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The morphology of salt water stress corrosion cracks in 8A1-1Mo-1V titanium alloy has been determined. In the interior of the specimens the cracks are brittle in nature and far more extensive than indicated by cracks visible at the specimen surface. The direction of propagation of the internal cracks is away from the plane of the specimen starter crack. These crack characteristics are explained in terms of internal stress state and presence of contaminants containing chlorides.

The concept of fail-safe structure has introduced requirements for evaluation of new types of material properties and new sets of conditions for the design of pressure cabins of high altitude aircraft. A brief review is given of the fracture toughness properties of candidate materials for the SST environment. The results of recent tests on residual strength and rate of crack growth in stiffened and unstiffened panels and cylinders made from titanium and steel are presented. The results of a titanium full-scale fuselage panel tested under heat (550–650 F) and cyclic pressure are discussed in light of SST design requirements.

The need for protecting thin gage Rene 41 from oxidation when heated above approximately 1550 F for extended periods is discussed. An evaluation of cladding as a means of protection is presented. It was found that oxidation protection for times up to 100 hr at 1800 F, or 10 hr at 2000 F, can be provided with cladding thickness of 0.001 in. However, interalloy diffusion and alloy depletion from the Rene 41 were problems with each of the potential clad alloys investigated.