Issue 32

I. Telichev, Frattura ed Integrità Strutturale, 32 (2015) 24-34; DOI: 10.3221/IGF-ESIS.32.03 32 It is known that the ratio of the radial crack length ( L rad.cr. ) to the hole diameter ( D hole ) has a considerable effect on the critical stress. Fig. 9 illustrates that the singular integral equations method allows obtaining the accurate result for any specific case of ( L rad.cr. / D hole )-ratio. The obtained results also illustrate the fact that for L rad.cr. / D hole >0.25, the hole with two radial cracks can be considered as a straight crack. Figure 9 : Critical stress for various ( L rad.cr. /D hole )-ratio In order to verify above method and illustrate its application, numerical calculations were performed and compared with results of impact and tensile tests of the 3-mm thickness specimens fabricated from alloy 2024 with ultimate tensile strength σ u =446 MPa, yield strength σ y =370 MPa, modulus of elasticity E =70000 MPa, Poisson’s ratio ν =0.33 and fracture toughness K c = 53.9 MPa m 1/2 . The critical CTOD was determined assuming the plane stress state and using the relation CTOD c =(K c 2 )/(σ y E) . To account the strain hardening effects the σ y was interpreted as an average of the nominal yield stress and ultimate tensile strength. The computational analysis predicted residual strength to within 5% of the experimental data given in [4]. The Fig. 10 and 11 illustrate a fair agreement of the obtained computational results with test data [15] where the specimens were perforated by 0.5 Ball projectile at ballistic velocities of 206-308 m/s and then subjected to the tensile tests. The specimens with thickness of 4.8 mm and dimension of 460×910 mm were fabricated from 7075-T6 alloy. The following input data were used for the analysis: ultimate tensile strength σ u =535 MPa, yield strength σ y =468 MPa, modulus of elasticity E =72000 MPa, Poisson’s ratio ν =0.33 and fracture toughness K c = 63 MPa m 1/2 for transverse grain and K c = 81.6 MPa m 1/2 for longitudinal grain. Figure 10 : Computational results vs test data [15] (7075-T6 Transverse grain). Figure 11 : Computational results vs test data [15] (7075-T6 Longitudinal grain).