On Delamination of (+ or - Theta sub m/90 sub n/2) sub s Laminates Subjected to Tensile Loading

Delamination initiation investigations of symmetric laminates consisting of angle ply and 90-degree plies were conducted. Five criteria were used to determine delamination initiation for a given set m and n of angle plies and 90 degree plies. In the criteria one and two, delamination moment rates delamination moment coefficients or DMC relative to the applied average axial stress and strain in laminates with uncracked 90 degree plies, were maximized. The same approach was used in the criteria three and four except that the laminates had cracked 90 degree plies. The fifth criterion was based upon establishing the maximum mismatch of Poissons ratios of angle plies and 90 degree plies. The expressions derived on the basis of the five criteria were numerically evaluated. The results of these studies indicated that the laminates designed on the basis of the fifth criterion, namely, maximum mismatch of Poissons ratios of angle plies and 90-degree plies had the minimum tendency to delaminate. Keywords Delamination, Laminated composites, Stress analysis, Peel stresses, Experimental data, Acoustic emission.