Showing papers on "Peening published in 1997"

Dry tape covered laser shock peening

Abstract: A method of laser shock peening a metallic part (8) by firing a laser (2) on a laser shock peening surface (54) of the part which has been adhesively covered by tape (59) having an ablative medium, preferably, a self-adhering tape with an adhesive layer on one side of an ablative layer and a confinement medium without flowing a confinement curtain of fluid over the surface upon which the laser beam is firing. Continuous movement is provided between the part (8) and the laser beam (2) while continuously firing the laser beam, which repeatably pulses between relatively constant periods, on a laser shock peening surface of the part. Using a laser beam with sufficient power to vaporize the ablative medium so that the pulses form laser beam spots on the surface and a region having deep compressive residual stresses imparted by the laser shock peening process extending into the part from the surface. The confinement medium may be supplied by a single layer of tape having a clear layer over the ablative layer or a thicker lap or thickness of laps of a tape with just an ablative layer wherein the extra thickness provides the confinement medium.

Adhesive tape covered laser shock peening

Abstract: A method of laser shock peening a metallic part by firing a laser (2) on a laser shock peening surface (54) of the part which has been adhesively covered by tape (59) having an ablative medium (61), preferably a self-adhering tape with an adhesive layer (60) on one side of an ablative layer (61), while flowing a curtain of water (21) over the surface upon which the laser beam (2) is firing. Continuous movement is provided between the part and the laser beam while continuously firing the laser beam, which repeatably pulses between relatively constant periods, on a laser shock peening surface of the part. Using a laser beam with sufficient power to vaporize the ablative medium so that the pulses form laser beam spots on the surface and a region having deep compressive residual stresses imparted by the laser shock peening process extending into the part from the surface.

Altering vibration frequencies of workpieces, such as gas turbine engine blades

Abstract: A method of modifying the vibration resonance characteristics of a workpiece includes the steps of determining a vibratory resonance condition frequency of the workpiece, determining the mode shape of said vibratory resonance condition, locating an area on the workpiece that includes a maximum curvature for the determined mode shape and vibratory resonance condition frequency; then laser shock peening the located area to create residual compressive stresses within the workpiece to shift the determined vibratory resonance condition frequency. A workpiece such as a gas turbine engine blade is also disclosed.

Precision deep peening with mechanical indicator

Abstract: An apparatus produces compressive stress in a component surface. Positioning of a contact area of the component surface is controlled to situate a contact area of the component surface relative to an indenter element. The indenter element is fixtured to cause an indentation at the contact area. The force of the indentation is measured as the indenter element contacts the contact area, and controlled responsive to the amount of force measured and the desired compression. The system allows deep compressive stresses to be generated without the surface damage associated with conventional peening.

Method and apparatus for ultra high pressure water jet peening

Abstract: The invention describes a method and apparatus for peening objects by means of ultrahigh velocity waterjet. The apparatus includes means for holding and producing relative motion in three dimensions of both the workpiece and the jet. Control means are provided to allow uniform and variable depth peening of complex shapes and automatic variations in relative speed, standoff distance, angle and pressure. The method includes the use of entrained disappearing particles in the waterjet to facilitate peening.

Ripstop laser shock peening

Abstract: The present invention provides a metallic article with at least one laser shock peened surface on at least a portion of the article and a plurality of volumetrically spaced apart laser shock peened protrusions extending into the article from said laser shock peened surface wherein the protrusions have deep compressive residual stresses imparted by laser shock peening (LSP). The invention may be further characterized by spaced apart circular laser beam spots on the surface from which the laser shock peened protrusions extend into the article such that the spots do not overlap. The present invention includes a method of laser shock peening a hard metallic article by firing a laser beam on different points of a laser shock peened surface of at least a portion of the article using a laser beam with sufficient power to vaporize material on the surface around laser beam spots formed by the laser beam at the points on the surface, flowing a curtain of water over the surface upon which the laser beam is firing, and firing the laser beam so as to form a plurality of volumetrically spaced apart laser shock peened protrusions extending into the article from the spots such that the protrusions have deep compressive residual stresses imparted by laser the laser beam. The surface may first be coated with an ablative material which the laser beam vaporizes and the method may be an on the fly method of laser shock peening which further includes continuously moving the article while continuously firing a stationary laser beam which repeatably pulses between relatively constant periods.

