Mechanical and bending characteristics of invar sheets

Abstract

Invar materials, with their extraordinarily low coefficient of thermal expansion, are increasingly becoming important for producing high precision and reliable components for instruments and electronic devices. As a result, springback behavior becomes extremely critical in forming these intricate precision parts from sheet base materials. To provide the reliable information needed for fabricating these components, the micro and macro properties of a commercially available cold-rolled invar sheet were examined, in order to provide basic information and to assess its forming behavior. Experiments were conducted to investigate the forming related tensile and springback properties of the sheet, with an emphasis on the springback evaluations. An analytical solution, based on a bilinear relationship between stress and strain, was selected and used to predict the springback of the sheets. A good correlation was found between the predictions and experimental data. As a result, the analytical formula selected is accurate enough to predict the springback behavior of an invar alloy. With the tensile properties being obtained, the analytical solution can be used to provide the springback information needed for designing complicated sheet-metal parts, as illustrated in the present study.