Process zone toughening

Fig. 18 Evolution of the frontal process zone size as a function of the fibres concentration for the 8 wt% rubber-toughened composites.

To overcome the above drawbacks, a new method based on essential work of fracture concept was introduced [Broberg, 1971, 1975]. In this method, it is proposed that when a cracked ductile solid, such as a toughened polymer blend is loaded, the fracture process and the plastic deformation take place in two different regions, viz. the inner process zone and the outer plastic zone. Much of the fracture work during crack propagation, dissipated in the plastic zone, is not directly associated with the fracture process. Only that work that goes into the fracture process zone is a material constant. Hence, the total fracture work, Wp should be separated into two parts, i.e., the essential work of fracture (i.e., the work required to create two new fracture surfaces, W),... 

Other than dilatation in the process zone, microcracks give rise to two other effects that influence toughening. Name one of them. 

The creation of a stress field in a two-phase brittle matrix material can be exploited for toughening since it will induce microcracks on application of an external load. Microcracks are created at the vicinity of the tip of a macrocrack forming a process zone [130], Using this mechanism, the elastic modulus within the process zone is reduced, the stress intensity at the crack tip is lowered and the toughness is increased. 

It appears that the toughening effect near a crack tip occurs as follows after initial deformation, cavitation occurs within or aroimd the soft phase in a zone surrounding the crack tip. This zone is known as the process zone. The newly created surface around these cavities in the process zone allows the latter to grow plastically, thus absorbing some energy. Localized shear deformations, often referred to as shear bands, may also grow from these cavities. If the volume fraction... 

The fracture process zone in concrete, in Toughening Mechanisms in... 

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