Qualification Testing Phase of Satellite Structure - Finite Element Analysis for Satellite Structures - page 263

Fig. 6.9 Basis-unit case

MBEI

layout [ 4 ]

Frame

Plate

Crack
Location 2

Crack
Location 1

so that its solution may be estimated in a couple of hours while it would otherwise
take days, or they may give wrong answers. Finite element modeling should
provide the following objectives: provide a model that will allow obtaining the
necessary information at the desired accuracy (e.g., strains, stresses, mode shapes,
displacements, and stiffness), and simplify the problem to the greatest extent while
still satisfying the objective.
Modeling the whole satellite structure is not an efficient way to investigate the
crack problem, in terms of running time. But to build a valid finite element model
for dynamic analysis of the basis unit, it has to be integrated with a virtual
(simplified model) of the rest of the satellite structure. The FE model will focus on
the basis-unit subassembly that has the cracks. Model is shown in Fig. 6.10 .
Substructure method is used to study the fatigue of satellite structure under
vibrations during air transportation. Boundary conditions are: fix in three direc-
tions the three cylindrical surfaces where the satellite is connected to the adaptor.
Aluminum alloy AMg6 is the main material for the basis-unit case. It has a
density of approximately 2,630 kg/m 3 , which is roughly one-third the density of
steel with slightly inferior strength. AMg6 alloy is used to manufacture and weld
constructions working at temperatures from -196 to +150 C. Mechanical elastic
properties of alloy AMg6 according to the standards are given in [ 4 ]. Titanium
alloy is used to manufacture the MBEI casing, operating within a temperature
range from -120 to +300 C. Titanium alloy is also selected because of its very
low creep deformation, which minimizes loss of stud tightness during the satel-
lite's service life. Mechanical properties of titanium alloy VT-16 are given in
Table 6.3 .
A linear kinematic hardening model or a nonlinear isotropic/kinematic hard-
ening can be used to simulate the behavior of materials that are subjected to cyclic
loading. The evolution law in these models consists of a kinematic hardening