Issue 41

S. Seitl et alii, Frattura ed Integrità Strutturale, 41 (2017) 323-331; DOI: 10.3221/IGF-ESIS.41.43 327 measured values of displacements in the specimen. The set of data for two selected specimen configurations are presented, particularly for the specimen YX9 a6_im16 and YX9 a19_im30, see for instance Tab. 2 for more details. Specimen Fracture test Optical measurements (DIC) Knésl & Bednář [5] YX9 a6_im16: P = 3.706 kN, a = 22 mm 6.02 6.06 6.01 YX9 a19_im16: P = 3.650 kN, a = 28.62 mm 9.34 9.10 9.45 YX9 a19_im30: P = 7.060 kN, a = 28.62 mm 18.07 18.60 18.28 Table 2 : Values of the stress intensity factors (SIFs) in MPa√m for three cracked specimens obtained: from fracture tests, via ODM from displacements measured optically by means of DIC, by using hybrid element analysis performed by Knésl and Bednář. It is clearly seen from the results introduced in Fig. 2 to 5, that the stress levels near the crack tip in the specimen YX9 a19_im30 (with longer crack and larger loading force) are much higher than in the specimen YX9 a6_im16 (with shorter crack and smaller loading force) as it is expected. Another very important conclusion is that the one-parameter fracture mechanics concept as well as the two-parameter fracture mechanics concept can describe rather precisely the stress state near the crack tip. The comparison between the purely theoretical results [5] and results based on the experimental measurement works very well. N = 1 N = 2 a) Knésl & Bednář [5] b) experiment + ODM Figure 2 : σ 1 crack tip stress approximation considering one and two initial terms of the Williams expansion on specimen denoted as YX9 a6_im16 (P = 3.706 kN, a = 22 mm): a) stress values calculated from the coefficients determined theoretically [5]; b) stress values calculated from the coefficients obtained by means of the ODM from the experimental measurements.