PSI - Issue 18

Mehdi Mokhtarishirazabad et al. / Procedia Structural Integrity 18 (2019) 457–471 . Mokhtarishirazabad / Structural Integrity Procedi 00 (2019) 000– 00

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Fig. 14. Effect of applying the linear scaling method for correcting the estimated Δ a UC for SENB samples with thickness of 10 mm and a/W = 0.2 and 0.5.

Steenkamp (Steenkamp 1988) is a comprehensive analytical study on the effect of these factors on compliance measurement on 3-point bending specimens. It reports that deformation of the specimen has the most significant effect on the measurements, while the effect of other factors is approximately 1%. It should be mentioned that, in literature, the effect of these factors has been taken in to account up to a limited amount of plastic deformation (up to 5 mm of plastic deflection) (Dzugan 2003; Steenkamp 1988) while the plastic deflection of more than 10 mm was observed in 316L in this study. To account for sample deflection effect, a correction factor is suggested by Steenkamp, FD , which increases with deflection of the sample. FD is proposed in the following form: � � � ����� � � (2) � � � � ∆ � (3) where α is the deformation angle as defined in Fig. 15 and Δ is the load line displacement. The effective compliance is therefore: � � � � � (4) where C is the experimental compliance and FD 0 is the FD at first unloading increment (fully elastic). In this experiment α was determined directly from the DIC images. Fig. 16 shows that employing the proposed correction by Steenkamp on sample SENB-B10-0.5 and SENB-B05-0.2 does not result in a consistent correction of the crack length measurement for samples with different thicknesses: it underestimates the crack extension in SENB-B10-0.5, whilst overestimating it for SENB-B05-0.2. Nevertheless, employing this method has improved the fitting of experimental and theoretical crack tip blunting. However, a better solution would involve use of a finite element method. This would have to account for large plastic deformation; the compliance estimations would also have to be corrected before UC could be used to estimate the crack length.