Developments of strain-based failure assessment diagram applications: measuring reference strain by displacement and a modified assessment method

Abstract

A modified strain-based failure assessment diagram (FAD) and a method of using the displacement of the outer boundary of the load (DOBL) to measure the reference strain in strain-based FAD (SB-FAD) application are established in this paper. Measuring reference strain by DOBL is a new method of introducing displacement to characterize reference strain and has a great potential of promoting the application of strain-based FAD. A modification parameter with a physical meaning of reflecting defect size, component geometry and material properties, is introduced to improve the SB-FAD Option 2 (one important SB-FAD assessing curve) and makes the assessment method conservative and safe. For some typical 2D and 3D crack structures in engineering, the modification parameter query tables are presented for the application convenience. The modified SB-FAD Option 2 is conservative and can be well combined with the method of using DOBL to measure reference strain in SB-FAD application. The two aspects of the developments of SB-FAD are of general practicality, and are illustrated in the paper to assess the structural integrity of 3D surface cracks in reel pipeline projects.