Hysteresis mechanical

Dielectric loss The dielectric loss factor represents energy that is lost to the insulator as a result of its being subjected to alternating current (AC) fields. The effect is caused by the rotation of dipoles in the plastic structure and by the displacement effects in the plastic chain caused by the electrical fields. The frictional effects cause energy absorption and the effect is analogous to the mechanical hysteresis effects except that the motion of the material is field induced instead of mechanically induced. 

Fig. 8. Dependence of the mechanical hysteresis AW (1, 2) of loading-unloading cycle and the change of internal energy AU (1, 2 ) on deformation1191. 1, 1 — filled PDMS rubber1221 2, 2 — star-SBS thermoelastoplastic1231...

Reinforced rubber displays considerable hysteresis, which is not observed in natural rubber. In fact, the existence of pronounced mechanical hysteresis can become a serious problem due to the generation of heat involved during high speed oscillatory loading (e.g., in a rapidly revolving car tire). In practice, the content of carbon black is chosen to achieve a desirable compromise between the reinforcing effect and the mechanical hysteresis that it can provoke. 

Mechanical hysteresis observed at small strains shows little recovery. 

The preceding equations provided a reasonable foundation for predicting DE behavior. Indeed the assumption that DEs behave electronically as variable parallel plate capacitors still holds however, the assumptions of small strains and linear elasticity limit the accuracy of this simple model. More advanced non-linear models have since been developed employing hyperelasticity models such as the Ogden model [144—147], Yeoh model [147, 148], Mooney-Rivlin model [145-146, 149, 150] and others (Fig. 1.11) [147, 151, 152]. Models taking into account the time-dependent viscoelastic nature of the elastomer films [148, 150, 151], the leakage current through the film [151], as well as mechanical hysteresis [153] have also been developed. 

It is widely believed that the presence of carbon black or other reinforcing fillers introduces substantial mechanical hysteresis into rubber. Certainly stresses during retraction are lower than during the initial stretching of a rubber, a... 

It is uncertain whether spider silks show actual characteristic properties even though many researchers have been interested in the physicochemical properties of spider silks.This is mainly due to the difficulty in obtaining sufficient numbers of dragline samples appropriate for thermal, optical and aging experiments, in preparing the samples with no mechanical hysteresis and in measuring the mechanical properties because the silk samples are very thin. 

The dragline samples for mechanical measurements and scanning electron microscopic (SEM) observation were prepared from a spider falling naturally from a wooden bar in order to avoid mechanical hysteresis, as shown in Fig. 4.43. 

Finally, the elastic modulus should be determined for draglines having no mechanical hysteresis and at different stages of the N. clavata spider s growth. 

Figure 6 Decrease in interfacial shear stress with mechanical hysteresis following scenario 1 (right) and scenario 2 (left) [1]...

This approach is clearly applicable to rubbers with low mechanical hysteresis, which exhibit non-linear elastic behaviour. However, because the energy release rate Gj is defined specifically for the case of linear elastic fracture, we deflne a new parameter J for the non-linear case ... 

Butyl rubber is ideal for automotive body mounts which connect the chassis to the body, damping road vibration. Road vibration generates low vibration frequencies. Butyl rubber can absorb and dissipate large amounts of energy due to its high mechanical hysteresis over a useful temperature range. 

Yilgor, 1. Eynur, T. Bdgin, S. Yilgor, E. Wilkes, G. L., Influence of Soft Segment Molecular Weight on the Mechanical Hysteresis and Set Behavior of Silicone-Urea Copolymers with Low Hard Segment Contents. Polymer 2011, 52,266-274. 

The material damping, or mechanical hysteresis, is related with the energy dissipation in the volume of a macro-continuous medium. This phenomenon takes place when a more or less homogeneous volume of material is subjected to cyclic stresses. As a result of inelasticity, a phase shift occurs between strain and stress and in the stress-strain coordinates, the geometrical locus of operational point becomes a loop, known as hysteresis loop, which evolves with the number of stress cycles and offer useful information upon the material state. 

The mechanical hysteresis of poly ether PUs investigated by Gorge et al was studied as a function of temperature, percent strain, and deformation energy. Hysteresis values remained small at low temperatures when the extent of the sample deformation did not disrupt the glassy matrix. This was readily evident at temperatures below the glass transition temperature Tg) of the polymer where the material did not formally yield. At temperatures above the Tg of the polymer, hysteresis remained small even at substantial strains levels and demonstrated the capabilities of the HS domains to act as physical crosslinks. At high emperatures, the percent hysteresis increased as the hydrogen-bonded HS domains weakened. 

The maximum mechanical hysteresis and residual strain, which were strongly dependent on the hard block content, occurred during the first cycle and the residual elongations and hysteresis decreased with temperature. 

The polymers in the form of films were subjected to uniaxial tensile tests at constant nominal strain-rate (0.03 s ). In addition, to investigate mechanical hysteresis, cyclic tensile tests were carried out, cycling between a fixed strain limit (300%) and zero load, with the same magnitude of strain-rate for loading and unloading. 

The mechanical hysteresis of a PU investigated by Gorce based on MDl/BDO and PTMO of molar 2 000 g/mol was also found to be sensitive to the temperature-dependent morphologies of this material and to the morphological changes induced by the strain level and deformation energy during a deformation cycle [291]. 

Figure 3.405. Influence of mechanical hysteresis on the profile of crack tip and of fracture surface for crystallisable rubbers [1184] (a) stretching (b) compression.

Yilgor I, et al. Influence of soft segment molecular weight on the mechanical hysteresis and set behavior of sihcone-urea copolymers with low hard segment contents. Polymer... 

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