Low speed mechanical properties

The tensile stress-strain test is most widely used. Owing to the viscoelastic nature of polymers, the test is only a rough guide to how a polymer will behave in a finished product. Often results of a single test conducted at one temperature and speed of testing are published. To get a clear understanding of a polymer it is required to have the tests at several temperatures, rates of testing and other conditions [Dukes, 1966]. 

There is no universally accepted set of definitions with regard to the tensile tests. The terms listed in Appendix 2 have been taken from the widely accepted norms (ISO/DIS 527, BS 2782, Methods 320A to F, ASTM D638-72). 

During the process of stretching, the specimen s dimensions orthogonal to the axis of applied force decrease and thus the area of cross-section decreases. For experimental convenience, however, tensile strengths are usually based on the original cross-section (A ) which is easily measured at the beginning of the experiment. 

From the point of view of mechanical performance, four types of materials have been identified. They are best discussed in terms of the stress-strain dependence  

Brittle, showing proportionality between stress and strain up to the point of rupture. Here the modulus, E = o/e is constant, independent of 

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The low-speed mechanical properties of polymer blends have been frequently used to discriminate between different formulations or methods of preparation. These tests have been often described in the literature. Examples of the results can be found in the references listed in Table 12.9. Measurements of tensile stress-strain behavior of polymer blends is essential [Borders et al., 1946 Satake, 1970 Holden et al., 1969 Charrier and Ranchouse, 1971]. The mbber-modified polymer absorbs considerably more energy, thus higher extension to break can be achieved. By contrast, an addition of rigid resin to ductile polymer enhances the modulus and the heat deflection temperature. These effects are best determined measuring the stress-strain dependence. 

Table 12.9. Sources for low-speed mechanical properties data of polymer blends, examples... 

Considering a mass of ceramic powder about to be molded or pressed into shape, the forces necessary and the speeds possible are determined by mechanical properties of the diy powder, paste, or suspension. For any material, the elastic moduli for tension (Young s modulus), shear, and bulk compression are the mechanical properties of interest. These mechanical properties are schematically shown in Figure 12.1 with their defining equations. These moduli are mechanical characteristics of elastic materials in general and are applicable at relatively low applied forces for ceramic powders. At higher applied forces, nonlinear behavior results, comprising the flow of the ceramic powder particles over one another, plastic deformation of the particles, and rupture of... 

The mechanical properties of titanium are comparable with those of steel it is more difficult to fabricate owing to the readiness with which it takes up, and is hardened and embrittled by, oxygen and nitrogen. Its strength, lightness, resistance to corrosion and the low thermal expansion have led to its employment in high-speed aircraft, naval and military projects and chemical research and industry. 

Different mixing speeds were used to see the effect of mechanical forces on the emulsion properties. As expected, at high speed (11,000 rpm), average particle size obtained was smaller than at low speed (7,000 rpm) and the viscosity was higher, as expected (see Table I). The lowest viscosity was not observed at the lowest mixing speed, however, but at 9,000 rpm. This surprising result is discussed later. 

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