Calculate total force from cauchy stress
by Patricia Garcia Cañadilla

Dear Robert,
I have a 2D body of hyperelastic material which contracts and I would like
to compute the total force developed by the body from the cauchy stress. I
am trying to follow some of your indications I found in this group, but I
still couldn't make it works. Could you please help me to fix the problem?
I am getting the following error:
key = (region.name, integral.order, integration)
AttributeError: 'dict' object has no attribute 'name'
I am trying to do the following, inside stress_strain post-processing
function:
def stress_strain(out, problem, state, extend = False ):
from sfepy.base.base import Struct
from sfepy.mechanics.tensors import StressTransform
from sfepy.mechanics.tensors import transform_data
from sfepy.discrete.common.mappings import get_normals
ev = problem.evaluate
field = problem.fields['displacement']
region = problem.domain.regions['Gamma']
integral = problem.integrals['i2']
n = get_normals(field,integral,regions)
stress = ev('dw_tl_fib_a.1.Omega(f1.fmax, f1.eps_opt, f1.s, f1.fdir,
f1.act, v, u )',mode='qp', term_mode= 'stress');
F = ev('ev_def_grad.1.Omega(u)',mode='el_avg');
transform = StressTransform(F)
Cstress = transform.get_cauchy_from_2pk(stress)
T = Cstress*n;
Force = ev('ev_surface_integrate.2.Gamma(T)')
And here it is part of the problem configuration file.
fields = {
'displacement': ('real', 'vector', 'Omega', 1),
}
materials = {
'solid' : (None, 'get_elastic_pars'),
'load' : (None, 'linear_tension'),
'f1' : 'get_pars_fibres1',
}
variables = {
'u': ('unknown field', 'displacement', 0),
'v': ('test field', 'displacement', 'u'),
}
regions = {
'Omega' : 'all',
'Fix1' : ('vertices in x < %.10f' % (fix_point + eps2), 'facet'),
'Fix2' : ('vertices in x > %.10f' % (fix_point - eps2), 'facet'),
'Fix' : ('r.Fix1 *v r.Fix2', 'facet'),
'Gamma' : ('vertices of surface','edge'),
}
ebcs = {
'fixb' : ('Fix', {'u.all' : 0.0}),
}
integrals = {
'i1' : ('v', 1),
'i2' : ('s', 2),
}