THE EFFECTS OF SURFACE LAYER ON PLASTIC DEFORMATION AND CRACK PROPAGATION

Chapter I--The crack propagation of 2014-T6 aluminum, titanium (6Al-4V), and 4130 steel (YS - 180,000 psi) was measured under plane stress and plane strain, and a comparison was made to determine the effect of eliminating or decreasing the surface layer (SLE treatment) on the cracking resistance of the specimens. The data show that, in all cases, the SLE treatment improves the crack resistance. The improvement is on the order of 2 to 5 times, depending on the stress intensity factor. A comparison between the SLE-treated and shot-peened specimens shows that the SLE treatment also improves the cracking resistance by about a factor of 2 over that obtained from shot-peening. The endurance limit of titanium (6Al-4V) tubing was increased from 70,000 to 90,000 psi by the SLE treatment. Tests made to assess the effectiveness of the SLE treatment on commercial 4130 steel tanks were inconclusive due to the large scatter in the crack propagation rates. Chapter II--It was shown that when specimens of 2014-T6 aluminum, titanium (6Al-4V), and 4130 steel (YS = 180,000 psi) were fatigued, the surface-layer stress increased. The number of cycles required to initiate a propagating crack was determined. The data show that a crack is initiated when the surface-layer stress attains a critical value. This value is independent of the cyclic stress amplitude. Based on these results, a new theory of fatigue has been proposed.

  • Corporate Authors:

    Army Materials and Mechanics Research Center

    Watertown, MA  USA  02172
  • Authors:
    • Kramer, I R
  • Publication Date: 1973-7

Media Info

  • Features: References;
  • Pagination: 94 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00048398
  • Record Type: Publication
  • Source Agency: Ship Structure Committee
  • Report/Paper Numbers: AMMRC CR 71-2/6 Final Rpt
  • Contract Numbers: DAAG 46-70-C-0102
  • Files: TRIS
  • Created Date: Nov 14 1973 12:00AM