An investigation of the fatigue properties of music wire and springs, which is now under way at the National Bureau of Standards, has resulted in the development of a reversed bending analysis method for predicting the approximate fatigue strength of helical springs wound from music wire. The study, which is being conducted by J. A. Bennett, H. C. Burnett and C. L. Stangaitis of the NBS mechanical metallurgy laboratory, has also yielded information about the mechanism of failure of wire springs?
Many ordnance devices such as machine guns and small arms are dependent on helical springs for their operation. These springs operate over a very large stress range and must maintain their original strength through thousands of cycles. Music wire is most frequently used for springs in ordnance devices because it is the strongest engineering material available. Small-diameter wire of this type is produced commercially with a tensile strength as high as 450,000 psi. The reversedbending study, made on four types of wire, is the first phase of the Bureau's investigation of helical springs. The work is sponsored by the Army Ordnance Corps.
In the NBS investigation reversed bending fatigue studies were made using two types of testing machines. One of these was designed and constructed at the Bureau ; the other was the Hunter wire fatigue tester. The NBS machine utilizes a rotating strut but differs somewhat from other machines of this type. Both machines operate on the principle that a rotating curved wire must reverse its points of maximum compression and tension once each revolution. Approximately 50 specimens of four types of wire were studied under reversed bending in the Hunter machine, and 100 specimens of each type in the NBS machine. When results from the two machines were correlated, no consistent difference in data was found.
Fatigue studies of short compression springs were made in another type of machine designed at the Bureau. In this device an electric motor and adjustable eccentric are attached to one end of a steel plate which is pivoted at its midpoint. Eight springs, four at each end, are mounted between the pivoted plate and a second fixed plate approximately two inches below. The four springs at each end are positioned * Communicated by the Director.
"Endurance of Helical Springs Related to Properties of the Wire," by H. C. Burnett and