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(Excerpt) INNOVATION: Low Plasticity Burnishing (LPB®) apparatus that produces a repeatable stable deep layer of compressive surface residual stress.
ACCOMPLISHMENTS: Developed and demonstrated LPB® as an affordable means of producing deep stable compression in metallic components; Produced compressive layer essentially stable at engine operating temperatures by LPB®; LPB® increases finite fatigue life by an order of magnitude, can double the endurance limit, and retard existing cracks.
Related National Aeronautics and Space Administration (NASA) Articles
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Government Articles: Federal Aviation Administration (FAA)
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(Excerpt) Friction stir welding (FSW) is a fairly recent technique that utilizes a nonconsumable rotating welding tool to generate frictional heat and plastic deformation at the welding location, thereby affecting the formation of a joint while the material is in the solid state. The principal advantages of FSW, being a solid-state process, are low distortion, absence of melt-related defects and high joint strength, even in those alloys that are considered nonweldable by conventional techniques. Furthermore, friction stir (FS) welded joints are characterized by the absence of filler-induced problems / defects, since the technique requires no filler, and by the low hydrogen contents in the joints, an important consideration in welding steels and other alloys susceptible to hydrogen damage. FSW can be used to produce butt, corner, lap, T, spot, fillet and hem joints, as well as to weld hollow objects, such as tanks and tubes / pipes, stock with different thicknesses, tapered sections and parts with 3-dimensional contours. The technique can produce joints utilizing equipment based on traditional machine tool technologies, and it has been used to weld a variety of similar and dissimilar alloys as well as for welding metal matrix composites and the for the repair of existing joints.
Government Articles: U.S. Department of Energy
FY05 Summary Report, Yucca Mountain Project, Lawrence Livermore National Laboratory
Energy Citations Database, U.S. Department of Energy Office of Scientific and Technical Information (OSTI)
(Excerpt) This report deals with the impact of fabrication processes on the localized corrosion behavior of Alloy 22 (N06022). The four fabrication processes that were analyzed are: (1) Surface stress mitigation of final closure weld, (2) Manufacturing of the mockup container, (3) Black annealing of the container and (4) Use of different heatsA of Alloy 22 for container fabrication. Surface Stress Mitigation: When metallic plates are welded, for example using the Gas Tungsten Arc Welding (GTAW) method, residual tensile stresses may develop in the vicinity of the weld seam. Processes such as Low Plasticity Burnishing (LPB®) and Laser Shock Peening (LSP) could be applied locally to eliminate the residual stresses produced by welding.
In this study, Alloy 22 plates were welded and then the above-mentioned surface treatments were applied to eliminate the residual tensile stresses. The aim of the current study was to comparatively test the corrosion behavior of as-welded (ASW) plates with the corrosion behavior of plates with stress mitigated surfaces. Immersion and electrochemical tests were performed. Results from both immersion and electrochemical corrosion tests show that the corrosion resistance of the mitigated plates was not affected by the surface treatments applied.
2.2.2. Low Plasticity Burnishing (LPB®): LPB® is a process by which a smooth hard ball is rolled over the surface of the metal to be burnished imparting compressive deformation. The treatment in the studied Alloy 22 welded plates was performed in two steps using balls of two different sizes, the larger one with an effective surface area of 0.0154 inch² and the smaller one with an effective surface area of 0.00067 inch². In the first step the larger ball was rolled at a pressure of 780 ksi (kilo pounds per square inch) to create compressive stresses to a larger depth. In the second step, the smaller ball was rolled at a pressure of 821 ksi to increase the level of compressive stresses near the surface. The LPB® treatment of the Alloy 22 studied plates was carried out at the Surface Enhancement Technologies Company in Cincinnati, Ohio. The burnished plate was called F4 and the coupons and specimens prepared from this plate were all named starting with the letter B.
Related U.S. Department of Energy Articles
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Military Articles: United States Air Force
Materials & Manufacturing Directorate Success Stories, U.S. Air Force Research Laboratory
AFRL Materials and Manufacturing Directorate (AFRL/RX) – (www.ml.afrl.af.mil)
(Excerpt) AFRL engineers, working with industry, have made significant progress in the study and application of low plasticity burnishing (LPB®) for the mitigation of stress corrosion cracking (SCC) and fatigue damage in high strength steels. LPB®, a process originated and patented by Lambda Technologies, has been previously demonstrated as an approach to substantially increase the foreign object damage (FOD) tolerance of turbine engine components. In the most recent investigation, researchers at AFRL’s Materials and Manufacturing Directorate (AFRL/ML) investigated the use of LPB® on 300M steel, widely used for aircraft landing gear. They compared the results to those obtained using conventional shot peening (SP), the current state of the art. The tests indicated that LPB® imparts persistent compressive residual stresses in 300M steel surfaces and that LPB®-treated specimens more effectively withstand fatigue, FOD-related damage, and SCC. Continuing research efforts could result in more durable steel components for military and commercial aircraft landing gear.
