GREENHILL'S FORMULA AND THE MECHANICS OF CABLE HOCKLING

In the application of marine cables as tension members, serious structural failures have occurred as a result of hockling (forming of a loop under torsion combined with insufficient tension). This report endeavors to establish a criterion on end torques and forces for preventing hockling. It is shown that for rods in tension the torque corresponding to Greenhill's 100-year-old formula defining the onset of bending is also the maximum torque which can be sustained at that tension. Thus, a straight rod or cable loaded by tension and the Greenhill torque is unstable, and Greenhill's formula modified by an appropriate safety factor provides the desired no-hockle criterion. For long straight rods or cables under tension T and twisting moment M, this criterion for stability is M sq less than 4TEI, where EI is the bending stiffness under load. The approach used was to numerically solve in nondimensional form the two-point boundary-value problem of the rod under axial end torques and forces. The report includes curves showing torques and forces for the possible range of deflection curves.

  • Availability:
  • Supplemental Notes:
    • Final Report on one phase of a continuing NRL problem.
  • Corporate Authors:

    Naval Research Laboratory

    4555 Overlook Avenue, SW
    Washington, DC  USA  20375-5320
  • Authors:
    • Rosenthal, F
  • Publication Date: 1975-11

Media Info

  • Features: References;
  • Pagination: 29 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00128445
  • Record Type: Publication
  • Source Agency: Ship Structure Committee
  • ISBN: Proj 023-03-45-5807
  • Report/Paper Numbers: NRL 7940 Final Rpt.
  • Files: TRIS
  • Created Date: Dec 29 1975 12:00AM