The plane-strain, work-hardening response of an internally pressurized cylinder containing surface flaws

Abstract

This paper describes two-dimensional (2-D) linear and nonlinear investigations of the basic fracture behaviour of a pressurized tube containing surface flaws. The effects of internal and external surface flaws are examined using the finite-element method. Applying symmetry, a quarter of the cross-section of a tube with a ratio of wall thickness to internal radius of 1 12 was modelled in a plane-strain mode. The tube is subjected to internal pressure loading only. Various ratios of crack length to tube thickness are modelled using 8-noded quadrilateral, isoparametric elements. Using the virtual crack extension (VCE) technique, the J-integral and the stress-intensity factor K are found for each model. These are nondimensionalized and plotted against the ratio of crack length/wall thickness. Using experimental tensile test data, the work-hardening curve is entered directly into the finite-element models for the internal and external surface flaws. The effect of internal pressure on the J-integral and K values for each crack length/wall thickness ratio is examined. To model the effect of crack-tip /ldblunting,/ rd prior to crack extension, the 1 √r singularity of the crack-tip elements is altered to a 1/ r singularity, i.e. an elastic, perfectly plastic condition is produced in the crack-tip elements. This condition is applied to all models, and again J-integrals and K values are produced for both internal and external surface flaws. Comparisons with handbook solutions, e.g. as found in the EPRI Elastic Plastic Fracture Analysis Handbook, are given. The accuracy and limitations of each determination of the J-integral, and hence the stress-intensity factor K, are compared and discussed.