Optical isodyne measurements in fracture mechanics

Abstract

Paper presents an assessment of capacity of three-dimensional isodyne stress analysis and its efficiency in nondestructive experimental stress analysis of plane and three-dimensional stress states. The actual three-dimensional stress state in the ASTM Standard Compact Specimen C(T) was taken as a representative example. Models of the Standard Compact Specimen C(T) were made of transparent polyester resins Palatal P6 and Homalite H101. Three families of optical isodynes, which represent three families of isodyne surfaces, were produced to determine all components of the stress state. Optical isodynes were produced using the scattered laser light as the information-carrying energy flow. To increase the resolution of the recordings the spatial modulation technique was used. Principles and techniques of measurements, recordings, and evaluation of isodyne fields are outlined. Two sets of normal and maximal shear stresses acting in the plane of the crack, between the crack tip and specimen boundary, are presented and discussed: stresses in direction of the crack; and stresses normal to direction of the crack. It is shown that the concept of a generalized plane stress state is not admissible in regions of high stress gradients. Results pertain to reliability of theoretical foundations of various analytical-experimental procedures of photomechanics.