0719 - 7.13 Stress–Strain Behavior 40 250 ● 173 FIGURE...

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Unformatted text preview: 7.13 Stress–Strain Behavior 40 250 ● 173 FIGURE 7.19 Typical stress–strain behavior to fracture for aluminum oxide and glass. 200 Aluminum oxide 150 30 20 100 10 50 Glass 0 0 0.0004 Strain 0.0008 0 0.0012 7.11 ELASTIC BEHAVIOR The elastic stress–strain behavior for ceramic materials using these flexure tests is similar to the tensile test results for metals: a linear relationship exists between stress and strain. Figure 7.19 compares the stress–strain behavior to fracture for aluminum oxide (alumina) and glass. Again, the slope in the elastic region is the modulus of elasticity; also, the moduli of elasticity for ceramic materials are slightly higher than for metals (Table 7.2 and Table B.2, Appendix B). From Figure 7.19 it may be noted that neither of the materials experiences plastic deformation prior to fracture. 7.12 INFLUENCE OF POROSITY ON THE MECHANICAL PROPERTIES OF CERAMICS (CD-ROM) MECHANICAL BEHAVIOR — POLYMERS 7.13 STRESS –STRAIN BEHAVIOR The mechanical properties of polymers are specified with many of the same parameters that are used for metals, that is, modulus of elasticity, and yield and tensile strengths. For many polymeric materials, the simple stress–strain test is employed for the characterization of some of these mechanical parameters.12 The mechanical characteristics of polymers, for the most part, are highly sensitive to the rate of deformation (strain rate), the temperature, and the chemical nature of the environment (the presence of water, oxygen, organic solvents, etc.). Some modifications of the testing techniques and specimen configurations used for metals are necessary with polymers, especially for the highly elastic materials, such as rubbers. 12 ASTM Standard D 638, ‘‘Standard Test Method for Tensile Properties of Plastics.’’ Stress (103 psi) Stress (MPa) ...
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