13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- Fig.8 Variation of stretch to fracture with aging time for CB filled rubbers aged at 120oC and at 70oC Fig.9 Variation of initial elastic modulus with aging time for CB filled rubbers aged at 120oC and at 70oC 3.2. Tear force-displacement curve and tear strength Tear fracture tests under a constant rate of 100mm/min were conducted at 23oC. Fig.10 shows the tear force-displacement curves for 15 vol% CB filled rubbers aged for various periods of time at 120oC. The tear strength defined by Eq.(1) is plotted as a function of aging time as shown in Fig.11. It is seen that the tear strength decreases in the early aging period, and increases with aging time when the aging time extends to 48 hours. Such decrease-increase trend with respect to aging time is similar to the variation of the tensile strength with aging time. Fig.10 Tear force-displacement curve for 15 vol% CB filled rubber aged for various periods of time at 120oC Fig.11 Variation of tear strength with aging time for 15 vol% CB filled rubber aged at 120oC 4 Conclusions The effects of thermal aging on the tensile and tearing fracture behavior of carbon black filled rubbers with different filler loadings have been investigated in this work. It is found that the initial elastic modulus increases with increasing aging time, while the tensile strength and tear strength decrease firstly with the increase in aging time and then increase when the age proceeds. Moreover, the change in mechanical properties due to thermal aging is found to be dependent on aging temperature, the higher the aging temperature, the more pronounced deterioration in tensile strength and stretch to fracture.
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