Strain rate properties

The low strain rate properties of the devltrified Y203-containlng silicon nitride have also been evaluated via four-point creep at 1200 C and found to be identical to those of the standard hot-pressed materials. For example, at 1200°C and at Imposed stress of 207 MPa, the steady state strain rate of hot-pressed AY6 was 3-6 X lO sec", while that of devltrified AY6 was 3.3 x 10 sec. This result is attributed to in-situ devitrification of the hot-pressed material during stage 1 creep before steady state (linear) creep is observed. 

Using Eq. 3.35 it is also possible to show that constant strain rate properties vary with temperature for a Maxwell model and would be similar to the results described earlier in Fig. 3.6 (see problem 3.6). 

Peter, S. and E. Woldesenbet, Nanoclay syntactic foam composites—High strain rate properties. Materials Science and Engineering A, 2008.494(1-2) 179-187. 

Articulated cartilage (AC) displays nonlinear, viscoelastic, and strain rate-dependent properties, in addition to the anisotropy properties. These strain-rate properties... 

One simple rheological model that is often used to describe the behavior of foams is that of a Bingham plastic. This appHes for flows over length scales sufficiently large that the foam can be reasonably considered as a continuous medium. The Bingham plastic model combines the properties of a yield stress like that of a soHd with the viscous flow of a Hquid. In simple Newtonian fluids, the shear stress T is proportional to the strain rate y, with the constant of proportionaHty being the fluid viscosity. In Bingham plastics, by contrast, the relation between stress and strain rate is r = where is... 

Perhaps more so than any other common metal, the mechanical properties of chromium (8,14—17) depend on purity, history, grain size, strain rate. ... 

L.E. Murr, Residual Microstructure—Mechanical Property Relationships in Shock-Loaded Metals and Alloys, in Shock Waves and High Strain Rate Phenomena in Metals (edited by M.A. Meyers and L.E. Murr), Plenum, New York, 1981, 607 pp. 

In the numerical calculations, an elastic-perfectly-plastic ductile rod stretching at a uniform strain rate of e = lO s was treated. A flow stress of 100 MPa and a density of 2700 kg/m were assumed. A one-millimeter square cross section and a fracture energy of = 0.02 J were used. These properties are consistent with the measured behavior of soft aluminim in experimental expanding ring studies of Grady and Benson (1983). Incipient fractures were introduced into the rod randomly in both position and time. Fractures grow... 

Karnes, C.H., The Plate Impact Configuration for Determining Mechanical Properties of Materials at High Strain Rates, in Mechanical Behavior of Materials Under Dynamic Loads (edited by Lindholm, U.S.), Springer-Verlag, New York, 1968, pp. 270-293. 

Strain rate also affeets tensile properties at test. An inereasing strain rate tends to inerease tensile properties sueh as Su and Sy. However, a high loading rate tends to promote brittle fraeture (Juvinall, 1967). The average strain rate used in obtaining a... 

Strength and Stiffness. Thermoplastic materials are viscoelastic which means that their mechanical properties reflect the characteristics of both viscous liquids and elastic solids. Thus when a thermoplastic is stressed it responds by exhibiting viscous flow (which dissipates energy) and by elastic displacement (which stores energy). The properties of viscoelastic materials are time, temperature and strain rate dependent. Nevertheless the conventional stress-strain test is frequently used to describe the (short-term) mechanical properties of plastics. It must be remembered, however, that as described in detail in Chapter 2 the information obtained from such tests may only be used for an initial sorting of materials. It is not suitable, or intended, to provide design data which must usually be obtained from long term tests. 

In many cases, less intense pressure or stress waves are encountered in which times to achieve peak pressure may be hundreds of nanoseconds or more. The study of solids under these conditions can be the source of mechanical, physical, and chemical properties of solid materials at large strain, high pressure, and high strain rates. 

These differences on the stress-strain behavior of P7MB and PDTMB show the marked influence of the mesomorphic state on the mechanical properties of a polymer. When increasing the drawing temperatures and simultaneously decreasing the strain rate, PDTMB exhibits a behavior nearly elastomeric with relatively low modulus and high draw ratios. On the contrary, P7MB displays the mechanical behavior typical of a semicrystalline polymer. 

The mechanical properties were obtained using a tensile machine at room temperature and for a strain rate of 1000%/h. Each reported value of the modulus was an average of five tests. The tensile modulus Et was taken as the slope of the initial straight line portion of the stress-strain curve. 

PPG would allow more metal at the expense of the oxidizer to further energize the composition. In addition, HTPB is frequently preferred over PPG because of its superior mechanical properties, better aging characteristics, and lower glass-transition temperature (Tg). The latter is especially desirable because at low temperature, the higher strain rates produced by motor ignition decrease the elongation of the composite rather markedly. 

K. Higashi, T.G. Nieh, and J. Wadsworth, "Effect of Temperature on the Mechanical Properties of Mechanically-Alloyed Materials at High Strain Rates," Acta Metall. Mater., 43 3275 (1995). 

Mechanical properties at 21°C, 65% relative humidity, using 60% minute strain rate)... 

Edwards e/a/. carried out controlled potential, slow strain-rate tests on Zimaloy (a cobalt-chromium-molybdenum implant alloy) in Ringer s solution at 37°C and showed that hydrogen absorption may degrade the mechanical properties of the alloy. Potentials were controlled so that the tensile sample was either cathodic or anodic with respect to the metal s free corrosion potential. Hydrogen was generated on the sample surface when the specimen was cathodic, and dissolution of the sample was encouraged when the sample was anodic. The results of these controlled potential tests showed no susceptibility of this alloy to SCC at anodic potentials. 

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