GB934642A - Method for parting-off a length from metal bar stock - Google Patents

Abstract

934,642. Breaking. FORGINGS & PRESSWORK Ltd. July 10, 1962 [July 13, 1961; June 23, 1962], Nos. 25359/61 and 24249/62. Class 83 (4). A method of parting-off a length from metal bar stock includes providing a sharp notch to weaken the bar in the position in which it is to be parted, and applying alternating stresses to induce rapid fatigue failure of the bar at the weakened section. In an example, a mild steel bar of 0.682 inch diameter provided with a circumferential V-notch 0.043 inch deep was gripped at one side of the notch by a stationary jaw and at the other side by a jaw capable of minute reciprocation in the direction of the axis of the bar. A basic tensile stress of 3.4 tons per square inch was applied to the bar through the jaws and an alternating stress of 13 tons per square inch was superimposed at a frequency of 40 cycles per second while the temperature of the bar in the zone of the notch was maintained at minus 60‹ C. The bar fractured after 41,900 stress reversals. The temperature applied to the stock may be progressively lowered with the development of the fracture. The alternating stress can be tensile, compressive, torsional, shear or bending stress or a combination thereof and applied mechanically, electrically, hydraulically or pneumatically. Any basic pre-stress may be of the same character as the alternating stress or different therefrom. The notch may be formed by mechanical working or cutting.