PSI - Issue 21

O. Berk Aytuna et al. / Procedia Structural Integrity 21 (2019) 120–129 O. Berk Aytuna et al. / Structural Integrity Procedia 00 (2019) 000 – 000

125

6

a)

b)

0 2 4 6 8 x10 -3

0.015

0.01

0.005

0

0.015

0.01

0.015 0.02 0.025 0.01 0.005 0

0.005

0

0.015 0.02 0.025 0.01 0 0.005

1 mm

Loading direction

1 mm

Fig. 4. Strain distribution map of the material fromdifferent time intervals (a) under uniaxial condition (b) under equibiaxial condition.

DIC results in ε xx direct ion of deforma tion during biaxia l testing of the ma teria l show different stra in distribution compared to uniaxia l testing (Fig. 4b). Instead of sharp, pronounced, and angled bands, there are diffuse and shifted bands formed under biaxia l stretching. In this case, the stra in-free b lue regions cover approximately one third of the gage area . Stra in va lues have a peak a t the edge region as in uniaxia l condition. However, the stra in is not loca lized a long the centerline of the PLC bands. The stra in is lower in the middle of the pit region compared to the edge regions. Previous work on the testing appara tus (Seymen et a l. (2016) showed tha t shear stra in is negligible a t the center region having 1 mm diameter during biaxia l stretching. Coincidenta lly, the continuity of the PLC band is disrupted a t the same region where there is no shear stra in, indica ting tha t the shear stra in is critica l in the forma tion of bands. Towards the end of the test, two PLC bands cross each other, which is v isible by X shape in the st ra in maps (Fig. 4b). Maximum detected stra in in the formed PLC bands is approxima tely 0.025 and it is very close to the uniaxia l condition. Moreover, the stra in loca liza tion during biaxia l stretching is observed a lways a t the same region. When stra in loca liza tions are examined, higher amounts are observed near the edge of gage, where it is twice the stra in accumula ted a t the center.

a)

b)

c)

Fig. 5. (a) Strain versus time plot of thematerial during uniaxial and equibiaxial stretching (b) zoomed viewof the circle in uniaxial region (c) zoomed view of thecircle in biaxial region.