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Discontinuous yielding and fracture initiation near a notch in mild steel

Citation

Krause, Daniel Julius (1968) Discontinuous yielding and fracture initiation near a notch in mild steel. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:07212014-092153135

Abstract

This thesis presents the results of an experimental investigation of the initiation of brittle fracture and the nature of discontinuous yielding in small plastic enclaves in an annealed mild steel. Upper and lower yield stress data have been obtained from unnotched specimens and nominal fracture stress data have been obtained from specimens of two scale factors and two grain sizes over a range of nominal stress rates from 10^2 to 10^7 lb/in.^2 sec at -111°F and -200°F. The size and shape of plastic enclaves near the notches were revealed by an etch technique.

A stress analysis utilizing slip-line field theory in the plastic region has been developed for the notched specimen geometry employed in this investigation. The yield stress of the material in the plastic enclaves near the notch root has been correlated with the lower yield stress measured on unnotched specimens through a consideration of the plastic boundary velocity under dynamic loading. A maximum tensile stress of about 122,000 lb/in.^2 at the instant of fracture initiation was calculated with the aid of the stress analysis for the large scale specimens of ASTM grain size 8 1/4.

The plastic strain state adjacent to a plastic-elastic interface has been shown to cause the maximum shear stress to have a larger value on the elastic than the plastic side of the interface. This characteristic of dis continuous yielding is instrumental in causing the plastic boundaries to be nearly parallel to the slip-line field where the plastic strain is of the order of the Lüder's strain.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Materials Science
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Materials Science
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Wood, David Shotwell
Thesis Committee:
  • Unknown, Unknown
Defense Date:1 April 1968
Record Number:CaltechTHESIS:07212014-092153135
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:07212014-092153135
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8572
Collection:CaltechTHESIS
Deposited By: John Wade
Deposited On:21 Jul 2014 16:50
Last Modified:21 Jul 2014 16:50

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