ABSTRACT
Every tightening method-torque, torque-turn, stretch, and tension control-has drawbacks and limitations. But each of these methods is good enough for many applications, thanks to the fact that most bolted joints are overdesigned and/or to the fact that we are usually not too concerned about the consequences of an occasional failure. In more and more applications, however, we are becoming concerned and would like to find a better way to control bolt tension and/or clamping force. Fortunately, a better way to control bolt tension, at least, is emerging: the use of ultrasonic techniques. These techniques allow us to get past dozens of the variables that affect the results we achieve with torque and/or turn control. They allow us to see and compensate for the elastic interactions and other factors that limit the accuracy with which we can tighten bolts with hydraulic tensioners. In short, they give us a new, more accurate, and often more convenient way to get the advantages of stretch control or strain gage control.
