1. Understanding structure-mechanics relationship of high density polyethylene based on stress induced lattice distortion.
- Author
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Wang, Zhen, Liu, Yanping, Liu, Chuntai, Yang, Junsheng, and Li, Liangbin
- Subjects
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POLYETHYLENE , *LATTICE dynamics , *SYNCHROTRON radiation , *LINEAR elastic fracture , *ENERGY dissipation - Abstract
Abstract The relationship between the macroscopic non-linear mechanics and the microscopic crystal structural evolution of pre-oriented high-density polyethylene (HDPE) is investigated by in situ synchrotron radiation wide-angle X-ray diffraction (WAXD) measurement over a wide temperature range from −10 to 130 °C. With the concept of stress-induced disordering of crystal, the ratio ( φ a / b ) of lattice parameters a to b is defined as a new structural variable, which can reflect the lattice distortion and then the microscopic stress state of orthorhombic crystal (O-crystal). According to the temperature-dependent non-linear variation of φ a / b with strain, the contributions of O-crystal and monoclinic crystal (M-crystal) to the macroscopic mechanics including linear elasticity, yielding, stress softening and strain hardening are clarified. It is found that M-crystal bears the main extensional stress once formed, although it survives within a limited strain window relying on temperature. By further combining the extensional phase diagram constructed in strain-temperature space, the HDPE deformation is recognized to undergo successively one-dimensional (1D) chain segments rotation of crystal, two-dimensional (2D) crystal plan shearing or slipping and three-dimensional (3D) recrystallization along with increasing strain or stress, demonstrating a multiscale structural transition and energy dissipation mechanism. Graphical abstract Image 1 Highlights • A new structural parameter is defined to characterize the lattice distortion and the microscopic stress state of crystal. • Multiscale structural evolutions of crystal are connected to the macroscopic non-linear mechanics of HDPE under deformation. • The research method can be generalized to other semicrystalline polymers to understand the structure-mechanics relationship. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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