Issue34

K. Nowak, Frattura ed Integrità Strutturale, 34 (2015) 507-514; DOI: 10.3221/IGF-ESIS.34.56 507 Focussed on Crack Paths Paths of interactive cracks in creep conditions K. Nowak Cracow University of Technology, Faculty of Civil Engineering, Institute of Structural Mechanics, ul. Warszawska 24, 31-155 Krakow, Poland kn@limba.wil.pk.edu.pl A BSTRACT . The paper contains plane strain analysis of uniformly stretched plate working in creep condition. The plate contains initial defects in forms of central and/or edge cracks working in mode I. These cracks are modelled by attributing critical value of damage parameter to preset points and therefore resulting in stresses set to zero (material does not support any loading). The Continuum Damage Mechanics constitutive equations are used to describe the creep crack growth problem and Finite Element Method Abaqus system is applied to solve corresponding boundary and initial value problem. Analysis of different initial cracks configuration has been performed. The crack path is defined by points in which damage parameter equals to critical one. Time to failure of the plate with single initial crack is achieved when the crack path spans its width. This time is calculated and compared to the time to failure of initially uncracked structure. For the plate with multiple cracks the paths starting from different cracks can develop independently until they merge and/or span the plate width. In each case the damage field is analysed and the direction of crack path development is determined. The analysis of crack propagation allows for determination of a distance between initial cracks for which the interaction between them is negligible. It is demonstrated that Continuum Damage Mechanics approach allows not only to model the development of initially existing cracks but also initiation of new, cross-spanning cracks and their kinking and branching. K EYWORDS . Creep damage; Crack paths; Cracks interaction; Integrity assessment. I NTRODUCTION valuation of remaining life time of a structure working in creep condition is important engineering problem. It is especially crucial if some initial flaws exist what may influence the cracks and their pattern development causing premature failure of the structure. For the structure working in elastic regime, the flaws can be modelled by the cracks and the structure can be analysed by Linear Fracture Mechanics (LFM) tools. Each single crack can be modelled independently and critical length of it can be evaluated. Much more complicated is the problem of cracks interaction. If distance between neighbouring cracks is comparable with the length of the cracks, they should be analysed together. This problem was analysed by many authors (e.g. [4, 5, 6, 9, 10, 12]). In frame of LFM the interaction is expressed in terms of Stress Intensity Factor (SIF). The cracks interaction can cause amplification of SIF or its decreasing. The former effect occurs mainly for coplanar cracks, the latter for parallel cracks due to shielding effect. In both cases the interacting cracks can be replaced by single substitute crack which size depends on dimensions and relative position of original cracks (cf. e.g. [10]). E