Toughness enhancements

Oxides such as CaO, MgO, and Y2O2 are added to Zr02 to stabili2e the tetragonal phase at temperatures below the tetragonal to monoclinic phase-transition temperature. Without stabili2et, the phase transition occurs spontaneously at temperatures below 850—1000°C, and no fracture toughness enhancement occurs (25). 

Tetragonal 2inconia is a stmctural ceramic that exhibits ferroelasticity and the toughness enhancement has been estimated to be as high as 5. An example of a partial hysteresis loop for this material is shown in Figure 4 (35). Domains do not have to be present prior to the stress... 

T. Kobayashi, H. Toda. Toughness enhancement based on fracture mechanical simulation of Al-SiC composite. Mater Sci Forum 242 193, 1997. 

Residual stresses and molecular orientation play an important role in the toughness enhancement of plastics, because toughness is primarily based on the mechanics of... 

Recently siloxane-imide copolymers have received specific attention due to various unique properties displayed by these materials which include fracture toughness, enhanced adhesion, improved dielectric properties, increased solubility, and excellent atomic oxygen resistance 1S3). The first report on the synthesis of poly(siloxane-imides) appeared in 1966, where PMDA (pyromellitic dianhydride) was reacted with an amine-terminated siloxane dimer and subsequently imidized 166>. Two years later, Greber 167) reported the synthesis of a series of poly(siloxane-imide) and poly(siloxane-ester-imide) copolymers using different siloxane backbones. However no physical characterization data were reported. 

Liu, Y. H., and Zumbrunnen, D. A., Toughness enhancement in polymer blends due to the in-situ formation by chaotic mixing of fine-scale extended structures, J. Mater. Sci. 34, 1921-1931 (1999). 

Toughness Enhancement by Introduction of Silicone Blocks into Polycarbonates of Bisphenol Acetone and Bisphenol Fluorenone... 

Epoxy modification provides the ability to cross-link with carboxyl-modified vinyl resins to give an all-vinyl reactive system that yields thermoset-like characteristics, most notably improved toughness, enhanced physical properties and superior chemical resistance (Union Carbide Corp., 19%). 

Apart from the nature of the actual rubber employed, the degree of toughness enhancement is influenced by a variety of factors, including the volume... 

On the basis of the SANS results, a molecular mechanism has been recently proposed for the toughness enhancement of DN gels [34]. This mechanism rationalizes the changes in molecular structure of the DN gel constituents observed via in-situ neutron scattering measurements, the composition dependence of the solution viscosity, and the thermodynamic interaction parameters of PAMPS and PAAm molecules obtained previously from neutron scattering studies. More specifically, this proposed mechanism provides an explanation for the observed periodic compositional fluctuations in the micrometer range induced by large strain deformation. 

Maximum Toughness Enhancement Achievable by Crack Trapping. In specimens containing well-bonded obstacles at an equivalent volume fraction of approximately 0.06 (R/L = 0.125), the maximum measured... 

Two parameters are of particular interest the diameter, D, of modifier particles and the distance, A, between particles (interparticle distance). Until now, the literature has given conflicting accounts of the influence of these parameters on different systems. HIPS and ABS have often served as model systems for producing new materials, but the fact that the morphologies as well as the micromechanical mechanisms of toughness enhancement can be different has not always been considered. 

Figure 11.17 (a) The effect of SiC whisker content on toughness enhancement in different matrices.(b) Toughening is associated with crack bridging and grain pullout of elongated matrix grains. 

Co-continuous morpholoey A different type of morphological structure, cocontinuity of the phases, can prove beneficial by drawing on properties of both constituents stiffness from a rigid polymer and high strain at break from a ductile one. This is illustrated by Kyu et al. (1991) who studied the toughness enhancement of PC/PMMA blends. The blends were prepared using three different procedures ... 

FIGURE 18.20 The effect of SiC whisker content on toughness enhancement in different matrices. 

Mus Musto, P., Ragosta, G., Scarinzi, G., Mascia, L. Toughness enhancement of polyimides by in situ generation of silica particles. Polymer 45 (2004) 4265—4274. 

An advantage of these composites is the increased resistance to fibre damage during composite processing which results from the intrinsic ductility of metallic fibres and the possibility of exploiting their plastic deformation for composite toughness enhancement [100]. A penalty is paid due to the relatively low thermal capability and poor chemical resistance of the metallic fibre reinforcement, limiting the application temperature and environment. 

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