78280z Posted October 20, 2009 Share Posted October 20, 2009 For all you engineers in here, I have a question about properly sizing a bolt in a joint (see http://img5.imageshack.us/img5/7610/bolt.tif). The rod ends are connected to members that will be in tension, so they will obviously apply a load to the 3/8" bolt at their point of intersection with the bolt. I have analyzed the bolt for double shear. Do I need to consider bending stress in this bolt due to the fact that the points of intersection of the bolt and rod ends are not directly next to the alum. angle? Thank you in advance for any replies, I really appreciate it! Quote Link to comment Share on other sites More sharing options...
letitsnow Posted October 20, 2009 Share Posted October 20, 2009 Unless I'm looking at your diagram wrong, that bolt is in single shear, which changes things significantly. What kind of loads are you talking about here? Grade 8 bolt? Quote Link to comment Share on other sites More sharing options...
Lazeum Posted October 20, 2009 Share Posted October 20, 2009 A bolt is not made to flex under load A bolt is used to create tension into a system to help friction to take the load. In your application to know the grade of the bolt (and the torque you should apply) you need to estimate the force each joint could introduce. Since I don't know what would be the load, I cannot answer your question with some figures. Here is a quick calculation: Radial load per joint / Friction = Min Proof load in Bolt You can use afterwards some charts for bolts (wiki), min proof load will provide you the size and the grade of the bolt you'd like to use. Another solution is to use a big bolt and call it a day if it is not intented to move to much (no loosening over time) This method help to get the correct stress inside a bolt to just reach the end of the elastic phase of the bolt. Quote Link to comment Share on other sites More sharing options...
240hoke Posted October 20, 2009 Share Posted October 20, 2009 stress = F/A, if its in double shear divide that by two. Compare your result to the bolts shear rating. Make sure you are looking at yield ratings and not ultimate. If they give an Ultimate, then multiply by aproximatly .060. Look at your safety margin and decide if its adequate. You'll probably be surprised at how strong a 3/8" grade 8 bolt is. Quote Link to comment Share on other sites More sharing options...
240hoke Posted October 20, 2009 Share Posted October 20, 2009 Just looked at your drawings. Bolts is definitly in single shear and with a offset like that you will want to look at the stress caused by the moment from the rod end. Analyze the outside diameter of the bolt right where it is mounted. That is going to be your highest stress area, just calculate the moment from the transverse component of the force on the rod end and go from there. Might want to pull out a book for the stress calc, shigleys is a good reference. Quote Link to comment Share on other sites More sharing options...
trwebb26 Posted October 20, 2009 Share Posted October 20, 2009 Definately single shear in your diagram and the weak link in this won't be the bolt... it'll be the aluminum channel you are bolting to. I don't know what your rod ends are supporting, but if it is a suspension part... you need to start over. Quote Link to comment Share on other sites More sharing options...
240hoke Posted October 20, 2009 Share Posted October 20, 2009 Yea what is hte function and how much load will it see? Quote Link to comment Share on other sites More sharing options...
rossman Posted October 20, 2009 Share Posted October 20, 2009 If you were working for me, I'd say go redesign the joint so that most of the load is taken in shear. That bolt is definitely in single shear and bending and, depending on the direction the load, is in tension too. Unless you get an even load on both of the rod ends, you are going to have a moment about the bolt taken by the relatively small angle bracket legs. A much better design would use u-sections and pass the bolt thru both walls. With those spacers you will still see quite a bit of bending in the bolt but that's probably unavoidable, assuming you need that much angle. Quote Link to comment Share on other sites More sharing options...
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