Growth, dynamic crack

Lindley, P.B., Relation between hysteresis and the dynamic crack growth resistance of natural rubber, Int. J. Fract., 9, 449, 1973. 

NR/modified EPDM, in which EPDM was modified by pendant sulfur, exhibited improved endurance to repeated stress over that of covulcanized EPDM-NR mbber blends (68). The effects of ethylene and diene contents in EPDM, blend ratio, dicumyl peroxide curing system on the physical properties, interfacial adhesion force, and dynamic crack growth were examined (69). As the ethylene and diene contents in EPDM increased, the physical properties, such as dynamic cut growth, adhesion to other component were also increased. The mechanical properties of the blends are compared to those of the pure components in Table 15.3 (56). The ultimate tensile strength of noncompatibilized blends is lower than that of pure NR, as expected since these blends are incompatible. 

We consider first the initiation of fracture from crack precursors. These are features of the material s microscopic structure that magnify applied stresses. The rate of development of cracks after initiation is treated next. Naturally, this depends on the local stress levels but also on the way in which these stresses vary with time. For example, rapid crack growth may take place if stresses are applied and removed frequently, whereas the crack may grow quite slowly, if at all, when the same stresses are held constant and never removed. This phenomenon of accelerated growth under dynamic stressing is termed mechanical fatigue or dynamic crack growth. It is treated in Sections 10.4.5 and 10.6. 

During the dynamic crack growth, local heat generation takes place at the crack tip. If the temperature is high enough, a plastic zone is formed at the tip (Fig. 3) and its traces are the so-called "arrest lines" which appear on the fracture surface after... 

Lindley, P. B. (1973). Relation between hysteresis and dynamic crack growth resistance of NR. Int. Journal Fracture 9,449. 

Simulation of Dynamic Crack Growth Using the Generalized Interpolation Material Point (GIMP) Method. 

The /V-alkyl-/V-aryl- -PDAs (where the aryl is phenyl and the alkyl may be cyclohexyl, 1,3-dimethylbutyl or 1-methylethyl) ate the most widely used /)-PDAs. These derivatives reduce the rate of crack growth and also the number of cracks. The alkyl-aryl- -PDAs are in general excellent antiozonants, particularly in dynamic environments. These derivatives are destroyed only slowly by oxygen and increase the scorchiness of the stock only slightly. These are intermediate in staining among the three classes of -PDAs. 

Even in the loading regime in which inherent flaw effects dominate the fracture process, further clarification of the fracture activation and growth process is needed. For example, dynamic crack branching leading to multiple fracturing is expected to constitute an important part of the breakage process. Such a cooperative and collective fracture process does not fit well within a... 

Autoffettage is a useful measure for statically as well as dynamically pressurized vessels (see section 4.1.5.1). There is also a benifitial impact on the decrease of the rate of crack growth and the increase of the critical crack depth. 

Y. Takagi and A. S. Kobayashi, Further Studies on Dynamic Fracture Response of Alumina and SiCw/Al203 Composite, in Symposium on Elevated Temperature Crack Growth, ASME, Vol. 18, eds. S. Mall and T. Nicholas, ASME, New York, 1990, pp. 145-148. 

Antiozonant Properties. Aromatic secondary diamines are the only class of organic chemicals able to reduce efficiently the ozone crack growth of vulcanizates under dynamic conditions and be acceptable at the same time from both the technical and toxicological points of view. The presence of a secondary aromatic amine moiety itself in a molecule is not a sufficient condition to attain antiozonants efficiency. (E.g., secondary monomaines are only antioxidants and flex-crack inhibitors without appreciable antiozonant activity. On the other hand, all N,N -disubstituted PD antiozonants are also efficient antoxidants and most of them also act as flex-crack inhibitors (1). Both these stabilization activities have to be considered in the complex antiozonant mechanism, together with some metal deactivating activity. 

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