Add Visitor Counter & Fasterner Tensioning

I've added a visitor counter to my bolg. Although I always think that I am the only one who enter this blog, it is still good to know that if there is someone else here. To write this bolg, I think the main purpose is to drop down some notes to myself. There are so many things in my mind, no matter job related or not, and this is a good time for me to sit down and re-organise the stuffs.

Recently, I am checking some information on bolt tightening. Bolting & Welding are two most popular methods to join machanical parts. As an inspector, some times we need to inspect the condition of bolts. When bolts are tightened, they become stressed in tension. Analysis shows that for a dry (means no lubricant, thread locker, or thread sealant) steel fastener, approximately 50% of the tightening torque applied is needed to overcome friction between nut turning against the joint surface. Another 40% is consumed overcoming friction between the mating threads. The remaining 10% develops useful tension in bolt. This is very interesting. That means if you add some lubrication on the mating threads and joint surface, a same given torque can produce greater preload stress in the fastener. On the other hand, if the joint preparation is not satisfactory and induce more friction, there will be insufficient clamping force on the joint.

Improperly tightened bolts may loosen under vibration, thermal cycles, or other in-service conditions. Such joints can also slip, generating undesirable load paths. It can also cause fastener tension to vary more widely under cyclic loads, leading to early fatigue failure.