On the tension–compression switch in soft fibrous solids

• Highlighting an inappropriate tension–compression switch for fibrous solids.
• Illustrating the consequences by using an inappropriate switch.
• Introducing a model that rectifies the problem.

Many soft fibrous solids consist of an isotropic matrix with strong embedded fibers. In continuum models of such materials it is often considered that the fibers do not support compression and that their contribution to the overall mechanical response should be neglected when they are under compression. A tension–compression ‘switch’ is used to turn off the contribution of the fibers in the model, but it is apparent that an inappropriate switch is often adopted and the predictions of the mechanical response can then be significantly different for different switching criteria. On the basis of a simple illustration this paper draws attention to the consequences of using an inappropriate switch, and identifies possible solutions. One of the possible solutions for rectifying the problem is provided in some detail by introducing a modified fiber distribution model and applying it to both plane strain and three-dimensional transversely isotropic fiber distributions.