Where C 1 ( \\ displaystyle C_ ( 1 ) ) is a material constant .
I 1 ( \\ displaystyle I_ ( 1 ) ) is the first invariant ( trace ) , of the right Cauchy - Green deformation tensor , i.e. ,
where C 1 ( \\ displaystyle C_ ( 1 ) ) is a material constant , and I 1 ( \\ displaystyle I_ ( 1 ) ) is the first invariant ( trace ) , of the right Cauchy - Green deformation tensor , i.e. ,