SURFACE TECHNOLOGIES

LASER SHOCK PEENING

Laser Peening (sometimes also referred as Laser Shock Peening) drives deep plastic strain into a part that creates a high magnitude residual compressive stress from 1 to 10mm below the surface. This enhances the fatigue strength, durability, damage tolerance, and resistance to stress corrosion cracking of critical metallic components.

Laser peening can form and correctively shape components, especially if the component is too thick to be conducive for shot peening. Curtiss Wright’s finite-element physics-based model of laser peening enables rapid virtual peening and thereby rapid optimization and assessment of expected performance.

Laser peening is an alternative for controlled shot peening where deep penetration, upwards to ½ in (12 mm), and low amounts of cold work is advantageous. Assessment of application identifies if one or both methods should be used.

Laser peening has made an important impact on the industry, providing a reliable and production-qualified technology. It offers designers the ability to surgically engineer residual compressive stress into key areas of components. This retards crack initiation and growth thereby enabling increased fatigue strength and component lifetime.

Benefits of Laser Shock Peening

  • Deeper residual compressive stress enabling better resistance to:
    • Low cycle, high stress situations (LCF)
    • High cycle, low stress situations (HCF) in a deteriorating surface environment
    • Loss of compressive stress in high temperature applications
  • Prevents failures from:
    • Erosion, Foreign object damage (FOD), Fretting, Pitting, Stress corrosion cracking (SCC), Galvanic and Cavitation erosion.
  • Clean surface condition enables applications where contamination and/or media staining cannot be tolerated.
  • Surface finish and topography are easily maintained and controlled.
  • Laser peening allows for excellent process and quality control. Since the key process parameters of laser energy and pulse duration are measured and recorded for each impact spot generated. It also has the ability to generate large curvature in thick component sections enabling advanced forming and form correction applications.

Applications for Laser Shock Peening

Laser peening is used to:
  • increase fatigue strength
  • prevent stress corrosion cracking
  • extend the service life of critical system components
  • fatigue enhancement for components operating at very high temperatures and 
  • increase the fatigue life of additive machined parts
  • Industries Using Laser Shock Peening

    Transportation:
    • Turbine engine blades and discs
    • Aircraft structures
    • Landing Gear 
    • Control Components
    • Ship Structure  and Propulsion Systems
    Energy and Electric Power Generation:
    • Gas and Steam Turbines
    • Nuclear Fuel Canisters – prevent stress corrosion cracking
    • Upstream and Downstream Energy Systems
    Automotive Medical Implants Marine Ships Recreational Sports

    Laser Shock Peening Process - Step by Step

    1. A thin stream of water is flowed over the surface to act as an inertial tamping layer.
    2. An output beam, roughly 20 Joules at 20 nanoseconds (i.e. 1000,000,000 Watts peak) from a Nd:glass laser is projected onto a workpiece, passing through the water
    3. The leading temporal edge of the laser pulse reacts within the metal surface or ablative layer rapidly ionizing and vaporizing surface material, forming and heating a plasma. 
    4. The pressure of the heated plasma builds to approximately 100kBar (1.5 million pounds per square inch) with the water serving to inertially confine the volume. This rapid pressure rise is highly controlled to be one to two times the dynamic yield stress of the metal, plastically straining the material as it penetrates
    5. The water is accelerated off the surface but only after the shock wave has propagated into the metal. 
    6. The mechanical response of the peened area to this deep plastic strain, .020 inch to .500 inch (1 mm to 12 mm depth) results in a deep residual compressive stress with characteristics depending on the material, stiffness, and the processing parameters. The deep level of compressive stress generated creates a damage-tolerant layer and a barrier to crack initiation and growth. This enhances the fatigue life and provides resistance to stress corrosion cracking and fretting fatigue. 

    Note: Multiple firings of the laser in a pre-defined surface pattern will impart a layer of plastic strain resulting in a deterministic deep layer of compressive residual stress. The process can be tailored to suit the product and potential failure mechanism or enable higher potential loads through weight-sensitive designs.

    Laser Peening Process

    Laser Peening of AI 6061-T6 Aluminum

    One benefit of an exceptionally deep residual compressive layer is shown above. The S-N curve shows fatigue test results of 6061-T6 aluminum. The testing consisted of un-peened, shot peened and laser peened specimens which clearly shows the lifetime and fatigue benefit of the laser process.

    Laser Peening of AI 6061-T6 Aluminum​

    Laser Shock Peening FEA Modeling of Components

    Finite Element Analysis (FEA) modeling capability accurately simulates the response of a customer’s part to laser peening.  

    Multiple iterations of process variables can be performed for the following benefits: 

    • Predict node-by-node stress and strain profiles
    • Enable accurate predictions of increased fatigue strength and life
    • Assess process benefits
    • Reduce costs of testing
    • Accelerate deployment schedules

    Laser Shock Peen Forming

    Laser Shot Peen Forming augments shot peen forming by generating greater depth of induced strain, thereby allowing forming of thicker material sections and extending the degree of curvatures possible.  It is helping to advance the use of machined stringers and ribs for integrally stiffened panels which reduces the need for fasteners. All this allows for lighter aircraft with more fuel efficient profiles. 

    High-Temperature Laser Shock Peening

    Conventional peening works for low temperature applications however at higher temperatures, surface treatments degrade through dislocation annihilation, stress relaxation, and grain coarsening.  Curtiss-Wright has developed a process, laser peening plus thermal microstructure engineering, and when applied to adaptive manufactured superalloys, it imparts thermally stable micro structrual modifications in materials.

    Curtiss-Wright (CW) has developed a novel technique, coined laser peening plus thermal microstructure engineering (LP + TME) that imparts thermally stable microstructural modifications in both conventional and additively manufactured (AM) materials.
    We continually work with industry leaders and researchers to advance our technologies. We have recently published papers in collaboration with the University of Alabama and Michigan State University (MSU). Learn more >>

    Multiple mobile laser peening systems have been deployed on several continents at customer’s sites providing the most cost effective and timely deployments.

    Contact Us