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:
  • Find a library where document is available. Order URL: http://worldcat.org/isbn/Proj02303455807
• Supplemental Notes:
  • Final Report on one phase of a continuing NRL problem.
• Corporate Authors:

  Naval Research Laboratory

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

Media Info

• Features: References;
• Pagination: 29 p.

Subject/Index Terms

• TRT Terms: Design; Mechanical failure; Mooring cables; Rope; Wire rope
• Old TRIS Terms: Cable failure; Rope technology
• Subject Areas: Design; Marine Transportation;

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