Griffith’s theory

To evaluate the influx solution experimentally for an A/B cantilever beam configuration as shown in Fig. 1, we apply Griffith s theory at the critical moment of fracture, such that the incremental change in stored elastic energy U. with change in crack length a, is Just sufficient to overcome the fracture surface energy S... 

Irwin [6-14] extended Griffith s theory to elastic-plastic materials and pointed out the three kinematically admissible crack-extension modes shown in Figure 6-10. These modes, opening, fonward-shear, and parallel-shear, can be summed to obtain any crack. 

The principle behind the phenomenon of fracture of materials can be described by having recourse to Griffith s theory. Alternatively, this can be done by introducing the concept of fracture toughness. 

Besides Griffith s theory, the fracture of materials can be described in terms of a property known as fracture toughness. The fracture toughness of a material refers to its resistance to fracture in the presence of cracks or discontinuities. Fracture toughness is represented by... 

From Griffith s theory, it follows in most general terms that the destructive stress concentration corresponds to a material s cohesive strength. 

The work done to propagate a unit area of crack is G. Griffith s theory assumes that no heat is dissipated and that the work is done to form the two new surfaces without plastic deformation taking place. The work needed to form a crack of length la is... 

The generalized theory therefore restores the explicit link between a continuum mechanics approach to fracture, which is of such great value in engineering design and practice, and the atomistic view which concerns us most in this review. This link has been lost since Griffith s theory was found to be inadequate for most real... 

Irwin proposed the concept of quasi-elastic fracture, which allows us to extend the limits of applicability of Griffith s theory [11], Irwin s criterion is valid not only for brittle materials, but also for elastic-plastic materials with significant plastic deformation developing until the moment of actual destruction of a material. 

From the particular relationship between the porosity, pore stracture and strength of cement pastes, valid for brittle materials, it was only one step to the application of the Griffith s theory for description of the physical properties of these materials description. 

In the mechanics of composite materials, the interpretation of adhesion characteristics is based on the Griffith s theory concerning to the fracture process. The Griffith fracture energy, U, which determines the critical tension that starts crack propagation, with a length equal to is given by the relation ... 

Failure in polymers may occnr in a brittle or a dnctile manner. Let us illustrate this using PMMA as an example, for which the tensile yield stress is about 90 MPa and K c is about 1.0 MPa.m. For a specimen containing a through crack, failure stress, is related to K ( by the equation based on Griffith s theory ... 

Theoretical tensile strength may be calculated from molecular cohesion in the atomic structure, but the effective strength of materials is, by a few orders, lower. The reasons, according to Griffith s theory, are local defects, cracks and flaws, with high stress concentrations at their tips. It is usually assumed that for ordinary Portland cement matrix the maximum tensile strain varies between 100 and 150.10 and may rarely attain 200.10". ... 

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