Abstract: In order to further study the relevance between the first and the second reserve bending in the process of parallel roller level of plastic hardening material. Roller level bending mechanical model is established based on hardening elastic-plastic material in accordance with the fundamental of engineering elastic-plastic mechanics. The stress relevance of the two reserve bending processes is described by analytical method and discussed out the changing process of residual stress distribution, moment and loading stress with the section bending process of the roller level. With this model it is demonstrated that moment ratio and curvature ration is not simple “M-C” relation any longer, but function related to the first curvature ratio, the second curvature ratio and hardening factors. It is theoretically proved the original curvature theory can not apply to multi-reserve bending leveling processes. Analytical results show that during the second reserve bending process, there are decreased elastic limit bending moment and the bending moment in leveling process but increased spring-back ratio. Considered hardening of the same material residual stress mean square deviation are 71.2 and 65.6, average rebound ratio are 0.49 and 0.43.

Key words: curvature ration, moment ratio, plastic hardening, residual stress, roller levelling