
Accession Number : ADA305952
Title : A New Look at Numerical Analyses of FreeEdge Stresses in Composite Laminates.
Descriptive Note : Technical paper,
Corporate Author : NATIONAL AERONAUTICS AND SPACE ADMINISTRATION HAMPTON VA LANGLEY RESEARCH CEN TER
Personal Author(s) : Raju, I. S. ; Whitcomb, J. D. ; Goree, J. G.
PDF Url : ADA305952
Report Date : DEC 1980
Pagination or Media Count : 38
Abstract : The edgestress problem for a (+/ 45)s graphite/epoxy laminate was examined in detail. A review of the literature on this problem showed that the interlaminar normal stress Az distributions along the interface between the +45 deg and 45 deg plies, obtained by various investigators, disagreed in magnitude and sign. In particular, a finite difference solution and a perturbation solution predicted a tensile Az, whereas the finite element methods predicted a compressive stress. Since a stress singularity exists at the intersection of the interface and the free edge, the differences in magnitude of the peak stress were expected, but not the difference in the sign. This paper investigates the reliability of the displacementformulated finite element method in analyzing the edgestress problem. Analyses of two wellknown elasticity problems, one involving a stress discontinuity and one a singularity, showed that the finite element analysis yields accurate stress distributions everywhere except in two elements closest to the stress discontinuity or singularity. Stress distributions for a (+/ 45)s laminate showed the same behavior near the singularity as found in the wellknown problems with exact solutions. The displacementformulated finite element method, therefore, appears to be a highly accurate technique for calculating interlaminar stresses in composite laminates. The disagreement among the numerical methods was attributed to the unsymmetric stress tensor at the singularity. (AN)
Descriptors : *STRESS ANALYSIS, *EPOXY LAMINATES, *GRAPHITE EPOXY COMPOSITES, STRESS STRAIN RELATIONS, MATHEMATICAL MODELS, LOAD DISTRIBUTION, FINITE ELEMENT ANALYSIS, TENSILE STRESS, DISPLACEMENT, MODULUS OF ELASTICITY, ACCURACY, FINITE DIFFERENCE THEORY, MATHEMATICAL PREDICTION, SHEAR STRESSES, PERTURBATIONS, NUMERICAL METHODS AND PROCEDURES, COMPRESSIVE STRENGTH, DELAMINATION, POISSON RATIO, STRESS CONCENTRATION.
Subject Categories : Laminates and Composite Materials
Mechanics
Distribution Statement : APPROVED FOR PUBLIC RELEASE