I am doing some simulations for UD pultruded composite beams in Abaqus. In my case the considered profiles are symmetric and solid. I wrote the following simple VUMAT to specify the material behaviour (1 being the fibre direction):
[FONT=courier new]e11 = props(1)
g12 = props(2)
v12 = props(3)
do k = 1, nblock
C Update stresses (direct & torsion shear)
stressNew(k,1) = stressOld(k,1) + e11 * strainInc(k,1)
stressNew(k,4) = stressOld(k,4) + g12 * strainInc(k,4)
C Define transverse strain increments (direct)
strainInc(k,2) = -v12 * strainInc(k,1)
strainInc(k,3) = strainInc(k,2)
This seems to work fine, but I still have two questions:
1. The subroutine manual states that it is necessary to define the transverse strain increments. However, I notice the results are the same when this step is omitted. Does Abaqus actually use these strain increments, and how?
2. Using a VUMAT, the transverse shear stiffness needs to be defined separately. When K12 = k G12 A, can we use the same shear correction factor k as for isotropic material? In some first checks against analytical calculation of a cantilever beam and simulation of a solid model this seems to hold fairly well, though there exists some error.