Creep dynamics

In a dynamic creep experiment, the shear strain for liquids can be written as (t)... 

CREEP, DYNAMIC - Creep that occurs under conditions of fluctuating ioad or fiuctuating temperatures. 

The minus sign in Eqs. (5.10) and (5.11) is the consequence of the strain lagging behind the stress. It can be shown that, for a viscoelastic liquid, the dynamic creep compliances are related to the creep compliance J(t) by the one-sided Fourier transforms ... 

For certain products long time dynamic (creep, fatigue, impact, etc.) mechanical load performances in different environments are required. Dynamic loading in the present context is taken to include deformation rates above those achieved on the standard laboratory-testing machine (commonly designated as static or quasi-static just reviewed). These slower tests may encounter minimal time-dependent effects, such as creep and stress-relaxation, and therefore are in a sense dynamic. Thus the terms static and dynamic can be overlapping. 

Fig. 8. Vibration-induced creep fracture, (a) Radially propagating dynamic fatigue fracture inside the material and (b) dynamic creep fracture in PS samples.

Typical creep curves for polyethylene (PE) and polypropylene (PP) at 23 °C are shown in Figures 18.2 and 18.3. Lin and co-workers [1] have discussed creep phenomena accuracy in reinforced polyamide (PA) and polycarbonate (PC) composites. The phenomenon of the increasing dynamic creep property and the temperature under tension-tension fatigue loading are compared between semi-crystalline and amorphous composites. 

Typical curves for polyethylene and polypropylene at 23°C are shown in Figures 2.2 and 2.3. Lin and coworkers [41] discussed the accuracy of creep phenomena in reinforced PA and polycarbonate (PC) composites. In this paper, the phenomenon in increasing dynamic creep and temperature under tension-tension fatigue loading is compared between semicrystalline and amorphous composites. 

For 0.25 wt% silica, the CR spectra also manifested a less pronounced effect of accelerating segmental dynamics (creep) at 40-80°C in the temperature region between the P- and a-transitions of PHEMA (Fig. 64a). This was explained as above by a partial or total collapse of intermolecular cooperativity of segmental motions. 

Next, if we impose a sinusoidal stress (dynamic creep test) or(0 = or e then the response will be... 

In Eq. 59, t) is also called the dynamic viscosity. In Eq. 55, 7o is the instantaneous compliance (sometimes called the glassy compliance and denoted by 7g) and is associated with solid-like elastic behavior while 1 /cor] is associated with liquidlike viscous behavior, which leaves 7 and 7" as the terms that are thus associated with viscoelastic behavior. Again, the reader should note that some authors introduce the dynamic creep components differently, by burying these terms into the definitions of 7 and 7". If one goes along with the latter definitions, Eq. 55 becomes... 

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