Even if the punch actually
moves at a nearly constant velocity, the results of the first simulation
attempt indicate it is desirable to use a different amplitude curve that allows
the blank to accelerate more smoothly. When considering what type of loading
amplitude to use, remember that smoothness is important in all aspects of a
quasi-static analysis. The preferred approach is to move the punch as smoothly
as possible the desired distance in the desired amount of time.
We will now analyze the forming stage using a smoothly applied holder force
and a smoothly applied punch displacement; we will compare the results to those
obtained earlier. Refer to
Smooth amplitude curves
for an explanation of the smooth step amplitude curve.
Define a smooth step amplitude curve named
Smooth1. Enter the amplitude data given in
Table 1.
Create a second smooth step amplitude curve named
Smooth2 using the amplitude data given in
Table 2.
Modify the RefHolderForce load in the
Holder force step so that it refers to the
Smooth1 amplitude. Modify the displacement
boundary condition RefPunchBC in the
Move punch step so that it refers to the
Smooth2 amplitude. By specifying an amplitude of
0.0 at the beginning of the step and an amplitude of 1.0 at the end of the
step,
Abaqus/Explicit
creates an amplitude definition that is smooth in both its first and second
derivatives. Therefore, using a smooth step amplitude curve for the
displacement control also assures us that the velocity and acceleration are
smooth.
Create a job named Forming-2. Give the job
the following description: Channel forming -- attempt
2.
Save your model, and submit the job for analysis. Monitor the solution
progress; correct any modeling errors that are detected, and investigate the
cause of any warning messages.
Evaluating the results for
attempt 2
The kinetic energy history is shown in
Figure 1.
The response of the kinetic energy is clearly related to the forming of the
blank: the value of kinetic energy peaks in the middle of the second step,
corresponding to the time when the punch velocity is the greatest. Thus, the
kinetic energy is appropriate and reasonable.
Figure 1. Kinetic energy history for forming analysis, attempt 2.
The internal energy for attempt 2, shown in
Figure 2,
shows a smooth increase from zero up to the final value. Again, the ratio of
kinetic energy to internal energy is quite small and appears to be acceptable.
Figure 3
compares the internal energy in the two forming attempts.
Figure 2. Internal energy history for forming analysis, attempt 2. Figure 3. Comparison of internal energies for the two attempts of the forming
analysis.
