Golynskiy I. Development of methods for diagnostic of stress state of material with crack using digital speckle-correlation of images

Object of study - stress state, that occurs in the material with a crack under mechanical loading. The purpose of research is to develop methods for diagnosing stress state of materials with a crack, based on its description by Williams' series. The next methods were applied: method of mathematical statistics, theory of information-measuring systems, optical systems theory, theory of measurement and measurement systems, approaches of quasi brittle fracture mechanics, methods of digital image correlation. Found that for the diagnostic of stress state of the cracked material using speckle correlation technology should use stress field in the material and not the displacements of surface of material, due to eliminate the influence of rigid body motion; developed and verified methods for derivation using digital image correlation: stress intensity factors, crack tip position coordinates, J-integral, limits of plasticity zone during the diagnostic of the stress state of the material; developed methods for compensation of influence of systematic errors in measured stress field components on the accuracy of the Williams' series parameters derivation; proposed to determine the angle of crack propagation as the direction from its tip to the centre-mass of the figure, limited by value of the critical third invariant of stresses. The results of the work are used in Company "Zahid-tehnoservis" for developing a system for estimation of crack propagation during nondestructive testing of loaded metal constructions.