In March of 2003, a baseline study
was concludes that showed how fast stress builds up in die casting H-13
material. Case Western's used their for this their repeatable and accepted dip tank test.
The results of this test, although still ongoing, showed that
after only a few cycles that tensile stresses enough to crack material are
present. These occurred after only 10 cycles. It is interesting
to note that the breakout phenomonon did not occur in this or any other
tessting of this nature where pressure and velocities were not involved.
Fluid dynamics were not part of this study. More on cavitation
effect can be found at this link
CAVITATION. The
Excel spreadsheet and
Power Point slides show how the
polished only
compressive stress points
in green changed to tensile
stress points in red. From
the results three hypothesis were drawn.
Cycling the die generates increased tensile
stresses that are relieved by cracking. Flexing the die surface through compressive
and tensile conditions lead to die failure. Decarburization may be softening the surface
reducing the yield strength.
This data confirms the importance of
compressive stress to protect against fatigue failure. |
