Small Punch Test Application in VUJE laboratories

Small Punch Test (SPT) samples have a great advantage in reducing the radioactivity of the irradiated materials due to their small volume and also for the determination of material properties, which are highly dependent on the local microstructure e.g. heat affected zone. The small sample volume give us the possibility of the basic mechanical properties estimation even when there is a lack of original testing material. Based on the advantages mentioned above, the SPT procedure was included as the new method for evaluation of the real state of the materials in the new designed and established surveillance programs. For these programs, in VUJE, there were prepared and are continuously tested more than 6 thousand SPT samples from a lot of different types of PCC materials and their local areas.

The principle of SPT testing procedure applied in VUJE is penetration of the disk specimen by hemispheric rod. The small punch experimental configuration is presented in the Fig. Disk shaped specimen has 8 mm in diameter and 0.5 mm in thickness. The specimen holder consists of a lower and upper die and holder body. Using this specimen holder, the specimens are prevented from cupping upward during punching and, therefore, plastic deformation is concentrated in the region below the punch rod.

Using relatively simple system with recorders of the load and deflection values, we can obtain the following data of basic mechanical properties:

  • The yield stress and ultimate tensile strength.
  • Ductile-brittle transition temperature (DBTT) measured by the Charpy test can be estimated from the results of temperature dependence of small punch energy determined from the area under the load – deflection curve.

Currently, it is used for evaluation the SPT test the CEN workshop agreement: “Small Punch Test method for Metallic Materials” CWA 15627:2007.

However, VUJE representatives are members of the working groups or otherwise cooperate to prepare standards for Small Punch Test, such as EN SP standard and ASTM, too.





Jana Petzová, VUJE, a.s., Slovakia,
Division for Diagnostic of Nuclear Power Components