Calculating Stresses on Inserts
Calculating Stresses on Inserts
(OP)
Does anyone know of a calculation to utilize for estimating the strength of inserts in plastics. The inserts I am speaking of are the ones to be thermally or ultrasonically installed. I want to know if I have to take into account the thread stress area or not. Seems like many variables to account for, looking for a formal way of analyzing. Any suggestions?





RE: Calculating Stresses on Inserts
defining the basis of these inserts.
Contact them first and go from there.
They must have many references in their
sales pitches.
RE: Calculating Stresses on Inserts
I would expect the manufacturer would have
the information that you are requesting.
Have no idea if you are talking about a press
fit application or is the insert threaded on
the od? If so I would use that as the basis
for the plastic pull out force to be calculated.
RE: Calculating Stresses on Inserts
If the loads mentioned above are combined, your stresses may have to be calculated by using the Morh circle concept.
RE: Calculating Stresses on Inserts
DS
RE: Calculating Stresses on Inserts
Normally you don't have to consider thread stress area since the inserts are much stronger than the polymer/insert interface. Most inserts have surface features to promote physical interlocking. This prevents easy calculation/analysis. A way to start is to calculate the interface shear area A:
A = π D L
where
π = 3.141 592 654
D = insert outer diameter
L = insert height
Then, the axial force resistance F is:
F = A τi
where
τi = the interface strength
The interface strength usually is unknown, but could be approximated using the polymer shear strength τp.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Calculating Stresses on Inserts
brass for the insert
what is the grade and material of the bolts?
and also the torque values you wish to impose?
There is a section in Machineries Handbook
that shows how to calculate the strength of
internal threads or how long they should be
in contact for different strength materials.
I assume you are using the thread locking
type insert keensert or solid inserts rather
than heli-coil style inserts. I also assume
the length is 2 times the diameter and you
are only concerned about the static calculations
and that the parts are not subjected to much
of a dynamic type loading. Everyone should
test their product for liability reasons as I
assume the strength of plastic is quite
variable as well as the surrounding structure
from design to design. I assume there is
enough material around the keensert to ensure
it will not fail from that condition. I would
expect material to exceed a circle at least one
and one half times keensert od.
RE: Calculating Stresses on Inserts