Stress analysis of stretchable electronic circuit

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Date
2018-08-01
Authors
Norhidayah Abdul Aziz
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Stretchable electronic circuit (SEC) is an electronic product that has been developed recently in serving human comfort in various applications such as sensor. It was started by introducing a circuit with interconnection concept using metallic material by controlling the size and the design of the interconnection embedded into a flexible substrate. The interconnection has been developed continuously by controlling types of material used and the design of the circuit to enhance its stretchability. This study presents the stress behaviour of the SEC using a polymer material of polydimethylsiloxane (PDMS) as the substrate and a new formulated mixed Silver flakes and PDMS as the circuit material in the form of liquid known as Ag-PDMS conductive ink. The mechanical behaviour of the substrate and conductive ink was characterized using tensile testing. Tensile test data were used in characterizing the material properties using a Neo-Hookean model and a multilinear plastic model for substrate and conductive ink respectively to represents the circuit’s behaviour in Finite Element Analysis (FEA) software. Several basic designs of SEC such as rectangular, zigzag and horseshoe shape were modelled using Solidwork and was exported to ANSYS Workbench for preliminary structural analysis. The analysis was conducted to determine the stress-strain behaviour of the circuit under different geometry and loading condition. Besides, the structural analyses were also conducted on a real prototype of thermal sensor circuit application. The deformation behaviour of the circuit was investigated to assess the structural integrity of the circuit under different geometry, loading and material. It can be seen that the critical area for the stress concentration depended on the loading direction either parallel or perpendicular to the circuit printing. Besides, it showed high stress concentrated at the inner side of crest area for both horseshoe and zigzag design. The yield stress for the conductive ink was 0.20 MPa. Meanwhile, the stress-strain results of the entire model showed that the maximum equivalent stress was below the yield stress for simple circuit limited to 10 % strain applied at 0.19 MPa. However, the maximum equivalent stresses for thermal sensor circuit is exceeding the yield stress for uniaxial vertical and biaxial loading at 66.66 % and below than 10 % plastic deformation respectively. The horizontal loading give no plastic deformation for thermal sensor circuit at maximum equivalent stress is 0.16 MPa.
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