Dynamic crack branching

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... 

M. Ramulu, A. S. Kobayashi, and B.S.-J. Kang, Dynamic Crack Branching—A Photoelastic Evaluation, in Fracture Mechanics Fifteenth Symposium, ed. R. J. Sanford, ASTM STP 833, ASTM, Philadelphia, PA, 1984, pp. 130-148. 

Brittle fracture, dynamic crack branching, crack wave interaction... 

Rubber Content. In the theories of toughening where the role of rubber particles is (a) to absorb energy directly or (b) to induce matrix yielding through stress concentration or hydrostatic tension effects, energy absorption should increase linearly with the number of rubber particles (proportional to rubber content if particle size is invariant). On the other hand, if dynamic craze/crack branching is the operative mechanism, evidence of an exponential law may be expected. The exponential form of the law may be derived as follows. 

THE THREE DIMENSIONAL STRESS FIELDS AT THE DYNAMIC CRACK TIP ASSOCIATED WITH THE CRACK BRANCHING IN PMMA... 

K. Ravi-Chandar and W. G. Knauss, An experimental investigation into dynamic fracture III. On steady-state crack propagation and crack branching, Int. J. Fract. 26, 141-154 (1984). 

Stress Corrosion Up to maximum of Branched cracks, Stainless steels in Almost any grade of Stresses—dynamic Use material which... 

Experimental Evidence. Morphology. Figure 3 (33) shows in phase contrast microscopy the development of crack or craze patterns around rubber particles in a toughened polystyrene. The lack of dependence of crack inclination on direction of stress is especially marked in this micrograph, and can be explained only by reference to dynamic branching rather than to crack or craze nucleation by stress raisers. Schmitt and Keskkula refer to the lines as craze cracks and cracks. ... 

In this paper we have calculated the three dimensional stress fields at the tip of the crack associated with the standing waves across the plate, assuming the waves modulate the stress intensity factor of the crack. Thus the present analysis takes account of these important experimental observations for the microcrack branching instability described above. We are unable, however, to clarify the direct cause of this instability but we have pointed out that the transient interference pattern of the standing waves could enhance the stress fields at the tip of the crack, as shown in Fig. 5, and possibly change the dynamics of the propagating crack. 

The oligomerization of propene on zeolite H-Y has been studied [33,37] by variable-temperature MAS NMR. Alkoxy species formed between protonated alkenes and oxygens of the zeolitic framework were found to be important long-lived intermediates in these reactions. Simple secondary or tertiary carbocations are either absent in the zeolite at low temperatures, or are so transient as to be undetectable by NMR even at temperatures as low as 163 K. There was, however, evidence for long-lived alkyl-substituted cyclopentenyl carbocations, which are formed as free ions in the zeolite at room temperature. At 503 K the oligomers crack to form branched butanes, pentanes and other alkanes. The final product was highly aromatic coke. The structure, dynamics and reactivity of an alkoxy intermediate formed from acetylene on zeolite catalysts have been investigated by Lazo et. al. [32]. 

Ravi-Chandar, K. and Kjiauss, W.G., An investigation into dynamic fracture. Ill - On steady-state crack propagation and branching. Int. J. Fract., 26, 141-154 (1984), Ravi-Chandar, K. and Knauss, W.G., An investigation into dynamic fracture. IV - On the interaction of stress wave with propagating cracks. Int. J. Fract., 26, 189-200 (1984). Pocius, A., Verbal communication, 1998. 

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