Failure modes tear test

There are three main types of failure by crack propagation as shown in Figure 10.3 1 (opening), II (sliding), and III (tearing). In real elements made with composite materials and subjected to external load, all modes appear in different combinations and it is not completely clear how to deal with that situation. The models proposed at present seem to still be dependent on the scale if in macro scale the tests executed according to these three modes are possible the obtained results characterize only the effects in the same scale with mean values of some correcting parameters. On lower scales probably all modes appear simultaneously or at least Modes I and II act conjointly. The mixed-mode fracture parameters may be calculated for linear elastic materials within the frames of LEFM, but their direct application to the cement-based composites is questioned. The considerations below are partly based on the paper by Brandt and Prokopski (1990). 

Figure 1 shows a compact tension specimen in which a starter crack propagated at a controlled rate such that the test could be stopped prior to specimen failure. Whitened areas above and below the fracture surfaces are a result of particle cavitation. This particular material was a flexibilized vinyl ester containing a rubber particulate phase. The large volume of material involved in the fracture process resulted in high toughness and a ductile tearing mode of fracture as opposed to the brittle fracture mode of the base resin. 

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