The effect of low‐temperature crystallization on the mechanical behavior of rubber

Abstract

In cold climates the correct performance of rubber components such as seismic isolators depends on them maintaining their elastic properties when exposed to prolonged periods at low temperatures. The high damping compounds developed for seismic isolation are normally especially prone to crystallization when exposed to subzero temperatures for periods of a few weeks. The effect of low-temperature crystallization on the mechanical stiffening of natural rubber is evaluated. The relationship between the shear modulus and amount of crystallization is measured using a technique in which the dimensional change and stiffness are monitored simultaneously. The relationship is found to be approximately independent of the crosslink density and the temperature of crystallization. It appears not to be realistically modeled by considering the crystals to behave as rigid filler particles but good qualitative agreement with experiment was obtained by modeling the crystals as a network of threads. Partially crystalline rubbers are found to yield under the application of a large stress like other partially crystalline polymers. Mechanisms for suppressing crystallization in rubber are discussed and the low-temperature stiffening of specially formulated rubber compounds for seismic isolation is presented. These results show that carefully formulated high damping natural rubber compounds can give adequate performance at low temperatures.

Effects of the long-term behaviour of isolation devices on the seismic response of base-isolated buildings

“…The outer region is also affected by an oxidation process, related to time and depending on the amount of oxygen, which produces a degradation of properties whose effects diminish moving towards the critical depth. Moreover, the HDRBs considerably increase their horizontal and vertical stiffnesses for decreasing values of the air temperature through rubber crystallization due to prolonged exposure to cold weather, whereas their cyclic behaviour does not change significantly at high air temperatures . Finally, it should be noted that ageing and air temperature do not affect the equivalent viscous damping ratio of the HDRBs significantly.…”

“…Mechanical properties of the HDRBs can also change significantly due to weather conditions: that is, variations in the environmental temperature over long periods of time, such as wide variations in air temperature between winter (e.g., with a mean value of 10°C) and summer (e.g., with a mean value of 25°C). Specifically, experimental tests carried out on the HDRBs show that both the stress level and the area encompassed by the hysteresis loop increase more than linearly whereas air temperature is decreasing, especially when the temperature drops below 0. Moreover, at a given temperature, these effects increase from soft‐to‐normal elastomer compounds and from normal‐to‐hard elastomer compounds .…”

An improved rheology model for the description of the rate-dependent cyclic behavior of high damping rubber bearings

“…After finding the optimal direction variation of the parameter, the corresponding parameter C; C þ i ; C À i À Á is selected and the step length D i is changed by Eq. (19) for the next step i þ 1.…”

“…Generally, rubbers tested at lower temperatures have shown larger rate dependence, hysteresis and Mullins' effect whereas these effects got gradually diminished at temperatures above the room temperature. Furthermore, Fuller et al [19] reports temperature history dependence of HDR due to crystallization effect on prolonged exposure to low temperature and associated increase in shear modulus. Amin et al [20] emphasizes on the role of loading history dependence due to fundamental Gough-Joule effect, determined by the entropy elasticity and inelastic energy dissipation or hysteresis on selfheating [22][23][24] of large rubber devices due to quasi-adiabatic mechanical process acting on it.…”

“…The effect of ambient temperature and the exposure history on constitutive behavior of rubber is addressed in Lion [18] and Fuller et al [19]. A recent comprehensive review of literature together with experimental observations on natural rubberpolybutadiene rubber (NR/BR) blend is provided in Amin et al [20].…”