Hysteresis heat build

Elastomers are often compounded with finely divided solids to reinforce the rubber and to reduce costs. The most important fillers are carbon blacks, silica and silicates, clays and whiting (calcium carbonate). " The particles are the source of reinforcement through their interactions with the rubber, among themselves and with the chemistry of the cross-linking process. Abrasion resistance, tear strength and tensile strength are simultaneously improved. However, hysteresis, heat build-up and compression set (permanent deformation) are also known to increase as the reinforcing ability of the filler becomes more pronounced. 

The study of the response of elastomers to forces which produce changes of motion in them. See Heat Build-up, Hysteresis and Resilience. 

When rubber is deformed the difference between the energy input and output is known as hysteresis. The loss of energy is consumed in internal friction and results in heat build-up. See Hysteresis Loop and Resilience. 

The ratio of the energy given up on recovery from deformation to the energy required to produce the deformation, expressed as a percentage. See Heat Build-Up, Hysteresis and Rebound Resilience. 

In parallel with this increase, certain undesirable properties which indicate viscoelastic behaviour become more marked as the proportion of carbon black is raised. These include stress-softening, compression set, hysteresis and heat build-up. Only comparatively insignificant increases become apparent, if at all, when nonreinforcing fillers are used. 

Knowledge of non-linear contributions to viscoelasticity is important for design of elastomer blends and composites for rolling resistance performance of tyres, hysteresis and heat build-up behaviour, and friction or grip characteristics. The importance extends beyond developing suitable blend and filler compositions, to the construction, geometry and tread pattern design of tyres to arrive at optimum performance. 

Increasing the load level is another way of accelerating the test. Here, again, it is important to do this cautiously and base it on the performance curves for the materials. The creep of the plastics is sensitive to the stress level and the range under consideration may be such that a relatively small increase in stress level will result in a large increase in creep level. In addition, since the part is also dynamically loaded, the increased stress level may lead to severe heat build up due to increased size of the hysteresis loop at increased stress levels and this could lead to catastrophic failure of the part. In any event, the data for the material should be carefully examined to see that the acceleration method used does not lead to erroneous results because any critical level factor is exceeded. 

Mechanically, rubbers may be expected to lose strength rapidly with increase in temperature, to show a large hysteresis in stress strain behavior, to exhibit marked creep and set, and to be greatly affected by rates of load application or frequency of repeated stress. Heat build-up, i.e., increase in temperature in service, as well as deterioration from environment (sunlight, oils, ozone, etc.) will reduce the valuable properties of many rubbers, both natural and synthetic. 

Elastomers, particularly those which caimot undergo strain-induced crystallization, are generally compounded with a reinforcing filler [9]. The two most important examples are the addition of carbon black to natural rubber and to some synthetic elastomers [164,165] and silica to polysiloxane rubbers [166,167]. The advantages obtained include improvements in abrasion resistance, tear strength, and tensile strength. Disadvantages include increases in hysteresis (and thus heat build up) and compression set (permanent deformation). 

Generally, the isotherm in retraction lies well below the isotherm in elongation, and the area between the two curves is a measure of the energy lost in an elongation-retraction cycle [56]. This phenomenon of hysteresis is illustrated in Fig. 6.3. It is of considerable importance since the associated heat build-up can increase the rate of degradation of an elastomer. The flexing of automobile tires is perhaps the best-known example of this effect. 

HDI Heat buildup An abbreviation for hexamethylene diisocyanate. The temperature rise within an elastomer due to hysteresis. In many end-use applications, an elastomer can be subjected to repeated cycles of deformation-relaxation. As this occurs, friction between the elastomer molecules generates heat. As elastomers have relatively poor thermal conductivity, the heat generated builds up over time, progressively increasing the internal temperature of the elastomer. If the temperature increases above 70°C, the elastomer physical properties can begin to reduce. Design of the elastomer part can play an important role in minimizing the effects of heat buildup. 

Therefore, the heat storage in the urban fabrics/buildings, including hysteresis, can be most easily parameterised from the radiation and surface cover information using the empirical objective hysteresis model (OHM) of Grimmond et al 1991 [236] ... 

---