taper stud / hole strength 1

[netzen]

I ran into a problem that need to use a 1:10 taper stud / bore connection to transfer loads, the smaller end of the taper is ~1.0" and the entire engage length is 1.125".

the stud is made out of hardened steel and material (cast iron, grade, etc.) on the female part is yet TBD.

could someone recommend a calculation method to estimate the joint fatigue capacity based on a certain loading?

many THX in advance

 

[ishvaaag]

Per your description it sounds a trunk cone passing in wedge action some compression, then some tensile stresses develop at the components. Will try later.

 

[netzen]

Thanks for checking it out!

The taper stud is conical shaped, so as the hole on the mating female part. Very typical configuration if you've seen a tie rod assembly used a lot on automotives.

 

[cntw1953]

Repeative load, cycle of stress reversal, metal properties are some of the controlling factors in estimating strength for fatigue. Have you post this on "Welding, Bonding & Fastener engineering" forum, from which you may gain more valuable responses.

 

[ishvaaag]

http://www.randomvibration.com/Papers/NAFEMS_Italy_paper.pdf

Yes I have started looking in the valve pdfs etc. However there maybe something simpler out there, mechanical formularies etc that I will be looking as well.

 

[netzen]

could there be a calculation method based on loads, taper ratio / engage length / material properties of the mating parts?

 

[ishvaaag]

At first it looks not a very promising detail. From what seen in an old AASHTO standard a D category might be inferred and so about 35 MPa allowable stress range for non redundant details and 49 MPa allowed for redundant details for 2 million cycles. These to be compared with the maximum variations in stress given by good 3D models that directly identify and eliminate the effect of stress concentration.

You can follow also the goodman method following fig. 2.2 at Roark's 6th ed (page 31) where you can extract the maximum stress range (reversal) when the average stress stays at some value. That is, you identify your average stress, then looking at the Goodman chart you identify how much you can deviate for that. This may or not suit your application. To trace the Goodman chart you will need to know sigma e, the endurance limit at complete reversal of stresses when the average stress is zero. This ranges for steels between 35 to 60% of sigma u ultimate (limit) tensile strength (see that at Pilkey's) and not to surpass 784.5 MPa.

Still to look at the mechanical formularies.

 

[cntw1953]

netzen:

Again, I think the welding/bolting forum, ME-material forum, or Automative Engineering forum is better place to seek help for this special application, which is rarely seen in Civil-Structural world if ever.

I believe fatigue is influenced by tightness of the connection (pre-load) as well. Good luck.

 

[ishvaaag]

I agree with cntw1953. Have been looking a varity of texts holding fatigue formulations but found not the case. What cntw1953 about the standing stress (related to preload) is directly seen in the Goodman chart, since you have to enter with it in abscissas to read the stress range at ordinates.

Anyway, even if the Goodman chart and more accurate analysis should give bigger allowable range of stresses, the wedge is really very steep, even more than a typical spear, so I think the estimate as inferred from AASHTO should not be much off-the mark... it might be even optimistic.