Polymers ductility values

From the Eq. (10.28) it follows, that large values d reaching, that is, ductile fracture can be realized either by enhancement or by C reduction. For polymers the value is connected with molecular mobility level, which can be characterized by fractal dimension of the chain part between entanglements [14], In Fig. 10.16 the relation between - 1) and q for the 10 studied in Ref [57] polymers is adduced, from which follows their approximate equality (deviation from the linear dependence for PAr, PSF andPASF is due to the condition 1 in the Eq. (10.1) nonfulfillment [58]. The dependence qj(-D, i - 1) for the 10 different polymers, adduced in Fig. 10.16, is identical to the similar dependence for HD PE samples with various length of notch, tested at different temperatures (Fig. 10.4), that indicates high community degree of the relation between q and... 

Other high performance polymer backbones have been explored as PEM materials in addition to poly-(arylene ether)s and polyimides. Ductile copolymers with high modulus and glass transition values are desirable PEM candidates. The hydrolytic and oxidative stability of many of these materials remains to be determined. Nevertheless, interesting synthetic methodologies have been employed to investigate these materials, which have been instructive in the search for new PEM candidates. 

The stress-strain curves for cortical bones at various strain rates are shown in Figure 5.130. The mechanical behavior is as expected from a composite of linear elastic ceramic reinforcement (HA) and a compliant, ductile polymer matrix (collagen). In fact, the tensile modulus values for bone can be modeled to within a factor of two by a rule-of-mixtures calculation on the basis of a 0.5 volume fraction HA-reinforced... 

Most acrylonitrile-butadiene styrene terpolymer (ABS) is produced as a graft of SAN onto a butadiene polymer backbone. This graft copolymer may be blended with more SAN or acrylonitrile elastomer (NBR) to improve its properties. ABS is more ductile than SAN. The Tt and the heat deflection temperature of ABS vary with the composition, and ABS may have one set of values for the PBD domains and another set for the SAN matrix. The permeabilities of ABS to oxygen, nitrogen, and carbon dioxide are much less than those of hope. 

For many years, several authors have tried to explain and predict the yield stress of polymers (crosslinked or not), as a function of the experimental test parameters (T, e) and/or structural parameters (chain stiffness, crosslinking density). These models would be very useful to extrapolate yield stress values in different test conditions and to determine the ductile-brittle transition. 

Many polymers, which are brittle in tension or bending, may readily yield in other types of deformation, and show a high ductility. In indentation hardness experiments, plastic indentation can often be made in relatively brittle materials. Hardness values thus obtained are a measure of the plastic properties of the brittle solid ... 

Table 13.12 gives the numerical values of the strength properties of a series of polymers. The data on the tensile strength are graphically reproduced in Fig. 13.62, where crmax (i.e. the tensile strength at break of brittle (linear) polymers and the tensile strength at yield of ductile (linear) polymers) is plotted as a function of E, the tensile modulus. As an approximation the following empirical expression may be used (drawn line) ... 

When seeking a polymer material for a CNT-based strain gauge, ductility and ease of processing are the key requirements. For that reason, polymethyl methacrylate (PMMA) and polyethylene (PE) are two candidate materials. Studies on the electrical conductivities of CNT-PMMA composites reported minimum percolation thresholds ranging from 0.084 to 1.3 wt% which depend on the type of CNT (SWNT or MWNT) and the dispersion technique. Such values are much lower than percolation thresholds reported for CNT-PE which rise up to 15 wt% (38). As a consequence, much higher conductivity values were reported for CNT-PMMA composites. For this reason, a PMMA matrix will be considered for the current... 

For this semi-ductile fracture mode, a method using two material parameters has been proposed to characterize the impact resistance of the polymer [11], The method takes account of an average value of the fracture energy during the stable propagation of the crack, and also the fracture energy at instability. In this case, the total energy absorbed by the sample to break, U, has been shown... 

Within this framework, one can imagine a two dimensional ductile-brittle transition criterion which would be composed of two perpendicular boundaries in the graph la-Mw (Fig. 7). The vertical boundary would correspond to a critical molar mass M c- In polymers of low crystallinity or fully amorphous, M c would be sharply linked to the entanglement molar mass M c 5Me. In polymers of medium to high crystallinity, M c would be the molar mass below which it is impossible to have values higher than lac- The horizontal boundary would correspond to U = lac-... 

The possibility to get geometry independent parameters constitutes a master trump to characterise properly a ductile polymer. However, whereas far from the ductile-brittle transition the evaluation of Kes is achieved easily, it is more challenging closer to it. The difficulties to determine reliable effective toughness values in this latter case and thus precise ductile-brittle transitions will be illustrated with grade iPP/EPR-1 tested at room temperature. 

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