SBIR-STTR Award

Low Plasticity Burnishing (LPB) has been shown to provide twice the HCF strength of shot peening, and four times the strength after FOD in Ti-6Al-4V and IN718 laboratory specimens exposed to turbine engine temperatures. The deep compressive layer produced by LPB is comparable to laser shock peening (LSP), and can fully arrest the growth of 0.020 in. deep fatigue cracks. LPB offers higher speed, lower cost, and better surface finish than LSP, and is performed on conventional CNC machine tools in a manufacturing or engine overhaul shop environment. The feasibility of applying LPB to compressor blades critical to the NAVAIR IHPTET and VAATE programs to improve damage tolerance and HCF life will be established in Phase I. LPB processing parameters and control software will be developed for following the complex surface of a compressor blade using existing tooling and 4-axis LPB facility. The HCF life and damage tolerance of LPB processed blades will be compared to the current practice of shot peening. Thorough documentation of HCF performance of LPB processed blades and development of an automated production LPB facility for blade rework will be undertaken in Phase II.

Benefits:
The anticipated benefit of the proposed effort to NAVAIR is substantial reduction in the total cost of aircraft ownership and improved fleet readiness. LPB blade processing will improve engine HCF life and FOD tolerance, resulting in reduced costs of both replacement parts and maintenance. Increased damage tolerance will reduce required inspection time for further man-hour savings and increased on-wing time. The initial cost savings for the T56-A-427 compressor alone are estimated at $3.6M annually. Current military expenditures of $2B annually to address fatigue of aging aircraft and legacy engines provide the immediate market for LPB and potential savings to the DoD. Commercialization will, therefore, begin with NAVAIR overhaul and then expand to other military aviation applications. LPB is well positioned for commercialization due to low costs of operation and capitalization relative to laser shock peening(LSP), and improved depth and stability of the compressive layer produced by LPB relative to shot peening. LPB can be applied easily during manufacturing operations with conventional CNC tools at engine overhaul centers for much less than new blade costs. Demand for improved HCF performance and cost reduction from military owner-operators will lead to LPB processing of new blades and other critical rotating parts during manufacturing. Military applications will be followed in the commercial aviation sector, driven by improved HCF performance and cost reduction. Potential secondary commercial opportunities for LPB to improve HCF performance in the aerospace, automotive, and power generation turbine industries are vast, and will follow the initial military applications over a period of several years.

Keywords:
high cycle fatigue (HCF), damage tolerance, total ownership costs, low plasticity burnishing, surface enhancement, improved maintainability, VAATE, legacy engines

Improved damage tolerance is critical to achieving reduced engine ownership costs and increasing safety and fleet readiness. In Phase I, low plasticity burnishing (LPB) was successfully demonstrated to improve the damage tolerance of the F404 1st stage fan blade by an order of magnitude through the introduction of high magnitude through-thickness compressive residual stress in the FOD sensitive leading edge. The objective of this Phase II research effort is to apply LPB to the F402 LPC-V1 trailing edge to immediately address an HCF safety related problem, and then to address the engineering issues necessary to transition LPB blade processing to the fleet. Reverse engineering methods will be established to efficiently develop LPB processing parameters and CNC code for other components. Finite element methods will be used to optimize the LPB residual stress fields and to predict the fatigue performance benefit for other blades and materials. The data necessary to predict fatigue performance, including thermal and overload relaxation to support long-range life prediction, will be generated. LPB processing will find initial Phase III application in Navy depots to increase damage tolerance of fan and compressor blades during engine overhaul, reducing replacement, maintenance and inspection costs. The introduction of LPB as a manufacturing process by engine OEMs will follow to extend the performance, improve safety and reduce the cost of ownership of military and commercial aircraft engines and ground-based turbines