Limits of applicability of the method of caustics in crack problems
Abstract
The state of stress in the neighborhood of the crack tip changes from plane strain very close to the tip to plane stress further away from the tip through an intermediate region where the stress field is three-dimensional. This situation complicates the experimental determination of stress intensity factors in crack problems by the method of caustics, since the values of the stress-optical constants entering into the evaluation equations change drastically when the stress state changes from plane strain to plane stress. In the present study a thorough investigation of the limits of applicability of the method of caustics in crack problems under conditions of plane stress is undertaken. The fact that the generatrix curve of the caustic, the so-called initial curve, should lie in the plane stress region introduces restrictions on the values of the applied loads, specimen dimensions and characteristic lengths of the optical arrangement for the correct application of the method. The limiting values of these quantities are defined when the specimen is illuminated by a parallel, divergent or convergent light beam. It is shown that direct application of the method may give erroneous results if certain conditions are not satisfied. Thus, the experimentalist following the results of the present study can safely apply the method of caustics to determine stress intensity factors in crack problems.
- Publication:
-
Engineering Fracture Mechanics
- Pub Date:
- May 1992
- Bibcode:
- 1992EnFM...42..251K
- Keywords:
-
- Caustics (Optics);
- Crack Tips;
- Plane Stress;
- Stress Distribution;
- Stress Intensity Factors;
- Fracture Mechanics;
- Light Beams;
- Three Dimensional Bodies;
- Structural Mechanics