Stress harden

Two questions remain, however why is the modulus enhancement, attributed primarily to these Interlocking loops, greater for the Ca and Sr lonomers than for the Ni, Zn, and Cd telechelics, and why is the stress-hardening behavior exhibited only by the telechelics neutralized with Ca and Ni Small-angle x-ray scattering (SAXS) and extended x-ray absorption fine structure (EXAFS) spectroscopy were employed to address these questions. 

The new metallocene catalysis leads to isomer purity in excess of 96%. It is also possible to produce branched, high melt strength PP, with extensional stress hardening, similar to that of LDPE [Phillips et al., 1992]. The new PP s show the melting point, T = 120-164°C. To enhance the performance, PP is usually blended (in the reactor or outside the reactor) with much more viscous PP-copolymers. As a consequence, one of the most serious industrial problem is homogenization of these materials [Luciani and Utracki, 1996 Utracki andLuciani, 1996]. 

Stress hardening due to alignment and tightening of highly stretched chains (Blanchard). 

There are three types of melt behavior in a simple shear flow dilatant (D) (shear thickening) Newtonian (N), and pseudoplastic (P) (shear thinning). Similarly, in an extensional flow, the liquids may be stress hardening (SH), Troutonian (T), or stress softening (SS). By definition, the response considered here is taken at sufficiently... 

Ceramics which, when indented, undergo the mechanisms listed above, with the exception of cracking, can be grouped as Mohr-Coulomb materials for which five parameters—E, a-y, v, H, and a—are needed to calculate hardness. Here E, a-y, and i> have their usual meaning while H is the stress hardening rate and a is the densification factor. Clearly if indentation causes densification then a and H must be closely linked. 

Figure 1.6. Schematic representation of indent shapes for materials with different constraint factors, (a) Mises material with Tabor constraint, (b) Mises material with Hill constraint or Mises-Coulomb material with o = —0.2, H 0.2E. (c) Mises-Coulomb material with no stress hardening but about 45% densification, typical of glass, (d) Little densification but large values oUi.

G, n, T. In such cases, one must switch to models that contain variable parameters, for example, the elements of nonlinear elasticity, G = G(y), nonlinear viscosity q = q(dY/dt), and variable yield stress (hardening) t = t (y). 

Fig. 1.3 Typical stress-strain curve of thermoplastic polymers (e.g. polyethylene). Four regions can be observed on the curve I elastic region, the slope of the curve at low strains gives the Young s modulus of elasticity E II yield point defined by yield stress Oy and yield strain By III strain softening IV stress hardening is observed in some polymers. Finally the sample breaks at its break-strain ej...

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