Thermal Effects on a Preloaded Bolt
Thermal Effects on a Preloaded Bolt
(OP)
I've done a search to no avail. What I have is a bolt that is a stainless steel M4x0.7, 15mm long bolt that is inserted through an aluminum housing and bolted to a brass resonator. The portion of the bolt that is threaded into the resonator is 8.5mm long, the rest is the part going through a clearance hole in the aluminum housing. It is preloaded with 24 in-lbs of torque. I can calculate/simulate the effects of the preloaded bolt with no change in temperature. However, I am interested in seeing the effects that temperature has on the system. I have done multiple searches with no luck... maybe someone can point me in the right direction?





RE: Thermal Effects on a Preloaded Bolt
a google for "thermal loading on bolts" gave a hit to roymech.co.uk which'll explain this in detail ... sort of wonder what searching you did ??
RE: Thermal Effects on a Preloaded Bolt
Calculate the thermal expansion of each item separately, making some necessary assumptions about the uniformity of temperature throughout the assembly.
Add the thermal expansion results back into the preload only numbers.
Back-calculate the remaining preload on the bolt.
RE: Thermal Effects on a Preloaded Bolt
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RE: Thermal Effects on a Preloaded Bolt
eal
Tension strain in the steel is
est
Let the length of engagement be unity, then the relaxed state for the aluminum and steel bolt would be
steel 1-estl
aluminum 1+eal
est= strain of preload in steel bolt
eal strain of preload in aluminum
But the force of preload is
(1) F=est*Est*Ab=eal*Eal*Aal
Were
Ab= crossectional area bolt
Aal aluminum bolt contact area
from this equation
(2) eal/est=K=Ab*Est/(Aal*Aal)
Est, Eal moduli of elasticity for steel, aluminum
Now heat up both lengths dT then the new relaxed lengths are
steel 1- est+ast*dT
Aluminum 1+eal +aal*dT
where
ast,aal = coefficiemnts of thermal expansion
Now the new difference in strains is
eal+est+(aal-ast)*dT
so the new preload will be in the ratio of the two strain differences
F*[eal+est+(aal-ast)*dt]/(eal+est)=F*(1+(aal-ast)*dt]/(eal+est)
where the eal and est are obtained from eq (2)
=\
RE: Thermal Effects on a Preloaded Bolt
F*[eal+est+(aal-ast)*dt]/(eal+est)=F*(1+(aal-ast)*dt]/(eal+est)
should be
F*[eal+est+(aal-ast)*dT]/(eal+est)=F*[1+(aal-ast)*dT/(eal+est)]
RE: Thermal Effects on a Preloaded Bolt
Also, Unbreako has a good reference in their engineering guide. The section discussing high temperature joints is a great reference for this type of problem. It's available for free on the web:
http://unbrako.com/docs/engguide.pdf
RE: Thermal Effects on a Preloaded Bolt
I'll work it out in the general case since you've stated no temperature change.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
RE: Thermal Effects on a Preloaded Bolt
have a look at this site and scroll down till you come to the heading thermal loading:-
h
basically you need to get the overall joint and bolt stiffness for your configuration, this site will show you how.
desertfox
RE: Thermal Effects on a Preloaded Bolt