PSI - Issue 60

Ganesh Nigudage et al. / Procedia Structural Integrity 60 (2024) 678–689 Ganesh Nigudage / Structural Integrity Procedia 00 (2023) 000 – 000

679

1. Introduction

Nomenclature ε t

In tensile testing, total elongation (%) In SP testing, elastic-plastic transition force (N)

F e

F h0/10,off

In SP testing, force at the intersection between the test record and a line parallel to the slope of the initial linear region with an offset of 0.1∙h 0 (N) In SP testing, force at the intersection between the test record and a line parallel to the slope of the initial linear region with an offset of 0.1 mm (N) In SP testing, force corresponding to a displacement value of 0.48 mm (N) In SP testing, force corresponding to a displacement value of 0.65 mm (N) In SP testing, maximum force (N)

F m

F 0.1mm,off

F 0.48mm F 0.65mm

F(v) f(v)

In SP testing, raw test force value. In SP testing, bilinear function used to determine F e In SP testing, initial specimen thickness (mm)

h o

SPT

Small Punch Test

v

Punch displacement (mm)

v f

In SP testing, punch displacement corresponding to a 20 % force drop with respect to maximum force (mm)

v m v 1p .

In SP testing, punch displacement at maximum force (mm)

In SP testing, punch displacement at the occurrence of the first significant pop-in (mm).

Yield strength in tensile testing

Tensile strength in tensile testing

Small punch testing (SPT), developed in mid- 1980’s, is a material characterization technique and has ability to use small, thin samples to assess mechanical properties. It is useful for evaluating material properties of component in service (Torres and Gordon, 2021). Small samples are required to study irradiation damage because there is limitation of sample size in irradiated material testing. SPT samples give an advantage in reducing the radioactivity of irradiated materials because of small specimen volume (Vaclavkova and Kupca, 2001). It can also be used to determine material properties that are dependent on local microstructure (eg. Heat affected zone-HAZ). It involves use of round disks of 3 or 8mm diameter, 0.25 or 0.5mm thick or square specimens (10mm side, 0.5mm thickness). The specimen is clamped between upper and lower die and is centrally loaded by a spherical ball using a punch, expanding it into a lower die. In place of spherical ball and punch, hemispherical punch can be used. The use of ball in place of hemispherical punch allows for replacing the ball after each test to prevent accumulation of damage to punch affecting subsequent tests. A bulge in disc occurs after test (Enrico Lucon et al., 2020). A schematic representation of SP test method is shown in Fig. 1. In small punch test, the specimen is subjected to combined bending and stretching. Typical force-displacement plot obtained in SPT, shown in Fig. 2, can be divided in five distinct regions as follows 1. Elastic region 2. Departure from linearity (elastic-plastic transition), 3. Local bending, transitioning to a membrane stress regime, 4. Membrane stress regime, and 5. Final failure region.