Plastics characteristic values

Broadly speaking, plastics characteristic values are measured... 

Figure 16 Characteristic values of glass fiber and flax fiber SMC molded plastics (absolute values and in reference to density) [58].

Generally, the mechanical and physical properties of natural fiber-reinforced plastics only conditionally reach the characteristic values of glass fiber-reinforced systems. By using hybrid composites made of natural fibers and carbon fibers or natural fibers and glass fibers, the... 

When used as substitutes for asbestos fibers, plant fibers and manmade cellulose fibers show comparable characteristic values in a cement matrix, but at lower costs. As with plastic composites, these values are essentially dependent on the properties of the fiber and the adhesion between fiber and matrix. Distinctly higher values for strength and. stiffness of the composites can be achieved by a chemical modification of the fiber surface (acrylic and polystyrene treatment [74]), usually produced by the Hatschek-process 75-77J. Tests by Coutts et al. [76] and Coutts [77,78] on wood fiber cement (soft-, and hardwood fibers) show that already at a fiber content of 8-10 wt%, a maximum of strengthening is achieved (Fig. 22). 

Unlike other aqueous dental cements, the zinc polycarboxylate retains plastic characteristics even when aged and shows significant stress relaxation after four weeks (Paddon Wilson, 1976). It creeps under static load. Wilson Lewis (1980) found that the 24-hour creep value for one cement, under a load of 4-6 MPa, was 0-7 % in 24 hours, which was more than that of a zinc phosphate cement (0-13 %) and a glass-ionomer cement (0-32%), but far less than that of the zinc oxide eugenol cement (2-2%). 

In this paper the recently developed techniques to characterize the mar resistance of coating systems were presented. The techniques base on methods that create a single scratch onto a surface. Characteristic values like the critical load as a measure for the transition from plastic behaviour to brittle fracture can be determined and used to rank different clearcoat systems and to compare these results with other physical properties. In the field of mar resistance the cross-linking density of the... 

Some characteristic values for engineering plastics have been derived from the literature data on creep measurements (see, e.g., Ogorkiewicz (1970)) and are given in Table 13.11. 

When grouting in sands and silts with short gel times or with very small grout volumes, particularly in strata overlain by clays, grouting pressures may be safely increased above the values based on cover alone. Such pressures cannot be computed without extensive laboratory test data since they are related to the plastic characteristics of the soils. However, it is reasonable to grout at pressures approaching twice the rule-of-thumb value. 

The plasticity characteristic /, was calculated as the ratio of the work spent for plastic deformation of the material to the total work spent for elastic - plastic deformation of a material under indenter. It is shown (Table 1), that X for 400 nm thickness molybdenum coatings is higher, than its value for chromium coatings of the same thickness. 

To estimate the plastic deformation, assume that the deformation occurs mainly in the shear bands. Introduce into the plastic deformation rate. Equation (5) nominal characteristic values for RDX, ° so that the plastic deformation rate reduces to dy/dt = 2T(t,U)Pc(t)x10 s. Approximating dy/dt = Ay/At and letting At = 5 x lO s, which is the measured time of the impact, gives Ay = T(t,U)Pc(t)x10 s. It will be shown in the following paragraph that for mild impacts slightly less than that required for initiation of chemical reaction in RDX, T(t,U)Pc(t) = 10 in crystals at the outer perimeter of the impacted sample. The plastic strain is Ay 10 which is close to the measured values of Ay = 10 to 20, (1000% to 2(KX)%). 

Identification of plastics [34] is carried out by a systematic procedure preliminary test, detection of elements, determination of characteristic values, and, finally, specific tests. For an exact identification, however, the test sample should first be purified so that it contains no additives (plasticizers, fillers, pigments, etc.) that may affect the results of an analysis. Purification is achieved by solvent extraction either the material is dissolved out and polymer is obtained by reprecipitation or evaporation of the solvent, or the pure polymer remains as the insoluble residue. The solvent varies, and a general method cannot be given. However, for many materials particularly for those in which additives do not interfere, the unpurified material can be investigated and qualitative preliminary tests used. 

As it is known, the work of fracture U, characterizing expenditure of energy on material deformation up to failure, is one of the most important plasticity characteristics. In paper [5] it was shown, that the fracture character of solids is determined by the fractal dimension df of their structure at 4-2. 50 brittle fracture is realized, at 4 2.50-2.67 - quasibrittle (quasiductile) fracture and at 4 2.70 - ductile fracture. This classification allows to suppose plasticity increase characterized by value U at raising df. Actually, the dependence U dj) shown in Fig. 3 confirms this assumption. This dependence is linear, the increase U is observed at raising df and zero value U is reached at 4=2.50, i.e., at brittle fracture. Since limiting (maximal) value df for real solid is equal to 2.95 then this allows to estimate... 

