Richard Clark wrote:
On Sat, 14 Aug 2004 01:08:12 GMT, Dave Shrader


SNIP


h, but let's get
extravagant and say 0.1%; then both strikes express all of 150
milli-watt-seconds of power.

Richard, I'm not going to try to out calculate you.

But, please tell the group what the junction temperature of any
semiconductor device is at transient thermal failure at 0.1 and 1.0
useconds.

Twenty years ago the USAF test data indicated that failure occurred at
0.5 microjoules!!! That's 300,000 times more sensitive than your numbers.

Note, it is extremely difficult to really achieve a 0.001 ohm mechanical
interconnect.

Secondly, the major electronic failure mode is from the coupling of the
magnetic field. A di/dt of 10^5/[1E-6] yields a value of 10^11
amperes/second. A one foot length of wire has a self inductance of
approximately one nanohenry [1*10^[-9]] and the di/dt impact is ... 100
volts peak from one end of the wire to the next.

Back in the olden days, twenty years ago, the action integral, that you
calculated was sufficient to burn a 0.5 inch diameter hole right through
titanium that was 0.1 inch thick. Note: the titanium alloy we used
melts at slightly below 2000 degree F.

The design issue is TRANSIENT THERMAL EFFECTS not average heating. At 1
microsecond the heat flow from the stressed area has not started. The
USAF required adiabatic heating as the peak temperature for the starting
condition for the transient thermal analysis. Restated, all the energy
is converted to instantaneous heat and then the thermal stress analysis
would be performed under that constraint.

Conclusion, lightning is a highly stressful environment.