Quoted from jsa:The issue with the trunk chipping is that as the soft plastic trunk ages, it hardens. As that happens, it can cause chipping. If you make the trunk harder, it absorbs even less shock, so you may be encouraging chipping.
For this reason, I installed dynomat inside my trunk bottom inside to absorb as much of the shock as possible. If/when the trunk gets too hard, I'm not sure there is much I can do outside of replacing it.
Others had done the fiberglass "fix" and had it last several years (and still going strong)... Here is one from this thread:
I guess we can look at it from different angles.... The trunk itself is brittle... We can all agree to that. The fiberglass method tries to make it solid as a rock... strong solid surfaces dissipate energy throughout the entire area, thus the impact, as long as the fiberglass is thick and strong enough, dissipates through the whole trunk and actually transfers some of the energy into the connections under the trunk as well. The fiberglass also is holding the trunk plastic together stronger than any sticky tape or even Dynamat adhesive. The fiberglass essentially bonds to the plastic vs. just sticking to it.
Now, the negative that I could see is that if you hit the exact same spot over and over, you could actually dent the trunk plastic. That would take a lot of super precise shots.
Now take the foam tape or Dynamat. They both are designed to absorb some of the impact. The foam probably has the most absorption because it can compress the most. It is also the least capable in preventing the trunk itself from flexing when hit and this, since the trunks are brittle as I first mentioned, would be the most susceptible to flexing to the point of cracking. Brittle objects break when experiencing flex... Now, maybe not enough flex happens with the foam, but just saying that the flexing is what will cause cracks first, and even that probably isn't a concern. Now the Dynamat is somewhere in the middle. It is more rigid that the foam, but has less absorbing properties too. That extra rigidity should mean less flexing and less chance for cracking. That said, it isn't bonded to the trunk, and isn't as rigid as the fiberglass.
Again, I am not knocking it, just going off of the logic above. I am sure that for all practical purposes any of these methods work well. It comes across like I am really disliking the foam, but I'm not. So many people have done that with great success. I just know that I had foam pieces inside my original trunk (installed by the previous owner) and that trunk was broken badly. I am sure that different foam, and maybe more strategic placement would have helped, but it has failed, so I wanted to look into something different.
That is when I looked beyond simple pinball trunks and into general science of strength, including impact fracture resistance. I came across scientific articles, yeah I dug that deep, about anything from the automotive and aerospace industries (carbon fiber) to simple concrete to military uses as ballistic armor where fiber-reinforced materials are used. (for plastics it is fiber-reinforced plastic, or FRP)... One of the more every day example is that of concrete. Concrete seems hard, but is actually considered very brittle. You can break and crack a concrete slab with a few hits with a sledgehammer. Now, if you reinforce that concrete with rebar, or even fiber mesh that is being used in a lot of places now, you may eventually "dent" or damage the surface if hit enough in the same spot, but you will have a much harder time creating that catastrophic crack. There are people that study these properties and you can find test results for that, as well as any fiber/resin composite reinforcements, where they test the resilience and strength of the materials in a testing lab. The reason I mention that is because in the concrete example, I kept telling myself that you have the ground under the concrete to act like an absorber (like the foam), but sure enough, there are people whose jobs are to test the stuff with nothing behind (or under) it. One of the tests that I found was a 24" x 24" x 4" concrete slab and a same sized slab with rebar, and another with the fiber mesh in the middle. These were all held up by 2 edges (sort of like a bridge only attached on 2 ends) and they used a press for a continuous pressure test as well as a dropped weight test. All were tested to their breaking points and obviously 2 slabs of each kind was used. The fiber mesh held together the best, the rebar was the most rigid, but its biggest strength was limited close to the rebar itself. The plain concrete failed pretty easily.
Another example would be the ballistic armor. When I found that information, it really seemed to hit home. How do you create a lightweight, super strong material that can stop projectiles? Fiber-reinforcemed plastics.... So many similarities to trying to protect our trunks from the pinball projectile to be ignored.
So I used those details, plus other information that is available online, that says that the best way to prevent something brittle from breaking is to not expose it to any stress, and the 2nd best was to prevent it from flexing. If that prevention also is bonded to the brittle material, should a crack occur, it will still hold up without chipping or losing chunks more-so than anything else.
So yeah, I over researched this stuff... Even so, I would still argue that someone using foam, which allows the most flexing of the brittle trunk, will still be very successful in significantly increasing the longevity of their trunks. Nothing can completely protect them from wear (short of a different material used for the trunk itself). I just went for a bit of overkill. Plus it gave me a good excuse to get a fiberglass kit. You would be surprised at how many uses you can find for adding fiberglass around the hour for repairs, or improved strength.
The only way that anyone would ever know how well these methods compare, under normal usage type tests, would be to get 3 identical trunks from same production runs, apply the impact reinforcement and/or absorber, and scientifically test them. Nobody is going to do that because they all seem to work just fine.
Whew. Enough rambling there. Again, that was all from my research a while back, but that does not mean that it is the end all, be all of this question and I am sure that a foamed trunk or dynamated trunk or fiberglassed trunk will all last a really long time. Almost as long as this post. LOL
Manchester, MI
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