Relationship ductile-brittle transition

From this therefore it is evident that the failure stress, ductile/brittle transitions which may be observed in plastics. According to line B, as the fiaw size decreases the failure stress tends towards infinity. Clearly this is not the case and in practice what happens is that at some defect size ([Pg.132]

Thus, the understanding of thermosets fracture needs the complete description of the yielding and the influence of both experimental variables, (T, e), on the one hand, and the relationship with structural parameters, on the other hand. Unfortunately, few results are available in the literature dealing with the ductile-brittle transition of thermosets. Very often it is stated that thermosets are more brittle than thermoplastics but this depends only on the location of the test temperature compared with the ductile-brittle transition temperature. 

Abstract The fracture properties and microdeformation behaviour and their correlation with structure in commercial bulk polyolefins are reviewed. Emphasis is on crack-tip deformation mechanisms and on regimes of direct practical interest, namely slow crack growth in polyethylene and high-speed ductile-brittle transitions in isotactic polypropylene. Recent fracture studies of reaction-bonded interfaces are also briefly considered, these representing promising model systems for the investigation of the relationship between the fundamental mechanisms of crack-tip deformation and fracture and molecular structure. 

In scheme A, step 3 must combine in principle a fracture property molar mass relationship and a molar mass critical value M c corresponding to the ductile-brittle transition. 

Fig. 11.27 Relationship between particle size and impact behavior for a typical super-tough thermoplastic blend. Points b and d mark lower ( ) and upper (o) ductile-brittle transitions. Schematic representation based broadly on data of Huang et al. (2006a) for a series of 80/20 rubber-toughened PA6 blends (From Bucknall and Paul (2009) reproduced with permission of Elsevier)...

A typical sample undergoes a ductile-brittle transition with increasing strain rate when tested at temperatures near to ambient. At low strain rates a yield point is observed, and the yield stress/strain rate relationship shows the character-... 

In linear poly(ester)s, predictions of the end of service time can be based on the relationship between the ductile-brittle transition and the entanglement limit of the molecular weight. However, for crosslinked poly(ester)s, this method is not applicable. The reasons for complications in the degradation behavior arise from the diffusion control of hydrolysis kinetics, heterogeneity of semi-crystalline polymers, and variation of the hydrophilicity with the hydrolysis conversion. 

Hardness and a ductile-to-brittle transition temperature (DBTT) have also been noted to follow a Hall-Petch relationship (Meyers, and Chalwa, 1984). Ductility increases as the grain size decreases. Decreasing grain size tends to improve fatigue resistance but increases creep rate. Electrical resistivity increases as grain size decreases, as the mean free path for electron motion decreases. 

Relationship of Brittle to Ductile Transition, as a Function of Molecular Weight of PVC [Adapted from Summers and Rabinovitch (9)]. 

Based on the observations and discussions presented here, a relationship between burial diagenesis, rock properties and faulting in sandstones has been generated. This is displayed in Fig. 11. As shown in this figure, the depth at which sandstones behave ductile or brittle when deformed will depend on the cementation processes during the burial diagenesis. It should be noted, however, that other factors such as strain rate and pore pressure will have impact on the indicated transition between ductile and brittle properties of sandstones as presented in Fig. 11. 

Not all polymers show cold drawing there are requirements such as a minimum molecular weight for strain hardening, and this has been extensively discussed elsewhere (see for example Ref. 5, pp. 271 and 322). It is clearly necessary for the polymer to be above its brittle-ductile transition, but this is a necessary rather than a necessary and sufficient condition for cold drawing. It should perhaps also be emphasised that there is no immediately obvious relationship between the glass transition temperature and the brittle-ductile transition temperature Tb (see for example Ref. 6). 

What is the relationship between the brittle-to-ductile transition and molecular weight for polyvinyl chloride ... 

Most ceramics are brittle at low and medium temperatures, and can be deformed plastically above the brittle-to-ductile transition temperature. The critical resolved shear stress (CRSS) then decreases rapidly with increasing temperature. In many cases there is a linear relationship between 1( (CRSS) and temperature, as first shown by Castaing for semiconductor crystals [17]. Examples are shown in Figures 9.1-9.4. For MgO in Figure 9.1 [5], the relationship is well obeyed for both easy slip on the... 

Relationships exist between Tg, T, and the type of termonomer introduced in the polymer and between Tg and the ductile to brittle temperature transition of polyketones in notched Izod or falling-weight impact strength test. For decene- or dodecene- containing grades Tm and Tg decrease simultaneously, while for propene-containing grades the opposite is observed (5). 

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