Abstract: In the process of reciprocating bending, any particle of the curved beam is subjected to cyclic tension-compression deformation. However, the mechanical behaviour of reciprocating bending is still not clear. In order to understand the evolution law of macroscopic mechanical behaviour in the process of reciprocating bending, the small strain cyclic tension-compression test of low cycle is carried out by the symmetric constant strain amplitude control model. The macroscopic performance on the 304 stainless steel and ST12 cold rolled plate under cyclic tension-compression loading is studied; the variation laws of elastic modulus, yield stress and plastic modulus with cycle times are investigated; the effect of prestrain is studied on the stable hysteresis loop. The experimental results show that 304 stainless steel and ST12 cold rolled plate are characterized by cyclic softening; after cyclic tension-compression loading, the elastic modulus, yield stress and plastic modulus of the two kinds of materials change obviously, and the tension and compression do not have consistency; cyclic tension-compression loading can annihilate the initial difference of mechanical properties caused by prestrain, and make the mechanical properties of materials become uniform. It is also indirectly proved that reciprocating bending can make the mechanical properties of the same layer of fibers be homogenized, which lays the foundation for the construction of the new constitutive relationship.

Key words: cyclic softening, cyclic tension-compression, mechanical behaviour, prestrain, reciprocating bending, sheet metal