If I tighten a bolt/screw to yield, can I use it again or is it broken?

Have a look at this article on tightening bolts to yield. Enjoy. Click through to the article. It is a short but interesting read.

An article by George Lorimer, Retired;
formerly of the G.M. Powertrain Fastener Lab.


“This question is on the minds of a lot of fastener engineers and people who use fasteners all the time. Lets examine what happens when you tighten a bolt into the yield area of a steel material. First of all lets look at the fastener close up and personal!..”

“…I ran some tests years ago and found that if I set up a test where I would yield a bolt by driving the head and then turn an additional 20 degrees I could find out whether or not the bolt was reusable. I set up my equipment to automatically tighten to some load that was the average of several tests to yield and then turn an extra 20 degrees, I then loosened the bolt and repeated the test again using the same bolt until it failed. The average times of tightening the bolts were 29 times to failure. There fore I concluded that I could reuse the same bolt at least 3 to 4 times before throwing it out. Of course the decision to reuse the bolt depends a lot on the type of joint it is used in, for example connecting rod bolts are a safety problem so I would not reuse them more than twice. Head screws or headbolts perhaps 2-3 times. Other places where bolts are tightened to yield could be cam bearing straps, oil pump drive gear fastener, flywheel to clutch plate assembly and crankshaft to clutch assembly as well as the vibration dampener on the crankshaft and the crankshaft bearing cap to block bolts.”

Thank you to @Desertfox for sharing this informative article.

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That would require some pretty good accounting practices to keep track of the number of times each bolt had been used.