Abstract: A fastener tensioning method and apparatus for obtaining a desired degree of tension in a fastener. The embodiment of this invention described utilizes the slope of the change in torque per change in rotation gradient to predict a rotation starting point independent of the rotation that occured in the torquing cycle up to the point of establishing a constant gradient. In the constant slope or gradient area of the torque rotation curve, rotation is considered linearly proportional to the tension in the fastener. A prescribed additional rotation is applied to the fastener utilizing the threads as a micrometer device for stretching the bolt to achieve the desired tension or fastener strain level. With appropriate system monitoring such as the total rotation, the maximum torque applied, the gradient slope, etc., the system can be adapted to inspect the fastener for applied tension as well as accurately control tension level.

Abstract: A fastener tensioning method and apparatus for obtaining a desired degree of tension in a fastener. The apparatus includes a means for applying rotation to a fastener, a means for measuring the torque applied by the means for rotating the fastener, a means for determining a rate of change of torque applied to the fastener with respect to the rotation applied to the fastener, a means for detecting when the rate of change of torque with respect to rotation becomes a constant, a means for accomplishing a desired amount of rotation of the fastener beyond the rotation required to achieve the constant rate of change of torque with respect to rotation, and a means for shutting off the means for applying rotation to the fastener in response to the total desired rotation being achieved. The embodiment herein described improves the well-known "turn of the nut" method for fastener tensioning by providing that method with a well determined starting point.