Characterizing shear transformation zones in polycarbonate using nanoindentation. (15th January 2016)

• Record Type: Journal Article
• Authors: Samadi-Dooki, Aref; Malekmotiei, Leila; Voyiadjis, George Z.
• Is Part Of: Polymer. Volume 82(2015)
• Page Start: 238
• Page End: 245
• Publication Date: 2016-01-15
• Subjects: Amorphous plasticity -- Glassy polymer -- Nanoindentation -- Shear transformation zones -- Nucleation energy; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; 547.7
• DOI: 10.1016/j.polymer.2015.11.049
• Languages: English
• ISSNs: 0032-3861

Abstract

Abstract: Shear transformation zones (STZs), as the Nano scale constituents which mediate homogeneous amorphous plasticity, have not been precisely characterized for glassy polymers yet. This study is aimed at obtaining the geometrical and micromechanical parameters pertaining to nanostructural deformation induced transitions in polycarbonate as a widely used amorphous polymer through performing systematic nanoindentation experiments on thoroughly prepared samples with different thermal histories. By examining the strain rate and temperature sensitivity of the flow, it is found that the geometrical properties of the STZs are only slightly dependent on the thermal history of the sample. STZs are shown to occur in almost flat ellipsoidal regions with the volume of 480 nm 3 which encompasses 5700 monomers, and with the transformation shear strain of about 0.02. The nucleation Helmholtz free energy for a single STZ is identified to be almost strain rate insensitive and calculated to be about 1.35 eV for the tested strain rates. The obtained results provide reliable and precise data required as inputs for solving boundary value problems in theoretical and numerical simulation studies of yielding and plasticity of PC at macroscopic level; and the nanoindentation experimental procedure outlined here could be used for characterizing other glassy materials. Graphical abstract: Highlights: Nanoindentation tests are conducted on PC at different strain rates and temperatures. Stress-based Arrhenius model is used to study the homogenous flow of PC. Shear Transformation Zones in PC are characterized geometrically and mechanically. The effect of the thermal history on the STZs properties is evaluated.