SEDL / STP / STP1244-EB / STP14643S

Constraint Effects on the Upper Shelf in Cracked Welded Specimens

Franco, C
Mechanical engineer and expert, fracture mechanics, FRAMATOME, Paris-La-Défense,

Gilles, P
Mechanical engineer and expert, fracture mechanics, FRAMATOME, Paris-La-Défense,

Eripret, C
Mechanical engineer, fracture mechanics, Electricité de France, DER, Les Renardières, Ecuelles,

Nallet, S
Mechanical engineer, University of Lyon, Lyon,

Pages: 29    Published: Jan 1995

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Abstract

Assessing crack initiation in welds is of importance for pressure vessels, since in safety analyses cracks are usually postulated in weldments. The toughness that represents the material's resistance to crack initiation is measured on specimens. The transferability problem of this parameter to cracked welds in structures of different geometry and subjected to different type of loadings is investigated. Detailed inite element analyses are conducted on specimens exhibiting a high mismatch between base and weld metal tensile properties, ductile tearing initiation is predicted using three different approaches. One is the local approach, which models the growth of cavities in front of the crack, the two other are the two-parameter approaches referenced as J-T and J-Q, which describe the singular crack tip stress-stain fields with the amplitude of the singularity and a second order term. In comparison to homogeneous weld metal specimens, it is concluded that the constraint effect in bimetallic specimens remains unchanged if the distance of the crack tip to the interface is not too small with respect to the ligament size and if the initiation load is less than the yield limit load.