Accession Number:

AD0260079

Title:

A REVIEW OF RECENT RESEARCH AT GALCIT CONCERNING FRACTURE INITIATION

Descriptive Note:

Corporate Author:

CALIFORNIA INST OF TECH PASADENA GRADUATE AERONAUTICAL LABS

Personal Author(s):

Report Date:

1961-04-01

Pagination or Media Count:

1.0

Abstract:

The mechanics of fracture initiation were investigated with particular emphasis on the effects of combined bending and extensional stress on an isotropic or orthotropic cracked specimen initial sheet curvature on the stress field in the vicinity of a crack and size and shape of the yielded region, or plastic enclave, near the point of the crack. It was found that according to Reissner theory, the circumferentiial distribution of surface stresses at the tip of a crack in an isotropic plate subjected to bending is identical to the extensional stress distribution. Second, the initial curvature of a cracked plate was associated analytically and experimentally with an elastic foundation supporting a flat cracked plate. Third, analytical solutions for both internally and externally cracked infinite elastic orthotropic plates were obtained. Fourth, an analysis of the plastic enclave at the crack point in an isotropic sheet was conducted for an externally cracked specimen, using relaxation methods. The area of the enclave is presented as a function of applied tensile stress. Based upon the size of the enclave, the plastic strain energy is estimated, and a ductile fracture criterion is proposed. A theory of fracture initiation is proposed for high-stress, low-cycle fatigue which, as a natural result, distinguishes between different orders of load spectra. Author

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Distribution Statement:

APPROVED FOR PUBLIC RELEASE