Cavitation Peening of Hydraulic Tubes for Fatigue Improvement

In order to reduce weight and improve performance, many new aircraft designs are using titanium hydraulic tubing because of it’s high strength to weight ratio and high pressure rating. Higher hydraulic pressures enable the use of small and lighter actuators, allowing further reductions in weight. A modern performance rotorcraft, such as the V-22 or the new CH-53K, can have as many as 500 hydraulic tubes, so low weight tubing becomes a critical requirement. However, the titanium hydraulic tubing has proved to be sensitive to very small surface flaws in lab tests. Scratches as shallow as 0.004” have been shown to cause failure in less than 50,000 cycles in the lab – or as little as 40 flight hours! The cavitation peening technology proposed in this project would make the tubing more robust and forgiving of flaws by inducing residual compressive stresses that are deeper than the anticipated flaws. Preliminary tests have demonstrated the process can dramatically increase notched fatigue life by more than 20 times at a projected cost of less than $50 per tube. The proposed project will build on the initial testing to demonstrate feasibility to the Primes and other stakeholders.