Development of Multiaxial Creep Testing Machine for Miniature Specimen

High temperature components such as boiler tube and jet engine turbine blade undergo multiaxial creep damage. Although multiaxial creep testing investigation is required for safety high temperature components designing, there are few commercial testing machines which can conduct multiaxial loading at high temperature. A new miniature cruciform specimen, which has a 5 mm square size plane stress gauge part, was designed by using FE analysis. A biaxial tensile loading creep testing machine was also designed to conduct multiaxial creep testing. The testing machine has 2 kN loading capacity and 1 kW furnace. We had also developed a non-contact displacement measuring method for the miniature specimen. This method uses conventional optical camera to get the surface observation photograph. Chasing the trace of the target mark painted at surface of the specimen, we can get the displacement of the specimen. The calculated strain value obtained from the non-contact displacement measuring method corresponds with the strain gauge value at room temperature. By using the multiaxial creep testing machine and the non-contact observation system, we can investigate not only deformation of the testing specimen but also surface conditions of materials during the creep testing.