numero25

Yu. G. Matvienko et alii, Frattura ed Integrità Strutturale, 25 (2013) 20-26; DOI: 10.3221/IGF-ESIS.25.04 24 M ETROLOGICAL VERIFICATION etrological verification of the developed approach is performed by using specially designed specimen #3V made from 2024 aluminium alloy ( E = 74000 MPa, μ = 0.33) shown in Fig. 3. Working part of this specimen is a thin plate of dimensions 120x48x5 mm 3 . A U-notch of length a 0 = 20 mm is initially made in the middle of the shortest side in a direction of the symmetry cross-section. The specimen is loaded by transverse force directed orthogonally to the notch line as it is shown in Fig. 3. Step-by-step notch increase process is firstly performed by narrow jewellery saw of width b 1 = 0.3 mm (notch radius ρ 1 ~0.15 mm). A scheme of the experiment involved resides in the following. External transverse load P n1 is applied to the specimen. The first exposure is made for a notch of current length a n-1 . Then notch length is increased by small increment Δ a n and the second exposure is made for a notch of the final length a n = a n-1 + Δ a n . During a process of notch length increasing a value of acting force is slightly decreased to P n2 due to a compliance of the force gage. Two interference fringe patterns recorded for the 4 th notch length increment are shown in Fig. 2. Interference fringe patterns are recorded for 7 notch length increments starting from initial notch length a 0 = 20 mm up to a 0 + a n = 32.9 mm. Experimental data are obtained for the same loading conditions: P n1 = 0.930 kN and P n2 = 0.846 kN. Dependences of SIF K I and T-stress T values from total notch length constructed accordingly to relation (6) and relations (9)-(11), respectively, are shown in Fig. 4. Note that SIF values obtained by formula (6) coincide with analogous data from formula (7) within 5 per cent because A n 3 values are practically equal to zero for all steps considered. This fact gives us a capability of reliable comparing experimentally obtained SIF values with analogous results of numerical simulation on a base of NASTRAN computer codes. Figure 3 : Drawing Specimen #3V and a scheme of its loading. (a) (b) Figure 4 : Dependencies of SIF K I (a) and T-stresses T (b) from total notch length for specimen #3V and specimen #4V. M