Abstract
This work combines experiments and finite element simulations to study the effect of pre-imposed cyclic loading on surface instability of silicon rubber under compression. We first fabricate cuboid blocks of silicon rubber and pinch them cyclicly a few times. Then, an in-house apparatus is set to apply uniaxial compression on the silicon rubber under exact plane strain conditions. Surprisingly, we find multiple creases on the surface of silicone rubber, significantly different from what have been observed on the samples without the cyclic pinching. To reveal the underlying physics for these experimentally observed multiple creases, we perform detailed nanoindentation experiments to measure the material properties at different locations of the silicon rubber. The modulus is found to be nonuniform and varies along the thickness direction after the cyclic pinching. According to these experimental results, three-layer and multilayer finite element models are built with different materials properties informed by experiments. The three-layer finite element model can excellently explain the nucleation and pattern of multiple surface creases on the surface of compressed silicone rubber, in good agreement with experiments. Counterintuitively, the multilayer model with gradient modulus cannot be used to explain the multiple creases observed in our experiments. According to these simulations, the experimentally observed multiple creases should be attributed to a thin and stiff layer formed on the surface of silicon rubber after the pre-imposed cyclic loading.
Highlights
Elastic surface instability of silicon rubber has been harnessed to realize the recoverable large deformation of flexible electronics for silicons, carbon nanotubes and graphenes [1,2,3,4]
We focus on two characteristics induced by cyclic pinching: the appearance of multiple creases and the observed critical strain 28% for the occurrence of multiple creases is smaller than that of single or double creases
We find that multiple creases are formed on the surface, which are significantly different from what have been observed for the specimen without pre-imposed cyclic pinching
Summary
Elastic surface instability of silicon rubber has been harnessed to realize the recoverable large deformation of flexible electronics for silicons, carbon nanotubes and graphenes [1,2,3,4]. Despite the abundance of crease formations in scientific and engineering applications, the underlying physics principles emerge only recently with the nature of creases being attributed to the broken symmetry of scale and translation [8]. With this regard, creases can be distinguished from the often discussed wrinkles [9,10,11,12,13,14]. When silicone rubber is used in engineering applications, it often experiences cyclic. A question naturally raises: can cyclic loading influence its surface instability behavior?
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