The modulus of elasticity E and hardness H are related to the elastic and plastic characteristics of the given material. A % value of 4.8 MPav was calculated by means of Eq. (4) for the Si3N4 material shown in Figs. 147 and 148. Various formulas for calculating fracture toughness have been pubUshed by Dinner and Stevens (1984), Evans and Charles (1976), Langier (1985), Evans (1979), Smith and Alavi (1985), and Munz and Fett (1989). All of these formulas maintain the fundamental dependence on c- ... 

Although extensive data for mixed-gas permeation in the plasticization regime are not available, good pure-gas values are available and illustrate some important points. The permeability of CO2 in various substituted polycarbonates shown in Figure 28 (111) increases with pressure above a certain characteristic value for each of the polymers. The shapes of the permeability curves are like the curve shown schematically in Figure 21. Plasticization occurs despite the fact that the downstream pressure is maintained at a vacuum of less than 1330 Pa (10 mm Hg). To determine when true transport plasticization occurs, the local diffusion coefficient Dap(Ca), which measures the ability of a penetrant to move through the membrane at a point where the local concentration of penetrant is equal to Ca, must be considered. The sorption isotherms for CO2 in the various materials are shown in Figure 29 (111), and application of the standard... 

Compared with commercial high-impact PS (HIPS), the droplet structures exhibit improved toughness and are transparent. In such blends with PS content up to 40%, a size of the PS droplets below a critical characteristic value can be realized with the effect that the PS droplets can be strongly plastically deformed (see Fig. 3.69). The comparison with the network yielding mechanism (Section 52.6.2) reveals the similarity and the possibility to toughen materials other than PVC using this effect [6]. 

Hence, the adduced above data have shown the physical grounds for often cited in literature correlations of impact toughness and fracture surface fractal dimension at any rate for polymers. And on the contrary, such grounds exist for correlations of plasticity characteristics or y) and r/g,. The Eq. (10.27) gives the possibility of the value prediction, since <7, as it follows from the Eq. (4.50), is a function of structure characteristic -Poisson s ratio V. In its turn, G and critical defect characteristics knowledge gives the possibility of p prediction [47]. 

For the evaluation of stress cracking resistance in polymers and/or finished plastic parts, there are standards targeted for material development that allow the determination of characteristic values using test specimens. There are also methods for testing component parts, such as pipes and containers, as well as in-house standards, e.g., provided by material manufacturers. 

Secreted mucus of a snail is a kind of non-Newtonian fluid that has the characteristics of a visco-plasitic (Bingham) fluid because the viscosity decreases with an increase of shear rate and the shear stress has a plastic yield value and increases with shear rate. 

In line with the common ISO standards, these characteristic values are measured by test methods standardized for thermoplastics (TP) and thermoset plastics (TS). Table 2.1 lists the standards for determination of rheological characteristic values in accordance with the DIN ISO 10350 data catalog [8, 66]. The literature can be referred to for the standards for determination of mechanical, thermal, and electrical characteristic values. 

The relevant characteristic values are shown again in diagrammatic form in Fig. 2.4. Fig. 2.5 shows typical strain/elongation diagrams for selected plastics by way of example. The reliability of the MID is determined by the mechanics of the polymer basic body, so materials characterized by strength (elongation strain) and ductility are eminently suitable (see curves (b) and (c). Fig. 2.4). 

FIGURE 2.4 Schematic a/e diagrams with characteristic values from tensile testing a) brittle plastic b) tough plastic c) stretchable plastic d) and e) softened plastic with E = tensile modulus of elasticity ... 

The dimensional stability of a plastic when exposed to heat is another crucial property. The Vicat method of determining a plastic s softening point and the heat deflection temperature (HDT) method are two ways of rapidly determining which polymers have suitable characteristic values. In both methods the test specimens are heated under defined load with a certain heating rate while deformation is measured. Vicat softening temperature and HDT are each defined as the temperatures at which deformation reaches a given value [8]. 

The dielectric constant is an expression of the ratio of capacitance of a capacitor with plastic as the dielectric to the capacitance of the same capacitor with air as the dielectric. The loss factor, by contrast, is a measure of the energy that an insulating substance in an alternating field transforms into heat and is therefore lost as electrical energy. The dielectric characteristic values are material constants. They are dependent on temperature and frequency range and also on ambient conditions such as humidity, for example [8]. 

Figure 2.12 also shows that thermal conductivity is always a directional characteristic value, an aspect that has to be taken duly into account in the framework of integrated MID product development with highly filled plastic compounds [77,135]. 

---