SS Bar Bending
SS Bar Bending
(OP)
I have an application where I am specifying a SS for a 1" bar ~5' long that will be subject to a bending load (i.e. supported on the ends and loaded in the middle). I am looking at 303 (drawn to 100,000psi), 416 H900 temper & 17-4 H900 temper. These materials are being evaluated based on corrosion, machinability, appearance, tensile strength & hardness for my application. What about bending? When I compare Modulus of elasticity's for each of these they are about the same in MPa.
Does this mean each bar will bend the same amount given identical loading below the yield strength?





RE: SS Bar Bending
Michael McGuire
http://stainlesssteelforengineers.blogspot.com/
RE: SS Bar Bending
If deflection is important to you, as it seems to be, fatter bar (or tube) will work better, even in less expensive alloys.
If you could describe your application in more detail, you could get a _lot_ more help with it here.
Same charge as always.
Mike Halloran
Pembroke Pines, FL, USA
RE: SS Bar Bending
The impact strength of 17-4PH, especially large size bar in the H900 and H925 conditions, may be very
low at subzero temperatures; consequently, the use of 17-4PH for critical applications at low temperatures
should be avoided.
RE: SS Bar Bending
I am going to start a new thread stating all my requirments for this product as I need help with selecting a Stainless Steel, manufacturing process, and finishing process.
RE: SS Bar Bending
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: SS Bar Bending
Is E a function of cross-sectional area? If the tube is that stiff there must be some other effect from the geometry. What could I do to my "shape" to make it stiffer? I thought increasing my tensile strength by going to different grades of stainless steel was the answer but I now know that is not the case!
RE: SS Bar Bending
the section mod is based on geometry. Knowing that and the materials modulus you can figure out the actual stiffness.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: SS Bar Bending
RE: SS Bar Bending
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: SS Bar Bending
RE: SS Bar Bending
If you need 150ksi tensile, you're pretty well screwed out of stainless, too.
Mike Halloran
Pembroke Pines, FL, USA
RE: SS Bar Bending
I found spec. sheets for 416 & 17-4 PH on www.alleghenyludlum.com that both show 150 ksi plus for these tempered at 900 deg.
RE: SS Bar Bending
RE: SS Bar Bending
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: SS Bar Bending
Mike Halloran
Pembroke Pines, FL, USA
RE: SS Bar Bending
The bar will be used for a high quality fitness product.
RE: SS Bar Bending
By analysis we found that the published physical values for 17/4 Cond A were quite variable. We found early on that if your design required ductility and toughness you had to heat treat. The recommendation that H1125 heat treatment was put forward by Armco early on to maximize the physical properties for shafts and fasteners.
17/4 doesn’t machine or cold work very well in Cond. A
Personally I’ve never seen or heard of a recommendation to use 17/4 in Cond A in a dynamic component.
RE: SS Bar Bending
I just don't seet he reason to go to that expense with this product.
Either 201 or a lean duplex in the cold finished condition should be enough.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: SS Bar Bending
SS is chosen for it's high quality appearance and resistance to corrosion. The 3 original reasons I was looking to increase tensile of the bar above our SS 303 prototypes were as follows:
1) Less bending under load (I now know Modulus is the driving factor)
2) Increased surface hardness. I have 1/4" wide bearings riding over the flat portions of the bar. Bearing is SS 440c @ 58-65Rc. Each bearing is loaded up to 50 lbs ontothe bar. The 303 began lifting (small chips) quite severely well before 40,000 cycles.
3) This bar will be lifted during exercise. I must guard against fracture if awkwardly dropped onto the floor. It will take abuse. A large safety factor is prudent.
For these reasons I am targeting a 150,000psi tensile. I may be able to go under this but must run cycle testing and analysis to validate.
My thread has wondered a bit but I need help defining a cost effective material and process to produce bars in volume. (see Material Selection Challenge thread)
Thanks to all!!!!
RE: SS Bar Bending
Regarding your #1:
Deflection of a beam (channel or tube are hollow beams) is more a function of the Moment of Inertia (I) than the modulus of the material.
Example: an I-Beam . . . increase its stiffness by increasing its height rather than the web width.
Reason: I= cube(h) * b * 1/12
Another way to look at deflection is through bending equations like :
y = P * cube(L) / 48 EI
for a simply supported 3 point bend.
So, deflection is inversely proportional to I and E. To decrease y, increase I or E.
But you can't control E since steel is 30,000 ksi and most stainless steels are 33,000 ksi and aluminum is 3,000 ksi. You can always control the Moment of Inertia through part geometry.
Strength and striffness are not the same.
You rule out aluminum alloys that would require only a modification to part geometry or the addition of a supporting internal steel channel.
There are filled and reinforced polymer materials that are sometimes more cost effective to manufacture after capital amortization.
If shiny is what you want, why not chrome plate steel? There is also an acid chloride zinc plate that is just as shiny as chrome and adds the corrosion resistance value.
Regarding #2:
Ever think of placing a less frictional material between the rolling part and the tube? Acetal (tradename Delrin) is used a great deal to reduce wear on moving parts, which by the way is the definition of "bearing". You can machine a rod of acetal to have an ID equal to your rolling parts OD. 50 lb-f is not sufficient enough to cause compressive failure, as long as the acetal is thick enough . . . see Moment of Inertia above.
Regarding #3:
On what formula are you basing the need for a strength of 150,000 ksi??
Remember that strength based failures are one of only three types: tensile, compressive, or shear.
In bending a beam is placed in a state called flexure. This is a composition of tenile (along the bottom beam axis) and compression (along the top beam axis) and shear (on a continuous profile, usually at the center). Failure is usually shear.
Have you thought about conducting a shear and bending moment diagram on your part from end to end? You'll have to know the formulas for shear and bending moment. One does involve a differential.
Mohr's Circle is another way to determine max shear.
Find a Strength of Materials book or ask for assistance from other Mechanical Engineers.