[Yuanfei Lin, Polymer] Microbuckling: A possible mechanism to trigger nonlinear instability of semicrystalline polymer
With the guidance of Prof. Li, the initial nonlinear instability of semicrystalline polymer is studied by PhD Yuanfei Lin et al. with the comparison of theoretical calculation and experimental results. The related work has been published in Polymer 154 (2018) 48–54.
Lamellar stack in semicrystalline polymers composed of alternatively arranged lamellar crystal and amorphous layers is one of the typical hard-soft laminated nano-composites. Considering the Poisson contraction effects during uniaxial tensile deformation along the normal direction of layers, microbuckling instability of lamellar stacks is first proposed as a new deformation mechanism to trigger the nonlinear mechanical behaviors in semicrystalline polymers. Based on the non-equilibrium process of crystallization and experimental observations, a three-phase structure with lamellar stack (crystal and interlamellar amorphous) and the amorphous matrix is proposed as a deformation unit in semicrystalline polymers. Based on the three-phase model and the proposition of buckling with shear mode, we deduce the theoretical critical strain for the sinusoidal microbuckling through linear stability analysis method. Taking hard-elastic isotactic polypropylene as an example, the theoretically calculated critical strain is in a good agreement with the experimental critical strain at temperatures below relaxation temperature Tα. These results suggest that elastic microbuckling is indeed a possible mechanism to trigger the nonlinear instability, which is different from current plastic deformation models with crystal destruction around yield in semicrystalline polymers.
This work is supported by the National Natural Science Foundation of China (51633009) and National Key Research and Development Program of China (2016YFB030250). The authors would like to thank Prof. Yong Ni (Department of Mechanics, USTC) for fruitful discussion. The SAXS experiments are carried out at the beamline BL16B in Shanghai Synchrotron Radiation Facility (SSRF).
Related links：
https://www.sciencedirect.com/science/article/pii/S0032386118308085
Experimental (, black circle) and theoretical (, red square) critical strain for microbuckling as functions of deformation temperature Td.
