I don’t know what to say but a big THANK YOU to all of you that have recently joined in on this thread. All of your postings, on just about any subject, add value and are carefully thought out. There are always certain particular names I look for on this forum and you guys are coming on-board this thread. Please hang around. My apologies for the length of this post . . . I promise shorter ones to come.
John, re your post #25 I agree a real world scenario would be best but the complexity could easily overwhelm people’s generosity and sharing at this point. FEA still takes CPU horsepower and I don’t want to get so complicated that enthusiasm is killed. I don’t know the computer ET now days but I can remember starting calcs that ran for 8 hours. If CPU power if not an issue I’m still after simplicity if only to get a basic picture or understanding, to help filter through the complexity.
There is essentially no typical real world scenario. As Glenn pointed out, in the more than 500 entries last year, every one of those were different! The number of attach points on any one cage can be 6,8,10,12, or 14. All would be approved by SCTA. The geometry of cage designs is about as individual as fingerprints! Everyone is different and none will be the same. Even a design from someone like Chris Alston who replicates roll bar kits from a NC mandrel bender will be “personalized” by the installer.
Here is the only common scenario. The rule book forces us to weld (or bolt) a ¼” plate to a piece of sheet metal approximately 0.035” thick. That would be a Vega, Monza, Camaro, etc. I have not measured Ford products. That base plate used to be only 1/8” thick but for some unknown reason was changed to ¼” thick. The purpose of this thread is to try and see how the increased thickness changed the failure mode and if some other thickness is more beneficial. We do need to see loading that produces failure. Again, for simplicity, let’s keep the load orthogonal.
To further complicate the issue there is no data on a Bonneville crash. If you watched the Danny Thompson crash video, a good engineer may be able to infer approximate G forces by measuring time and distance but that would be only one data point. Regarding the landing attitude of the car . . . who knows? In other words; on a 10 point cage did one corner hit first, 4 corners, or more than that at the same time, etc? I have seen anything you can imagine and Glenn has seen a ton more. There is no typical accident at Bonneville. That being said, I “think” G-loading could be 10, 20, or 30Gs . . . on single or multiple members! So our model loads, most likely should be greater than 5,000lbs.
A real world model would be at least 500 plus individual scenarios and 500 solid model cage designs. We simply can’t go there. Let us focus on a generic sheet metal patch, bounded on all sides, a perpendicular force, and vary the base-plate thickness. Let’s get that picture first. Complexity can be added according to thread interest.