numero25

A.S. Chernyatin et alii, Frattura ed Integrità Strutturale, 25 (2013) 15-19 ; DOI: 10.3221/IGF-ESIS.25.03 18 zz I II zz zz zz xx 2 K cos K sin T 2 2 2 r T E T                   Here, K is the elastic stress intensity factor, r and  are the polar coordinates in plane x0y, zz  is the strain in the z - direction, E and ν are the Young modulus and Poisson’s ratio, respectively. The terms xx T and zz T are the amplitudes of the second order terms in the three-dimensional series expansion of the crack-front stress field in the x - and z - directions, respectively. The stress intensity factor is calculated in a number of points (at variable values of r a / 20  ) using the following equation   I xx 0 xx xx r K 2 | | | 2                (2a)   II xx xx r K | | 8            (2b) The obtained values of the stress intensity factor are extrapolated to the point r =0. To evaluate the distribution of the stress intensity factors along the crack front, this procedure is used for a number of orthogonal to the front of the crack plane (x0y). Their location is characterized by local coordinate s along the front which starts from the center of the crack front and finishes at the point located on the body surface. The magnitude of the T -stress terms is defined through stress components for the points on the crack surface as follows xx xx xx 1 T 2               (3a) zz zz zz 1 T 2               (3b) The determination of the non-singular T xx - and T zz -stress is similar to the calculation procedure for the stress intensity factor including extrapolation to the point r =0. The distribution of the singular (K I , K II ) and the non-singular (T xx , T zz ) terms along the crack front (in the absence of the probe hole) is shown in Fig. 3. The stress intensity factor K II is negligible as it is expected for the surface crack and loading conditions under consideration. It can be also seen that the non-singular terms are significantly changed along the surface crack front. In contrast to the T xx -stress, the T zz -stress approaches the maximum value at the center of the crack front. C ONCLUSIONS t was shown that combining experimental and computational method can be employed for estimating operational loading conditions, the singular and the non-singular stress terms in a series expansion of the three-dimensional elastic stress components along the surface crack front. The proposed method is based on comprehensive comparison between deformation responses (for measurement points on the surface of the engineering components) obtained experimentally and from numerical solution of the corresponding boundary problem of solid mechanics. The distribution of the singular ( K I , K II ) and the non-singular ( T xx , T zz ) terms along the surface crack front is computed. A CKNOWLEDGEMENT he authors acknowledge the support of the Russian Foundation of Basic Research (Grant N 12-08-91158- NSFC_а). I T