Notched Unidirectional Boron/Aluminum: Effect of Matrix Properties

Abstract

The manner in which matrix properties affect the notched behavior of unidirectional boron/aluminum is assessed. Data are presented for center- notched tensile specimens of as-fabricated boron reinforced 1100 and 6061 aluminum. Results are also given for a heat-treated B/6061. The notched response of these materials shows significant differences. A shear-lag analysis, formulated for finite-dimensioned monolayers made from work-hardening constituents, is shown capable of explaining such effects. The calculated rela tion between load and notch opening displacement for a uniform traction boundary condition is indistinguishable from that for a displacement condition when the matrix yield strength is sufficiently high. For such cases, the predicted relation is in excellent agreement with experiment. Specimens with a relatively low matrix yield strength exhibit different behavior: the predicted relation be tween load and notch opening displacement depends strongly on the type of boundary condition applied. This is a consequence of widespread matrix yielding. These two predictions bound the experimental data. Also discussed are calculations which indicate that nonuniform fiber spacing and flaw geometry have little effect on fiber stresses. The growth of shear cracks does ap pear, however, to substantially alter the response of notched boron/aluminum.