Determination of η<inf>p</inf> factor for clamped SENT thin sheet specimens of an Interstitial Free steel

The present study addresses determination of the plastic “eta factor” ηp for single edge notched tensile (SENT) specimens of an interstitial-free (IF) steel sheet (thickness = 1 mm) for crack depth ratios in the range of 0.2 to 0.9. Two well-established ηp determination methods for thick fracture mechanics specimens proved adequate for the present purpose. Analyses using load-displacement data from mechanical tests and also from 3-D finite element simulations were used to verify the applicability of one of these adopted methods up to extensive crack tip necking even beyond crack initiation. Further analyses indicate that ηp thus determined (i) can be used for fatigue pre-cracked sheet specimens, and (ii) is consistent with the contour integral definition of J integral. Use of ηp thus determined for measuring initiation fracture toughness in notched specimens is also illustrated.