Classification of stress-intensity factors from isochromatic-fringe patterns

The stresses in the local neighborhood of a crack tip have been used to develop a relation between the isochromatic-fringe orderN, its position parametersr and θ and the stress field expressed in terms of stress intensities,KI,KII, and a far-field stress σox. This relation was programmed and a plotting routine was developed to map isochromatic (σ1 − σ2) fields in the neighborhood of the crack tip.The stress intensitiesKI andKII and the far-field stress σox were varied and isochromatic fields were constructed for each combination. As bothKII and σox influence the size, shape and orientation of the isochromatics loops in a systematic manner, the pictorial representation of the isochromatic fields can be used to classify the state of stress (KI,KII and σox) at the crack tip. Isochromatics which classify six different states of stress have been illustrated and methods used to determineKI,KII, andσox in five of the six states are given.