Valanis-Landel equation

Shen 39) has also considered the thermoelastic behaviour of another widely used phenomenological equation of state, the so-called Valanis-Landel equation. Valanis and Landel40) have postulated that the stored energy function W should be expressible as the sum of three independent functions of principle extension ratios. This hypothesis leads to the following equation of state... 

There is another approach which uses the concept of strain energy and principal strains only it is called the Valanis-Landel equation [4]. It assumes that the total strain energy may be subdivided into those corresponding to each of three principal strains ... 

Because of this usefulness it is important to have relatively simple experiments available to obtain the VL function. Kearsley and Zapas (97) have shown that either simple extension combined with simple compression or torsion with normal force measurements can be used to obtain the VL function. Valanis and Landel (98) used pure shear measurements. The equations for the torsional measurements arise from the relationship between w X) and Wi and W2 given by... 

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