# Accession Number:

## ADA305952

# Title:

## A New Look at Numerical Analyses of Free-Edge Stresses in Composite Laminates.

# Descriptive Note:

## Technical paper,

# Corporate Author:

## NATIONAL AERONAUTICS AND SPACE ADMINISTRATION HAMPTON VA LANGLEY RESEARCH CEN TER

# Personal Author(s):

# Report Date:

## 1980-12-01

# Pagination or Media Count:

## 38.0

# Abstract:

The edge-stress problem for a - 45s graphiteepoxy 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 displacement-formulated finite element method in analyzing the edge-stress problem. Analyses of two well-known 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 - 45s laminate showed the same behavior near the singularity as found in the well-known problems with exact solutions. The displacement-formulated 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