  The parameters of the triangular domain wall network in bilayer graphene with
a simultaneously twisted and biaxially stretched bottom layer are studied using
the two-chain Frenkel-Kontorova model. It is demonstrated that if the graphene
layers are free to rotate, they prefer to stay co-aligned upon stretching the
bottom layer and the regular triangular network of tensile domain walls is
formed upon the commensurate-incommensurate phase transition. If the angle
between the layers is fixed, the regular triangular network of shear domain
walls is observed at zero elongation of the bottom layer. Upon stretching the
bottom layer, however, the domain walls transform into the tensile ones and the
size of the commensurate domains decreases. We also show that the parameters of
the isosceles triangular domain wall network in twisted bilayer graphene under
shear strain can be determined through purely geometrical considerations.
Experimental analysis of the orientation of domain walls and period of the
triangular network would, on the one hand, contribute to understanding of the
interlayer interaction of graphene layers, and, on the other hand, serve for
detection of relative strains and rotation between the layers. Vice versa
external strains can be used to control the parameters of the triangular domain
wall network and, therefore, electronic properties of twisted bilayer graphene.
