Tension test poisson ratio

Another effect o(f orientation shows up as changes in Poisson s ratio, which can be determined as a function of time by combining the results of tension and torsion creep tests. Poisson s ratio of rigid unoriented polymers remains nearly constant or slowly increases with time. Orientation can drastically change Poisson s ratio (254). Such anisotropic materials actually have more than one Poisson s ratio. The Poisson s ratio as determined when a load is applied parallel to the orientation direction is expected to... 

The critical values are generally obtained from a standard tensile test. Once the critical values are obtained the application of any (or all) of these criteria in conjunction with a dependable stress analysis is straightforward. Here we demonstrate the method by a simple example. Let us assume that it is desired to determine the torque required to cause failure of a 25 mm in diameter shaft constructed of an homogeneous isotropic plastic with a failure stress in tension, o, of 7 x 10 N/m. Assume further tlmt the modulus of elasticity, E, for this plastic is given by 3 x 10° N/m, and that is has a Poisson ratio of 0.3. We will explore the prediction of the three criteria just discussed. 

In the uniaxial tension test (Fig. 2.8), there is usually a transverse strain, i.e., a strain perpendicular to the applied stress. This can be used to define a second elastic constant, Poisson s ratio (v), as the negative ratio of the transverse strain (e.j.) to the longitudinal strain (s ), i.e., v= -Sj/cl- For isotropic materials, it can be shown from thermodynamic arguments, that -1< u <0.5. For many ceramics and glasses, v is usually in the range 0.18-0.30. 

Based on the stress-strain diagram the values tensile stress at yield cXy and tensile strength at maximum (7m as well as the associated normative yield strain and nominal strain 8tM or normative strain 8m at tensile strength as well as strain at break 8b can be calculated (Eqs. 4.6. 11). For completely recorded diagrams the nominal strain at break 8tB can be determined additionally (Eq. 4.12). Because of the dependence on software and test equipment, especially sampling rate, the tensile stress at break (Tb should not be used (Eq. 4.13). Due to the viscoelastic behaviour of the plastics modulus of elasticity in tension is determined as secant modulus between the strain limits of 0.05 % and 0.25 % (Eq. 4.14). If the transverse strain is recorded simultaneously using strain gauges Poisson ratio jl can be calculated (Eq. 4.15). 

Biaxial tension tests similar to those described by McGo wn and Kupec (2004) can be used to determine Poisson s ratio (proposed equations for evaluating Poisson s ratio (y) tiom biaxial tests and comparing the moduli between biaxial and uniaxial loading are provided by Perkins et al. (2004)). 

Engineering constants (sometimes known as technical constants) are generalized Young s moduli, Poisson s ratios, and shear moduli as well as some other behavioral constants that will be discussed in Section 2.6. These constants are measured in simple tests such as uniaxial tension or pure shear tests. Thus, these constants with their obvious physical interpretation have more direct meaning than the components... 

Simple continuum mechanical treatment of the behavior of uniform materials (isotropic) that are tested by pulling the ends of a long thin specimen in tension (uniaxial tension) leads to the following relationship between the shear modulus G, and E, the tensile modulus, where v is Poisson s ratio. 

Mechanical testing is the determination of the behavior of a material caused by some applied loading. The material is loaded in its bulk form via a mechanical testing machine (i.e., MTS, Instron, etc.) and its properties are evaluated. Typically these include the elastic modulus or stiffness, the yield strength, the fracture stress or ultimate strength, the elongation, and Poisson s ratio. These properties depend on the mode of loading, such as tension, compression, shear, or flexure. 

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