Efficient laser peening

Abstract: A method of laser shock peening a workpiece including the steps of laser shock peening at least one surface of the workpiece so that it extends over an area of the workpiece and forms a region having compressive residual stresses imparted by the laser shock peening extending into the workpiece from the surface, and firing a laser beam to produce the laser shock peened surface with more than one row of laser beam spots, wherein adjacent laser beam spots and/or rows are one of touching or spaced apart from each other.

Laser shock peening with tailored multiple laser beams

Abstract: Method of changing the residual compressive stresses of an area of a workpiece by tailoring multiple laser beams applied to the workpiece. In one embodiment, a relatively long duration laser pulse is applied to the workpiece followed by a relatively short duration laser pulse. Other tailoring embodiments used to increase the total residual compressive stress of workpieces include blending two laser pulses, or splicing them utilizing a first short sliced-type beam combined with a relatively long duration, high powered gaussian laser beam pulse. A third embodiment utilizes two or more laser beams or pulses of different wavelengths.

Laser shock peening apparatus with a diffractive optic element

Abstract: A laser peening apparatus, including a laser generator to generate a laser beam having a first cross-sectional shape; and a diffractive optic element. The diffractive optic element changes the laser beam to a second cross-sectional shape. The apparatus also includes demagnifying and magnifying lenses. The diffractive optic element may create a second cross-sectional shape such as rectangular, hexagonal, or even split the laser beam into multiple beams. The diffractive optic element may also create a second cross-sectional shape of the laser beam varying in intensity thereacross or varying in energy distribution.

Laser shock peening method and reflective laser beam homogenizer

Abstract: A method for laser shock peening a target surface generates laser pulses from a cavity dumping oscillator having an optically-pumped laser and directs the pulses against the target. A first technique uses pulses having rectangular cross section. A second technique passes each generated pulse two or more times through the same optical amplifier before directing the pulse against the target. A third technique drives the laser with a time pulse of electric current having a rectangular shape. A reflective laser beam homogenizer uses two abutting mirrors to split a laser beam into two equal halves and then uses an odd number of additional mirrors to reflect each half first behind and then to the opposite one of the two mirrors to be reflected back as a beam having interchanged halves.

Laser Peening of Metals - Enabling Laser Technology

Abstract: Laser peening, a surface treatment for metals, employs laser induced shocks to create deep and intense residual stresses in critical components. In many applications this technology is proving to be superior to conventional treatments such as shot peening. The laser peening process has generated sufficiently impressive results to move it from a laboratory demonstration phase into a significant industrial process. However until now this evolution has been slowed because a laser system meeting the average power requirements for a high throughput process has been lacking.

Balanced electromagnetic peening

Abstract: An electromagnetic peening apparatus includes a first electromagnetic coil having a first face configured to conform to a first surface of a workpiece, and a second electromagnetic coil having a second face configured to conform to a second surface of the workpiece. A carriage positions the first and second coils in abutting contact with the workpiece at respective first and second faces and surfaces. A power supply powers the coils to produce electromagnetic force therein to plastically deform the workpiece at the first and second surfaces to effect a compressive layer therein.

Analysis of results on improved welded joints

Abstract: Recents studies have shown that the use of improvement techniques on welds allows an increase in the level of admissible fatigue strength (even more than 100%). The aim of this study was to collect and validate literature data, create a data base containing the joint characteristics and fatigue results, make a statistical analysis of the data in order to quantify the effect of parameters influencing the fatigue strength and propose new S-N curves which are compared to those given in Eurocode 3. Four improvement techniques (grinding, TIG dressing, hammer peening, shot peening) and four joint types (butt, T joints, cruciform and longitudinal joints) were taken into account. Joint thicknesses less than 25 mm loaded in air with a stress ratio R between 0 and 0.1 were selected. Three classes of yield strength for the base metal were considered: 600. All S-N curves were above those of as-welded assemblies. The best results were obtained with hammer peening. The larger increase in the fatigue strength due to the use of improvement techniques was due to the occurrence of an initiation phase in addition to the crack propagation phase. During the initiation phase, the extension of existing crack-like defects is slowed down or even stopped. The duration of this phase increases with the total fatigue life.

