Effects of Laser Peening on Residual Stress and Fatigue Life of Al 7049-T73, A-656 Steel and Al5059 Weldments and Ti-6Al-4V PDF Download
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Author: Jasleen Bhoon
Publisher:
ISBN:
Category :
Languages : en
Pages : 178
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Author: Jasleen Bhoon
Publisher:
ISBN:
Category :
Languages : en
Pages : 178
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Author: Chanh Hung Truong
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ISBN:
Category :
Languages : en
Pages : 164
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Author: Harold Luong
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Category :
Languages : en
Pages : 196
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Category : Aluminum alloys
Languages : en
Pages : 18
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Author: National Aeronautics and Space Adm Nasa
Publisher: Independently Published
ISBN: 9781726673556
Category : Science
Languages : en
Pages : 38
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Fatigue and crack growth tests have been conducted on 4340 steel and 2024-T3 aluminum alloy, respectively, to assess the effects of shot peening on fatigue life and the effects of shot and laser peening on crack growth. Two current programs involving fixed and rotary-wing aircraft will not be using shot peened structures. Since the shot peening compressive residual stress depth is usually less than the 0.05-inch initial damage tolerance crack size, it is believed by some that shot peening should have no beneficial effects toward retarding crack growth. In this study cracks were initiated from an electronic-discharged machining flaw which was cycled to produce a fatigue crack of approximately 0.05-inches in length and then the specimens were peened. Test results showed that after peening the crack growth rates were noticeably slower when the cracks were fairly short for both the shot and laser peened specimens resulting in a crack growth life that was a factor of 2 to 4 times greater than the results of the average unpeened test. Once the cracks reached a length of approximately 0.1-inches the growth rates were about the same for the peened and unpeened specimens. Fatigue tests on 4340 steel showed that the endurance limit of a test specimen with a 0.002-inch-deep machining-like scratch was reduced by approximately 40 percent. However, if the "scratched" specimen was shot peened after inserting the scratch, the fatigue life returned to almost 100 percent of the unflawed specimens original fatigue life. Everett, R. A., Jr. and Matthews, W. T. and Prabhakaran, R. and Newman, J. C., Jr. and Dubberly, M. J. Langley Research Center NASA/TM-2001-210843, NAS 1.15:210843, ARL-TR-2363, L-18065
Author:
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ISBN:
Category :
Languages : en
Pages : 26
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Author: Marc Edward Hopkins
Publisher:
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Category :
Languages : en
Pages : 244
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Author: Yixiang Zhao
Publisher:
ISBN:
Category :
Languages : en
Pages : 203
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Laser shock peening (LSP) is a novel surface treatment process that generates deep compressive residual stresses and microstructural changes and thereby dramatically improves fatigue strength of critical metal aircraft engine parts. In the past, researchers have evaluated the mechanical effects of LSP experimentally through residual strain/stress measurements, microhardness measurements or fatigue life improvement. A number of microstructure characterizations have been done on variety laser shock peened materials. However, getting better view of how LSP brings about changes in the microstructure and establish quantitative relations between LSP parameters and residual strain/stress distributions, microstructure and texture evolution is still challenging. The present study was undertaken to develop a basic understanding of the effects of LSP on the residual strain/stress distributions, texture evolution and deformation microstructural changes in Ti-6Al-4V alloy. Scanning Electron Microscopy, Scanning Probe Microscopy, Conventional X-ray Diffraction, Synchrotron X-ray Diffraction, Electron BackScattered Diffraction, microhardness and nanoindentation have been used to characterize the laser shock peened Ti-6Al-4V alloy samples. The microstructure and surface modification of laser shock peened sample are outlined in terms of laser shock peening processing parameters. Naked laser peened samples show prominent evidence of surface melting and recasting. Little difference between the peened and virgin materials can be found in the taped laser peened samples surface microstructures. Depth-resolved characterization of the residual strains and stresses was achieved using high-energy synchrotron X-ray diffraction as well as by conventional X-ray diffraction. Compressive residual strain at peened surface and tensile residual strain in the interior of the sample are found in taped samples. Naked LSP-treated samples show tensile residual stresses at peened surfaces, then dramatically change to compressive within short depth. Multiple diffraction peaks in the synchrotron X-ray diffraction patterns were used to analyze the residual elastic strain and plastic strain distributions in the LSP-treated Ti-6Al-4V samples. Anisotropic elastic lattice strain response in the hexagonal close-packed alpha titanium was revealed by Williamson-Hall plots of the peak broadening data. The depth profiles of mean diffraction ring width in synchrotron X-ray diffraction and FWHM in conventional X-ray diffraction give evidence of anisotropic plastic strains in the laser peened Ti-6Al-4V samples. Furthermore, using the whole pattern fitting method the Structure-Texture-Microstructure-Phase-Stresss combined analysis was performed based on the synchrotron diffraction data. The evolution of maximum pole intensity values from surface to interior proves that laser shock peening can change the texture in the laser peened samples. The near-surface and through-the-depth changes in strain/stress, texture and microstructure in samples were correlated with the laser processing energy levels applied on the samples. Residual stress relaxation in LSP-treated Ti-6Al-4V alloy due to the sample sectioning was also studied using SXRD and CXRD and was found to be significant to small section widths (to about 8 mm), but not as significant at larger widths, though the sectioning was found to introduce complex gradients. Finally, the local property changes were examined using microhardness and nanoindentation and near-surface hardening due to LSP treatment was noted and related to the plastic strain generated by the process.
Author: Theresa Elizabeth Pistochini
Publisher:
ISBN:
Category :
Languages : en
Pages : 222
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Author: United States. National Aeronautics and Space Administration
Publisher:
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Category :
Languages : en
Pages :
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