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Effect of some processing and service conditions on the mechanical properties of an engine mount compound
Natural rubber is used for a variety of applications and especially in tyres and anti-vibration mounts, because of its superior mechanical properties. The useful (service) life of the rubber can be affected by the presence of flaws introduced during fabrication and by conditions experienced during s...
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Format: | Dissertation |
Language: | English |
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Online Access: | Request full text |
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Summary: | Natural rubber is used for a variety of applications and especially in tyres and anti-vibration
mounts, because of its superior mechanical properties. The useful (service) life of the rubber
can be affected by the presence of flaws introduced during fabrication and by conditions
experienced during service. In order to assess and predict the functional life of a natural
rubber (NR) engine mount compound, the effect of ageing and the presence of deliberately
introduced flaws on the physical and failure properties were determined.
Accelerated ageing was carried out at temperatures ranging from 70°C to 110°C at times of between one hour and five weeks. Static and dynamic measurements were used to quantify
the effects of ageing on properties and assess ageing mechanisms.
Stiffness of the compound increased with ageing time while tensile strength and elongation at
break decreased. Aerobic degradation mechanism of Ahagon Type I and III were
predominant. The activation energy of ageing, in terms of its effect on tensile strength was
found to be 93 kJ/mol for a cure temperature of 140°C and 86 kJ/mol for a cure temperature
of 150°C when the Time Temperature Superposition method was applied. The tensile
strength after ageing for 13 weeks at 50°C was predicted to be 18.7 MPa, which was very
close to the experimental value of 19.0(± 2.25 SD) MPa.
The presence of weld lines introduced before scorch did not significantly affect the tensile
properties if sufficient time was allowed for healing, with the healing time reducing with
increase· in cure temperature. The activation energy for healing was found to be 31 kJ/mol for
rubber cured between 110°C and 150°C. The presence of flaws, such as pinholes of varying
sizes had a significant effect on both tensile strength and fatigue life, with the pin hole
equivalent intrinsic flaw size estimated to be about 200μm. [Continues.] |
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