It is well known that a long straight rod twisted by two moments can loose its stability under certain conditions. Such type of buckling is observed in the most visual form in case of thread and cable...

It is well known that a long straight rod twisted by two moments can loose its stability under certain conditions. Such type of buckling is observed in the most visual form in case of thread and cable torsion.

If the thread is twisted, it quickly obtains a curvilinear shape approximately like the one presented in Fig. 105. It is absolutely evident that if the thread is stretched under torsion then we obtain a visible increase in torque under which the thread looses stability. It is always necessary to stretch a cable during winding processes.

Taking a simply supported rod (Fig. 106) as an example, determine the critical value of torque and ascertain its dependence on tensile force.