GEOMETRICAL EFFECT ON CREEP IN CROSS WELD SPECIMENS

Cross weld creep testing is an experimentally straightforward method t o estimate the creep strength in a welded joint. Interpretation of the results can be complicated by a complex of interacting creep properti es in the weldment and differences in the stress distribution between uniaxial load cross weld creep test specimens and welded components. S tress distributions in cross weld specimens are in the present study a nalysed by a fraction model of the cross weld with four constituents, namely weld metal; coarse grained heat affected zone (HAZ); fine grain ed HAZ; parent metal. Evaluated data from each constituent are used fo r finite element calculations of the multiaxial stress distribution. T he effects of weld and parent metal minimum strain rate ratio in the c ross weld specimen are studied, comparing results of an as-welded and a postweld heat treated 1Cr0.6Mo weldment. It is found that stress enh ancements appear. These enhancements can be higher when the weld and p arent metal strain rates mismatch than for matched weldments. Geometri cal effects such as the influence of the diameter of the specimen and the fraction of each constituent are then studied. It is found that th ere is a quite significant life enhancement with increasing diameter. Different rupture criteria may result in different estimation of this increase of creep life. For some weldments the cross weld specimen of a larger diameter may have a creep strength comparable with that of a pure parent metal or weld metal specimen. The location of the maximum stress enhancement in the specimen can also be altered when the diamet er is changed. The change of the HAZ width has certain influence on th e creep life of the specimen while the change of weld width in a pract ical range does not show such influence.