WORKING LOAD ANALYSIS AND STRENGTH ESTIMATION FOR BOLTED JOINTS DURING ACTUAL MACHINE OPERATION

摘要

Serious problems caused by bolted joint fatigue breakage still occur. This is because working load evaluation and durability strength evaluation have been insufficient in the product design stage, in the test stage of machine lifetime prediction, in the trial production stage, in the prototype machine test stage, and so forth. In this paper, we propose a method for measuring and analyzing the load on bolted joints used in a machine under actual operation. Working load measurement under actual machine operation and the results of its analysis are shown as load frequency diagrams. This is very important information for realizing the concept of simultaneous multiple design. An example of the measurement analysis method of the load (three types of the loads; axial force, bending moment, and the torsional torque) added to the bolted joint shank which comes out at the time of the actual machine operation is shown. The reliability of assessing the strength and durability of bolted joints is considered from the viewpoint of limited-lifetime (finite-lifetime) design using Miner's rule with cumulative loosening damage models and fatigue limit (infinite-lifetime) design. As an example, we measured the working stress and evaluated the strength of a bolted joint of an actual machine to verify the usefulness of the proposed method. Also, examples of strength evaluation are shown to illustrate finite-lifetime and infinite-lifetime prediction. Moreover, the practical process and presumed example of fatigue life prediction are shown. It is considered as a contribution at the improvement of strength reliability and the load analysis method of the bolted joint of machine develop-ment stage and failure analysis stage. Our findings are also expected to eradicating accidents involving bolted joints in machines.