Abstract
Bending yield stresses (Spring limit) of copper alloy and stainless steel flat springs decrease considerably when they are subjected to plastic deformation by stretching or bending them in the opposite derection. Hereunder is presented a report of the investigation performed of the degree of decrease in spring limit and the material factors in the specimens in heat treatment and the effect of the rolling direction on the axis.
The results are as follows:
(1) The spring limit of a thin shaped flat spring decreases when the stress applied on the spring has a opposite direction to pre-stress, and increases when it has the same direction.
(2) The spring limit of the specimen subjected to pre-stretching stress decreases wlth increase of pre-plastic strain over the elastic limit, and is constant when the pre-stretched plastic strain becomes higher than 0.2%. This constant minimum spring limit Kbmin is about 10 to 25kg/mm2, and this value is about 1/10 to 1/2 of the spring limit before deformation.
(3) The spring limit of the specimen subjected to pre-bending stress increases by the bending, and decreases by bending it in the opposite direction. The spring limit that decreased by bending it in the opposite direction can be improved as the deformation increased on the opposite side.
(4) The spring limit of the specimens containing different materials, heat treatments, degree of cold reduction and specimen axis decrease similarly when pre-plastic strain applied, and these factors will affect Kbmin a little.
(5) The decrease of spring limit by stretching or bending plastic deformation is due to Bauschinger effect.
