Constraint Loss Correction Between SENB And SENT For Welded Joint Specimens Based On Weibull Stress Criterion

Sakimoto, Takahiro (Steel Research Laboratory, JFE Steel Corporation) | Igi, Satoshi (Steel Research Laboratory, JFE Steel Corporation) | Endo, Shigeru (Steel Research Laboratory, JFE Steel Corporation) | Suzuki, Shinichi (JFE Steel Corporation) | Østby, Erling (SINTEF)

OnePetro 

ABSTRACT

Constraint loss correction procedure using Weibull stress criterion is specified as ISO 27306 in 2009. This procedure provides critical CTOD to brittle fracture in structural component with the defect using the critical CTOD obtained from standard fracture toughness test specimen through the equivalent CTOD ratio β. Although the difference of the plastic constraint condition can be easily revised by using equivalent CTOD ratio β, there are few examples applied to the welded joint evaluation. This paper presents the plastic constraint loss correction between SENB and SENT specimens for base plate and weld joint using equivalent CTOD ratio β. The CTOD in SENT specimen is predicted from that in the SENB test results that tested at lower shelf CTOD temperature such as -60°C based on the critical Weibull stress criterion. Critical Weibull stress is calculated with taking account of internal stress distribution in plate thickness, critical fracture volume along the crack tip with reference to coarse grain heat affected zone and initial crack shape. The minimum of three equivalents CTOD in SENT tests show good agreement with the predicted CTOD from the SENB test results using this procedure.



INTRODUCTION

In recent years, the construction of oil and gas industry structures is expanding to northern area such as the arctic region (Welsch, 2011). In this area, one of important concerns is to obtain sufficient high toughness of welded steel structure at low design temperature of -60oC. It can be challenging to achieve high fracture toughness in structural steels at very low temperature (Akselsen, 2011). Single Edge Notched Bend (SENB) specimen with deep through thickness crack geometry is widely used for standard fracture toughness test. This specimen provides lower bound fracture toughness of material due to the high plastic constraint at the crack tip. Single Edge Notched Tension (SENT) with shallow surface crack specimen is designed to obtain similar plastic constraint at crack tip in the actual structure.