Shear crack propagation

The advantage of using the STM for analyzing shear transfer and designing shear reinforcement for pedestal anchorages is the elimination of questionable assumptions related to the size and shape of the concrete breakout cone, the crack location (whether the shear cracks propagate from the middle of pedestals, front-row anchors, or back-row anchors), and the amount of shear reinforcement that is effective to restrain the concrete breakout cone. 

Fig. 2. Illustrations of forces to which adhesive bonds are subjected, (a) A standard lap shear specimen where the black area shows the adhesive. The adherends are usually 25 mm wide and the lap area is 312.5 mm. The arrows show the direction of the normal apphcation of load, (b) A peel test where the loading configuration, shown by the arrows, is for a 180° peel test, (c) A double cantilever beam test specimen used in the evaluation of the resistance to crack propagation of an adhesive. The normal application of load is shown by the arrows. This load is appHed by a tensile testing machine or other...

Other researchers have substantially advanced the state of the art of fracture mechanics applied to composite materials. Tetelman [6-15] and Corten [6-16] discuss fracture mechanics from the point of view of micromechanics. Sih and Chen [6-17] treat the mixed-mode fracture problem for noncollinear crack propagation. Waddoups, Eisenmann, and Kaminski [6-18] and Konish, Swedlow, and Cruse [6-19] extend the concepts of fracture mechanics to laminates. Impact resistance of unidirectional composites is discussed by Chamis, Hanson, and Serafini [6-20]. They use strain energy and fracture strength concepts along with micromechanics to assess impact resistance in longitudinal, transverse, and shear modes. 

The analysis depends on whether the interfacial failure occurs by yielding or by crack propagation. The simplest analysis is based on interfacial yielding where the shear stress is assumed to be distributed uniformly over the interface from top to bottom. According to this analysis, the interfacial shear stress increases uniformly until every location in the interface gives way simultaneously. 

Fig. 3.29. Modes of interlaminar crack propagation (a) Mode I opening mode (b) Mode II sliding shear...

In the shear strength criterion, the debond crack propagates when the maximum IFSS at the debond crack tip z = L - tj reaches the shear bond strength, tb, i.e. 

The occurrence of earthquakes is a highly studied phenomena by geologists. The role of solid surfaces in such phenomena is obvious. Especially, faults are known to contribute to many earthquakes. Faults are treated as shear cracks, the propagation of which may be understood through the application of fracture mechanics. The stability of any fault movement, which determines whether the faulting is seismic or aseismic, is determined by the frictional constitutive law of the fault surface. It is well established that, once a fault has been formed, its further motion is controlled by friction (between the solid surfaces), which arises from contact forces across the two solid surfaces. 

It shows that shear bands are formed during crack propagation at room temperature, in agreement with the observations from thin film deformation... 

As a result of the increase in stress and/or strain, shear bands develop in a large fraction of the sample but, at a certain point, a crack appears and starts to propagate. Several mechanisms for energy absorption, associated with the presence of particles, become active during crack propagation. 

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