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For static and dynamic material behavior of Thermoplastic Elastomers

Thermoplastic elastomers (TPEs) were examined as to their material properties under monotonic and cyclic stress. They were submitted to mechanical investigations as well as thermoanalytical and microscopic examinations.

Conducting stress-strain trials, limiting stresses or limiting strains can be determined, reflecting initial significant changes in structures under monotonic load. The levels of load applied in the beginning must be lower than this limit, in order to show characteristic changes in characteristic values over the course of the stress test. Just as the stress-strain trials, pressure tests generate a pronounced kink of the curve. Material hardnesses significantly affect the courses of the characteristic values. This is visible in the fact that the compressive deformation curves shift towards higher stresses, as hardnesses increase. The secant modulus also increases with hardness. The same correlations reveal in the compression set.

Increased hardness will step up the compression set. At increased and constant loads, cyclic tests show characteristic changes in characteristic values. With the non-reinforced modifications, strain changes give clear indications as to changes in structures, while damping additionally shows cracking phases and cracking progress in the reinforced types. At low loads, strains increase only slowly and homogenously, while above a critical load, superproportional changes in characteristic values are obtained. The level starting from which significant qualitative strain increases are initially produced is considered as being the stress limit.

Investigations conducted on PP/EP(D)M blends show that crystallization behaviour is largely determined by the EP(D)M particles contained. For instance, the rate of spherulite growth is diminished as EP(D)M content is stepped up, which is due to increased impediment to growth. SEM investigations clearly reveal the two-phase structures of the blends, particularly in specimens stored in n-heptane. Increase in loads apparently lead to microscopic and then macroscopic stretching.

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