Stress distribution in outer and inner plies of textile laminates and novel boundary conditions for unit cell analysis

The local stress–strain distribution in a unit cell of a textile laminate depends on the distance of the ply to the surface, the number of plies in the laminate, and the stacking sequence. A conventional meso FE analysis employs boundary conditions for a unit cell of the textile composite based on the assumption of periodicity in the thickness direction. In that case, the stress concentration can be drastically underestimated, especially in outer plies. This paper describes the interaction of plies, local stresses and displacements. To avoid the analysis of the whole laminate and to reduce it to the boundary value problem on one unit cell only, novel boundary conditions are introduced. These conditions are based on the analysis of a single unit cell: they account for the number of the plies in the laminate, distinguish between the outer and inner plies, and reproduce the meso stress–strain state with good precision.