Comments by "Richard Kudrna" (@richardkudrna7503) on "Solar Eclipse Timer"
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The temperature effect on brittleness (say water was about 4 degC), was probably not a huge deal. But, I was taught that the reference stress is a function of the cure temperature plus the affect of volume change at cure. In other words, if an epoxy resin is cured at say 80 deg C, then it is “born” at that temperature. So any temperature above or below creates stress in the system. But, many composite systems have a step change of volume upon cure, so the reference, or “zero thermal stress point” , shifts accordingly. So even if cured at the example 80 degC, it might actually reach zero stress at say 100 degC. Now a complication; these systems usually have a different thermal coefficient at each axis. So you encounter the zero stress point for each axis at different temperatures. I have had in my hands data sheets that ignore this. More misery; variations cause actual properties different from data sheets. So the model may differ from reality. Usually overdesign can eat these up. But what about systems that don’t have massive margins? Like here, they crashed into the real limits. I wonder what the real end product was like?
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@solareclipsetimer if on board electronics were damaged then the sub was hit hard. When an aircraft suffers a strike on the ground the maintenance people do checks. If the aircraft (or sub) was connected by ground cable then usually (not always) this is one attach points. Was the sub in its transport cradle with no services interface to the dock? Say it was not, but that adequately intimate submarine to cradle to local soil existed. Say the lighting attached to the local high point (catamaran mast), then the cat was on a cradle of high impedance to ground, so the sharp prop blade created a field, charge built up, and it jumped to the sub, then earth. We cannot know the peak currents in the pressure hull but by examining the catamaran prop the size of the pit gives some indication. Why did equipment die on the sub? Let’s say the electronics has their negative power and chassis tied to submarine chassis earth. The ground may have moved up to a large voltage able to cause breakdown within a unit between earthed items and items floating.
By asking a lighting engineering company to investigate, they could have looked at damage, looked at the “ground model” of the sub, and commented on risk of plasma tunnelling into the stressed pressure hull. Lighting can be seen as very broadband power. From DC to GHz. Tiny reactance between items can result in buildup and discharge.
You can do an experiment with AC where you take a block of resin, make it perfect, and stress it to failure with high voltage RF. Now make another with some bubbles. It will fail much sooner. The bubbles look like capacitors and instead of forming a linear voltage gradient through the insulator, voltage builds up at the bubble walls and much more RF current will flow. So your test article that measures 1 gig resistance at DC will arc through after a minute at 1 KV across it. I write this to help explain why lighting is so lethal to systems not designed to accommodate. If anyone is going to write up regulations for composite subs, they will want to talk to an EMI / Lightning person. Or, cover the boat with a metal net well earthed. Even now, an investigator might be able to find out what systems were lighting damaged and maybe someone saved items. By looking at the cradle, finding that cat prop, looking at the drawings of the sub, a sense of the risk for a plasma hole to have formed could maybe be established. The wreckage might show this damage. I think it’s possible a 0.001” carbon tracked hole maybe let water in, or cascaded to failure.
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