Micromechanical Properties

Abstract

The term micromechanical properties of polymers (or micromechanics of polymers) represents quite a broad topic, which comprises three principal areas: the measurement of micromechanical properties, the interpretation of micromechanical behavior, and the imaging of microstructure changes during deformation and fracture. Our contribution covers all three aspects of micromechanics in Polymer science. The first part focuses on the measurement of micromechanical properties by indentation methods, which dominate in the field of micromechanical properties measurement; the other micromechanical characterization methods are just mentioned briefly. The second part deals with the interpretation of micromechanical behavior, that is, with the correlations among molecular structure, supermolecular structure (morphology), micromechanical properties, and macromechanical properties of polymers. The third part describes imaging of microscopic processes during deformation and fracture or, in other words, how the deformation of polymer materials influences their morphology and vice versa.

Correlations between Microscale Indentation Creep and Macroscale Tensile Creep of Polymers

“…For polymers, the great majority of experiments were performed with the Vickers tip [ 35 ], and so the most frequently reported quantity is Vickers microhardness ( H V ). Special MH measurements can yield also microcreep ( C V ) and microplasticity ( P V ) as explained elsewhere [ 7 ]. The basic relation for microcreep determination was introduced by Balta-Calleja and co-workers [ 36 ], who studied the time-dependent part of the plastic deformation of the polymer surface under the indenter and noticed that ( H ) decreases with time according to a simple relation: where H 0 is a coefficient reflecting both sample properties and experimental conditions, and n is a constant furnishing the rate of creep of the material.…”

“…Microscale creep experiments (microcreep) are less common, but they can be performed easily by means of modern microindentation or nanoindentation hardness testers (indentation creep; ISO 14577). In comparison with macrocreep, the maximum stresses during the microcreep indentation measurements are usually higher (above Y ), the experiments are shorter (measurement times from tens of seconds to minutes), and the specimens can be much smaller (the typical indent size on a polymer surface is 10–100 μm) [ 6 , 7 ]. More detailed explanation and comparison of macrocreep and microcreep experiments is given below in Section 2 , but even the basic pieces information within this paragraph indicate that microcreep experiments show two important advantages: (i) significantly shorter measurement times and (ii) smaller testing specimens.…”