An unconventional type of fatigue-testing machine

Abstract

When any elastic system is subj ected to a range of load, the energy stored in the system fluctuates between two values corresponding to the maximum and minimum loads of the cycle. Since the driving unit usually supplies energy at a constant rate (corresponding to losses in the machine), the energy given out by the specimen during one quarter cycle must be stored in some manner and then returned during the following quarter cycle. In existing types of fatigue-testing machine this energy is stored in a rotating mass (flywheel) and gives rise to cyclic variations in its speed. The object of this note is to indicate that the energy can be better stored in an oscillating mass which is, ideally, attached directly to the specimen. When this is done the full specimen load is transmitted through a direct (solid) connection and does not travel through the linkwork to the operating mechanism of the machine. As a consequence the operating mechanism can be made much lighter, the driving power required is considerably reduced and the machine can be run at a much higher speed (if desired). The dual problem of starting the machine and also ensuring stable operation can be solved by the use of a 'slipping clutch' already employed successfully in another connection.