Manufacturing Simulation Using Finite Element - Finite Element Analysis for Satellite Structures - page 287

Fig. 7.16 Finite element
model of single impact sphere
size for the panel is of size 0.1 mm near its top and gradually increasing to 0.5 mm
at the bottom of the panel. Similar element size of 0.1 mm is chosen for the sphere,
while the stand has element size of 1 mm. The sphere is modeled as rigid body,
and a contact surface is defined with the top of the panel with frictionless contact.
The bottom of the panel is constraint to the top of the stand. The perfect way to
model the interaction between the panel and the stand is to add a contact surface.
Adding contact surface between panel and stand is not necessary as the shot
peening process for fatigue improvement is a surface process and will increase
running time. It is recommended to add a contact surface between the panel and
the stand in case of shot peening for forming. As shot peening for forming sim-
ulates the spring back of the panel due to stored kinetics and residual stresses, the
interaction between the panel and the stand will has an effect.
Boundary conditions are shown in Fig. 7.17 . The bottom of the stand is fixed in
x, y, and z directions. In an attempt to reduce running time, only 10 9 10 mm of
the panel is modeled with symmetry boundary conditions applied on three sides of
the model. The symmetry boundary condition applied on each side is to add the
effect of shot peening of the adjacent 10 9 10 mm area. If the modeled volume is
at the edge of the panel, then the symmetry boundary condition is applied on three
sides only.
The speed of shot impact is modeled in two analysis steps. In the first step, the
velocity boundary condition is applied on the reference point of the spherical shot,
and running the simulation for very short time (1e-9 s). Followed by the second
step analysis, while canceling the velocity boundary condition and running sim-
ulation for (7e-6 s). Simulation time is not standard and it is a function of the shot