Proportionality limit

The calibration graph for the probe using a strength machine, has been shown in Fig. 7 It can be observed that the dependence of indications of the device of Wirotest type on the loading is linear within the proportionality limit scope. After unloading the indications do not return to zero, but show own stress caused in effect of plastic deformation of the tested sample... 

Material Young s modulus, E, GPa Proportionality limit d, % extension Shear modulus, G, GPa Poisson s ratio, P Bulk modulus, B, GPa "... 

The second group exhibits the phenomenon of drawability. This manifests itself in the stress-strain behavior (curve II in Fig. 2.21) as follows At first these materials behave in a similar way to those of curve I. The proportionality limit lies at low values, and the deformation with increasing load is also quite small. Then, suddenly, a large extension occurs, even though the load remains constant or becomes smaller. The material begins to flow and the stress-strain curve sometimes runs nearly parallel to the abscissa. The point at which the... 

If a force is applied to wood within the proportionality limits, the wood will bend and if the force is released, the wood returns to its original form with an elastic recovery. In contrast, if the wood is dried under stress, a substantial superposition of stresses occurs in conjunction with the drying and shrinking process. Since the ordering of macromolecules or larger structural elements under tension is different from those under compression, as the water molecules are removed, new hydrogen bonds can form between different subunits of the structure to support the distorted structure in its new form. 

Recently Puski (20) determined the effects of proteolysis on the water absorption, viscosity, and gelation properties of a soy protein isolate. The water absorption of enzymically hydrolyzed soy protein isolate increased in direct relation to the enzymic treatment. Apparently as the number of polar amino and carboxyl groups increased, the uptake of water increased proportionately. Limited proteolysis of the soy protein isolate resulted in a decided decrease in the viscosity and gelling properties. 

A special pneumatic multiposition low-temperature impact testing machine was developed to allow investigation of impact strength with samples inside the coolant bath, containing liquid helium. The impact test machine is shown in Fig. 6. It enables investigation of the temperature dependence of fracture, crack propagation, and maximum and proportionality limit loading. 

Fig. 7. Temperature dependence of crack initiation (dc) and propagation (dp), maximum load (PmaxX and dynamic proportionality limit (Pprop) for Fe-18Cr-10Ni-Ti steel with notch radii (p)of 0.25 and 1.0 mm.

K - constant characterizing the phase interface resistance to plastic deformation Pmax maximum loading PpTop = dynamic proportionality limit... 

The moduli of elasticity determined by stress / strain measurements are generally much lower than the lattice moduli of the same polymers (Table 11-3). The difference is to be found in the effects of entropy elasticity and viscoelasticity. Since the majority of the polymer chains in such polymer samples do not lie in the stress direction, deformation can also occur by conformational changes. In addition, polymer chains may irreversibly slide past each other. Consequently, E moduli obtained from stress/strain measurements do not provide a measure of the energy elasticity. Such E moduli are no more than proportionality constants in the Hooke s law equation. The proportionality limit for polymers is about 0.l%-0.2% of the... 

Strain produced. Above this so-called proportionality limit, the relationship between stress and strain can be quite different (Section 11.5). For this reason, the modulus of elasticity of polymers is usually measured over a strain of 0.2% and over a time of 100 s. Moduli measured over higher strains or longer times are lower. 

Thus, in contrast to lattice moduli, moduli of elasticity obtained from stress/strain measurements are not measures of the energy elasticity, because of the effects of entropy-elasticity and viscoelasticity. Moduli of elasticity have more the character of being solely proportionality constants in a Hooke-type law. The proportionality limits are 0.05 % extension for steel and 0.1-0.2% for polymers. Above these so-called proportionality... 

I is consequently called the proportionality limit or the elastic limit. The latter name is incorrect because of the entropy-elasticity remaining above the point I. According to definition, the proportionality limit is reached when the sample shows a remaining 0.1 % strain after removal of the stress. The technical elastic limit is defined as an extension of 0.2%. 

---