Fracture energy and strength were determined for three series within a sodium borosilicate glass‐Al 2 O 3 dispersed composite system. The average particle sizes of the Al 2 O 3 dispersions were , and μm. Within each series, composites containing 0.10, 0.25, and 0.40 vol fractions of the Al 2 O 3 dispersed phase were vacuum hot‐pressed. The fracture energy was determined at 77°K with the double cantilever specimen configuration. Strength was measured by a 4‐point flexural test. A significant increase in fracture energy was observed (up to 5 times the fracture energy of the glass without second‐phase dispersion). The fracture energy depended on the interparticle spacing and average particle size of the Al 2 O 3 dispersion. These results could best be explained by a previously proposed model for the interaction of a crack front with a second‐phase dispersion. Surface roughness also contributed to the increased fracture energy. Some composites were strengthened significantly relative to the glass without a dispersion. Calculation of the crack size showed that the Al 2 O 3 dispersion increased the crack size of the glass by ∼1 to 3 times the average particle size of the Al 2 O 3 dispersion. Thus, the dispersion increased both the fracture energy and the crack size. These opposing parameters ultimately determined the strength behavior of these composites.
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F. F. Lange (1971) studied this question.
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