1. The aluminum-boron plastic fails by means of volume failure during tensile loading, i.e., by gradual cumulation of fractures of the fibers and separation of the fibers from the matrix. 2. The degree of fragmentation of the fibers of the aluminum-boron plastic in cyclic loading is lower than in static tensile loading. 3. The maximum value of the degree of fragmentation of the fibers P depends on the dimensions of the specimen and the reinforcement coefficient. In the case of the aluminum-boron plastic, the variation of the reinforcement coefficient from 0.17 to 0.38 reduces the value of P from 25 to 5%. 4. The length distribution of the fragments of the fibers in the fractured aluminum-boron plastic shows a maximum corresponding to the theoretically calculated ineffective length of the fiber. 5. The theoretical values of the strength of the unidirectional composite calculated in accordance with [1] taking into account volume failure are in satisfactory agreement with the experimental results. © 1984 Plenum Publishing Corporation.