Stress/strain effects

Detailed modelling studies on heat transport in such systems, to be published elsewhere, are easy to develop since the thermal conductivity, thermal diffusivity, and the heat capacities of the various fiber components are known. The stress/strain effects are almost completely asserted in a thin surface layer of the Hytrel, because of the poor conductivity of this sheath and the underlying viscoelastic RTV. However, Hytrel has an extremely high... 

Repolymerization is a patented [28] concept by the author to explain new and novel rheology and stress/strain effects in thermoplastics and thermosets obtained with... 

Maximum strain theory in three dimensional. Includes nonlinear shear stress (strain) effect. 

Fig. 6. The effect of rate of extension on the stress—strain curves of rayon fibers at 65% rh and 20°C. The numbers on the curves give the constant rates of...

Fig. 3. Effect of temperature and strain rate on stress—strain diagram of Ti—5% Al—2.5% Sn where A—E correspond to the strain rates 1.6x10, ...

The effect of temperature on PSF tensile stress—strain behavior is depicted in Figure 4. The resin continues to exhibit useful mechanical properties at temperatures up to 160°C under prolonged or repeated thermal exposure. PES and PPSF extend this temperature limit to about 180°C. The dependence of flexural moduli on temperature for polysulfones is shown in Figure 5 with comparison to other engineering thermoplastics. 

Cord materials such as nylon, polyester, and steel wire conventionally used in tires are twisted and therefore exhibit a nonlinear stress—strain relationship. The cord is twisted to provide reduced bending stiffness and achieve high fatigue performance for cord—mbber composite stmcture. The detrimental effect of cord twist is reduced tensile strength. Analytical studies on the deformation of twisted cords and steel wire cables are available (22,56—59). The tensile modulus E of the twisted cord having diameter D and pitchp is expressed as follows (60) ... 

Figure 6.15. Stress-strain response of shock-loaded Al-4 wt.% Cu as a function of heat treatment illustrating the effect of the Bauschinger effect on the response of the 6 condition compared to the solution-treated microstructure.

Figure 6.16. Stress-strain of shock-loaded silicon bronze contrasted to the annealed alloy showing evidence of a Bauschinger effect.

Figure 10.5. Effect of polymer density, testing rate and temperature on the shape of the stress-strain...

Figure 10.6. Effect of temperature on the tensile stress-strain curve for polyethylene. (Low-density polymer -0.92g/cm . MFI = 2.) Rate of extension 190% per minute ...

Corrosion effect of forming Elongation X gauge length Standard hydropress specimen test True stress-strain curve Uniformity of characteristics... 

Fig. 1.3 Effect of material temperature on stress-strain behaviour of plastics...

This example illustrates the simplified approach to film blowing. Unfortunately in practice the situation is more complex in that the film thickness is influenced by draw-down, relaxation of induced stresses/strains and melt flow phenomena such as die swell. In fact the situation is similar to that described for blow moulding (see below) and the type of analysis outlined in that section could be used to allow for the effects of die swell. However, since the most practical problems in film blowing require iterative type solutions involving melt flow characteristics, volume flow rates, swell ratios, etc the study of these is delayed until Chapter 5 where a more rigorous approach to polymer flow has been adopted. 

As a starting point it is useful to plot the relationship between shear stress and shear rate as shown in Fig. 5.1 since this is similar to the stress-strain characteristics for a solid. However, in practice it is often more convenient to rearrange the variables and plot viscosity against strain rate as shown in Fig. 5.2. Logarithmic scales are common so that several decades of stress and viscosity can be included. Fig. 5.2 also illustrates the effect of temperature on the viscosity of polymer melts. 

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