Issue 7

S. K. Kudari et alii, Frattura ed Integrità Strutturale, 7 (2009) 57-64; DOI: 10.3221/IGF-ESIS.07.04 62 variation of r p /a against σ / σ y as obtained from these analytical models were also computed and the results are superimposed in Fig.5 . It is clear from all the results depicted in Fig.5 that: (a) none of the analytical models satisfactorily explain the present experimental results and (b) elastic-plastic FEA describes the experimental results in the best manner for the entire range of investigation. Figure 4 : Typical variation of microhardness along the entire ligament of a CT specimen. Figure 5 : Comparison of the experimental and FEA results with various analytical methods. All the experimental results on PZS evaluated in the present investigation on IF steel along with the FE results are compiled based on normalized J (J/a σ y ) and normalized σ ( σ / σ y ) in Fig.6 and Fig.7 respectively. These figures shows that the experimental results are in good agreement with the FE results plotted against both the reference parameters. These plots infer that the experimental results of PZS are in excellent agreement with the results of FEA when examined with respect to any of the reference parameters at lower applied stress or J-integral levels. At higher applied stress or J levels it is observed that experimental measurements of PZS are marginally lower than that of FEA in the investigated steel. This may be possibly attributed to the following reasons: (i) interaction of compressive plastic zone with the crack-tip plastic zone and (ii) measurement difficulties. Figure 6 : Variation normalized plastic zone size (r p /a) estimated by microhardness technique and FEA vs. normalized J-integral (J/a σ y ) in SENT and CT specimens Figure 7 : Variation normalized plastic zone size (r p /a) estimated by microhardness technique and FEA vs . normalized applied stress ( σ / σ y ) in SENT and CT specimens.