Determination of η_p factor for clamped SENT thin sheet specimens of an Interstitial Free steel

The present study addresses determination of the plastic “eta factor” η_p 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 η_p 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 η_p 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 η_p thus determined for measuring initiation fracture toughness in notched specimens is also illustrated.