Yield stress intensification

The value % can be determined within the frameworks of polymers plasticity fractal concept [35] according to the Eq. (4.9). The dependence of on shows increasing at growth [102]. At small values all crystallites are subjected to disordering owing to that yield tooth in BPE curves stress-strain is absent and these curves are acquired the form, which is typical for rubbers. Hence, stress decay beyond yield stress intensification is due tox growth [103],... 

Glass transition temperature Secondary transition Extension ratio Maximum extension ratio Craze intensification stress Craze initiation stress Tensile strength Compressive yield stress Drop in after yielding A measure of strain softening Test frequency... 

In contrast, cast iron piping has recognized brittle characteristics. The design basis for cast iron therefore does not assume that localized yielding or deformation will reduce stress intensification. As a resulf the design protocol for cast iron includes the quantification and direct input of external loading factors that can generate localized stress intensification [44]. 

The example explained in the following illustrates process intensification at the level of basic chemical and physical processes. Again, it concerns an equilibrium reaction, in which the equilibrium is strongly on the educt side and a slightly volatile component has to be removed from the system to displace the equilibrium. However, the equilibrium does not occur spontaneously, so the use of a reaction column is not possible. Therefore, a high-stress field develops with high yield and duration of thermal stress. 

Let us consider further reasons of pol5rmer chains breaking at so small stresses, which can be on order lower than ftacture macroscopic stress (i.e., at h5rpothetical k = 0.1). The reasons were pointed for the first time in Refs. [1, 26]. Firstly, anharmonicity intensification in fracture center gives the effect, identical to mechanical overloading effect [26]. Quantitatively this effect is expressed by the ratio of thermal expansion coefficient in fracture center and modal thermal expansion coefficient [5]. The second reason is close inter communication of local yielding and fracture processes [ 1]. This allows to identify fracture center for nonoriented polymers as local plasticity zone [27, 28]. The ratio uJ(X in this case can be reached -100 [5]. This effect compensates completely k reduction lower than one. So, for PC ala 70, K- = 0.44, a. = O.IE. 700 MPa and fiien o = o a /K,a 23 MPa, that by order of magnitude corresponds to experimental value Oj. for PC, which is equal approximately to 50 MPa at T= 293 K [7]. 

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