Page 41 - Using ANSYS for Finite Element Analysis Dynamic, Probabilistic, Design and Heat Transfer Analysis

28 • using ansys for finite eLement anaLysis
250 uniform-thickness layers per element. Alternately, the element allows
125 layers with thicknesses that may vary bilinearly over the area of the
layer. An advantage with this element type is that you can stack several
elements to model more than 250 layers to allow through-the-thickness
deformation slope discontinuities. The user-input constitutive matrix
option is also available. SOLID46 adjusts the material properties in the
transverse direction permitting constant stresses in the transverse direc-
tion. In comparison to the 8-node shells, SOLID46 is a lower order ele-
ment and finer meshes may be required for shell applications to provide
the same accuracy as SHELL91 or SHELL99.

2.2.1.5 SoLiD191—Layered Structural Solid element

SOLID191 is a layered version of the 20-node 3-D solid element
SOLID95, with three degrees of freedom per node (UX, UY, UZ). It is
designed to model thick-layered shells or layered solids and allows up to
100 layers per element. As with SOLID46, SOLID191 can be stacked to
model through-the-thickness discontinuities. SOLID191 has an option to
adjust the material properties in the transverse direction permitting con-
stant stresses in the transverse direction. In spite of its name, the element
does not support nonlinear materials or large deflections.
In addition to the layered elements mentioned earlier, other composite
element capabilities exist in ANSYS, but will not be considered further in
the chapter:

• SOLID95, the 20-node structural solid element, with KEYOPT
(1) = 1 functions similarly to a single-layered SOLID191 including
the use of an orientation angle and failure criterion. It allows non-
linear materials and large deflections.
• SHELL63, the 4-node shell element, can be used for rough,
approximate studies of sandwich shell models. A typical applica-
tion would be a polymer between two metal plates, where the bend-
ing stiffness of the polymer would be small relative to the bending
stiffness of the metal plates. The bending stiffness can be adjusted
by the real constant RMI to represent the bending stiffness due to
the metal plates, and distances from the middle surface to extreme
fibers (real constants CTOP, CBOT) can be used to obtain output
stress estimates on the outer surfaces of the sandwich shell. It is not
used as frequently as SHELL91, SHELL99, or SHELL181, and
will not be considered for anything other than sandwich structures
in this section.