Actual Three-Dimensional Stresses in Composite Structures and in Local Effects in Homogeneous Structures. Case Studies

Abstract

The major purpose of this paper is to present empirical evidence on the actual stresses in the components of the homogeneous and adhesively bonded composite structures. The presented evidence was obtained by using the advanced strain gages technique, and the theories and techniques of three-dimensional isodyne stress analysis. It is shown that a two-dimensional analytical treatment often yields errors not only in the magnitude but also in the sign of the evaluated stresses. Validity of some basis notions accepted in engineering mechanics is discussed, and ranges of their practical applications in composites designing are suggested. Case studies encompass: examples of incorrect predictions of some analytical solutions; stresses in the region on notches; stresses along the crack tip; lack of uniqueness in formulation of the stress concentration factor and of the stress intensity factor; stresses in a double lap joint; stresses in a three-ply structure, three-dimensional stresses caused by local effects. It is shown that the isodyne stress analysis supplies reliable data on the actual stress states. Such data are needed for testing analytical predictions in the stress analysis, and for testing reliability of various experimental techniques. They are also needed as a foundation for development of more advanced analytical simulations of stress states, which would be able to account for the fact that the stresses in composites are inherently three-dimensional.