High temperature cyclic pressurization of titanium ducts for use in aircraft pneumatic systems

During service operation, the pneumatic system of a commercial aircraft is subjected to hot air pressure cycles, causing the stresses developed in the material to be of cyclic nature. Commercially pure titanium is one of the various metallic materials selected for use in the pneumatic system components. In order to provide information concerned with the service performance of the titanium ducts and their effects on material behavior, it was developed a pneumatic workbench capable of reproducing the temperature and pressure cycles found in flight conditions. This work has shown that it is feasible to conduct laboratory tests aimed at simulating the aging process suffered by the pneumatic system ducts. Their tensile and fatigue properties were observed to change in response to pressurization tests, and these changes were not related to chemical composition or surface degradation. The fractographic analysis of a failed duct revealed that fatigue cracks can nucleate in the vicinities of welding flaws and grow through the wall, causing a pressure drop due to air leakage.