Monsanto Fatigue to Failure Tester

Another fatigue-testing device is the (Monsanto) Fatigue to Failure Tester. This instrument measures the ultimate fatigue fife as cycles to failure. Tensile-like samples are stretched at 100 cycles per minute at a preselected extension ratio. Samples can be strained over a range of 10 to 120 percent. The fatigue performance of compounds can be measured (number of cycles to failure, i.e., rupture) and compared either at constant extension ratio (strain) or at constant strain energies (work input). 

The larger batches, each weighing 275.35 g, were mixed in a Brabender Prep Mixer measuring head, electrically heated, air cooled, with stock temperature thermocouple, fitted with Banbury-type rotors) at 40 rpm. The start-up procedure was similar to that used with the smaller mixing head however, the amount of masticated rubber temporarily removed from the mixer (to make room for the addition of the bulky carbon black) was scaled up from 10 g (taken from the 70-g batch) to 40 g. Fatigue resistance was measured by the Monsanto Fatigue to Failure Tester (ASTM D 4482). 

Fig. 8 Fatigue life (Monsanto Fatigue to-Failure Tester) as a function of strain amplitude and dispersion rating for N-330 carbon black.

Fatigue life by Fatigue-to-Failure Tester (Monsanto) at room temperature and at least 48 specimens for each polymer and each crosslink density. Experiments were performed on several sets of specimens, both notched and un-notched, gum and black compounds, at several crosslink densities and strain amplitudes. Data reported here were obtained on un-notched specimens, 136% maximum strain amplitude in the case of black compounds and notched specimens, 68% maximum strain amplitude in the case of gum compounds. 

Polybutadienes with vinyl contents of 10 7 and 72.4% have been selected for further fatigue-to-failure analysis. Fatigue life measurements have been performed on a large number of specimens by means of the Fatigue-to-Failure Tester (Monsanto). Carbon-black-filled compounds with 50 phr N330 carbon black were cured with conventional curing system at 145°C. Curative levels have been chosen to obtain vulcaniza-tes at several levels of 300% modulus. Fatigue tests were performed on un-notched specimens at room temperature and at several deformation amplitudes. Data discussed here were obtained at 136% strain amplitude. 

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