Issue 41

P. Gallo et alii, Frattura ed Integrità Strutturale, 41 (2017) 456-463; DOI: 10.3221/IGF-ESIS.41.57 457 To the best of the authors’ knowledge only a few solutions related to the localized time-dependent creep-plasticity problems are available in literature. Nuñez and Glinka [13] proposed a solution for non-localized creep strains/stresses at the notch root, based on the linear-elastic behavior of the material, the constitutive law and the material creep model. The formulation was derived by using the total strain energy density rule proposed by Neuber [14]. Considering the U-notched specimens (2 α =0 and ρ ≠0) very good results were obtained using this method. The main aim of the current paper is to extend the method proposed by Nuñez and Glinka to blunt V-notches. For this aim, the Creager and Paris [15] equations were substituted with the Lazzarin and Tovo [16] equations. Finally an approach for fast evaluation of the stresses/strains at notches under non-localized creeping condition is proposed which doesn’t require any complex and time-consuming FE non-linear analyses. Output of the proposed approach can be used as input for creep life prediction models based on local approaches. E VALUATION OF STRESSES AND STRAINS UNDER NON - LOCALIZED CREEPING CONDITION FOR BLUNT V- NOTCHES uñez and Glinka [13] presented a method for the estimation of stress and strain at U-notch tip, subjected to non-localized creep. The method was based on the Neuber [14] concept extended to time dependent plane stress problems and on the introduction of KΩ parameter introduced by Moftakhar et al. [17]. It can be assumed in fact that the total strain energy density changes occurring in the far field produce magnified effects at the notch tip. For this reason, the total strain energy density concentration factor is introduced in order to magnify the energy at the notch tip. The introduction of this parameter and of the far field stress and strain contribution in the Neuber’s time dependent formulation is the main difference within the non-localized and localized creep formulation that, instead, can be easily derived directly by extending the Neuber’s rule. Details about the original formulation can be found in the original works Nuñez and Glinka [13] and in Gallo et al. [18]. The key to extend the Nuñez-Glinka method to blunt V- notches is the assumption of the Lazzarin and Tovo [16] equations to describe the early elastic state of the system. (a) (b) Figure 1: (a) Coordinate system and symbols used for the stress field components in Lazzarin-Tovo equations; (b) coordinate system and symbols used for the elastic stress field redistribution for blunt V-notches. The Lazzarin-Tovo equations, in the presence of a traction loading, along the bisector (x axis), can be expressed as follows, as a function of the maximum stress (see Fig. 1):                 1 1 1 1 1 1 1 1 1 1 1 1 0 0 1 1 1 1 1 1 0 1 1 3 1 4 3 1 3 1 max r r r r r r r                                                                                      (1) N