Application of Photoelasticy for Study of Lamellar Cracks.

Abstract

In rolled sheets, non–metallic inclusions are distributed along the thickness of the sheet as narrow lines running parallel to the rolling direction. Such inclusions are the nuclei of lamellar cracks. This work presents the application of the photoelastic method for study of lamellar cracking. Photoelastic models of samples with long artificial fissures set in the area of the sheet axis were studied along with other encountered inclusion distributions. The studied samples were placed in a polariscope and subjected to uniform tension; isochromatic images were obtained. Changes in the stress state in the area of the inclusion were observed as the load increased. Stress concentration leads to the formation of lamellar cracks – the joining of voids in the direction parallel to the exterior surface of the sheet (so–called ”terraces” are formed) and at angles (so–called ”jogs” are formed). The results of photoelastic tests were compared with the results of numerical calculations using the finite element method.