This paper describes a new possible approach to fatigue design of aerospace components founded on probabilistic bases compared with safe life and damage tolerance that are founded on deterministic bases. A numerical tool have been introduced and explained together with the experimental activity for its validation analyses. For a typical aerospace component, such as a lap joint panel, an acceptable maximum risk level has been established and the maintenance program has been planned to ensure operating life without catastrophic failures. The analysis has shown that this new approach introduces several benefits in fatigue design.

In the nuclear fusion reactor, ITER, the Loss of Coolant Accident (LOCA) in the Vacuum Vessel has to be managed with pressure suppression systems working at sub-atmospheric pressure. The operating conditions differ considerably from those experienced in the fission nuclear power plants such as BWR. The direct condensation at sub-atmospheric conditions is not sufficiently known, therefore, the effectiveness of systems operating at these particular conditions have to be investigated experimentally. A research program is being carried out at the University of Pisa, funded by ITER, in order to study the steam direct condensation for nuclear fusion reactor conditions. For this purpose, an experimental test facility was designed and built and an extended experimental program was performed. Video cameras were used to visualize the steam condensation at different mass flow rates. This paper deals with the elaboration of images of the steam jet flowing from a hole in the water. The steam condensation regimes depend on three governing parameters: downstream exit pressure, water temperature and steam mass flow rate per hole. Moreover, the condensation regimes are characterized by different shapes of steam jet. The image analysis permitted to determine the heat transfer coefficient in the stable condensation regime at sub-atmospheric conditions. The results obtained are compared with those correspondent at steam condensation at atmospheric pressure, emphasizing the great importance of the downstream exit pressure and the subcooling on the steam condensation.

In this paper, the growth of long fatigue cracks up to failure in aircraft components is studied. A deterministic model is presented, able to simulate the growth of fatigue through cracks located at rivet holes in lap-joint panels. It also includes criteria to assess the link-up of collinear adjacent cracks in a MSD scenario. To validate the model, a fatigue test campaign was carried out on riveted lap-joint specimens in order to produce experimental crack growth and link-up data. Accurate measurements of naturally occurred surface cracks were automatically performed by the Image Analysis technique, thus allowing the tests to run 24 h a day. The comparison between experimental tests and numerical simulations is good, thus confirming the model as a useful tool for the assessment of fatigue life of aircraft riveted joints

No abstract

This article deals with the fatigue propagation of multiple cracks in finite width holed panels, which are typical of aircraft structural components. Theoretical studies in the literature have been considered and critically analyzed. Some of them have been translated into analytical models and implemented in a computer code. To check the effectiveness of the used models, a fatigue testing campaign has been conducted on six different configurations of notches and cracks. The comparison between experimental results and those obtained from the implemented models has shown a good agreement