Ideal rubber normal stress difference

Non-linearity shows up in the second finding. We observe that simple shear is accompanied by the development of a non-vanishing normal stress difference < xx — The effect is non-linear since it is proportional to the square of 7. The result tells us that in order to establish a simple shear deformation in a rubber, application of shear stress alone is insufficient. One has to apply in addition either pressure onto the shear plane gzz < 0) or a tensile force onto the plane normal to the x-axis a x > 0), or an appropriate combination of both. The difference Gxx zz is called the primary normal stress difference likewise Oyy — Ozz is commonly designated as the secondary normal stress difference. As we can see, the latter vanishes for an ideal rubber. 

For simple shear, we have thus obtained again linearity for as for ideal rubbers, but non-vanishing values now for both, the primary and the secondary normal stress difference. 

The secondary normal stress difference vanishes, as was the case for an ideal rubber... 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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