The Small Punch Creep Test - a tool to rank and qualify creep properties – comparison cast and additive manufactures 316 Stainless steels

There has been a significant increased attention for miniaturized mechanical tests in the recent decade. One example is the small punch test where a small is disk placed in a die with a circular hole and loaded by an indenter. The load and deflection are then used to deduct tensile, creep, and also fracture properties. A CEN as well as an ASTM standards for the small punch test have recently been published and the small punch test is now included in the RCC-MRx design code to assess material properties. The small punch test requires very small material volumes and the test is relatively simple to conduct, but the modelling is quite challenging. This is particularly true for creep deformations that generally include significant plastic deformation; stress and strain fields vary across the disk; forward-creep and relaxation occur simultaneously; the friction between the indenter and the disk has a significant influence on the deformation and time to rupture. Nevertheless, there is a very good transferability between the small punch and the standard uniaxial creep test for creep ductile materials. The interpretation and the assessment of the small punch creep test becomes much more difficult and questionable when creep ductility is reduced. The presentation will illustrate these issues by through uniaxial and small punch creep tests and numerical simulations for cast and additive manufactured 316 stainless steels where the cast form has higher creep ductility. We will explain and justify the differences and the implications for the small punch test as a future standard test for screening new materials and assess ageing effects.