Stress-free layers in photoinduced deformations of photoelastomer beams

• Investigation of the stress-free layers in photoelastomer beams.
• Computation of the number of stress-free layers under bending and illumination.
• Identification of dimensionless parameters that determine the stress-free layers.
• Investigation of how variation in real parameters modify the stress-free layers.

Nematic liquid crystals combined with long molecular chains to form liquid crystal elastomers are capable of large extension. When such liquid crystal elastomers contain azo dyes to constitute photoelastomers, illumination can trigger large contraction. Beams made from such photoelastomers possess a non-uniform illumination and hence photostrain across their cross-section, resulting in bending and highly non-linear stress distribution. Due to the non-linear stress distribution, there can be more than one stress-free layers within the beam. In this paper, we present a dimensionless parametric study of nematic photoelastomer beams under the combined effects of light and mechanical loads. We show how the number of stress-free layers depends on three dimensionless parameters. The paths traced out by the system in the space of dimensionless parameters by varying the different real parameters are investigated, showing how the number of stress-free layers changes when e.g. the thickness or the mechanical load of the elastomer beam is varied. These results are important if the strain induced director rotation is not negligible.