動的荷重下におけるねじ結合部のストリッピング発生メカニズムの検証

抄録

Thread stripping is one of the typical failure modes of threaded assemblies subjected to static tensile overload, but it has not been recognized as a failure mode under dynamic loading. However, the accidents were reported recently that the stripping had occurred in two different types of threaded assemblies subjected to repeated tensile load. If these events are true, we should care about the stripping strength of threaded assembly in service as well as self-loosening and fatigue failure.
This study aims to confirm the possibility of the stripping in dynamically loaded threaded assemblies, and to clarify the failure mechanisms so as to avoid such types of failure. Experimental investigations for different types of bolt-nut joints are performed, and it is clarified that the stripping may occur by three different causes: (1) reduction of the number of threads engaged due to the fatigue crack growth at the first thread root of a bolt, (2) increase of the load share rate due to the permanent deformation or the permanent set of a specific thread (or threads), and (3) fatigue crack initiation at the thread root of a nut.