Crack bifurcation

Crack bifurcation in the B4C-SiC woven fabric based laminate. The B4C and SiC woven fabric layers cannot be distinguished under the optical microscope. 

The important case of specimens with a fixed total thickness was considered in Ref. [40]. There are certain features of crack bifurcation under these conditions, such as that if the sample with a fixed total thickness has too large a number of layers there will be no bifurcation. Layer thickness and composition are important and efficient parameters to control the bifurcation in laminates. The effect is comparable with a crack bridging phenomenon [21], The bifurcation mechanism increases the laminate fracture toughness by approximately 1.5-2 times. 

Design of layered composites with crack bifurcation in compressed layers... 

Lugovy, M., Orlovskaya, N., Slyunayev, V., Gogotsi, G., Kuebler, J., Sanchez-Herencia, A., Crack bifurcation features in laminar specimens with fixed total thickness, Composite Sci. Tech., 62, 819-830, 2002. 

Fig. 6.96 Origins of microcracks include a chemical deposits sometimes leading to crack bifurcation (ARCO, 1250 °C, 140 MPa, flexure), b isolated large grains (ARCO, 1200 °C, 125 MPa, flexure), and c large grain clusters (ARCO 1250 °C, 170 MPa, flexure). Bars = 10 pm [93]. With kind permission of John Wiley and Sons...

In the B (60% till) tank samples, a circumferential rolling direction for the plate forming the section of the barrel where the cracks originated was indicated (Venart, 1996). The originating ruptures formed in this section may thus possibly be linked to the early crack bifurcation that was unique to this trial. This process caused a portion of the tank to circumferentially separate and rocket nearly 450 m. It is well known that fracture toughness is a... 

Figure 3.498. Schematic of possible failure mechanisms near T- oriented fibers (1) tendency to form zig-zag crack profiles and crack bifurcations (2) short-circuiting of cracks between cracks at fiber ends or broken fiber sites (3) formation of crazes and cracks at fiber ends and along their well bonded interfaces at the onset of fiber pull-out (4) as (2) in more detail (5) fiber debonding and pull-out in case of a poorly bonded system [1267],...

Experimental data are adequately described by the theory in as long as a phenomenon of bifurcation does not occur. In this latter case, the Kj is reduced because it has to distribute over the two new crack tips created. This actually means that any crack bifurcation can drastically reduce corrosion. 

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