A model is presented to explain premature fracture of titanium- boron composites as a result of interaction to form titanium boride. Three failure modes are identified. The titanium boride cracks at a strain of 2500 x 10-6 but the cracks result in a smaller stress concen tration than the preexisting flaws in the boron up to a boride thick ness of 1000 Å. Between 1000 and 5000 Å, failure initiates at the cracks in the boride at a strain that varies inversely with the square root of the thickness. Above 5000 Å of boride simultaneous failure of boride and boron filaments occurs.
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