Photoelastic methods to determine KI, KII and KIII of internal cracks subjected to mixed mode loading

The ever increasing research of performances and lightness leads engineers and manufactures toward the development of heavily loaded components, subjected to multiaxial fatigue loads, made of materials with improved surface mechanical properties. In these cases it is not rare the development of internal cracks, whose propagation involves mixed-mode conditions; where an accurate prediction of the growth rate and of the crack path requires the knowledge of the stress intensity factors concerning modes I, II and III. In this paper, an original method for the experimental determination of these quantities is described. It is based on the photoelastic technique and allows to obtain internal cracks with regular shape without using any cutting device.