by capterdi
 P: 44 Hi, It´s been quite a while since the last time that I had to solve a classic statics load problem (about 20 years ago). Here is my problem: I have a simple "C" type hook (please refer to attachment "Gancho.jpg") made of 25.4 (1 inch) diameter commercial steel (for example cold rolled steel) And I need to know which would be the maximum load that the hook can withstand. Thank you in advance. Attached Thumbnails
 P: 8 Maybe I am late with this response, but I learned an analytical technique last year for finding the stresses in curved members. Its called the "Winkler-Bach Method". It is based on the assumption that transverse planar sections in the curved parts of the member are do not deform. "plane sections remain plane". If you still want to know about it let me know and I will show a quick analysis for one of the curved parts. With that, you should be able to do it for the rest of the curved parts. Heres what you need to know first: 1) What is the radius of curvature of each of the bends. The drawing attached does not indicate this. THIS TECHNIQUE IS WORTHWHILE ONLY IF THE CURVATURE OF THE MEMBER IS COMPARABLE TO ITS CROSS-SECTIONAL DIAMETER 2) What is the maximum tensile strength the steel and safety factor in the design. 3) What failure criteria need to be considered for the material. I would probably put the maximum shear stress in the member at half the tensile strength of the material if cracks are not a concern. 4) Perform a static analysis to determine the forces and moments where the curved parts are tangent to the "straight" members. The forces and moments can be related to the applied load on the hook. 5) use My/I=-Ey/(r0-y)*r0*(1/r-1/r0) M- moment acting on curved segment Use principles from statics (Newtons 2nd law) to relate the applied load to 'M' I- moment of inertia = pi*(1 inch)^4/32 y=d/2=0.5" r0- distance from centroid of curved member to the location where the stress is to be determined r- distance from center of curvature to location where stress is to be determined I use this a lot with FEA to check the maximum stresses in a model (FEA results distribute stresses accurately, but the maximum values are often off by at least 10%, and usually 15% in my experience.) If all you want to do is find the static loads and moments, you need to specify the location. My knowledge leads me to believe that the most stress will occur in one of the curved segments. Justin justin0741@msn.com By the way, I am getting my masters next year (not related to materials though I've had quite a bit of training related to the subject), so if you're impressed tell your hiring manager.
 P: 44 Hi Justin, Great! Thank you. I´m interested in the method, and would like to understand it so to solve my hook problem through calculus. Regards, Carlos
P: 44

[QUOTE=justin0741;1798637]
If you still want to know about it let me know and I will show a quick analysis for one of the curved parts. With that, you should be able to do it for the rest of the curved parts.

Justin:

Ok. What you described below the quoted paragraph is the quick analysys for one of the curved parts? Are those the formulas that I should understand and apply?
 P: 44 "THIS TECHNIQUE IS WORTHWHILE ONLY IF THE CURVATURE OF THE MEMBER IS COMPARABLE TO ITS CROSS-SECTIONAL DIAMETER..." Ok..all radii involved are 20 mm (the inner curve of the material is 20 mm). So, I think it complies with this criterion...right?
 P: 8 Yes. it does. However, the bend at the top of the hook appears top have a significantly larger bend radius than the other ones. Are you sure they are all the same? If the drawing you provided has a uniform scale, they definitely are not all the same. Confirm this, and we can continue. once you know the bend radii you should first use geometry to find the length of the straight segments of the piece. Then you can do a static analysis to relate each of the moments to the applied load.
 PF Patron Sci Advisor P: 2,207 Overall, this is not a very good design for a hook. The corners act as stress concentrators that subject several parts of the hook to large bending stresses. Additionally, the round cross-sectional geometry gives large stresses at the edges of the material. I would recommend buying a hook from McMaster-Carr that suits your lifting requirements, rather than bending one out of 1" rod.
 P: 44 At the top of the hook the bend radius is 50 mm. Mech Engineer: your recommendation sounds good. The problem is that someone came up with the idea of fabricating this hook as I show it in the sketch, and start using it. So I was asked to work out from a theoretical point what the "safe" maximum load is going to be, and may be to put a sticker on the hook stating something like "Caution - Max. load = ??? kg.
 P: 44 And now I will have to apologize to everyone. At this time I realize that it was not a good idea from my side to start such a thread precisely 2 days before going to vacations. I´m going to be one full month out of my workplace, and so not going to be able to go into more detail around this issue. But I seriously promise that around August 14 I will resume follow-up on this thread. Again, I feel sorry for any inconvenience.
 P: 1 Hi , Sorry For Getting In This Discussion Out Of Nowhere , I Need To Know If Anyone Can Help Me Here , I Am Making , Desing , Calculating To Build A C Type Hook . My Concern Is That I Need To Know What Are The Rules That You Or One Needs To Certify This Hook Ones Is Already Build . Let Me Explin Myself Better , There Is Rules That Can Make This Hook After Construction Be In Legal Status. In The Company Where I Work For Ther Has Been A Lot Of Accident And Recently One Hook C Type Broke In Half . If Anyone Can Hell Me I Will Really Appreciated , I Have Been Looking Everywhere In The Internet And Defferent Books. Thank You For Your Help percin@ualberta.ca