doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Shooting Fox with annealed frame?

A Mike, I'm really impressed with your research and consideration of beam mechanics - good work. However, on with the discussion.

"But by increasing the yield point of the steel the frame can take more displacement without plastic bending."
Remember, only the CH steel case has a higher yield; the low carbon steel part is unchanged.

"And since spring rates go up with some power(d squared or d to the power of 1.5 etc...) of displacement and a higher yield point receiver can take more displacement it's spring rate is higher right before plastic failure that a "soft" frame.

No, spring rate is a force per displacement number. A "hard" spring will have more spring force than an equal soft spring, but only after the "soft" spring has yielded and the "hard" spring has not and continues to deflect without yielding. The two will have essentially the same spring rate if of equal dimensions. Spring rate must not be confused with spring force; spring force is spring rate times deflection.

In the case of the action/frame, it does, indeed, act like a beam with a strain gradient across it. However, the bulk of the stress will still be carried by the far more massive "soft" core. The case will add only "steel" strength to resist bending. The fact that the case is "hard" will add nothing extra until after the core has yielded. In a yielded frame, the "soft" core will resist returning to original dimensions and the "hard" case will attempt to force the "soft" core back. The "hard" case will be able to return the "soft" core part way back. It would take a very thick case to return it most of the way. As the yielded action moves toward original dimension, the yielded core would increase its resistance (spring force) and the spring force from the case would decrease. Once yielded, the case will not be able to overcome the core and return the action all the way to original dimensions.

Questions? Comments? Opposing views?

DDA

My head is harder than before I read all this.....

Gun talk get you excited jOe.

I perused Marks 10th Edition today at my library and looked at the sections on steel and on beams.
I could not find any discussion on calculating or measuring yield stress with a work hardened surface. If you can point me to a section, I will try to find it in a copy. Please include the edition and page number(s) as I am sure the UW Mechanical EngineeringDepartment will have copies archived.
In any event it is a moot point as I don't believe any of this information was available or used by the designers of the Fox shotgun at the turn of the century(1900) or so.
The original question concered whether it was safe to shoot a Fox with an annealed frame.
The correct answer would be yes because the steel was in a mild condition to start with and the lack of case hardening does nothing to the strength of the reciever.-Dick

Thanks,Bobby

Dick_dup1, this thread had gone on for 10 pages of obscure theory and stuff I didn't understand. Your posts have all seemed authoritative and clear. I too appreciate your last post, Thanks...Geo

Dick I bet you missed what I wrote later Saturday. From a few posts up the thread. I added an edit (in Red) to one post and added two more:

Don thanks for the kind words.

A spring's spring rate goes up with the displacement. At 2" displacement the spring rate might 100lb/in. at 3" displacement the spring rate might be 500 lbs/in. So my contention that the receiver gets stiffer (spring rate goes up) as the receiver is flexed more is correct.

In the beam example the displacement (stretching) at the bottom of the beam is twice as much at the surface as it is half-way between the surface and the line that is neither in compression or tension.

And since the surface has had the yield point raised by case hardening the surface can stretch more before it yields and goes into plastic deformation. And since the point half way between the surface and the zero tension line is only stretching half as much as the surface it doesn't stretch enough to reach it's yield point even though it's yield point is lower.

And since the maximum deformation is at the surface and since the spring rate of the metal in the surface goes up as it deforms (like a spring has a higher spring rate at 3" displacement than it does at 1") the bulk of the load is carried by the exterior of the frame.

Don I repeat, it is not a simple matter of calculating the percentage of the cross section that has been case hardened and then pro-rating that increased yield strength into the strength of the frame. The exterior of the frame carries more because it has %deformed more and so is in higher tension than the interior. The interior point at the zero tension line is not providing any resistance at all because it is, by definition, at zero tension.

So case hardening a frame increases it's ability to resist plastic deformation.

I agree with Mikee. It's not a simple binary answer. Casehardening goes much deeper than would be portrayed by the numbers. The resultin effect is more htan "notheing".

The simple binary answer was back on page one.