PSI - Issue 37

3

Shirsha Bose et al. / Procedia Structural Integrity 37 (2022) 131–138 Bose et al., 2021/ Structural Integrity Procedia 00 (2019) 000 – 000

133

Fig. 1: Schematic of model dimensions for square (a) and circular (b) micro-islands (not to scale).

2.3. Boundary conditions and mesh type Due to structural symmetry, the micro-islands were modelled considering their quarter with appropriate symmetric boundary conditions as shown in Fig. 2. A maximum strain of 5% was applied in tension to the collagen substrate. For both cases, the mesh assigned to the layers were formed with 8-node linear brick, reduced integration with hourglass control, hybrid, constant pressure elements (C3D8RH). Mesh refinement was introduced at the collagen chromium interfacial region to obtain appropriate results. It is worth mentioning that the data presented here were extracted after the finite-element simulations converged.

Table 1: Material properties used in simulations Entity Material definition

Young’s modulus (GPa)

Poisson’s ratio

Yield strength

Reference

Gold

Elastic-perfectly plastic

53

0.42

230

(Espinosa and Prorok, 2003; Lin, Tong and Shiu, 2008; Wang and Prorok, 2008) (Thornton and Hoffman, 1989; Cordill et al., 2010)

Chromium

Elastic-perfectly plastic

280

0.21

160

Material definition μ 1 (MPa) μ 2 (MPa) μ 3 (MPa) α 1 (MPa) α 2 (MPa) α 3 (MPa) Ogden model (N = 3) 9.975 0.217 -6.541 1.486 2.637 -2.90

Collagen

Reference

Dry Wet

(Bose et al., 2020) (Bose et al., 2020)

Ogden model (N = 3)

0.345

0.001

-0.338

0.857

3.264

0.703

3. Results and discussions The stress distribution in different layers of the sensor is presented and discussed in this section along with the interfacial damage for both types of micro-islands. 3.1. Stress distributions The spatial stress distributions in metallic layers of gold and chromium for both square and circular micro-islands are shown in Figs. 3a and b, respectively. The corresponding stress accumulation on the collagen substrate for both