X-Ray Evaluation of Deformation and Fatigue Damage of Aluminum Laminate Films

Abstract

Aluminum laminate films have been widely used for packing materials of lithium ion battery and other electronic devices, and the emboss process is commonly used for shaping films for packages. Thermal stress cycling due to on-off switching of devices may result in thermal fatigue of aluminum layer of laminated films. In the present paper, the X-ray diffraction method is applied to detect the progress of deformation and fatigue damage of aluminum layer in laminate films subjected to tensile deformation and fatigue. The full-width at half maximum (FWHM) was increased with tensile strain. Fatigue loading increased FWHM, and also induced ratcheting extension, which was identified as an indicator of fatigue damage progress. The relation between FWHM and ratcheting strain is nearly identical to that obtained in tensile deformation. The residual stress as received was compression due to mismatch of thermal expansion between aluminum and plastic layers. The compressive residual stress increased with fatigue ratcheting extension as well as with tensile deformation, and the amount of increase of compressive residual stress with film extension is nearly identical between two deformation modes. The increase of compressive residual stress was caused by deformation mismatch between aluminum and plastic layers during extension of films. The contraction of films may introduce tensile residual stress in aluminum layer. The tensile residual stress in the aluminum layer was measured at emboss corners of laminate films.