how to simulate screw torque

[rafpax]

hi, I'm raf


I have to analyze a motorbike's caliper (made in two separate parts) with its support plate. The problem is to silmulate the screw torque between the two parts and between tha caliper and the support.


Howdo yousimulate the screw and the screw torque.I tried using a beam element to simulate the screws and a thermal load to simulate the screw torque.Do you think it's ok?


Thanks in advance


raf





p.s. sorry for my english..I know it's very bad...but I'm studing

 

[james.lynch]

Are you using Wildfire 2.0?

 

[ankarl]

Thats the way to do it (and with contact regions as well).


Dont know if there is other possibilities in Wf2 as James is indicating.


regards
Anders

 

[james.lynch]

MAJOR advances in Wildfire 2.0... simply click 2 edges and put in a "Fastner" between the two and specify preload in an input field!


[url]http://www.ptc.com/appserver/it/icm/cda/template_lib/rel_not es/note.jsp?im_dbkey=20741[/url]


Much easier.. the other way broke my heart last year! I got it to work eventually but it wasn't as easy as the suggested technique said! maybe my modle was a bit to complex..

 

[james.lynch]

This may help a bit also..
"According to Bickford (1974) the bolt must be stretched to act as a clamp, this stretch is a strain, and therefore introduces a tensile stress on the fastener. There is also usually a bending stress on the fastener because, very rarely is the head of the bolt perpendicular to the threads and it is also rare that the top and bottom surfaces of the fastener material are exactly parallel. Bickford (1974) goes onto say that when a person stops tightening some of the stresses which have been introduced will disappear up 10%-20% of the initial axial tension can be lost, this is called embedment relaxation.<?:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><O></O>
The conventional tightening methods only provide a vague indication of the bolt tension. In uncontrollable situations using torque as a measure of tension that can lead to an error as large as

 

[ankarl]

<DIV =O v:shape="_x0000_s3074">
<DIV style="TEXT-ALIGN: center; mso-line-spacing: '100 20 0'; mso-margin-left-alt: 216">

 

[james.lynch]

How true that is!


but up to a 50% error is a very "loose" definition of being Approximately right!

 

[burnsp]

James is right - you should not use screw torque to produce (simulate) the clamping force. Unknown friction, relaxation, measurement errorand temperature changes all add up to significant errors when using applied torque to estimate bolt tension (clamping force).When calcualting this, all these variables must be estimated and each has a significant range. Under controlled conditions,

 

[lbotez]

What about "torque to yield" as a method of having a small clamping forceerror? Anyone has experience with this method? Of course simmulating such a thing in Pro/Mechanicamight beimpossible due to fastener non-linear behaviour.

 

[rafpax]

thanks for all your input...


first,I have a question for James Lynch, Could you tell me where to find more information about what Bickford says about the clamp connections, I supposed it's a book...


I considered the screw torque because, we use this parameter to check the caliper assembly (it's simple to check with a torque wrench).


In my calculation, the stress generated by the "screw torque" are concentrated near the screws and the value is very high (in this region I found stress very high).I need to understand if this value is real (at the moment I can't compare my results with lab test).


Thanks bye

 

[james.lynch]

Bickford is pretty much "the father" of everything we know about bolts..


Bickford, J. H. 1974. An introduction to the Design and Behaviour of Bolted Joints. New York. Marcel Dekker INC


ISBN: 0824792971
Book ID: ME-1200
Pages: 992
Publisher: Marcel Dekker



http://www.omega.com/bobi/productpage.asp?id=ME-1200


All for only $150

I found it hard to get so I got the university toget it on interlibrary loan..


but well worth it if you're doing a lot of bolt analysis..


rafpax.. check your private messageinbox.. or give me your e-mail address

 

[james.lynch]

2005-03-07_081849_bolts_compressed.zip


rafpax, I managed to take out some of the info that you dont need and make a pdf of it so here is some more information. Enjoy the speil! It was for one of my modules abot this time last year, havent read it since but it should point you in the right direction for some research anyway!


Enjoy! and hope it helps


James