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... 

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. 

Sue et al. (1997) reported results for the same LC epoxy monomer cured with various hardeners. KIe values could be increased up to 1.89 MPa m1/2. Observations of fracture surfaces indicated that crack bridging, crack branching, and crack deflection were the main toughening mechanisms. 

Crack branching is a common feature in failure of ceramic components. Cracks branch at a critical velocity, which is of the order of half the speed of sound in the specific glass under study. The acceleration of crack initiation to the critical velocity depends on the energy dissipation available from the release of stored energy. The energy source can be applied stress, prestressing or residual stress. 

A transverse cross-section through the fracture initiation site was examined by metallography. The fracture surface profile was found to be relatively flat and there was no crack branching. The microstructure showed dark-etching-tempered martensite. Further no plastic deformation was observed at the fracture initiation site. 

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. 

Interfacial cavitation, microcracking, diffusion and crack branching due to the viscous flow of the glass phase during creep-fatigue. 

Fig. 24 Images of a cast PMMA sample after testing in IPA at AK = 0.6 MPa Vm Left Macroscopic view of crack branching along main crack front, right SEM picture of fracture surface...

The present study is restricted to a quasi-static formulation and focusses on the beginning of crack propagation. Therefore, our attention has been devoted to exploring possible causes for the onset of the brittle to ductile transition for such loading conditions. Therefore, arguments based on inertia effects are not invoked, nor is crack branching at high crack speeds [15]. 

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

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

No observations of crack-branching or multiple delamination propagation (common in multidirectional lay-ups [2, 5]) in either type of cross-ply laminate have been reported. 

The model experiments of Xu and Rosakis on low-speed impact over sandwich structures were simulated applying cohesive models. The simulation captures qualitatively the main experimental observations. The most relevant correspondence is in the development of the first crack at the interface between the layers, the presence of shear stresses along the interface, which renders the crack shear driven and often inter-sonic, and the transition between interlayer crack growth and intra-layer crack branching. The effects of impact speed and bond shear strength are also investigated and highly satisfactory predictions are obtained. 

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