Crack driving force and ultimate strength of thick-walled CHS X-joints with near-toe cracks

Abstract

This paper presents numerical studies on the static strength of the HSS (high strength steel) thick-walled CHS X-joints with near-toe surface cracks under the brace axial tensile load. The analyses cover a comprehensive array of joint geometric parameters and crack configurations. The 3-D FE models couple a global, topologically continuous mesh and a separate, local crack-front model through mesh-tieing. The plastic collapse loads as well as the crack driving forces (measured by the J-values) have been computed to assess the two competing failure mechanisms: the plastic collapse failure and the fracture failure. The predicted strength reduction data with respect to the crack area are compared with the equation in existing design codes. The design equation proves to be conservative especially for the high ß joints. The effects of fracture failure on the cracked joint strength are also investigated. Copyright © 2011 by the International Society of Offshore and Polar Engineers (ISOPE).