Abstract
This paper concentrates in defining an equation for crack length of a specimen Single Edge Notch Bend – Four Point (SENB-4P), applying the so-called Back-face Strain (BFS) method for a large extension and precision. The specimen type SENB-4P is well known and used in fatigue testing. The standard (ISO 12108)1,(1) provides a complete description of the specimen SENB-4P, however, this standard does not specify how SENB-4P could be used applying a BFS method to measure crack growth during a fatigue test. Moreover, there is lack of the literature concerning with BFS method applied to SENB-4P specimen for measuring crack propagation2. The existing work presents a relative short crack length with high level of imprecision. It is noteworthy that the majority of fatigue tests have a crack monitoring via Direct Current Potential Drop (DCPD), however its use in corrosive media is something still quite questionable and costly. In this work, two methods were used: simulation by Finite Elements Analysis and Fatigue Testing (air and in corrosive media), with monitoring of crack, a SENB specimen of API 5L X70 steel(2) , widely used in offshore pipelines. A methodology is presented herein, for using the technique of BFS in the specimen immersed in corrosive medium SENB. At the end of the test, the fatigue curves were compared to the curves of (BS 7910)3,(3).
