STUDIES OF SOME BRITTLE FRACTURE CONCEPTS

Linear elastic fracture mechanics is used in evaluation of the fracture toughness disclosed by the arrest of cleavage fractures in notched and welded wide plate specimens. Fracture toughness values also are obtained from strain field measurements in the vicinity of propagating cracks on the verge of arrest in 6-ft-wide plates. The results clearly show the trend towards "toughening" at higher temperatures and the major role residual stress fields can play in driving fractures. An experimental investigation was conducted to investigate the influence of welding on the yield behavior of metal from the thermally affected zone in the vicinity of a weld. The rate-temperature dependent component of the yield stress appears to be the same for base metal and metal from the thermally affected zone, but the yield stress of the thermally affected zone metal shows a substantially increased rate-temperature independent component. A critical stress model for the prediction of brittle cleavage fracture is developed and applied to cleavage initiation, propagation, and arrest. The model approximately accounts for inelastic behavior near a flaw by truncating the elastic stress distribution. Effects of rate, temperature, notch acuity, local strain hardening, residual stress, and propagation velocity are considered; the model demonstrates good qualitative representation of the effects of these parameters on the susceptibility to cleavage. Correlations with experimental results show the model is capable of quantitative representation of the effects of rate and temperature on the applied stress required for the initiation of brittle cleavage fracture and the stress required for continued cleavage propagation. The study suggests that low-stress cleavage initiation at service temperatures can be associated with a marked local reduction of critical fractures, stress, that residual stresses can be responsible for the propagation through sound metal of fractures initiated in damaged material, and that the critical fracture stress and fracture mechanics approaches are equivalent when applied to cleavage propagation and arrest.

• Corporate Authors:

  University of Illinois, Urbana-Champaign

  Urbana, IL  United States  61801

  Ship Structure Committee

  National Academy of Science, 2101 Constitution Avenue, NW
  Washington, DC  United States  20418
• Authors:
  • Wright, R N
  • Hall, W J
  • Terry, S W
  • Nordell, W J
  • Erhard, G R
• Publication Date: 1965-9

Media Info

• Features: References;
• Pagination: 86 p.

Subject/Index Terms

• TRT Terms: Cleavage fracture; Cracking; Elasticity (Mechanics); Fracture mechanics; Heat affected zone (Metals); Plate bearing test; Residual stress
• Identifier Terms: Ship Structure Committee
• Uncontrolled Terms: Crack initiation; Crack propagation
• Old TRIS Terms: Crack arrest; Residual stresses
• Subject Areas: Marine Transportation; Materials;

Filing Info

• Accession Number: 00331939
• Record Type: Publication
• Source Agency: Ship Structure Committee
• Report/Paper Numbers: SSC-170 Final Rpt.
• Contract Numbers: NObs-86688
• Files: TRIS
• Created Date: May 21 1981 12:00AM