pipe Subjected to Internal Pressure

Engineering Journal ◽

10.4186/ej.2018.22.6.151 ◽

2018 ◽

Vol 22 (6) ◽

pp. 151-163

Author(s):

Jirapong Kasivitamnuay ◽

Pairod Singhatanadgid

Keyword(s):

Internal Pressure ◽

Reference Stress ◽

Fracture Assessment ◽

Reference Stress Approach

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Weight Functions for an External Longitudinal Semi-Elliptical Surface Crack in a Thick-Walled Cylinder

Journal of Pressure Vessel Technology ◽

10.1115/1.2842270 ◽

1997 ◽

Vol 119 (1) ◽

pp. 74-82 ◽

Cited By ~ 6

Author(s):

A. Kiciak ◽

G. Glinka ◽

D. J. Burns

Keyword(s):

Stress Intensity ◽

Stress Intensity Factors ◽

Surface Crack ◽

Complex Stress ◽

Weight Functions ◽

Stress Distributions ◽

Intensity Factors ◽

Reference Stress ◽

Pressurized Cylinder ◽

Walled Cylinder

Mode I weight functions were derived for the deepest and surface points of an external radial-longitudinal semi-elliptical surface crack in a thick-walled cylinder with the ratio of the internal radius to wall thickness, Ri/t = 1.0. Coefficients of a general weight function were found using the method of two reference stress intensity factors for two independent stress distributions, and from properties of weight functions. Stress intensity factors calculated using the weight functions were compared to the finite element data for several different stress distributions and to the boundary element method results for the Lame´ hoop stress in an internally pressurized cylinder. A comparison to the ASME Pressure Vessel Code method for deriving stress intensity factors was also made. The derived weight functions enable simple calculations of stress intensity factors for complex stress distributions.

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