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ABSTRACT--When designing composite materials, the presence of stress concentration at locations such as circular notches is unavoidable. Such locations in structural elements arise from joints required to form a structure. The stress concentration, observed around the notch, is quantified by the stress concentration factor K. This quantity is normally calculated analytically and/or numerically and is an important design parameter. In this work, the experimental technique of remote laser Raman microscopy is used for the in situ measurement of K in Keviar 49 fiber/epoxy composite plates containing a circular hole. The results obtained by this technique are compared with those calculated analytically and by finite element analysis. Both analytical and numerical methods underestimate the experimental results for maximum K by approximately 10 percent, which is considered reasonable within experimental error. In addition, very good agreement between analytical and experimental data is obtained for the decay of the stress concentration factor as a function of distance from the edge of the hole. The numerical results, however, overestimate the decay K with distance from the notch boundary and only converge at relatively large distances.KEY WORDS~Composites, laser Raman microscopy, stress concentration, notch, strain measurements Composite materials are used as structural elements because of their resistance to environmental attack (wear, corrosion) and high specific properties. One of the most important problems that needs to be solved when designing with composites is that of stress arising near discontinuities. Discontinuities such as joints are required for assembling a structure, and imperfections such as voids, cracks, cutouts and so on are unavoidable when working with composites. Knowledge of the magnitude and extent of the stress concentration in these structures/materials is crucial for the prediction of the location of first failure and subsequent damage propagation. Original manuscript submitted : July 22, 1999. Final manuscript received: February 28, 2000 circular notch or a crack tip is the presence of a singularity of 1/47, where r is the distance from the notch boundary. 2 Several researchers have proposed analytical expressions of the stress field in an infinite plate containing stress concentration locations. Early attempts worth mentioning are those of Lekhnitskii 3 and Savin 4 for the case of perforated plates. Muskhelishvili's 5 complex potential functions for isotropic media were used to solve the boundary value problem. Theocads and Philippidis 6 later proposed a corrected solution for a special orthotropic plate that had equal complex roots of the characteristic equation and compared their results to the stress concentration along an elliptic boundary derived according to Lekhnitskii's and Savin's solution.Tan 7 used Lekhnitskii's approach to predict the remaining strength of a notched composite laminate under in-plane loading. Tan 8-1~ also proposed three fracture models called effective point, e...