PSI - Issue 68

Mr. Parthasarathy Iyengar et al. / Procedia Structural Integrity 68 (2025) 446–452 P. Iyengar, J. Mardaras, S. Soe / Structural Integrity Procedia 00 (2025) 000–000

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exhibits a high level of brittleness due to triaxiality. Tensile testing was carried out to obtain Force-displacement plots and the following observations linked to Fig. 6 below were made. The geometry of the specimen is as shown in Fig. 6 below. • The orange elastic dye applied to NRB (R) highlights ductility at circumference followed by brittle crack. • NRBs with 8 mm dia. exhibited higher ductility than 10mm dia. • Force-Displacement plots indicated circumferential ductility followed by brittle failure.

Fig. 6. (a) A uniaxial tensile coupon; (b) top-section halves of notched specimen with die applied to “R”; (c) lateral view of notched specimen

The tested cross-section of 6 mm tensile coupon in (a) is visually compared with a 10 mm NRB in (b) and (c). Geometry of the notch of a tensile tested lathe-machined NRB are specimen are shown in Fig. 7 (a) by measurements. Since the plane-strain condition is related with linear elasticity, the end of its tangent on the plot was marked as “PNRB” and this load was used to determine K 1 as per the Stress Intensity formulation for NRB by Wang (1996) which has also been adopted by Dharne et al (2015). The calculated value will be hereforth referred to as “KNRB”. A notch which is measured and a force displacement plot used to arrive at a value of KNRB which agrees with an indicative K 1C value of 2024-T351 as per MMPDS are shown as part of Fig. 7 (b) below 31.5 MPa√m is in proximity to MMPDS (2019) with a value calculated to be 34.06 MPa√m.

Fig. 7. (a) A typical lathe produced notch; (b) Force-Displacement diagram and the calculation of K 1 (i.e., KNRB) using Wang’s formula

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5. Inferences 5.1. K1si application to aircraft aluminium alloys

Based upon observations with respect to 2024-T351, inconclusive results are seen with respect to obtaining coupon ‘size independent’ values. However, a corollary from testing performed with increased ligament length, even when beyond ASTM E 399, has showed negligible impact to calculated K Q . Perhaps the mindset for K 1si applicability needs