ISSN:
0021-8995
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
It was demonstrated that the mechanical stress-induced βα-transformation in isotactic polypropylene (iPP) is associated with considerable toughness enhancement. This toughness improvement depends on the test conditions (loading frequency). The toughness of β-iPP was superior to the α-iPP by 13% under static (characterized by a load frequency of ca. 5 × 10-4 Hz) and 70% under dynamic (tensile impact with a loading frequency in the range of ca. 3 × 102…103 Hz) conditions, respectively. By applying the essential work of fracture (EWF) concept to single-edge notched tensile (SEN-T) specimens it was shown that for the toughness upgrading observed, energy dissipation in the enlarged plastic zone is responsible. The occurrence of the βα-transformation was evidenced by differential scanning calorimetry (DSC). Based on DSC measurements it was found that the degree of βα-trans-formation depends on the local strain. At high strain values the βα-conversion is complete (at elogation at break in uniaxial static tensile test), while this transformation is only partial at lower strains (at tensile impact). In addition, in the plastic (or deformation) zone the βα-conversion changed locally, and can be used for mapping of this region. © 1996 John Wiley & Sons, Inc.
Additional Material:
11 Ill.
Type of Medium:
Electronic Resource
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