Abstract
The elastic compliance for the double cantilever beam (DCB) specimen currently used in NACE TM0177 Method D was obtained more than twenty years ago but only for the chevron notch configuration. Recently, the DCB compliance for the chevron notch, 32 mm electric discharge- machined (EDM) and 35 mm EDM crack starters were all measured and compared. The experimental program consisted of multiple, direct load versus arm displacement measurements for all three geometries in as-machined condition and at various crack lengths created by fatigue pre-cracking. All DCBs were machined from an API* C110 grade. Based on the experimental data and statistical evaluation shown, a more accurate equation was determined for the chevron notch and new equations determined for the 32 mm and 35 mm EDM geometries. The results show an insignificant difference in compliance between the chevron notch and the 32 mm EDM geometries. This allowed the determination of one compliance equation for both geometries and the recommendation to not use the 35 mm EDM configuration. Also, the data allowed for the calculation of an effective starting crack size for the chevron notch. The impact of these findings are: a new, common compliance equation for chevron and 32 mm EDM DCBs; recommendation not to use the 35 mm EDM DCB; more consistent calculation of KIapplied and Klimit for future DCB testing; and the ability to recalculate KIapplied and Klimit for all past DCB test using the new chevron notch equations.
