PSI - Issue 60

S.K. Chandra et al. / Procedia Structural Integrity 60 (2024) 203–213 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Nomenclature , ∆ , , , ,

notch/crack length, crack extension -integral, stress intensity factor specimen ligament length, sheet specimen thickness parameters used in optical measurement of strain hardening exponent, notch root radius actuator displacement, specimen free length extension CTOD, critical value of CTOD for crack initiation displacement at original notch/crack tip for gage length 5 mm yield stress, ultimate tensile strength CTOA, critical CTOA CTOA estimate from 5 measurement critical CTOA estimate from ( 5 ) crack tip opening angle

, , 5 , , ( 5 ) ( 5 ) CTOA CTOD DENT SENT

crack tip opening displacement double edge notched tension single edge notched tension

2. Experimental 2.1. Test material

The material used in the present study is an interstitial-free (IF) steel sheet of 1 mm thickness ( ) supplied by TATA Steel, Jamshedpur, India. The steel chemistry in wt. pct.: C - 0.0018, Mn - 0.064, Si - 0.002, P - 0.009, Al - 0.0359,N - 0.0018, Ti - 0.04 and balance Fe. Tensile properties of the steel at three different nominal strain rates are reported in Table 1. Hollomon work hardening model ( = ) has been used to determine the value of the strain hardening exponent ( ) . In doing so, engineering stress-strain data in the region spanning over 0.2 pct offset yield strength to tensile strength have been converted to true stress ( ) and true plastic strain ( ) and then - data have been plotted on double logarithmic scale. The slope of the log – log plot has been considered as strain hardening exponent. In the present investigation it was observed that with increase in nominal strain rate, the yield strength ( ), ultimate tensile strength ( ) and strain hardening exponent ( n ) increased slightly, whereas the percentage of elongation to failure decreased. Table 1. Tensile property at different strain rates Strain Rate (s- 1 ) Yield Strength (MPa) Tensile Strength (MPa) Total Elongation (%) ( ) 10 -4 162.62 324.23 44.6 0.241 10 -3 168.25 338.68 43.12 0.247 10 -2 184.51 348.43 42.2 0.248 2.2. Specimens and testing SENT and DENT specimens with varying ligament lengths ( ) were machined in longitudinal (L-T) orientation having external dimensions of 90 mm × 30 mm × 1mm (free length between grips 60 mm) and notch tip radius = 0.1 mm (Fig.1). The ligament lengths for the present study were chosen such that ≫ 4 , to cover the expected initial transients in (cf. [5], [18]) before the regime where attains a constant value, . In this regard, it is to be noted that as there is no specific standard for metallic SENT or DENT specimens the large-size CT and MT specimen