Design of a small punch test apparatus for cryogenic environments using conduction cooling

Design of a small punch test apparatus for cryogenic environments using conduction cooling

This study aims to design a Small Punch Test (SPT) apparatus for cryogenic environments using conduction cooling. SPT is a non-destructive testing method developed to evaluate material softening and embrittlement in applications such as power plants and fusion reactors. Compared to conventional tensile testing, SPT offers economic advantages in terms of miniaturization and repeatability. However, existing cryogenic SPT rely on liquid helium or evaporated helium gas, which involve high costs and inefficiency. In this study, a cryogenic cooling system utilizing a cryocooler was developed to eliminate the use of liquid helium, along with a rotary sample holder designed to enable testing of multiple specimens in a single cooling cycle. Key design considerations included minimizing external heat intrusion, optimizing thermal management of the load application structure, designing flexible copper connectors suitable for rotation, and applying multilayer insulation (MLI) to reduce radiative heat loads. In particular, the conduction cooling path was optimized to ensure that the specimen temperature could be stably maintained below 20 K, while minimizing displacement in the load application structure and enhancing thermal stability tailored to the characteristics of SPT. The proposed testing apparatus significantly improves cost efficiency and testing productivity compared to existing systems, and it is expected to set a new standard for material property evaluation in cryogenic environments.