numero25

A.S. Chernyatin et alii, Frattura ed Integrità Strutturale, 25 (2013) 15-19; DOI: 10.3221/IGF-ESIS.25.03 15 Special Issue: Characterization of Crack Tip Stress Field Combining experimental and numerical analysis to estimate stress fields along the surface crack front A.S. Chernyatin, Yu.G. Matvienko, I.A. Razumovsky Mechanical Engineering Research Institute of the Russian Academy of Sciences, Moscow, Russia A BSTRACT . Combining experimental and computational method for determination of the singular and the non- singular stress terms along the front of the 3D surface crack is proposed. Evaluation of the terms is based on comprehensive comparison between deformation responses (for measurement points on the surface) obtained experimentally and from numerical solutions of the corresponding boundary problem of solid mechanics. The proposed approach allows carrying out an adequate and a comprehensive assessment of stress fields in the vicinity of the surface crack front. K EYWORDS . 3D surface crack; Stress intensity factors; T-stresses; FEM; Minimization problem; Numerical experiment. I NTRODUCTION ne of the main trends in the development of methods for assessing of strength and lifetime of damaged structures, working under extreme loading conditions, is the application of fracture mechanics and, in particular, the methods for an analysis of the crack initiation process in the engineering structure. In this case, it is very important to estimate the singular and the non-singular stress terms in the Williams series solution along the crack front. It should be noted that these stress terms are dependent on crack and body configurations as well as loading conditions (e.g., [1, 2]). At the same time, operational loading conditions of engineering components can strongly differ from design conditions due to crack- or notch-like defects, assembly and residual stress, etc. To solve this problem, combining experimental and computational method can be employed for estimating operational loading conditions, the singular and the non-singular stress terms along the 3D surface crack front. The present paper deals with the approach which is based on comprehensive comparison between deformation responses (for measurement points on the surface of the engineering components) obtained experimentally and from numerical solutions of the corresponding boundary problem of solid mechanics. As a result, loading conditions, distribution of the singular ( K I , K II ) and the non-singular ( T xx , T zz ) terms along the surface crack front can be estimated. S TATEMENT OF THE PROBLEM he object of research and numerical simulation (by means of FEM) is an elastic half-space with a semi-elliptical crack (length 2a , depth b ) orthogonal to the surface. Homogeneous tensile stresses σ x , σ y are applied in two orthogonal directions. Displacement fields on the surface for certain specimen configuration can be measured by electronic speckle interferometry (ESI) or computed by numerical experiment. It is necessary to estimate the stress intensity factor and the T -stress terms along the crack front by means of an analysis of these displacement fields. The problem can be solved by two steps. Firstly, the parameters b , σ x , σ y should be estimated by the following procedure [3]:  generation of the experimental data ( e i * ) for the displacement fields; O T