Effects of stretching and cycling on the fatigue behavior of polymer-supported Ag thin films

The fatigue behavior of silver films on polyethylene-terephthalate substrates is studied for various levels of film thickness, pre-stretch, sample width, and applied strain range. Films with large pre-stretch have a shorter fatigue life, with failure caused by strain localization (films thicker than 100 nm) or intergranular crack formation (100 nm film). There is a significant effect of film thickness on how the strain range affects the fatigue life – we observe ‘smaller is better’ behavior for films subjected to a total strain range of Δεt=1.0%, while the opposite is true when the total strain range increases to 2.0%. We attribute this difference to a shift in failure mechanism with strain amplitude from typical fatigue failure to a more ductile-type failure. Our experimental results are well described by the Coffin–Manson relationship and a failure mechanism map is drawn based on the experimental results. Considering stretchability and long-term reliability, design suggestions are made to optimize the fatigue life of coatings subjected to uniaxial stretch and fatigue.