Laser Peening Proves to be the Solution for the B-1B Lancer’s Engine Failures

Beginning in 1991, the B-1B Lancer’s F101 engine began experiencing failures of titanium turbine blades due to foreign object damage (FOD) caused by ice and hard objects ingested into the engine. Chunks of blades that broke loose, in some cases, did irreparable damage to the rest of the engine. To avoid grounding the B-1 fleet, the Air Force required a manual inspection of all the fan blades before each flight. The time-consuming leading edge inspections involved rubbing the leading edge with cotton balls, cotton gloves and even dental floss. If a single snag was detected, the blade was replaced prior to the next flight. In 1994, over one million man-hours at a cost of $10 million per year were required to complete the engine inspections and keep the B-1 flying.

General Electric Aircraft Engines (GEAE) investigated an innovative technology, called Laser Shock Peening (or laser peening), as a potential solution to increase the durability of titanium fan blades and decrease the sensitivity to FOD. Laser peening uses a high energy laser pulse to create an intense shock wave into the surface of metal parts. The shock wave imparts deep compressive residual stresses, which greatly improve the blade’s fatigue properties and toughness.

The high cycle fatigue performance of laser peened blades is remarkable. Damage to an F101 blade can reduce the fatigue strength from about 75 ksi to less than 20 ksi, which is less than half of the design requirement. However, when laser peened blades are comparably damaged, they retain a fatigue strength of 75-100 ksi. Thus, laser peening restores the structural integrity of damaged fan blades! Sensitivity to FOD defects up to 1/4 of an inch in F101 blades was virtually eliminated.

In 1995, the USAF authorized the production development of laser peening, bringing this technology out of the lab and into a production environment. Jeff Dulaney founded LSP Technologies, Inc. (LSPT) in 1995 to provide laser peening equipment and services to industry and the U.S. military. By 1997, GEAE had proven the beneficial effects of laser peening and began production application to F101 blades, using four laser peening systems designed and built by LSPT.

Application of laser peening avoided over $59 million in blade replacement costs, secondary damage engine repair costs, and cost avoidance from airfoil failures. Avoiding catastrophic engine failures over the remaining life of the B-1B/F101 program is estimated to have saved another $40 million.

Due to this success, laser peening was applied to solve similar problems for the F110 engine blades for the F-16 Falcon, and the USAF estimates similar cost savings to the B-1B/F101 program.

LSP Technologies, Inc. has continued to improve LaserPeen® processing equipment and processing methods. With the newest generation of LaserPeen® processing equipment and the RapidCoater™ system for automating the coating overlays used in the process, LSPT has reduced the cost of LaserPeen® processing dramatically making the process affordable for many new applications!

Overall, the potential savings from laser peening are expected to easily approach $1 billion when calculating this impact over all engines in the Air Force fleet!


Laser Peening of Raptor Engine Components

Aerospace applications of laser peening include many gas turbine engine components, such as airfoils and integrally bladed rotors (IBRs) because of the enormous benefits of preventing fatigue failures and improving damage tolerance for these critical parts.

 

LaserPeen® Processing of Raptor IBRs Production at LSP Technologies, Inc.

Laser peening is a Production Process for the fan blades of GE Aviation’s F110 engine that powers the Falcon and Lancer.

– F110-GE-129 Engine (F-16 C/D Falcon)
– F110-GE-100 Engine (F-16 A/B Falcon)

– F101-GE-102 Engine (B-1B Lancer)

– Joint Strike Fighter

Production use of the laser peening on the fourth stage Integrally Bladed Rotor (IBR) for Pratt & Whitney’s F119-PW-100 engine, which powers the US Air Force’s F/A-22 Raptor, started at LSP Technologies in March 2003.  LaserPeen® processing increases the damage tolerance and enhances the fatigue performance of this IBR.

 


Applications of Laser Peening to Titanium Alloys

Originally presented at the ASME/JSME 2004 Pressure Vessels and Piping Division Conference, July 25-29, 2004.

Authored by David W. Sokol, Allan H. Clauer, Ravi Ravindranath.

ABSTRACT
Laser peening has been a commercial surface enhancement process for over six years, and has been gradually expanding the number of applications being laser peened in production ever since. LSP Technologies has been a major developer of the process and new applications for laser peening. It has developed production laser peening systems and innovative laser peening technology to increase throughput and reduce cost. Some of these production and technology developments will be discussed in this paper. Also, an evaluation of applying laser peening to increase the fretting fatigue resistance of titanium alloys, based on Ti-6Al-4V has been made. Included in this evaluation is the use of small spot laser peening to enable the processing of the inside of small, generally inaccessible areas such as the insides of holes and slots. Laser peening with either large or small spots dramatically increased the fretting fatigue life under both R=0.5 and R=0 fatigue conditions with three different contact pad pressures. Fretting fatigue life was increased by at least 25 times. Actual increases in fatigue life and fatigue strength could not be determined because most specimens ran to the runout life of 106 cycles without failure. The laser peening does not appear to affect the fretting behavior, but instead inhibits the initiation of fatigue cracks at the fretting cracks developed from the fretting process. The compressive residual stress from laser peening also would slow the growth rate of any fatigue crack that does eventually initiate at a fretting crack.

INTRODUCTION
LSP Technologies has designed and built two production laser peening systems with the support of the Air Force Materials and Manufacturing Directorate. In 2003 it began production laser peening of an integrally bladed rotor for the F119 engine being built by Pratt & Whitney. To increase throughput and reduce the cost of the process, several technology improvements have also been developed and are being implemented into production. Among these is the RapidCoater™ system, which allows continuous processing of a part. Under a NAVAIR Phase II SBIR, LSP Technologies has investigated the effect of laser peening on fretting and fretting fatigue in dovetail slots. An outcome of this program is a laser peening system that enables the interior of dovetail slots to be accessed by laser peening. Because of the dovetail geometry, small spots (<1 mm in diameter) and underwater laser peening were used to treat the interior of the slots.

To download the entire article as a pdf: Applications of Laser Peening to Titanium Alloys