首页|A NEW STRESS-INTENSITY FACTOR SOLUTION FOR AN INTERNAL SURFACE CRACK IN SPHERES
A NEW STRESS-INTENSITY FACTOR SOLUTION FOR AN INTERNAL SURFACE CRACK IN SPHERES
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This paper describes a new stress-intensity factor (SIF) solution for an internal surface crack in a sphere that expands capabilities for this common pressure vessel geometry。 The SIF solution employs the weight function (WF) methodology that enables rapid calculations of SIF values。 The WF methodology determines SIF values from the nonlinear stress variations extracted in the uncracked geometry， e。g。， from service stresses and/or residual stresses。 The current approach supports two degrees of freedom that denote the two crack tips located at the deepest location and the surface of the sphere。 The geometric formulation of this solution enforces an elliptical crack front， maintains normality of the crack front with the free surface， avoids non-physical crack shapes with protruding "ears "， and supports two degrees of freedom for fatigue crack growth from an internal crack tip and a surface crack tip。 The new SIF solution enables all spherical geometries with the exterior diameter greater than or equal to four times the thickness。 This WF SIF solution has been combined with stress variations common for spherical pressures vessels: internal pressure on the interior surface， uniform tension on the crackplane， andbending on the crackplane。 These stress variations facilitate solution usability。 This work builds on earlier efforts for an external surface crack (PVP2021-61397[1]) and provides a comprehensive solution capability for spheres。 This paper provides a complete overview of this solution。 We present for the first time the geometric formulation of the crack front that enables the new functionality and set the geometric limits of the solution， e。g。， the maximum size and shape of the crack front。 The paper discusses the bivariant WF formulation used to define the SIF solution and details the finite element (FE) analyses employed to calibrate terms in the WF formulation。 A summary of verification efforts demonstrates the credibility of this solution against independent results from FE analyses。 We also compare results of this new solution against independent SIFs computed by FE analyses， legacy SIF solutions， API 579， and FITNET。 These comparisons indicate that the new WF solution compares favorably with results from FE analyses。 Finally， we summarize the capabilities of this solution in NASGRO®。
Stress-intensity factorFracture mechanics
James C. Sobotka、Yi-Der Lee、Joseph W. Cardinal、R. Craig McClung
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Southwest Research Institute®, San Antonio, TX, USA
ASME Pressure Vessels & Piping Conference
Bellevue(US)
2024 Proceedings of the ASME Pressure Vessels & Piping Conference
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