Abstract
In sheet metal forming, spring-back phenomenon is important issue and microscopic evaluation of materials is required. In this study, In order to clarify relationship between the changes of material structure or material properties and the plastic strain, analysis and experiment were performed. First, the changes of through-thickness distribution for mild-steel sheets were measured by analyzing the cross-sectional microphotographs of material structure. And next, the relationship between Young's modulus or hardness and the plastic strain was investigated by cyclic nano-indentation testing by which micro regional material properties can be obtained. Consequently, the distributions of grain oblateness and its changes caused by V-bending were quantitatively obtained by analyzing the microphotographs. Moreover by cyclic nano-indentation testing, hardness was decreased by increasing plastic strain. Though the quantitative evaluation of Young's modulus was tough work and we couldn't find peculiar tendency, stable value of it could be measured where maximum indentation load was larger than 1000μN.
