Design of 20 mm-Sized Miniature Cruciform Creep Specimen

This study discusses the design of small-sized cruciform creep specimens with an external dimension of up to 20 mm. One of the reliable methods for assessing remaining life is destructive testing. It is desirable to reduce the size of test specimens which limits the damaged area affected by sampling. Cruciform specimens, which allow for multiaxial creep tests over a wide range of principal stress ratios, have been studied for miniaturization, and a 50 mm-sized specimen has been developed. Further miniaturization will require consideration using FEM. In this study, the effect of the structural dimensions of the cruciform creep specimen, particularly the dimensions of each part such as the arm length and slits, on the generated stress was examined using 63 patterns of elastic analysis. The dimensions of the cruciform creep test specimens were determined using the knowledge gained from the elastic analysis, and the validity of the designed 20×20×4 mm-sized specimens was confirmed by the elastic-creep analysis. The gauge section achieved plane stress condition and resulted in a von Mises equivalent stress of approximately 200 MPa with an applied load of 1.25 kN. The volume of the specimen could be reduced to 1/680 of that of conventional bulk specimens.