Abstract
Motivated by advances in flexible electronic technologies and by the endeavour to develop non-destructive testing methods, this article analyses the capability of computational multiscale formulations to predict the influence of microscale cracks on effective macroscopic electrical and mechanical material properties. To this end, thin metal films under mechanical load are experimentally analysed by using in-situ confocal laser scanning microscopy (CLSM) and in-situ four point probe resistance measurements. Image processing techniques are then used to generate representative volume elements from the laser intensity images. These discrete representations of the crack pattern at the microscale serve as the basis for the calculation of effective macroscopic electrical conductivity and mechanical stiffness tensors by means of computational homogenisation approaches. A comparison of simulation results with experimental electrical resistance measurements and a detailed study of fundamental numerical properties demonstrates the applicability of the proposed approach. In particular, the (numerical) errors that are induced by the representative volume element size and by the finite element discretisation are studied, and the influence of the filter that is used in the generation process of the representative volume element is analysed.
Highlights
Flexible electronics need to be stretchable and foldable
A direct comparison of the latter with experimental results is not feasible for the metal thin films that are in the focus of the present contribution, interesting differences in the evolution of the mechanical and the electrical material parameters are observed which are important for the development of non-destructive electric potential-based testing methods as elaborated in, e.g., Tada et al (1996, 1997), Tada (2006)
The present contribution is based on the experiments documented in Cordil et al (2017) where a bilayer made of a 200 nm Cu film with a 10 nm Cr adhesion layer on a 50 μm Upilex Polyimide substrate was cyclically strained and analysed by using in-situ resistance measurements and confocal laser scanning microscopy (CLSM) imaging
Summary
Flexible electronics need to be stretchable and foldable. cyclic loading causes more mechanical damage in terms of crack nucleation and growth than monotonic stretching or flex to connect loading (Glushko et al 2017; Kreiml et al 2019). Characteristic properties like the crack onset strain (COS) are determined, and the evolution of the mechanical damage in terms of TTCs and localised necking is studied with optical microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) or confocal laser scanning microscopy (CLSM) methods (Renault et al 2003; Leterrier et al 2004; Cordill et al 2010; Jin et al 2011; Cordill et al 2015, 2016; Etiemble et al 2019; Cahn et al 2020). A direct comparison of the latter with experimental results is not feasible for the metal thin films that are in the focus of the present contribution, interesting differences in the evolution of the mechanical and the electrical material parameters are observed which are important for the development of non-destructive electric potential-based testing methods as elaborated in, e.g., Tada et al (1996, 1997), Tada (2006).
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