Overstrained interatomic bonds in PM polyimide

Abstract An attempt has been made to determine the true stresses on interatomic bonds in uniaxially stretched PM polyimide films. The amount of stress was determined from displacements of the interatomic vibration frequencies. It was found that an external stress of 61 kgf/mm 2 is distributed very unevenly among the bonds: 95% of the bonds are under a stress equal to the external stress, but the stress on the remainder of the bonds varies within wide limits, and reaches 1900 kgf/mm 2 .