TWI Industrial Member Report Summary 1034/2013
By Philippa Moore, Henryk Pisarski and Tyler London
Single Edge Notched Tension (SENT) specimens for fracture toughness testing are undergoing standardisation. With no current standard method to determine CTOD for these specimens, the need to evaluate the possible choices for determining CTOD was addressed in this report. Silicone crack replicas and FEA models were used to compare double clip and J formula methods. Recommendations were made for the best methods to include in a testing standard.
SENT specimens measure higher fracture toughness than the standard SENB bend specimens, so are increasingly used. The need to develop a standard method is urgent to avoid inconsistencies in test methods giving inaccurate results.
The recommendations from this work were:
- Using a pair of clip gauges to estimate CTOD (double clip method) was shown to be simple, practical and sufficiently accurate.
- This method will be recommended for the SENT test standard.
- The most accurate formula to estimating CTOD from J was from Shen and Tyson (2009).
- There are practical problems with testing SENT specimens with a/W as small as 0.1. A lower limit of a/W=0.2 should be placed on the SENT crack length.