Energy dissipation, viscoelastic

Rubber failure upon application of stress is delayed by i) viscoelastic energy dissipation and il) crystallization upon strain of the base polymer. A peculiar rubber failure, namely fatigue failure, is also affected by the same factors. The presence of carbon black or other reinforcing agents does not diminish the contribution of the base polymer on fatigue resistance. 

Rubber failure by application of stress has been studied extensively owing to its overwhelming scientific and practical interest. In particular, two mechanisms have been pul- forward as relevant in delaying rubber failure. The first mechanism is based on viscoelastic energy dissipation, which can be increased by increasing the glass transition of the base polymer, or by other routes such as the use of additives or controlled network imperfection. The second mechanism is... 

INCREASING VISCOELASTIC ENERGY DISSIPATION INCREASE CONTENT OF VINYL 1... 

The elastic nature of fiber and shear stress concentration at the fiber ends affected the tan 6 value when incorporated in a composite material, which is related to the additional viscoelastic energy dissipation in the matrix material [15], Figure 13.8 shows a selection of tan 6 curves in which it can be seen that the tan 6 peak shifted to the higher temperatures, broadened, and decreased as the kenaf whiskers content increased. The decrease of tan 6 value indicated the reduction of macromolecular mobility of the fiber surface environment, whereas better interaction between kenaf whiskers and matrix can be concluded [16]. 

It is noteworthy that the values of Gc from Tables 1 and 2 are measured for similar laminates and that the differenees in the values of Gc arise from the fact that the tests were undertaken at different rates of test. The rate being significantly lower for the results shown in Table 2. The value of Gc does of course encompass (a) the intrinsic energy needed to rupture the inter-atomie and moleeular bonds acting across the interface (or in the materials forming the interface, if cohesive failure in these materials occurs), and (b) the plastic and viscoelastic energy dissipated locally in a process zone ahead of the peel front. This latter energy loss will be... 

Finally, the fact that the value of Gc includes plastic and viscoelastic energy dissipation means that the peel test does not usually directly measure the intrinsic adhesion, even when the locus of failure is exactly at the interface between the materials forming the laminate, or joint. (Except in those rare cases when the test is conducted under conditions such that the plastic and viscoelastic energy dissipation tends to zero [23,39].) Also, if the measured peel force is used as the only parameter to be calculated, rather than the value of Gc, then it should always be borne in mind that the measured peel force will reflect changes in the geometric details of the peel test. Thus, inevitably, interpretation of the results from peel tests based simply upon knowing the values of only the measured peel forces will... 

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