Use of the Shadow Spot Method in Evaluating J for Ductile Steels.
Abstract
Caustic curve patterns obtained by the shadow spot method have been used in the past to give direct optical measurement of the elastic stress intensity factor in nominally brittle material. An advantage of the optical shadow spot method is that it provides a direct measure of the intensity of the crack tip stress field. The method is based on the idea that the value of the stress intensity factor can be related to features of the optical field obtained by transmitting parallel light through the crack tip region of a transparent specimen or by reflecting light from the surface of an opaque specimen. Most structural materials that contain cracks undergo substantial plastic deformation under rising load prior to onset of crack growth. Recently, the range of applicability of the shadow spot method was extended to the elastic-plastic power hardening materials. It was noted that the value of Rice's J-integral can be viewed as a plastic strain intensity factor. Methods for measuring values of J for ductile fracture specimens are available but the methods are indirect, in the sense that values of J are inferred from other measured quantities, typically load-deflection data. The shadow spots obtained in the test should be formed by reflection of light arrays from points well within the crack tip plastic zone where the one parameter plastic intensity singular field is dominant. The method of caustics provides a measurement which is customarily interpreted on the basis of plane stress theory.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 01, 1986
- Accession Number
- ADA166834
Entities
People
- A. Marchand
- C. C. Ma
- J. Duffy
- Lambert Ben Freund
Organizations
- Brown University