Ice axe supported on tape - loads and boundary conditions

[barthez89]

I'm analysing ice axe according to standard. It is supported on some kind of tapes and force is also applied by this tape (fig. 1). I'm not sure what restraints to use and how to apply it. I created surfaces 15mm width (width of tapes according to standard) on half of shaft (for both supports and force)(fig. 2). What translations and rotations should I fix? On attached screen I left translation in Z direction in both supports (which is direction along shaft) and as you can see (fig. 3) max Von Misses stress is 2790 MPa (material Tensile Yield Strength is 503 MPa).
To sum up:
1.What restraints should I use?
2.Are these surfaces for supports and force appropriate for this case?
3.Should I be worried about this high stress values on the edges of supports?

 

[barthez89]

Could anybody help?

If I did't present my problem clearly enough just let me know.

 

[btrueblood]

I would ignore the "hot spots" near the edges of the support areas, knowing that the strap will deform in real life, and the load on the shaft will look more like a parabolic normal force - like that when modelling a bearing contact force distribution. Take a look at Roark's Formulas for Stress and Strain, under the contact loading (Direct Bearing Loads) chapter.

 

[barthez89]

I was considering bearing load but I can only apply this to cylindrical faces and in my model part of those surfaces are flat so I have no idea how to apply this force. And what you think about restraints in the supports?

 

[racookpe1978]

1. Your FEA model (in yellow, with the small point high-stress area where the support meets the yellow pin) has a flat bottom, but the end view of the "same" part x-x y-y view shows an oval bottom.

2. Your pin is at a high stress point ONLY at the corner where a non-existant not-modeled fillet weld would attach the mount to the pin. Thus, instead of the mount-to-pin load being spread across a real-world area of real-world area between the two parts, the stress is concentrated to an infinitely small point at the corner where the two touch.

If that were your actual part, yes it would likely fail there..

 

[barthez89]

I'm not sure if I get everything you wrote (I'm not native English speaker so I may not understood this correctly) but in response to 1. - fig.1 just shows method of testing ice axes. My model has flat bottom. And in response to 2. (this is the part which I could misunderstood) there aren't any welds. In this testing method ice axe is hanging on some fabric straps so it definitely shouldn't fail in those points in real world. I'm just not sure how to model this to get good results.

 

[ukbridge]

Post better sketches please, the first one is good but would pref additional sections, elevations and a plan. A 3D one would be fantastic if possible too. What are the elements called up by note 1, tension plates? Would need more specifics, but I am a civil/structural engineer so apologies if it is obvious!

Knowing very little about what the problem is, the stressed area in question seems like a stress concentration to me. Try introducing chamfers or another similar detail which would help reduce this unwanted effect. More importantly have you validated your model? Have you checked the sum of reactions equal are equal to the Force F, or what I assume are the horizontal point loads without any notation? I know these are probably very basic/patronising questions but we've all had our share of f**k ups, myself included! Have you done a simple stress analysis, e.g. distributing the force F to the two hangers/tension plates (?). You will likely need to do this anyway to design your welds.

 

[racookpe1978]

If your real-world ice pick (the yellow pin) is only suspended by the slings at two points and is not fastened to the slings by anything but gravity and friction, then it will never break at those suspension points when hit on the end by a hammer. It cannot break at the suspension points, but ONLY at the end where it is hit by the hammer, or at the point where the tip hits the "ice".

Your model must be constrained artificially by your equations incorrectly.

 

[barthez89]

Number 1 in fig.1 is tape (it's tape used in mountaineering but it doesn't matter) so there aren't any welds. Just ice axe hanging on tapes with force applied also by tape. I attached photo which shows how it looks like more or less.

 

[barthez89]

Of course in this picture it's not an ice axe becouse I don't have one. I just show the way how it's supported.