The effect of mechanical twinning on the tensile modulus of polyethylene

Structural and mechanical studies have been made on low-density polyethylene sheets, in some of which mechenical twins were introduced by uniaxial plastic deformation. In Part I of the paper the results on isotropic sheets, cold-drawn to different extents (up to 150%), are discussed. Measurements on specially annealed sheets, cold-drawn to different extents (up to 150%), are presented in Part II of the paper. The effects of mechanical twinning are discussed in semi-quantitative terms, based on a distribution of twin planes and directions in the oriented sheets.