Micromechanical Properties

Abstract

An overview of successfully applicable techniques, particularly electron microscopy and scanning force microscopy, is given for the study of micromechanical mechanisms and properties in different polymers. Using modern developments in instrumentation, observation of real in situ deformation of structural details at the same place of a sample (eg, lamellae in polyethylenes) is possible. Crazing formation in amorphous polymers (polystyrene, styrene–acrylonitrile, polycarbonate) and tough‐brittle transitions depending on deformation temperature are described. General mechanisms of toughening and, in particular, effects of rubber‐toughening (eg, role of particle size, shape, and particle cavitation) in amorphous (high impact polystyrene, acrylonitrile–butadiene–styrene) and semicrystalline polymers (toughened polyamide, polypropylene, and polyethylene blends) are discussed. Individual deformation steps are summarized in a “three‐stage mechanism of toughening.” Processes of deformation of amorphous, interlamellar regions, twisting and breaking off of lamellae in semicrystalline polymers can be directly shown. Unusually large plastic deformations can be revealed in di‐, tri‐, and star‐block copolymers with a new “thin layer yielding mechanism.” Improved knowledge of micromechanical properties allows a deeper insight into the influence of morphology on mechanical properties and enables a defined modification of the morphology for improving the mechanical behavior of polymers for many practical applications, in a sense, “microstructural construction of polymers.”

Polymer Fracture

“…Values of φ are available for bending (13), and G c may be found by measuring the energy to crack initiation and via equation 26. In any test, the three parameters at fracture (a, G c , K c ) can be measured and various combinations of E and G determined.…”