Intrinsic toughness

In this case is the intrinsic toughness experienced by the crack tip (equal to Kj for a single-value toughness material) and is the toughness associated with the microstmctural shielding term (equal to zero for a single-value toughness material). 

In the case of thermosets toughened with thermoplastics particles (Sec. 13.4), this mechanism may be of a considerable importance because of the intrinsic toughness and/or ductility of these particles. 

Over the millennia, food plants and animals have been selected and bred to reduce their intrinsic toughness animals have developed strategies for coping with foods that are difficult to harvest and chew. For instance, the parallel sclerenchyma... 

DETERMINATION OF INTRINSIC TOUGHNESS VALUES USING A PLASTIC ZONE CORRECTED LEFM ORIGINAL APPROACH... 

If the energy release rate of the bent beam is greater than a critical intrinsic toughness of the unpinned DCB, G/c, the delamination will propagate. 

The ratio at-/ay, which describes the ease of brittle fracture relative to shear yielding, is a good indicator of the intrinsic toughness of linear amorphous thermoplastics. It is very useful in ranking such polymers in terms of their predicted relative toughness. For example, af/ay is... 

The influence of physical aging on the comparative and intrinsic toughness of PEEK and PPS carbon-fiber composites was determined by Ma et al. [1992]. Both types exhibited a loss of toughness with increase in aging time and temperature. The PEEK composites tended to retain more impact toughness but after aging were less ductile than the PPS composites. 

Figure 1.2 Typical schematic tensile stress-strain curves for polymers (a) brittle, amorphous thermoplastic, (b) same polymer with toughening additive, (c) intrinsically tough, semi-crystalline thermoplastic. The curves should be taken only to convey trends and not relative breaking stresses, which vary with the precise materials...

Typical stress-strain curves for plastics are shown in Fig. 1.2. The figure shows qualitatively (a) the steep, but non-linear curve associated with amorphous, brittle thermoplastics such as unmodified polystyrene, (b) the equivalent graph for a similar brittle thermoplastics material to which rubber has been added to produce a high impact grade and (c) an intrinsically tough thermoplastics material, such as a nylon (polyamide). 

In the above relations, Tq is intrinsic toughness, is the extrinsic toughness mechanism (crack-tip shielding), Rq is the fracture resistance energy and R is the crack resistance energy contribution. The critical condition for crack extension is then given by ... 

True toughness or intrinsic toughness T and Ep effects large... 

Equations (5.11) and (5.12) show us that to build in resistance to flaw generation in ceramic systems Hy must be decreased while increasing Kc. However, once a sample is flawed, the intrinsic toughness parameter alone is important. 

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