ON STRENGTH SCALING OF COMPOSITES WITH LONG ALIGNED FIBERS

Strength measurements of a specially made composite material are repor ted; The material consisted of an epoxy matrix and the reinforcement o f one layer of well aligned and equally spaced glass fibers. For a cer tain range of fiber spacing lambda, matrix initiation strength sigma(c ), under uniaxial tension, and lambda were related as sigma(c) root la mbda approximate to kappa. Dimensional analysis indicated that the con stant kappa was proportional to the matrix fracture toughness. Using r eported data on matrix initiation strength of a borosilicate glass-SiC composite under bending, a similar relation was suggested between sig ma(c) and the maximum fiber spacing, sigma(c) root lambda(max) approxi mate to constant. The latter relationship was also applicable to harde ned cement paste with the largest void on the fracture surface as the appropriate length scale. The results outlined in this paper suggest t hat, for a range of fiber spacing, matrix initiation strength is dicta ted by a Griffith type flaw proportional to the fiber spacing (uniform case) or the largest fiber spacing (non-uniform case).