Peening process with reduction of dielectric breakdown to increase peak pressure pulse

Abstract: The present invention provides a method of laser shock processing that can be used in a production environment that increases the peak pressure of the shock wave applied to the workpiece that increases residual compresses stresses therein. Such improvement is created by a reduction of dielectric breakdown of the transparent overlay layer utilized. The method includes the steps of applying a transparent overlay such as water over the workpiece and reducing or limiting the thickness of the transparent overlay material. An alternate embodiment of the invention to reduce dielectric breakdown incorporates the use of a changing or circularly polarized laser beam as opposed to a linearly polarized laser beam.

Laser peening hollow core gas turbine engine blades

Abstract: A hollow workpiece includes an outside surface through which a port opens to the hollow interior, and a laser peened area on the surface of the workpiece. The laser peened area is created on the surface while the hollow interior is at least partially filled with a substance other than air. A method of laser peening a hollow core gas turbine engine blade includes the steps of providing a hollow core gas turbine engine blade, filling the hollow core with a substance other than air, and then, laser peening the hollow core gas turbine engine blade.

Laser Gas Nitriding of Ti-6AI-4V Alloy

Abstract: Laser gas nitriding of Ti-6A1-4V has been investigated with both CO2 and Nd:YAG lasers. Results indicate that Nd:YAG laser in pulse mode provides a better surface finish and a lower cracking severity than CO2 laser. A crack-free nitrided layer has been obtained by optimizing the processing parameters. Titanium nitride (TiN) significantly increases the hardness of the nitrided surfaces. The amount of titanium nitride produced depends on the processing parameters, such as laser pulse energy and nitrogen concentration. With optimized parameters, the nitrided surface is somewhat rougher than the polished base metal but much smoother than the shot peened surface. The shrinkage effect in the laser melt zone produces surface residual tensile stresses regardless of the processing environment. Preheating or stress relieving after laser nitriding can significantly reduce the residual tensile stress level.

Friction boring process for aluminium alloys

Abstract: A friction boring process creates a corrosion resistant fine grain microstructure in the wall surfaces of holes bored in aluminum alloy materials. A rotating tool is inserted directly into the aluminum material, or into a pre-drilled pilot hole, at a sufficient rotational velocity and feed rate to cause working that extends beyond the diameter of the tool, frictional heating, and extraction of aluminum material by metal deformation rather than cutting action as with a conventional drill bit. Burring, smoothing, and otherwise removing aluminum material extracted from the hole may be performed by a finishing segment that limits insertion depth of the tool. Frictional heating generates a temperature sufficient for rapid recrystallization of the remaining worked metal to form a fine grain microstructure to a depth of about 2.5 mm in the hole surfaces. Corrosion protection is retained even if some fine grain material is removed during a subsequent reaming operation. Friction boring is fast, suitable for a wide variety of aluminum alloy compositions, and easily adaptable to initial fabrication of aluminum components or to field repair of assembled structures such as on aging aircraft. The process creates a fine grain corrosion and fatigue resistant surface microstructure in aluminum alloy holes without the use of peening, heat treatments, or environmentally objectionable chemicals and coatings.

Modifications of mechanical and electrochemical properties of stainless steel surfaces by laser shock processing

Abstract: Laser Shock Processing (LSP) consists on focusing a high energy pulsed laser beam on metals to create shock waves and thereby, generate compressive stresses. These stress are similar to those of conventional mechanical treatments like short peening. Nevertheless, at LSP the affected depths are greater and the surfaces keep their roughness and hardness. The present study compare the effects of LSP on the surface mechanical properties of two stainless steels: an austenitic (AISI 316L) and a martensitic (Z12 CNDV 12.02). The surface effects are characterized in terms of microstructure, hardening and residual stress levels (measured by X-ray diffraction technique). The effects of LSP on the pitting corrosion resistance of the martensitic stainless steel in a NaCl 0.01 M + Na2SO4 0.01 M solution are presented. Electrochemical tests were carried out by using open circuit and polarization techniques, to determine electrochemical parameters (free and pitting potentials, passive current densities). Laser-induced work-hardening effects were shown to be more important in the case of 316 L for which they strongly depend on the impacts repetition and the laser power density. Significant modifications on localized corrosion properties were noticed for each treatment condition (8 GW/cm2 - 20 ns pulses and 40 GW/cm2 - 2,3 ns pulses) i.e. pitting potentials were not modified but free potentials were shifted to anodic values and passive current densities reduced.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Stress Control in Sputtered Silicon Nitride Films

