However, a trade-off of such stiff networks is reduced toughness.
Recent studies of the yttria partially stabilised zirconia porcelain interface have revealed the presence of near-interface porcelain nanovoiding which reduces toughness and leads to component failure.
The layer-structure of LaPO4 phase and its weak bond with Gd2Zr2O7 matrix could cause the initial increase in the toughness, and the growth of LaPO4 grains might contribute to the reduced toughness.
Reduced toughness in this modified alloy relative to unalloyed NiAl Cr Mo) is attributed to the lack of plasticity in the precipitate-strengthened matrix and partial loss of the aligned lamellar microstructure by Hf and Si alloying.
In contrast, the wear volume and wear rate of the samples treated for 60 min were higher than those of untreated samples, presumably due to the higher hardness and reduced toughness of the samples treated for 60 min.
Compatibilization reduced toughness, but at VB contents of 15 wt% or more, both the modulus of elasticity and the tensile strength significantly increased with respect to the uncompatibilized blends.
This may be due to the maximum shear stress being closer to the film substrate interface, or reflect reduced toughness in the thicker films that are less able to deform as the substrate deforms plastically during the repetitive contact test.
Long (∼20 micron) aligned CNTs add significant toughness in steady state (>1 kJ/m2 increase for marine epoxy) via CNT pullout and by driving the crack through tortuous paths around and through microfiber bundles/tows, whereas shorter CNTs produce less toughening (or even reduced toughness in aerospace epoxy), which is attributed to increased microfiber matrix cohesive failure.
In addition, it has been reported that some primates, including the chimpanzee (Pan troglodytes), consumed leaves with higher green-red values than the leaves they avoided-sensory mechanism that correlated with key nutritional variables, such as increased protein and reduced toughness.
These two mechanisms that act to reduce bone toughness are coupled, Ritchie says, in that the increased stiffness of the cross-linked collagen requires energy to be absorbed by "plastic" deformation at higher structural levels, which occurs by the process of micro cracking.
