Cracked plates with bonded elastic circular inclusions inside a matrix were subjected to an impact tensile loading. The influence of the inclusion on the propagation of an initial edge-crack was discussed in this paper. Two types of specimens were tested, that is with hard or soft inclusions surrounded by soft or hard matrices respectively. It has been shown that bi-, or tri-furcations of the propagating crack have persistently occurred at the region of mesophase between matrix and circular inclusions. The phenomenon of splitting of the initial crack was common in both types of specimens, For the definition of the prevailing stress field, the dynamic stress intensity factors were evaluated at different positions of the crack, as well as the crack-velocities along the main crack or its branches during their propagation. It was observed that the crack initiation in soft plates with hard inclusions was followed by the emission of Rayleigh waves, which contributed to the mode of fracture of the composite. Isochromatic patterns were also used to simulate the stress-field of the propagating cracks against the inclusions at distinct time-instants where the propagating crack was frozen at this instant and static photoelastic analysis was applied. These approximations gave satisfactory results with the cracks advancing inside the composite plates.

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Parallel series of ellipsoidal inclusions, aligned along their major axes, whose centers are arranged in arrays inside a matrix, result generally in an orthotropic composite. When these arrays of inclusions constitute stacks placed at equal spacings through the thickness of the composite, the material is transformed into a transversely isotropic material. Considering this simplified problem, the effective elastic properties, i.e., the longitudinal and transverse elastic and shear moduli, as well as the respective Poisson's ratios, are evaluated in this paper. The solution of the problem was made in terms of the aspect ratio of the inclusions, their volume fraction and, finally, the succession of the constituent phases inside the composite. Employing Eshelby's theory for the stress field around a single ellipsoidal inhomogeneity, which is surrounded by the effective anisotropic composite medium, and Mori-Tanaka's concept for considering the mutual interaction of the neighboring inclusions inside the matrix, we evaluated the effective properties of composites containing ellipsoidal inclusions parallel dispersed inside the matrix. The whole analysis provides, in a closed-form solution, interesting results concerning the anisotropy, as well as the stiffness of anisotropic composites, reinforced with ellipsoidal inclusions. These findings reveal that the anisotropy is merely increased in composites consisting of soft matrices and reinforced by hard needle-shaped inclusions, whereas the stiffness is affected by both the shape of inclusions, as well as by their mutual concentrations. Furthermore, introduction of different constituent phases inside the composites indicated that intense variations of stiffness occur, especially for composites consisting of hard matrices containing soft inclusions. The results of the paper concerning effective elastic properties of anisotropic composites with ellipsoidal inclusions can be applied in case of unidirectional discontinuous fiber composites, where the fibers are simulated by ellipsoidal inclusions. Also, the evaluation of the elastic properties in hard composites with enough soft inclusions provide information for the mechanical as well as the fracture behavior of hard composites weakened by internal through cracks.

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