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Instabilities and Failure in Soft Fiber Composites: analysis, simulations, and 3D printing

By Stephan Rudykh (Technion)
Co-authors: Viacheslav Slesarenko (Technion)

We examine the response of fiber composites with hyperelastic phases subjected to compression along the fiber direction. The applied compressive loading may lead to development of elastic instabilities upon achieving the critical strain. To estimate the critical strains corresponding to the onset of macroscopic instabilities associate with the loss of ellipticity, we obtain the homogenized response of transversely isotropic fiber composites, and evaluate the effective tensor of elastic moduli. We show that the onset of instabilities can be predicted by a closed form explicit expression in terms of the material properties and volume fractions of the constituents. The analytical estimations are compared with 3D finite element simulations, and an excellent agreement is reported. However, instabilities may develop at smaller length-scales first; to capture the onset of these microscopic instabilities, we idealize the microstructure as 2D periodic layered composites, and perform the microscopic instability analysis. We derive an explicit estimate for critical strain and critical wave length of the buckled wavy shapes. Finally, we experimentally observed the existence of these macroscopic and microscopic modes of instabilities in periodic layered structures, and in 3D fiber composites. The results for the critical strain and wavelength are found to be in good agreement with the theoretically and numerically predicted values. Moreover, we experimentally show that the microscopic instabilities in the composites with rate-dependent phases can be significantly tuned by the applied strain rate. Finally, we use the multimaterial 3D printing to fabricate some bio-inspired composites with soft interphases, and we analyze their failure mechanism under different loading conditions.

Ⓒ Photos:Toerisme Leuven