LOW CYCLE FATIGUE PROBLEMS IN SHIPBUILDING: CRACK PROPAGATION IN COARSE-GRAINED ZONES OF THICK PLATES

In welded plate structures subjected to cyclic loading fail-safe design is mainly a matter of disposing of reliable information about rate of crack propagation and maximum permissible length of cracks. In many cases the latter is connected to the danger of brittle fracture. In ships and other large plate structures introduction of--from an economical point of view very attractive--the one-run welding methods has resulted in reduced safety with respect to brittle fracture. That is why in the Delft University Ship Structures Laboratory low cycle fatigue tests have been carried out at subzero temperatures with 3000 x 500 mm (118 x 19.7 in.) specimens containing transverse electro-gas (EG) or electro-slag (ES) welds. In the heat-affected zone (HAZ) 26 and 30 mm (1.02 and 1.18 in.) long notches were provided for. Plate thicknesses were 34 and 46 mm (1.34 and 1.81 in.). The material was normalised Nb-containing steel with 344 N/sq.mm (22.3 tonf/sq. in.) yield point. The main purpose was to let fatigue cracks 'travel' through the HAZ in order to find weak spots. A remarkable phenomenon was found, viz. the occurrence of small brittle 'steps' during the fatigue testing. Additional small-scale bending tests have proved that these brittle steps were not only a consequence of the heterogeneity of the HAZ, but were connected to the damage induced at the tip of the crack by the cyclic loading. Comparisons are further made between the fatigue-crack propagation in the axially loaded large specimens and in the specimens loaded in bending. Some of the latter had been given a HAZ-simulating heat treatment.

• Supplemental Notes:
  • This is Paper #16 of the Fatigue of Welded Structures Conference, The welding Institute, Brighiton, England, July 6-9, 1970.
• Corporate Authors:

  Delft University of Technology

  Ship Structures Laboratory
  Delft,   Netherlands 
• Authors:
  • Nibbering, JJW
  • Lallenan, A W
• Publication Date: 1970-7

Media Info

• Features: References;
• Pagination: 16 p.

Subject/Index Terms

• TRT Terms: Cracking; Fracture mechanics; Heat affected zone (Metals)
• Uncontrolled Terms: Crack propagation
• Old TRIS Terms: Low cycle fatigue
• Subject Areas: Marine Transportation; Materials;

Filing Info

• Accession Number: 00072518
• Record Type: Publication
• Source Agency: Ship Structure Committee
• Report/Paper Numbers: No. 16
• Files: TRIS
• Created Date: Dec 19 1974 12:00AM