Accession Number:

ADA243585

Title:

A Coherent Gradient Sensor for Crack Tip Deformation Measurements: Analysis and Experimental Results

Descriptive Note:

Corporate Author:

CALIFORNIA INST OF TECH PASADENA GRADUATE AERONAUTICAL LABS

Report Date:

1989-01-09

Pagination or Media Count:

26.0

Abstract:

Presently, several optical methods are being used for measuring elastic or plastic crack tip deformations under quasi-static or dynamic loading conditions. Among the commonly used techniques, photoelasticity measures principal stress differenced while moire methods and interferometry map in plane or out of plane displacements. In the method of caustics, non-uniform displacement gradients due to crack tip deformations result in the formation of a shadow spot. Subsequent interpretation of theses optical measurements through an assumed asymptotic field description enables one to evaluate the so-called stress intensity factor SIF K1 or the J-integral which are widely used in characterizing fracture behavior of materials. In most of the above methods, one often encounters the difficult question of whether the choosen experimental technique provides adequate control over the sensitivity of measurement. This becomes relevant because of the wide range of magnitudes of deformation that may occur near a crack tip. Typically, interferometric methods are preferred for the measurement of elastic deformations while for larger deformations the resulting fringe density often overwhelms the recording capabilities.

Subject Categories:

  • Mechanics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE