Excessive contact stress under the bolt head 1

[homutow]

I am calculating a design where plastic cover (material similar to Bakellite) is clamped with a bolt. I have calcualted the pressure under the bolt head and it was about three times the compressive stregth. I would like to ask if anybody had experience with too high contact stresses, what are the failure modes under such conditions, what may happen?? Any suggestions welcome
Regards

 

[desertfox]

hi homutow

Apart from cracking the plastic rendering it useless, if the material doesn't crack but yields and deforms permanently under the pressure, your bolt preload is lost.
The bolt should only be tightened to give the required preload for the safe and reliable function of the joint.
You could spread the load under the bolt head by using a large washer between it and the plastic which might help.

desertfox

 

[homutow]

Thanks desertfox for the answer.

 

[desertfox]

Your welcome homutow

desertfox

 

[Tmoose]

For metal components holokrome warns against exceeding the yield stress

 

[EdStainless]

You sometimes see metal inserts in covers to prevent crushing the plastic cover when someone uses a large wrench.

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Plymouth Tube

 

[chicopee]

Bakellite being a thermoset plastic will crack. Since bakellite is extensively used for electrical components you could also defeat its insulating properties.