Related U.S. Air Force Articles
Low Plasticity Burnishing Effective For Enhancing Turbine Engine Durability, Materials & Manufacturing Directorate Success Stories, AFRL Materials & Manufacturing Directorate (AFRl/RX)
Engine Structural Integrity Program (ENSIP), Page 152, Department of Defense Handbook
Military Articles: United States Navy
Department of the Navy SBIR/STTR Success Stories: Lambda Technologies, Affordable Surface Enhancement
Department of the Navy SBIR/STTR Program, NAVAIR, Office of Naval Research
Navy SBIR/STTR – (www.navysbir.com)
(Excerpt) Aircraft engines, both turbine and turbo-prop, are subject to high cycle fatigue (HCF) that can lead to engine failures. Further, foreign object damage (FOD) caused by the ingestion of debris (i.e. rocks, screws, shrapnel, etc.) into the engine creates crack initiation sites that exacerbate the effects of HCF. At a minimum, damaged vane, fan, and compressor blades can lead to increased inspections and additional maintenance actions that can negatively impact fleet readiness and operational tempo. At worst, the combined effect of FOD and HCF may cause catastrophic engine failures with severe consequences including mission failures, aircraft damage and loss of life.
To address these issues, Lambda developed its patented Low Plasticity Burnishing (LPB®) surface enhancement technology to strengthen the engine components and extend their useful life. From a materials design standpoint, all mechanical surface enhancement methods develop a layer of compressive residual stress following mechanical deformation of the surface. The methods differ in how the surface is deformed and the magnitude and form of the resulting residual stress and cold work (plastic deformation) distributions. The improved Lambda LPB® method produces a deep layer of high compression with improved surface finish, lower cost and minimal “cold” work.
Navy Transition Assistance Program, U.S. Department of the Navy’s Small Business Innovation Research (SBIR) Program Office
Dawnbreaker, Inc. – (www.dawnbreaker.com)
(Excerpt) About the Technology: Extensive inspection and maintenance programs are required to detect and replace critical blades with as little as 0.005-inch deep Foreign Object Damage (FOD). The estimated $400M expended annually for High Cycle Fatigue (HCF) greatly increases the total ownership cost of military aircraft. Lambda’s Low Plasticity Burnishing (LPB®) produces deep levels of compressive residual stress in steel, titanium, aluminum, and nickel-based alloys and improves damage tolerance and fatigue life using conventional Computer Numerical Controlled (CNC) machine tools. The affordable LPB® processing is easily incorporated into existing manufacturing and overhaul operations and improves engine life and performance while reducing ownership costs by mitigating foreign object damage, Stress Corrosion Cracking (SCC), corrosion fatigue, and fretting fatigue.
Military Articles: United States Department of Defense
United States Department of Defense TechMatch Success Stories
United States Department of Defense TechMatch – (www.dodtechmatch.com)
(Excerpt) Low Plasticity Burnishing (LPB®) is an engineered surface enhancement that produces deep levels of beneficial compressive residual stress in steel, titanium, aluminum and nickel-based alloys. The deep compression has been shown to dramatically improve both damage tolerance and fatigue life, and is essentially a manufacturing operation performed using conventional CNC machine tools in a machine shop environment. LPB® processing can be easily incorporated into existing manufacturing and overhaul operations. LPB® offers an affordable, effective and available means of both improving engine life and performance while reducing ownership costs by mitigating common damage mechanisms such as foreign object damage, stress corrosion cracking, corrosion fatigue and fretting fatigue.
Related Department of Defense Articles
Friction Stir Processing, Defense Advanced Research Projects Agency (DARPA), U.S. Department of Defense.
Aerospace Engineering Online Magazine, SAE International
(Excerpt) Craftsmen for centuries have improved the strength of metals with hammering. Today, aerospace manufacturers use shot peening to place similar strength-inducing deformations into metal components. Now, in a process that goes one better than shot peening, an industry/military team has made significant progress in the study and application of low-plasticity burnishing (LPB®) for the mitigation of stress corrosion cracking (SCC) and fatigue damage in high-strength steels. The process of LPB® was originated and patented by Cincinnati, OH-based Lambda Technologies. It previously has been demonstrated as an approach to substantially increase the foreign object damage (FOD) tolerance of turbine engine components.