Matt Whiting wrote:
Dick wrote:

Help an old mind come to the correct conclusion G.

The situation is (2) steel straps side by side and fully in contact
with a bolt hole at each end . One is 4130 with about 80,000 psi
tensile and the other a heat treated 4130 to a 124,000 psi tensile
strength.

Is the combination strength 80,000 or 124,000 or
204,000 psi tensile??

Thanks, Dick


Probably none of the above. I don't know of any way to simply "combine"
the yield strengths of two different materials. Typically, you would
look at the Emod of both materials, compute n, use that to convert the
area of the weakest material to be equivalent to that of the strongest
material, determine epsilon under the maximum load you expect to see,
and then convert that back to sigmas for both materials and then
determine if you have exceeded the yield strength of the weaker material.


Matt

Dick,

Problems like this need to be solved by deflection methods, as long as
the loads are less than ~70% of the yield strength (in the elastic
region )and the strap areas are equal, then the load divided by the
cross sectional area of the two straps will be the total stress. This
works because as long as the load on each strap is in the elastic region
the Modulus of Elasticity is very close for all steels, 29 x 10**6psi
if memory serves. The ultimate tensile strength of material only comes
into play after the "elastic limit" has been reached. At which point
your part is on its way to breaking. It then has started to work
harden, though it may not break, it is not the same anymore. If the
areas are not equal, the elastic stretch of each strap will be different
and a more complicated "free body diagram" would be needed to even get
close.
Ask any 2nd or 3rd year Mechanical Engineering student to borrow their
"Shigley" stress textbook. It will have examples of the more complicated
situations and problems as well. There may be other issues such as
stress risers that may cause other problems. Heck you could even have a
student turn the whole thing into a pretty cool Senior Project.

Good Luck,

Mike Butler