Controlled Yield Material for Shear Failure
Controlled Yield Material for Shear Failure
(OP)
I am in search of a material to add a controlled failure piece to a current valve design. I am looking for a material that has a tensile strength capable of taking the operating load of the valve (approx. 35000 psi tensile yield), but that shears at a relatively low and predicable value.
My rough calculations are based on Shear Yield = 2/3*Tensile Yield, but we are now exploring the use of brass for this part and it seems that this assumption is invalid for brass. If there is some relation that is constant then the geometry can be adjusted to take that into account.
Other than the estimate of shear strength as some fraction of tensile yield, there is another issue. If there is a constant relationship to yield then we need to specify a relatively narrow band of tensile yield in order to get the corresponding narrow band in the shear yield that will allow us to predict the failure of the threads within the required window.
When we order material, can we just specify this narrow band of tensile yield (5000 or 10000 psi)? How will this affect the cost of the material (rough percentage)? Further, if anybody has any suggestions for a material, they would be welcome. We have looked some at ceramics, but keep coming back to the brass.
My rough calculations are based on Shear Yield = 2/3*Tensile Yield, but we are now exploring the use of brass for this part and it seems that this assumption is invalid for brass. If there is some relation that is constant then the geometry can be adjusted to take that into account.
Other than the estimate of shear strength as some fraction of tensile yield, there is another issue. If there is a constant relationship to yield then we need to specify a relatively narrow band of tensile yield in order to get the corresponding narrow band in the shear yield that will allow us to predict the failure of the threads within the required window.
When we order material, can we just specify this narrow band of tensile yield (5000 or 10000 psi)? How will this affect the cost of the material (rough percentage)? Further, if anybody has any suggestions for a material, they would be welcome. We have looked some at ceramics, but keep coming back to the brass.





RE: Controlled Yield Material for Shear Failure
RE: Controlled Yield Material for Shear Failure
Existing materials for the connecting pieces are 17-4 and 4130. Material for the piece to fail is to be determined.
The worst it shoud see is salt air. This took aluminum of our list.
~Ben
RE: Controlled Yield Material for Shear Failure
RE: Controlled Yield Material for Shear Failure
RE: Controlled Yield Material for Shear Failure
One of my main concerns is getting a material that will shear at a predictable value. The data sheets taht I have seen specify a minimum value for tensile yield, but no maximum value, so it could come in at anything. Is it possible to just specify a band of acceptable yield strength (either tensile or shear)?
~Ben
RE: Controlled Yield Material for Shear Failure
RE: Controlled Yield Material for Shear Failure
RE: Controlled Yield Material for Shear Failure
RE: Controlled Yield Material for Shear Failure
Further, we are trying avoid the situation where the end user can just grab a commercial piece and shove it in there with no control over whether or not it will work.
~Ben
RE: Controlled Yield Material for Shear Failure
You could set up a simple torsion test to determine shear strength vs hardness and from this establish your hardness range limits. I cannot tell you the extra cost but you can get some suppliers to hardness test a heat lot to fullfill yuor requirements.