Abstract: We show that stress in sputter-deposited silicon nitride films can be controlled, making either compressive or tensile stress films achievable. These films were deposited via reactive rf magnetron sputtering using an elemental Si target and N2 as a reactive gas in an Ar ambient. Variation of stress as a function of deposition pressure and N2/Ar gas mixture ratio was examined over a wider range of these two parameters than in previous work. More importantly, this parameter space includes conditions which produce near-stoichiometric Si3N4 films over a wide range of deposition pressures. We demonstrated that both low compressive stress and even tensile stress can be achieved at the proper deposition conditions. The film stresses as a function of deposition pressure or N2/Ar gas flow ratio are explained in the context of previously developed peening models.

Design of experiments to investigate residual stresses and fatigue life improvement by a surface treatment

Abstract: — The careful design of experiment (DOE) technique has been utilized to analyze the residual stress state and to investigate the fatigue life improvement of a material (nitriding steel) subjected to thermal and mechanical treatment. Nitriding treatments have been performed on several specimens which have been subsequently shot- peened, varying the main parameters controlling the process. The design of experiment method has been accomplished in order to evaluate the influence of the main shot-peening parameters on the distribution and values of the residual stresses close to the surface, and also in order to estimate the influence of these parameters on fatigue resistance.

Method of shot peening a hardened metal product with shot having high hardness

Abstract: A method for shot peening a hard metal product that has a hardened surface. The method includes projecting shot on the hardened surface of the hard metal product. The ratio of the Vickers hardness of the shot to that of the hardened surface is 0.8-1.6, and the diameter of the shot is 30-250μ.

Fan vane for gas turbine engine

Abstract: PROBLEM TO BE SOLVED: To extend the life of the fan vane of a gas turbine engine by providing an area having deep residual compressing stress added by a laser impact peening (LSP). SOLUTION: The fan vane of a gas turbine engine is provided with a metallic aerofoil 34 having a front end, a rear end and a tip outside a radial direction and at least one laser impact peening added surface 54 provided along the front end having deep residual compressing stress added by a laser impact peening (LSP) entering the aerofoil 34 from the laser impact added surface 54.

Ti-6Al-4V合金ショット材の高温疲労特性

Abstract: The effect of shot peening on the fatigue strength of Ti-6Al-4V alloy was investigated in the temperature range of 20°C to 450°C. In order to evaluate separately the individual effects of compressive residual stress, strain hardening and surface roughness induced by shot peening, the results obtained were discussed by the Murakami's √area parameter model which could predict fatigue strength using two parameters of defect size (√area) and Vicker's hardness (HV), and the effect of static mean stress (σm) could also be considered in the model. Shot peening increased fatigue strength at 20°C-350°C, but decreased at 450°C. The reduction at 450°C was due to surface roughness because compressive residual stress was decreased during fatigue loading. At 450°C, by comparing the fatigue strength of the rough surface specimens with that of the surface polished specimens, the defect size (√area) equivalent to the surface roughness was evaluated to be approximately 76μm. At 20°C-350°C, the fatigue strength observed could be regarded as that obtained by adding the contribution of compressive residual stress (static mean stress) to the fatigue strength of the specimens with the defect size of 76μm. The compressive residual stress predicted by the model showed reasonable values quantitatively. Drilling holes equivalent to √area of 93 and 185μm decreased fatigue strength markedly. The holes, however, were crushed by shot peening. For example, √area of 185μm was decreased down to about 55μm. Therefore, the fatigue strength of the drilled and shot-peened specimens increased drastically and was comparable to that of the shot-peened specimens without drilling holes but with the rough surface of 76μm.