Flex fatigue life

Like HIIR, EPR has a fully saturated backbone and has only unsaturation points available for vulcanization cross-linking in very small percentages of the pendent diene modifier (EPDM). It is an excellent aging compound with high flex fatigue life even when heavily loaded with fillers and is utilized in PCT white sidewalls. 

Flex Fatigue Life 4-100 fold — 100 fold -1000 fold... 

Flex Life - Flex fatigue life is the total number of cycles that a specimen can be flexed in a prescribed manner before failure occurs. Failure is defined as physical breakdown of the specimen material. A number of methods such as MIT, Ross and De Mattia are used to measure flex life. See also Fatigue Life. 

Unlike crosslinker content, the level of carbon black In the elastomer did not significantly affect cure time (Table VII) but did have a dramatic effect upon flex fatigue life. In order to obtain high flex life, the maximum loading of carbon black was limited to 80 phr. 

FIGURE 7.13 Vulcanizate properties —, 300% modulus (Mpa) —, DeMattia flex fatigue life (kHz X 10"-1) -0-0-0-, % retention of ultimate elongation after 2 days at 100°C. 

The contours for flex fatigue life are complex. The test is run such that the specimens are about equally strained however, there is some question as to whether the tests should be run at equal strain or at equal strain energy (Gent et al., 1964 McCall, 1969). For some cases, where strain is restricted by fabric reinforcement, fatigue test data should be compared at equal strain amplitude. For other applications, where the strain is not limited, the tests should be run at equal strain energy. The contours as presented here can be interpreted in terms of either constant strain or constant strain energy All points on the chart can be compared at an approximately equal strain per cycle however, if we interpolate... 

Specifically designed as an 80 Shore A durometer TPE, this is a diamine chain extended version of Corethane . Coremer solution cast films have a low initial modulus and high flex fatigue life. Information as to longterm biostability is not available at this time (Tables 4.4 and 4.13). 

Crystallinity is an important consideration in injection molding because of the impact of a part s crystalline eontent on its properties and appearance. Most polymers are semicrystalline, meaning that there is a relatively large volume increase as the polymer melts and becomes entirely amorphous. After a part has been molded, the rate at which it is cooled (the speed of cooling the part) will determine the extent of its recrystallization. For example, flex fatigue life and transparency increase when crystallinity decreases. Mechanical strength and various moduli increase at higher crystallinity. 

Butadiene Rubber (BR) added at levels of up to 10% to improve processing of S-grades (reduced mill sticking) however, a reduction in flex-fatigue life may be observed. BR also improves low-temperature brittleness. 

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