Abstract
In the design of precision instruments containing a screw fastening, it is necessary to estimate residual torsional deformation remaining in the fastened body after fastening by bolts. Here, based on the three-dimensional theory of elasticity, torsional deformation is analyzed for cylindrical fastened bodies. It is revealed that the residual torsional deformation does not spread throughout the whole fastened body but it is restricted in the vicinity of the bolt hole. A new formula is established for estimating residual torque in a bolt due to screw fastening, by considering the gap between the torsional angle released in a bolt after fastening and that in a fastened body. The formula is examined experimentally to give a much better estimation than those suggested so far. Finally, a method of estimating the residual torsional deformation is proposed for designing precision instruments.
