StonGard's response to the message board
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Joined: Oct 2000
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From: Portola Valley
Quote:
Posted by Jeff:
Question? If you heat up something doesn't the heat travel the entire surface of what you heating. It doesn't mean that it was isolated to a particular location. Have you ever seen a broken windshield? There was an initial hit and it spread correct. My point here is if the interior of the lens area was extremely hot from sitting out in the sun with no way of releasing the heat wouldn't it cause it to expand. Additionally adding the heat from the HID's and brights, wouldn't it cause more expansion??! As it cooled wouldn't it contract the same amount that it expanded if it was still flexible? Simple physics says yes.
Jeff:
Unfortunately, the physics of thermodynamics are more complicated than you make them. Plastics are generally poor thermal conductors. As a result, the insulating effect of the turning signal under one part, and the clear access to the light under another part would undoubtedly lead to a substancial difference in temperature accross the lens.
Your analogy to the windshield is flawed because in that case, we are speaking of a completely different failure mode in a completely different material. Grazing is a completely different behavior than cracking, even though it is made up of many small cracks. It is in fact grazing because the cracks didn't spread accross the material. Finally, failure behavior of glass is very different from that of polycarbonate.
Your basic question about expansion and contraction is true however. The question is why is this behavior only affecting a StonGuard user... and no other high temperature users.
Dan
Posted by Jeff:
Question? If you heat up something doesn't the heat travel the entire surface of what you heating. It doesn't mean that it was isolated to a particular location. Have you ever seen a broken windshield? There was an initial hit and it spread correct. My point here is if the interior of the lens area was extremely hot from sitting out in the sun with no way of releasing the heat wouldn't it cause it to expand. Additionally adding the heat from the HID's and brights, wouldn't it cause more expansion??! As it cooled wouldn't it contract the same amount that it expanded if it was still flexible? Simple physics says yes.
Jeff:
Unfortunately, the physics of thermodynamics are more complicated than you make them. Plastics are generally poor thermal conductors. As a result, the insulating effect of the turning signal under one part, and the clear access to the light under another part would undoubtedly lead to a substancial difference in temperature accross the lens.
Your analogy to the windshield is flawed because in that case, we are speaking of a completely different failure mode in a completely different material. Grazing is a completely different behavior than cracking, even though it is made up of many small cracks. It is in fact grazing because the cracks didn't spread accross the material. Finally, failure behavior of glass is very different from that of polycarbonate.
Your basic question about expansion and contraction is true however. The question is why is this behavior only affecting a StonGuard user... and no other high temperature users.
Dan
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Joined: Mar 2001
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From: Phoenix
Originally posted by SCS2k
I'm very flattered that my headlights are garnering almost as much interest as Jennifer Love-Hewitt's butt. (I never know where to put the hyphens).
I'm very flattered that my headlights are garnering almost as much interest as Jennifer Love-Hewitt's butt. (I never know where to put the hyphens).
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Joined: Oct 2000
Posts: 251
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From: tupelo
OK, OK, OK.......I fess up. I did it. i went by SCS2k's house and took a very small "ball peen hammer" and spent several hours working to achieve the starred effect he now has. now that the truth is out, everyone can relax. i will answer all emails and personal messages on tuesday as i will be in the midwest making crop circles this holiday weekend..........
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