Fracture-based correlation of uniaxial and small punch creep data

A critical problem of small punch test is determining the relation between this test and the conventional uniaxial test. In high-temperature creep conditions studied by constant-force variant of small punch test, this problem is often approached empirically by comparing force in small punch test and the applied stress in conventional creep test of the same duration, i.e. of the same time to fracture. A different approach is used in the evaluation of constant-rate small punch test: the force is normalized by the square of specimen thickness or, recently, by the product of the specimen thickness and a relevant deflection. Modifications of this advanced approach in the creep area are examined in the present paper. The deflection observed at fracture of specimen in small punch creep test is taken as a starting normalization quantity. The suggested correlations are illustrated by means of data obtained by creep testing of steels usually employed in power plants (P91, P92) or proposed for heavy-duty service (Eurofer'97).